Ovarian steroidogenesis in the proestrous hamster

Abstract

In the proestrous hamster, in response to the LH surge, there is a dramatic and sustained increase in serum progesterone (P) and transitory increases in testosterone (T), estrone (E₁) and estradiol-17β (E₂). Ovarian steroidogenesis in the proestrous hamster was analyzed in detail by studying: 1) concentrations of these steroids in the whole ovary, antral follicles (AF) and the nonantral follicular portion of the ovary (NAO) at 1200 h (prior to the LH surge), 1500 h (during the LH surge) and 1800 h (after the LH surge); 2) in vitro steroidogenic production by the AF and NAO, as well as the whole ovary (removed before 1200 h, 1500 h and 1800 h and 3) in vitro effects of LH, FSH and P on steroidogenesis of ovaries removed before the LH surge and incubated for 2 h. P concentration was the same in AF and NAO at 1200 h but increased slightly in the AF with the onset of the LH surge. Both the concentration and production rate of P increased from a minimum at 1200 h (1 ng/mg/h) to a maximum by 1800 h (30 ng/mg/h) in the ovary, AF and NAO. On the other hand, the concentration of T, E₁ and E₂ was selectively greater in the AF at all times. Maximum T production occurred in the ovaries removed during the LH surge (150 pg/mg/h) followed by a significant decline by 1800 h. However, AF produced negligible amounts of T at all times. In the NAO, the production of T was essentially the same (about 20 pg/mg/h) in all 3 incubations. The production of E₁ and E₂ was much greater in the AF than in the NAO, especially between 1200-1500 h. By 1800 h, the levels and synthetic capacity for estrogens in the ovary, AF and NAO declined to baseline levels, while the production of P was still very high. These studies indicate that in the proestrous hamster, steroidogenesis in the NAO which largely represents the interstitial compartment is limited to the production of P and androgens and only a negligible fraction passes down the pathway to form estrogens. On the other hand, steroidogenesis is more complete in the AF where it can proceed efficiently as far as estrogens. LH (5-250 ng/ml) added in vitro increased the production rate of all steroids whereas 1 ng LH increased only the synthesis of E₂. FSH (100-200 ng/ml) also stimulated E₂ production but not E₁. Higher concentration of FSH (250 ng/ml) resulted in overall increases in P, T, E₁ and E₂ possibly due to contamination with LH. Exogenous P (10, 100 ng/ml) had no effect on T or E₁ synthesis, but E₂ production was enhanced.