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ウサギの着床機構に関する基礎的研究 : 特に周着床期の子宮内膜の組織および血管系の変化
https://az.repo.nii.ac.jp/records/3185
https://az.repo.nii.ac.jp/records/3185120f8df2-2b07-4438-8fb5-63cc74ccc942
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diss_dv_otsu0209_1 (62.5 MB)
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diss_dv_otsu0209_2 (15.7 MB)
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diss_dv_otsu0209_3 (14.7 MB)
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diss_dv_otsu0209_jab&rev (210.6 kB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||||||
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| 公開日 | 2013-01-29 | |||||||||
| タイトル | ||||||||||
| タイトル | ウサギの着床機構に関する基礎的研究 : 特に周着床期の子宮内膜の組織および血管系の変化 | |||||||||
| タイトル | ||||||||||
| タイトル | Fine changes in the endometrium during early pregnancy in rabbits : the progressive changes in the vascular system in the endometrium during the peri-implantation periods | |||||||||
| 言語 | en | |||||||||
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| 言語 | jpn | |||||||||
| 資源タイプ | ||||||||||
| 資源タイプ | thesis | |||||||||
| 著者 |
二宮, 博義
× 二宮, 博義
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| 抄録 | ||||||||||
| 内容記述タイプ | Abstract | |||||||||
| 内容記述 | 生殖生理学の研究分野では，着床の問題は最も，重要であると同時に，むずかしい問題の一つである。昔から多くの研究があり，その機序は次第に明らかにされてきている。しかし，今日なお多くの不明の点をかかえているのが現状である。着床過程を調べる場合，重要な因子として，一つは，blastocystsと子宮内膜の変化およびそれらの相互関係の問題，いま一つは，そうした変化の背景となっている子宮内膜の血管系の変動の問題がある。後者の子宮の血管系については，従来の報告のほとんどが，非妊娠時の周期的変化，あるいは妊娠後期のすでに胎盤が出来上がった時点での血行を調べたものである。周着床期(着床前後；periimplantation period)の子宮内膜の微細血管系についての検索は，ほとんどないようである。こうした事情から，著者はウサギを用い，周着床期の子宮内膜の微細血管の変化を，樹脂鋳型走査型電子顕微鏡法により，詳細に観察することにした。なお，妊娠子宮と比較するために，非妊娠および偽妊娠子宮についても同様に調べることにした。 材料および方法: 材料には，日本白色ウサギを使用した。妊娠子宮を得るために，発情徴候を示したメスにHCG(human chorionic gonadotropin)50i.u.(国際単位)を注射し排卵を誘起させ，次いでオスと交尾させた。偽妊娠子宮を得るために，HCG50i.u.を注射した。ウサギでは着床が妊娠7～8日に起こるので，妊娠3，5，6，7，8，9日の妊娠子宮を用意した。方法は，メタアクリル酸メチルエステルモノマーに硬化剤を加え，これを腹大動脈より子宮の血管系に注入した。樹脂の硬化後，子宮を摘出し，20%KOHに浸漬して組織を溶解させ，子宮内膜の血管系の鋳型を得た。これを金の蒸着後，走査型電子顕微鏡で観察した。また，注入前に一部の子宮組織を摘出して組織検査用とし，樹脂鋳型法で得られた所見と対照した。 観察結果: 非妊娠時の子宮内膜の血管系は，放射動脈・静脈，それに上皮下毛細血管網で構成されており，放射動脈は直線的で，走行中はほとんど枝を出すことはなく，上皮下ではじめて多くの枝を出し，そこに上皮下毛細血管網を形成していた。この毛細血管は特徴的で血管の口経は一定せず，10～20μmの間隔でくびれた部分が配列しており，数珠様(beads-like)であった。妊娠が成立すると，着床前でも，すでに血管系に顕著な変化および発達が見られ，放射動脈・静脈は太く長く伸びるようになり，上皮下の毛細血管は，数珠様構造を失い，著しく拡張しかつ長く伸展し，そこに特有の毛細血管網を形成していた。組織学的には，血管壁は次第に薄くなり，従来の壁構造を失い，内膜上皮細胞も次第に分泌性腺細胞に変っていった。着床日を過ぎると，血管系はますます発達し，その規模を増してきて，特に上皮下の毛細血管にいろいろな変化が起こり，微細(4～10μm)な血管や血洞を形成するようになっていた。さらに着床2日後では，栄養膜合胞体層(lacunae)と母体側の血管の連絡が認められた。組織学的には，間質の脱落膜化，trophoblastの間質への侵入および母体血管への浸食，さらに偽好酸球の血管壁への浸食等が認められた。一方，偽妊娠子宮の血管系をみると，着床前日(妊娠6日)までは，正常の妊娠のそれとほとんど同じに発達するが，着床日を過ぎると，血管系の発達は起こらず，逆に偽妊娠9日になると，血管系の退行が起こり，上皮下の毛細血管には狭窄したり断裂したものが出現することが認められた。 考察: 樹脂鋳型標本を走査電子顕微鏡で観察するという新しい技術で，これまでに知り得なかった知見をいくつか得ることができた。着床前に，すでに子宮内膜の血管系は著しく発達し，内膜上皮細胞も分泌細胞化するが，こうした変化は，子宮内のblastocystsの生存に必要な子宮蛋白(blastokinin，uteroglobulin)の分泌と深い関係があるものと考えた。着床後に，内膜の血管に偽好酸球が無数出現して，これが血管壁を侵食するようになるが，これは，微細血管の形成と密接な関係があるものと推察した。妊娠・偽妊娠の子宮内膜の血管系を比較してみると，着床前日(妊娠6日)までは，まったく同様な発達を示すが，着床日を境にして，両者に決定的な相違が生じてくることが分かった。すなわち，妊娠子宮では，血管系の発達は進行するが，偽妊娠では第9日になると，微細血管に退行性の変化(非妊娠時の血管系への回復)が開始されることがわかった。従来の報告では，通常の子宮への回復は，偽妊娠第15～20日とされているが，実際の微妙な変化は，すでに第9日から始まっているものと考えた。偽妊娠子宮を用いて，卵移植の実験がこれまでよく行なわれているが，第9日以降での移植が全く成功しなかったということは，こうした子宮内膜の微細血管系の変化が，一つの原因になっていたであろうと思われる。 |
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| Abstract | ||||||||||
| 内容記述タイプ | Other | |||||||||
| 内容記述 | The vascular corrosion casting/scanning electron microscopic technique was used to investigate fine changes in capillaries in the endometrium during the peri-implantation periods. Rabbits on Days 3, 5, 6, 7, 8 and 9 of pregnancy were used. Pseudopregnant rabbits also were used for comparison. In pregnant rabbits, a remarkable and progressive vascular development was observed during the whole periods of the peri-implantation. The capillaries surrounding uterine glands were well developed, increasing in number and diameter of cross sections by Day 6. On day 7, marginal capillaries located just under the epithelium were rough-surfaced, indicating extravasation of blood and enhancement of vascular permeability. On Day 9, capillaries at the implantation site had numerous fine budlike protrusions (4 to 10μm in diameter) assuming microaneuysms. In pseudopregnant rabbits, the vascular pattern in the endometrium showed changes quite similar to those seen in pregnant rabbits, by Day 6. After Day 6, however, the vascular system did not show any progressive changes as it showed in pregnancy. Numerous torn-off capillaries were found on Day 9, as a possible sign of degeneration of the endometrial vascularity. The rabbit is one of the animals favorable to the study of implantation. Since ovulation is induced by copulation as well as by injection of gonadotropins, various events of pregnancy can be timed rather accurately. Pregnancy lasts 30 to 33 days involving a pre-implantation period of 7 days and an active gestation period of 23 to 26 days. The basic features of the rabbit endometrium during pegnancy were first described by Krichesky (1942). Although more detailed descriptions of the histological changes in the endometrium during pregnancy have been published by Amoroso (1967), Larsen (1962) and other investigators, very little information is available concerning progressive fine changes in the endometrial vascular system during peri-implantation period. Hafez and Tsutsumi (1966) reported the vascularity to a relatively small degree during early pregnancy in the rabbit. They studied light microscopically and revealed intact surrounding tissues of vessels. Such a histological method, however, is insufficient for elucidating the exact three-dimensional ramifications and connections of the vessels because of the limit resolution and insufficient depth of focus of the light microscope. The scanning electron may be used in conjuction with acrylic resin vascular casts with a hope to surmount the problem and to reveal the three-dimensional microvasculature in the uterine mucosa. Scanning electron microscopy of corrosion casts of the endometrial vasculatrue has been already used by Roger (1982), who showed the vessels around the implantation site in mice, and by MacDonald (1976), who described and increase of capillary network density at the implantation sites in swines. As for rabbits, the vascular corrosion casting/scanning electron microscopy on the vascular changes has not been available so far. The present research was undertaken to elucidate changes in the endometrial vascularity together with those in the epithelial cells during pseudopregnancy and to compare these changes with the peri-implantation changes which should occur during normal pregnancy. Materials and Methods Fifty-six rabbits were caged individually, before mating to avoid pseudopregnancy. Pregnant rabbits were autopsied on days 3 to 9 of gestation (counted from the day of coitus), and pseudopregnant rabbits were autopsied on days 3 to 9 after induction of ovulation by an injetion of HCG (human chorionic gonadoropin). Each animal was anesthetized by an intravenous injection of sodium pentobarbital, and bled through the common carotid artery. In addition to the analysis of the fine vascularity established in the injection-replica by scanning electron-microscopy, the left uterine horn was ligated and removed for histological and scanning electron microscopical examination. (1) Histological sections. Segments of the uteri were fixed in 10% buffered neutral formalin, dehydrated, cleared, and embedded in paraffin. Serial sections cut at 4μm were stained with hematoxylineosin, azan, elastica-Van Gieson or PAS stains. (2) Segments for scanning electron microscopy. Tissues were washed gently with physiological saline solution and then fixed with 3% glutaraldehyde. The tissues were then washed in distrilled water and dehydrated in a graded series of ethanol. Following dehydration, the samples were dried with liquid CO_2 in a critical-point drying instrument and the coated with glold in an ion-sputterer. (3) Corrosion casts for scanning electronmicroscopy. The right uterine vasculature was drained and filled with a plastic medium by injection through the abdominal aorta at the level anterior to the iliac artery. The plastic medium consisted of methacrylic methyl ester monomer with 1% benzoyl peroxide as a catalyst, 1% dimethylaniline as an accelerator, and 15% dibuthylphthalate as a plasticizer. After injected plastic medium was polymerized, the specimens were subjected to corrosion with 20% sodium hydroxide, washed in running water, and then dried. The resin casts thus obtained were dissected into pieces under a binocular microscope, each piece being mounted on a metal block, coated with gold in an ion-sputterer, and observed under a scanning electron microscope (JSM-1) with an accelerating voltage of 10kv. Brief review of anatomy of the rabbit uterus The rabbit uterus consists of two horns and is situated entirely in the pelvic and abdominal cavities. It appears to vary considerably in position between multiparous and nulliparous rabbits. Each horn is cylindrical, but slightly flattened dorsoventrally, so that in cross section it is elliptical. Its length averages 4 to 5cm and its diameter about 0.6cm. The left and right uterine horns join the vagina at the caudal part independently. Each horn attaches the abdominal and pelvic walls with the aid of an extensive peritoneal fold, the uterine broad ligament, which extends from the sublumbar region and the lateral pelvic wall to the dorsal border of the horn (mesometrial side) and contains vessels and nerves to and from the ovary and uterus on its side. The wall of the uterus consists of three coats. The serous coat (perimetrium), for the most part, fast adheres to the muscular coat, and is continuous with the broad ligament. The muscular coat (myometrium) consists of a circular inner layer and a longitudinal outer layer of smooth muscles. Between the two layers is a well-defined area from which many blood vessels pierce the inner myometrial layer to enter the mucous membrane. Lymphatics are confined to this muscular coat. The absence of lymphatics in the endometrium is probably insufficient to make it immunologically privileged, but might delay the immunological response (McLean and Scothorne, 1970). The mucous membrane (endometrium) located inner side of coat appears brownish red with naked eyes. It is covered by the epithelium, and contains numerous long, branched tubular uterine glands in the stromal elements. The endometrium composes symmetrical pairs of longitudinal folds: a pair of placental fold which is the largest and situated on either side of the groove corresponding to the insertion of the mesometrium; a pair of ob-placental fold which is the smallest and opposite to the mesometrium; a pair of peri-placental fold which is intermediate in position and size. The uterine gland of the rabbit is branched tubular and is lined by either cuboidal, columnar, or pseudostratified epithelium. The luminal epithelium undergoes hypertrophy and hyperplasia, and shows a strong secretory activity during pregnancy. Both qualitative and quantitative changes in uterine fluid composition during the period of implantation are reported, and may be concerned with the s rvival of the developing blastocysts (Aitken, 1977; Veithlauf, 1976,1978; McLaren, 1973). The endometrial epithelium consists of ciliated cells and non-ciliated secretory cells. Cyclic structural changes occur at certain stages of the estrous cycle and pseudo- and normal pregnant stages. Non-ciliated secretory cells are numerous, whereas ciliated cells are very rare. The architectural pattern of the surface epithelium and the number of the ciliated cells vary with endogenous hormonal stimuli to facilitate the transportation of gametes and the release of secretory granules from the secretry cells (Hafez and Kanagawa, 1972). Furthermore, fine enfoldings of the epithelium together with the ciliated cells may act as a 'sperm passage' leading to the site of fertilization, a 'sperm barrier,' or a 'sperm reservoir.' A Note on Terminology The nomenclature of the main vessels used in this report is that proposed by the International Commitee on Veterinary Anatomy Nomenclature. In the study of microcirculation with resin cast specimens the strictly anatomico-histological or functional terms of the vessels cannot be used because the soft tissues are rmoved for maceration. The nomenclature adopted is, therefore, based on the topographic position of the vessels in the vascular system according to the suggestions of Zweifach (1960). Some terms previously used by Hafez and Tsutsumi (1966), Tsutsumi (1967) are also adopted. Results 1. Non-pregnant (estrus) stage 1-1. Histology of the endometrium By light microscopy, the endometrium composed three pairs of folds, placental, peri-placental, and ob-placental. The epithelium was composed of non-ciliated and ciliated cells. Many neutrophils were present under the eithelium. The endometrial stroma was edematous with hypertrophic stromal fibroblasts, consisting of a loose network of collagenous fibers interspersed with amorphous non-staining stromal substances. By scanning electron microscopy, the surface of non-ciliated cells were slightly convex, hexagonal, and were covered with small nub-like microvilli. The ciliated cells were sparsely distributed among non-ciliated cells. Cell boundaries of the epithelial cells were distinct. 1-2. Vascular pathways to the uterus and the endometrial vascularity The vessels supplying the uterus were found to vary so greatly in diameter and tortuosity, according to specimens, body weights of the animals, perfusion pressures of the injected material, and viscosity of the medium, all of which are not discussed precisely in the present study. The uterine branch of the vaginal artery was originated from the vaginal artery as a ramification of the internal iliac artery, passing with a slight tortuosity in the mesometrium, craniad and in parallel to the uterus, to end by anstomosing with the uterine branch of the ovarian artery near the ovary. In its course, the uterine branch of the vaginal artery gave rise to the mesometrial arteries at regular intervals which ramified into 3 to 4 branches prior to bifurcation just before entering the uterine wall, similar to those in several other animal species; dog (Del Campo, 1974), cat (Del Campo, 1974), rat (Williams, 1948; Del Campo, 1972), camel (Ghazi, 1981), sheep (Lee and O'Shea, 1981; Dobrowolski and Hafez, 1970), mare (Ginther, 1972), guinea pig (Del Campo, 1972), hamster (Del Campo, 1972). The mesometrial artery, then, penetrated into the uterine wall to the site between the longitudinal and circular muscular layers, and branched therefrom into the circumferential uterine arteries surrounding the uterine wall to anastomose with those on the other side of the uterine horn. The circumferential arteries gave rise to some branches anastomosing each other to form a coarse arterial network at the site between two muscle layers where the network supplied many small branches to the muscle layers to form the myometrial plexus. The capillaries in the myometrial plexus tended to run parallel with muscle fibers; capillaries in the outer longitudinal muscle layer constituted those along the long axis of the uterus; those in the circular layer constituted transversally arranged capillaries. The circumferential arteries, then, gave rise to many twigs, as the radial arteries, at right angles to their origin. The radial arteries slightly tortuously coursed to the luminal surface in the endometrium. In their course, the radial arteries supplied many capillaries among which two principal intrauterine capillary plexuses, endometrial and subepithelial, were formed. The endometrial plexus consisted of a coarse capillary network, arteries running radially with slight tortuosity, and veins being much more voluminous than arteries and anastomosing each other to form a dense venous network in the stroma. The subepithelial plexus consisted of many capillaries to form a dense fine network which supplied the uterine glands. Capillaries surrounding the opening of the glands showed a honey comb in arrangement. Interestingly, some of these capillaries showed characteristic features in such a way that they were irregular in diameter with marked constrictions and sinus-like swellings which made each capillary "beads-like." These two vascular plexuses, endometrial and subepithelial, were formed in three pairs of folds in the endomerium, running longitudinally to the uterine horn; the placental fold located on the mesometrial side was the most vascularized, the ob-placental fold located on the antimesometrial side was the least vascularized, and the peri-placental fold located between the former two folds was intermediately vascularized. Venules arose from capillaries of each plexus of the three folds and coursed generally with the corresponding arteries. The uterine vein was close to the mesometrial attachment throughout the length of the uterine horn, less tortuous but thicker than the corresponding artery. 2. Pre-implantation stage (Day 3 to 6) This stage is characterized by general growth of the epithelial components, especially the glands. Vascular permeability increases and secretory products of both glands and luminal epithelium show a steady increase in amount. The blastocysts reach the uterine cavity by Day 5. Their attachment to the endometrium, however, does not yet occur by Day 7. 2-1. Histology of the endometrium By light microscopy, the three pairs of major folds developed remarkably and became tall. The epithelium became pseudostratified, and the glands prolifereated by Days 3 to 5. By Day 6, histological evidence showed that the epithelial secretory activity became strong. The endometrial stroma appeared much more vascular and edematous than in non-pregnant (estrus) stage. All vessels in the stroma were prominent, enlarged and congestive. The vascular wall became thin. The nuclei of the endothelial cells in small vessels and in capillaries were prominent and protruded into the vascular cavity. Neither extravasation of blood nor pseudo-eosinophil cell was seen at this stage. By scanning electron microscopy, mucosal folds had begun to invaginate into narrow recesses. The ciliated cells were decreased in number and located sporadically, and disappeared by Day 6. The non-ciliated cells came to show convex surfaces and further protruded with a dome-like shape each by Day 6. The foregoing histological characteristics in the endometrium during this period were very similar to those in pseudopregnancy, so that the identification of pregnancy and pseudopregnancy was impossible at this stage. 2-2. The endometrial vascularity The endometrial vascular bed also developed markedly with drastical changes in the vascular pattern. Arteries and veins in the placental fold elongated straightly and increased in diameter. These vessels were much more voluminous than those during estrus. They ran parallel to each other in the core of the placental fold and spred out near the subepithelial plexus. The subepithelial plexus became thick and prominent. Capillareis in the plexus, which increased in number, were dilated and elongated. They ran around uterine glands with slight tortuosity. Those characteristic beads-like capillaries, which were observed frequently in the estrus endometrial vascular system disappeared. Some of these capillaries which lost the beads-like structure ran somewhat straightly to the uterine cavity to end at T-junction with marginal capillaries which ran just under the epithelium. The marginal capillaries with a slight tortuosity formed an arabesque network and merged into venules. These venules drained into veins in the cores of the folds after taking a slightly convoluted course. In the capillaries surrounding uterine glands and in the marginal capillaries, surface roughness and elliptical depressions were frequently observed, presumably being resulted from protrusions of nuclei of the endothelial cells. There was no characteristic feature as a sign of extravasation of blood. Additionally, there were no clear differences in the vascular pattern between the conceptus and the interconceptus by Day 6. In pseudopregnancy at this stage, changes in the vascularity were almost the same as the changes seen in pregnancy. 3. Implantation stage (Day 7) Implantation in the rabbit occurs as a complex series of events taking place over a period of two days; the blastocyst adheres firstly to the anti-mesometrial area of the uterus on Day 7 and secondly to the mesometrial area on Day 8. 3-1. Histology of the endometrium By light microscopy, the placental fold was more expanded at the apical parts with an increased amount of the subepithelial stroma and with an increased degree of vascularity. Minor foldings were gradually and increasingly formed on the fold, each folding becoming elaborately slender with a core of connective tissues. The uterine glands underwent concomitant changes in such a manner that they were elongated and dilated to encroach upon the cores of these minor foldings. The epithelial cells of both the minor foldings and the uterine glands were begining to make the "dome-like" protrusions at the apical cytoplasm, the protrusions which suggested a strengthened secretory activity of the epithelial cells. The endometrial stroma appeared much more vascular and edematous than that in the pre-implantation stage. Pseudo-eosinophil cells were commonly observed in the surface epithelium, vascular walls, and endometrial stroma. Small nests of hemorrhage and extravasation were found in the subepithelial plexus. Vascular walls became thinner. The ob-placental fold was markedly reduced in thickness. The mucosal minor foldings were not formed, and the uterine glands were greatly reductive. The epithelium was still simple columnar. Pseudo-eosinophil cells did not appear. The connective tissues around the vessels appeared slightly edematous. In some areas, individual endometrial epithelial cells lost their cell boundaries to make independent symplasmic masses among the remaining individual cells. These masses together with individual cells were enslaved and destroyed by the overlying symcytiotrophoblast which invaded between intact endometrial cells to the basal lamina. The trophoblastic masses which first adhered to the endometrium was termed "pegs" by Allen (1971). The peri-placental fold showed changes similar to those in the placental fold. In addition, the interconceptus also showed changes almost similar to those in the interconceptus of the pre-implantation stage. By scanning electon microscopy, the minor mucosal foldings of the placental fold came to be more branched than those in the pre-implantation stage. Consequently, among masses of these slender foldings were formed relatively wide crypt-like fossae. The epithelial cells came to be characterized by apical cytoplasmic dome-like shaped protrusions. 3-2. Endometrial vascularity At this stage, three to five implantation chambers began to appear as local swellings located at regular intervals in each uterine horn, and therefore, areas of the conceptus and interconceptus could be clearly recognized. The vascular bed in each major fold except for the ob-placental fold became more and more voluminous, but the fundamental vascular arrangement seemed to be not so different from that in the pre-implantatin stage by Day 6. The uterine lumen remarkably increased in width, with the development of the blastocyst. The placental fold became larger and the cores of the folds increased in size. The vessels, especially veins, increased 3 to 4 times in diameter as compared with those at the non-pregnant stage. The subepithelial plexus reached a maximum in thickness. Capillaries in the plexus became abundant and were stretched. The surface of capillaries appeared to be more rough with more frequent elliptical depressions representing nuclear indentations than before. Many resin leakages suggestive of hemorrhage and/or fragility of vessels were observed in the marginal capillaries just under the uterine epithelium. In the ob-placental fold, the vascular bed became drastically thin. The original complex capillary arrangement of the endometrium was completely lost, resulting in a simple capillary network. This was due to the rapid expansion of the blastocyst toward the ob-placental fold by stretching the uterine wall. There were no features showing extravasation in capillaries in this fold. The surface of marginal capillaries, however, was rough sporadically from portion to portion. In the peri-placental fold, the vascular bed developed at about the same rate as in the placental fold. Additionally, the vascular arrangement was similar to that in the placental fold. Resin leakages, which were seen frequently in the placental fold, were hardly observed in capillaries in the peri-placental fold. The surface of capillaries, however, were rough with nuclear indentations of the endothelial cells just as seen in the placental fold. Interconceptus area (non-implantation site): Of interest was that the fundamental vascular system at this site on Day 7 of gestation was similar to that at the pre-implantation stage on Day 5. In the pseudopregnant uterus at this stage, the histological and vascular structure did not show any progressive developement, but remained just as in earlier stages, in contrast to the normal pregnant uterus at the same stage of days. Thus, definitive differences became clear between the normal and the pseudo-pregnancies by day of implantation, Day 7 after coitus. 4. Post-implantation stage (Days 8 to 9) As mensioned previously, the first adherence of the blastocyst occurs on the anitmesometrial side on Day 7, and one day later the second adherence occurs at the placental fold on the mesometrial side to form the definitive placenta at this site, when the blastocyst is approximatedly 10mm in diameter. The conceptuses become clearly recognizable as local swellings of the uterine horn. 4-1. Histology of the endometrium The placental fold became remarkably developed, whereas the ob-placental folds diminished in size by a pressure of the blastocyst. All epithelial cells changed into symplasma. Following the formation of symplasma, fusion of the syncytiotrophoblast with it proceeded. The syncytiotrophoblast invaded maternal tissues and penetrated uterine blood vessels, causing small hemorrhages in all conceptuses. All muscle cells in the vascular walls and fibroblasts in the lamina propria changed into decidual cells by this day, 2 days after implantation. Numerous pseudo-eosinophil cells were found in blood vessels and the connective tissue of the lamina propria. Some pseudo-eosinophil cells invaded vascular walls and penetrated the connective tissue. Vessels in the lamina propria of the placental fold became more voluminous and elongated. The subepithelial capillaries came to form well-defined capillary complex with numerous fine aneurisms. 4-2. Endometrial vascularity In the placental fold, the vasculature developed to the maximum extent with remarkable changes. Arteries in the lamina propria elongated straightly and increased in diameter. These changes in arteries were not so remarkable as compared with those in veins. Veins were dilated much more remarkably than before. The veins anastomosed each other and formed a large venous network. The implantation area was specialized by the vascular characteristics. The subepithelial plexus lost its original vascular pattern, irregularly arranged with local sparsity. The plexus came to have many clusters of granualr structures (10 to 35μm in diameter) in capillaries. The clusters, which were directly connected to the radial arteries, might represent fine vascular cavity consisting of surface sinuses and trophoblast lacunae. Interestingly, numerous fine bud-like protrusions of approximately 4 to 10μm in diameter began to appear on the capillaries and small vessels. These fine protrusions were observed to be frequently fused each other and formed a "mulberry." In some cases, the mulberries connected two adjacent capillaries to shunt them. The marginal capillaries lost the arabesque arrangement and were dilated remarkably to reach approximately 50μm in diameter, draining into the surface blood sinuses. The dilated capillaries, however, were observed to have many constrictions of approximately 2.8μm in diameter. The venules draining blood from the marginal capillaries were very narrow before merging into the veins in the center of the fold and dilated abruptly to produce a "bottle-neck" at the level of the post-capillary region. Resin lumps which might represent hemorrhage areas were observed at many sites of the lamina propria of the placental fold. In the ob-placental fold, the vasculature became minimum density and completely lost the original vascular pattern. The capillaries did not show any characteristic changes as seen in the placental fold. In the peri-placental fold, the vascularity developed remarkably as in the plcental fold. The general vascular pattern also was similar to that in the placental fold. The capillary arrangement of the subepithelial plexus, however, was still like that of the implantation stage on Day 7. The bud-protrusions were also frequently observed. The endometrium of pseudopregnancy at this stage was similar to that in the earlier stage, with little progressive development. However, some regrressive change, i.e., sloughing of the epithelium came to appear. Vascular changes, such as fine aneurysms, blood sinuses, hemorrhages which were characteristic in normal pregnancy, were not obseraved. However, many occluded or torn-off capillaries became apparent in the subepithelial plexus in which the number of capillareis was reduced. Discussion The present study on the endometrial vascularity of the rabbit revealed a fine vascular arrangement at non-pregnant stage and a remarkably rapid growth and differentiation of the vascular system at early pregnant stages. The present observations on the histological changes in the endometrium during early pregnancy are in general agreement with findings of earlier investigators. The present study suggests that scanning electron microscopy of the cast of vasculature may provide a useful method for elucidation of fine changes in the vessels. Artefact, such as vascular "blow-out", because of their characteristic appearance, is easily recognizable when present, but in fact, it occurs infrequently. Since the present study is in harmony with that of earlier investigators in terms of histological changes, the following discussion will be defined to the progressive changes of the endometrial vascularity. 1. Non-pregnant stage The present study shows that some discriminations in the vascularity can be made between rabbit and other animal species. In the human uterus, numerous arterio-venous anastomoses are found between terminal branches of the radial arteries and veins. These anastomoses are so thick in diameter that they are called "venous lake" (Kigawa, 1971). In the rat uterus, the radial arteries are developed well, showing a marked tortuosity at the mesometrial area to form a characteristic arterial arragement so-called "mesometrial triangle" (Williams, 1940). Neither the venous lake nor mesometrial triangle was found in the rabbit uterus. The above mentioned variations in the vascular patern from animal to animal may be related to both the way of temporal attachment of the blastocysts and the way of development of the placenta. Numerous characteristic capillaries with beads-like structures were found in the rabbit endometrium. Such structures were also found in the rat endometrium at the stage of estrus (the author's unpublished observation). This characteristic beads-like structure is not an artefact caused by disruption of the vessels through the resin injection, since it can be found histolgocally in serial sections. These beads-like capillaries seem respond endogenous hormonal effects, since they disappear both in pregnant rabbits and in ovarectomized rabbits (the author's unpublished observation). 2. Pre-implantation stage An increase of the vascular permeability is well known at this stage. As the localization of implantation sites can be visualized grossly by the pontamine Blue reaction (Ender and Schlafke, 1969), many investigators have accepted this intravascular injection of the dye to identify implantation sites. The subepithelial plexus shows drastic changes. Capillaries surrounding uterine glands are elongated and increased in vascular density and diameter. In addition, the surfaces of these capillaries are rough with nuclear indentations from the endothelial cells. These changes in the vascularity may largely reflect the high secretory activity and the enhancement of the vascular permeability, in the light of the fact that secretory products of both glands and luminal epithelium show a steady increase in amount during early pregnancy (Urzua et al., 1970). There is no clear difference in structrue of capillaries betwen the conceptus (implantation site) and the interconceptus at this stage by Day 6. The similarity in vasculature between pseudo- and normal pregnancis during early stages has been reported by Hafez and Tsutsumi (1966) in rabbits and by Williams (1948) in rats. The results of this study on the rabbits have confirmed their findings. There is no clear discrimination in vascular structure between pseudo- and normal pregnancies during pre-implantation stages. 3. Implantation stage On Day 7, the rabbit blastocyst first begins to contact with the uterine epithelium on the antimesometrial side, and therein, trophoblastic knob is formed and penetrates the endometrium. As such, the blastocysts cling to the implantation sites until the definite implantation takes place on the mesometrial side (Enders and Schlafke, 1971). This transient antimesometrial contact serves to anchor the blastocysts in the implantation chamber until the mesometrial implantation can be well established (Enders and Schlafke, 1971). The vasculature on the antimesometrial side at this stage develops poorly without marked characteristic features, indicating that the blastocyst-contact on this side is not associated with the vascular development and that this first transient implantation is limited to functional degree of hanging the blastocyst on the uterine epithelium. However, as the penetration of the trophoblastic knob proceeds, it takes a more intimate relationship with the maternal blood vascular system, thus ideally facilitating the exchange of substances between the mother and the embryo (Enders and Schlafke, 1971). The mesometrial or the second (definitive) implantation site shows a marked development in that the vasculature in the plcental fold is composed of well-stretched and swollen radial arteries and veins, thickened subepithelial capillary plexuses, and characteristic marginal capillaries. These compositions may have significant relations to the formation of the definitive chorioallantoic placenta. According to Roger et al., (1982), rats show a development in the endometrial vasculature quite different from that found in rabbits. The vasculature at the implantation site in rats is well formed and the vessels appear to have larger luminal diameters than those in the interimplantation regions have. These differences between the rabbit and the rat are probably due to differences in the mode of implantation and in the form of the definitive placenta. Implantation in rabbits is superficial or central, while that in rat is interstitial (Perry, 1981). The gestational evolution of the endometrium is observed similar both in pseudo- and normal pregnancies by Day 7, just as observed by the earlier investigators. According to Hafez and Tsutsumi (1966) and Loeb and Smith (1930), the mucosal elevation is due to glandular proliferation. Davies (1973) suggested that this elevation is stromal and rises above the level of the openings of glands, emphasizing that this has important implications for analysis of the implantation process. The present observations on the surface structure of the endometrium with a scanning electron microscope are well in harmony with Davies' suggestion. 4. Post-implantation stage The endometrial vasculature in the placental fold shows a maximum development at this stage. Numerous fine bud-like protrusions or surface irregulalities, which are possibly corresponding to micro aneurysms noted by light microscopy, are observed in the fine blood vessels in the placental fold. These features may be the first changes in the cpaillaries after implantation. They seem to be important structures for the future blood sinus formation or capillary hemorrhage generally found in the earlier stage of pregnancy. The present observations on histological sections show that many pseudoeosinophil cells invade into the vascular wall and infiltrate the decidual tissue. These heterophil leukocytes aiso appear in the vagina following mating. According to David et al., (1977), within 45 minutes after mating in the rabbit, numerous heterophil leukocytes adhere to the endothelium of venules in the vagina. These leukocytes pass through endothelial cells and migrate to the stroma. Subsequently, they immigrate the vaginal lumen where they actively engulf spermatozoa. They seem to play an important role both in fertilization and in formation of aneurysm, blood sinus, and hemorrhage. The present study confirms that sloughing off of the epithelium and occlusion or torn-off of capillaries begin on Day 9 of pseudopregnancy. According to Chang (1949) who investigated the fate of transferred rabbit ova or blastocysts in accord with the ovulation time of recipients, the transferred ovum or blastocyst fails to develope into young when transferred into pseudopregnant uterus after Day 9. Therefore, the above-mentioned degenerative changes in the epithelium and capillaries seem to be responsible for the failure in growth of the ovum transferred after Day 9 of pseudopregnancy. Investigations are now in progress in relation to the changes in the fine blood vessel in the endometrium of the rabbit during different pregnancy. Further studies are to deal with the question of whether the delicate changes which should occur in the fine vessels of the rabbit are of a nature similar to that found in the rat. In addition, a special attention should be paid in relation to the cause of abortion frequently occuring at the end of pregnancy in the rabbit. Acknowledgements The author wishes to express his cordial thanks to Drs. Tsunenori Nakamura, Tatsuomi Ouchi, and Yasunobu Eguchi, Professors of Azabu University for invaluable advices and reviewing cordial manuscript. |
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| 学位名 | ||||||||||
| 学位名 | 獣医学博士 | |||||||||
| 学位授与機関 | ||||||||||
| 学位授与機関名 | 麻布大学 | |||||||||
| 学位授与年月日 | ||||||||||
| 学位授与年月日 | 1983-04-13 | |||||||||
| 学位授与番号 | ||||||||||
| 学位授与番号 | 乙第209号 | |||||||||
| 著者版フラグ | ||||||||||
| 出版タイプ | AM | |||||||||
| 出版タイプResource | http://purl.org/coar/version/c_ab4af688f83e57aa | |||||||||
