Analysis for the 5alpha-steroid reductase in the bovine ovary with (14C)-progesterone and (14C)-testosterone

Follicle-stimulating hormone and luteinizing hormone regulate the synthesis mechanism of dihydrotestosterone in sheep granulosa cells

Steroid hormones and receptors play important roles in female reproduction, and their expression patterns affect follicular growth and development. To examine the expression of dihydrotestosterone (DHT) synthases (5α-reductases (5α-red1 and 5α-red2)) and androgen receptor (AR) during follicular development, and the regulation of DHT signalling by follicle-stimulating hormone (FSH) and luteinizing hormone (LH), we have used enzyme-linked immunosorbent assays, quantitative real-time polymerase chain reaction, immunohistochemical staining and Western blotting to examine DHT synthesis in small (≤2 mm), medium (2-5 mm) and large (≥5 mm) sheep follicles. Expression of 5α-red1, 5α-red2 and AR was observed in ovine ovaries, and with the development of follicles, the expressions of 5α-red1 and 5α-red2 mRNA and protein increased, but the levels of AR mRNA, protein and DHT level decreased. In addition, granulosa cells were treated with FSH (0.01, 0.1 and 1 international unit (IU)/ml), LH (0.01, 0.1 and 1 IU/ml) and testosterone (T, 10^-7  M) to evaluate the effects of FSH and LH on DHT and oestradiol (E2) synthesis and 5α-red1, 5α-red2 and AR expression. We found that FSH and LH upregulated 5α-red1 and 5α-red2 in sheep granulosa cells, but downregulated the concentration of DHT and expression of AR. Meanwhile, FSH and LH significantly upregulated the expression of aromatase (P450arom) and secretion of E2. This result indicates that although FSH and LH promote the expression of 5α-red1 and 5α-red2, T is not transformed into DHT, but E2. This study reveals the reason why DHT concentration is downregulated in large follicles and lays a foundation for further exploring the synthesis mechanism of DHT during follicular development.

Dihydrotestosterone synthesis in the sheep corpus luteum and its potential mechanism in luteal regression

Corpus luteum (CL) regression is a complex physiological process. Previous studies have shown that dihydrotestosterone (DHT) may be involved in regulating CL regression, but the mechanism is still unclear. In this study, we evaluated the localization of the two isoforms of DHT synthetase 5α-reductase (5α-red1 and 5α-red2) and androgen receptor (AR) in sheep CL, and investigated 5α-red1, 5α-red2, AR, and DHT levels at different luteal stages of CL (early, middle, and late phase) by immunohistochemistry, quantitative real-time polymerase chain reaction, and western blot analysis. Moreover, we cultured luteal cells from middle phase CL and treated them with different concentrations of DHT (10^-10 -10 ^-6  M) and the AR antagonist flutamide (10 ^-5  M), to evaluate whether DHT is involved in the regulation of progesterone (P4) secretion and progesterone nuclear receptor (PGR) expression and whether these effects are regulated by the AR pathway. We also investigated the effects of DHT and flutamide on prostaglandin F2α (PGF2α) secretion and apoptotic gene and protein expression. Our results showed that 5α-red1, 5α-red2, and AR were expressed in the CL, and their expression and DHT levels were changed during the luteal phase. DHT was involved in mediating P4 and PGF2α secretion and PGR and apoptotic gene and protein expression. The effects of DHT on CL were at least partially regulated by the AR pathway. This study reveals the mechanism of action of DHT on sheep CL regression and lays the foundation for further exploration of androgen regulation of CL function.

The levels of 5alpha-dihydrotestosterone in follicular fluid in healthy and atretic ovine follicles

Dihydrotestosterone (DHT) induces follicular atresia under experimental conditions. However, whether it causes any antagonistic effect under natural condition is not known. In the present study, we investigated concentrations of DHT in follicular fluid and correlated them with concentrations of estradiol-17beta (E2) and its androgen substrates, androstenedione (A4) and testosterone (T), in healthy and atretic follicles of sheep. Merino ewes were treated twice with PGF2alpha (PG) to synchronize estrus. The ovaries were recovered at 14 days after the second PG (luteal phase) or 24h after the third PG given 14 days after the second PG (follicular phase). Follicles were dissected and their size and appearance were recorded. Follicular fluid was collected from follicles larger than 3.5mm and concentrations of E2, progesterone (P4), A4, T and DHT were determined by RIA. The inhibitory effect of DHT on conversion of T to E2 was tested in cultured granulosa cells. Appreciable levels of DHT were observed in the follicular fluid of ovine preovulatory follicles. The levels of DHT were much lower than those of E2, A4 and T, irrespective of physiological conditions of follicles. No difference was found in DHT concentration between healthy and atretic follicles. Dihydrotestosterone marginally inhibited aromatization of T in granulosa cells but this effect was only observed when the levels of DHT were 10 times higher than that of T in culture medium. These results indicate that DHT is present in ovine preovulatory follicles but its levels are not sufficient to exert any antagonistic effect on follicular development.

Androstenedione and progesterone production in vitro by the inner or the outer theca cells in preovulatory follicles of gonadotropin stimulated calves

This study reports some of the steroidogenic characteristics of the interna and externa theca cells taken from young and eCG primed calves. These cells were isolated from large healthy follicles. The were separately cultured for 3 days in absence or in presence of steroid substrates. Androstenedione (A4) and progesterone (P4) were measured by radioimmunoassay (RIA). In control conditions, A4 levels, higher in interna than in externa cells (P < 0.001), decreased during cultures (P < 0.01). In both cell types, A4 increased in presence of 17 alpha-hydroxypregnenolone (17OHP5), pregnenolone (P5) and 22R-hydroxycholesterol (22R-chol)(*P < 0.05) but not with P4 or 17 alpha-hydroxyprogesterone (17OHP4)(P > 0.05). The most efficient substrate was dehydroepiandrosterone (DHEA) (P < 0.005). In control conditions, P4 levels increased in both cell types. They were higher in externa than in interna cells on day 1, the reverse was observed on day 3. P4 levels increased after addition of 22 R-chol and P5 (P < 0.005) but not with 17OHP5, 17OHP4 and DHEA (P > 0.05) from day 1 in externa cells and only on day 3 in internal cells. P4 levels measured on day 1 were lower than the quantity of P4 added as a substrate. These results, obtained with theca cells from young calf follicles, indicate: 1/A4 is synthesized by the delta5 pathway and 17 alpha-hydroxylase activity decreases in vitro, 2/externa and interna cells differ by the quantities of A4 and P4 produced, 3/both lack precursors to produce A4 and P4 but their 3 beta-hydroxysteroid dehydrogenase activity subsists, 4/P4 could be metabolized during the first 2 days in both cell cultures.