Supplemental Observations on Structural Changes in Stigmal Tissue of Hen's Ovarian Follicle in the Process of Ovulation

鶏の排卵は卵胞スチグマ部の破裂によってもたらされる。本研究は形態学的観点から, スチグマの破裂機構を明らかにするため, 排卵に伴うスチグマ組織の構造的変化を調べた。所見は次のとおりであった。
1. 成熟卵胞のスチグマ部は, 本来的に特徴的構造を具えていた。この部は, 卵胞壁の厚さの大部分が外卵胞膜層によって占められ, また, 血管の分布が著しく劣っていた。外卵胞膜層は線維結合組織であり, 層状に配列するシート状の膠原線維束によって緻密に構築されていた。
2. 排卵直前にはスチグマ部の顆粒層と外卵胞膜層に大きな構造的変化が現われた。スチグマの顆粒細胞は空胞様に変性し, 破裂部位では扁平化して消失した。一方, 外卵胞膜層の膠原線維束は単線維または細線維に解疎し, 薄い線維層となった。
3. 上記のようなスチグマ組織の構造的変化は, その変化像から判断して単なるスチグマの拡張に伴って二次的に生じたものではなく, むしろ何らかの酵素的作用によってもたらされたものと推察された。
4. 排卵後に卵胞は急に収縮した。これに伴って顆粒層は基底膜とともに卵胞膜層から剥離し, 顆粒細胞は空胞様変性を伴う退行過程に入った。
5. 以上の所見から, スチグマ破裂は, 先行的にスチグマ組織の崩壊, 脆弱化がもたらされ, これに卵胞膜の張力が加わることによって引きおこされるものと考えられた。

Structural changes occurring in the process of ovulation were examined morphologically in the stigmal tissue of the hen's ovarian follicle to clarify the mechanism of ovulation. The examinations were carried out mostly by scanning electron microscopy and partly by conventional light microscopy. The findings obtained are as follows.
1. The stigma of the follicle, where rupture occurred, had a characteristic structure favorable for rupture. Its wall was occupied by the theca externa for the most part. The theca externa was composed of collagenous connective tissue. In it, collagen fibers tended to run parallel to the longer axis of the stigma. The blood supply was very poor in the stigma. Particularly, the theca externa lacked blood vessels running vertically.
2. In the theca externa, collagen fibers were bound together into sheet-like bundles, arranged densely in layers. Granulosa cells lining the inner surface of the stigmal wall were cuboidal in shape and possessed a prominent cytoplasmic process and numerous fine microvilli.
3. Immediately before the time of ovulation, the compact bundles of collagen fibers were dissociated into a sparse network of fibers or fibrils. The change was presumed to have been induced by the action of some proteolytic enzymes. The granulosa cells of the stigma were involved in characteristic vesicular changes suggesting the release of cytoplasmic inclusions.
4. The regressive changes of the granulosa cells in the post-ovulatory follicle were characterized by marked vesicular changes accompanied with the decomposition of the cell body.
5. From the findings mentioned above, ovulation was assumed to be induced in hens by a combination of the preceding decomposition of the stigmal tissue by certain proteolytic enzymes and the tensile strength of the follicular wall.