Summary. Collagenase-dispersed theca cells from the 3rd and 4th largest ovarian follicles (T3) were responsive to LH stimulation of both oestrogen and androstenedione production, whereas theca cells from the largest follicle (T1) failed to respond to the gonadotrophin stimulation. Similarly, 8-bromo cAMP and forskolin were more effective in stimulating oestrogen and androstenedione production in T3 than in T, cells, indicating that post-receptor events were involved in the decreased LH responsiveness of T, cells. The C17–20-lyase activity, as measured by conversion of [3H]17-hydroxyprogesterone to androstenedione, was greatly reduced in T, cells as compared to T3 cells. The results demonstrate that a decrease in C17–20-lyase activity, in addition to a decrease in aromatase activity, contributes to the loss of LH-stimulated steroidogenesis in mature theca cells.
R. K. O'Keefe and B. L. Marrone
Summary. Isolated theca cells (2 × 105/ml) were pre-incubated for 1 h in the presence or absence of clomiphene citrate (10−12–10−4 m). Ovine LH (50 ng/ml) was added and cells were incubated for an additional 3 h. A 50% inhibition of LH-stimulated androstenedione and oestrogen production was obtained with doses of 10−8 m and 2 × 10−7 m clomiphene, respectively. Furthermore, the effect of clomiphene on LH-stimulated androstenedione production was reversed by washing clomiphene from the cells before stimulation with LH. In subsequent experiments, the effects of clomiphene on C17–20-lyase and aromatase activities were examined. Conversion of [3H]17-hydroxyprogesterone to androstenedione was inhibited by 50% when theca cells were pretreated with 10−5 m-clomiphene. In addition, conversion of testosterone to oestrogen by theca cells was inhibited in a dose-dependent manner by clomiphene, with 50% inhibition occurring at a dose of 5 × 10−6 m. The results show that clomiphene treatment in vitro inhibits androgen and oestrogen production in theca cells by inhibitory effects on the activities of C17–20-lyase and aromatase. In addition to the widely-accepted effects of clomiphene on the hypothalamic—pituitary axis, the present findings add further support to the suggestion that clomiphene exerts direct effects on ovarian steroidogenesis.
B. L. Marrone and E. K. Asem
Summary. LH was used to stimulate cAMP production in theca cells from the 5 largest preovulatory follicles of hens and this was related to LH-stimulated androstenedione production in the same cells. cAMP production was stimulated by LH to the same extent in theca cells from each follicle. However, LH was not effective in stimulating androstenedione production in theca cells from the largest follicle (T1), although androstenedione production was greatly increased by LH in the smaller follicles (T2–T5). Effects similar to those of LH on cAMP production were observed in response to forskolin, indicating that the intrinsic adenylate cyclase activity was similar in theca cells from each follicle. In addition, forskolin was unable to stimulate androstenedione production by T1 cells. Our results provide evidence that the levels of receptor-mediated and non-receptor-mediated cAMP production are similar in theca cells from the 5 largest follicles. We conclude that the step that restricts the ability of T1 cells to produce androgen is distal to cAMP generation.
Keywords: cAMP; theca; LH; follicular maturation; domestic hen