Histochemistry and ultrastructure of pre- and post-ovulatory follicles in the ovary of the goldfish, Carassius auratus

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Abstract
Pre- and post-ovulatory follicles in the goldfish ovary were investigated histochemically and ultrastructurally. Special cells in the thecal layer of preovulatory follicles of yolk-laden oocytes showed 3β-hydroxy-Δ5-steroid dehydrogenase (3β-HSD; EC 1.1.1.145) activity typical of steroid hormone synthesis. Ultrastructurally, these thecal cells possess organelles characteristic of steroid-producing cells: mitochondria with tubular cristae and agranular endoplasmic reticulum. Unlike thecal ceils, the granulosa cells contain organelles typical of protein-secreting cells. These findings strongly suggest that only the special theca cells are sites of estrogen synthesis in the goldfish ovary.Postovulatory follicles, 6–10 h after ovulation, were characterized by a highly vascular thecal layer and hypertrophied granulosa cells. A weak but definite 3β-HSD activity occurs in both special theca cells and granulosa cells. Ultrastructurally, the granulosa cells contain many lipid droplets and numerous Golgi elements, suggesting the possible immediate transformation of granulosa cells to lutein cells during the ovulation. However, 30 h after ovulation, both granulosa cells and special theca cells showed advanced degenerative features and these data do not seem to support the hypothesis of an endocrine role for the older postovulatory follicles of the goldfish.

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