Correlation of plasma estradiol-17 beta and progesterone levels with ultrastructure and histochemistry of ovarian follicles in the white-spotted char, Salvelinus leucomaenis.

Plasma estradiol-17 beta and progesterone profiles were correlated with morphological changes in ovarian follicles during the preovulatory and postovulatory periods in the white-spotted char, Salvelinus leucomaenis, Plasma estradiol levels were highest in September, and were followed by a sharp drop in October; they remained very low throughout the postovulatory period. There was a good correlation between plasma estradiol levels and the gonadosomatic index, thus suggesting that estradiol is responsible for the synthesis of vitellogenic proteins. Plasma progesterone levels were very low in August, began to rise in September and reached a peak soon after ovulation; progesterone remained high for several days after ovulation. A preovulatory rise in plasma progesterone levels was recorded, and this is discussed in relation to the induction of oocyte maturation. In the preovulatory follicles, neither granulosa cells nor special thecal cells (ST cells) showed delta 5, 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity. In the young postovulatory follicles, in contrast, the ST cells showed intense 3 beta-HSD activity with extensive agranular endoplasmic reticulum and numerous large mitochondria, while granulosa cells did not show 3 beta-HSD activity. These results strongly suggest that the ST cells are the major sites of progesterone synthesis during the postovulatory period.