Estradiol-17β Biosynthesis by the Early Bovine Fetal Ovary During the Active and Refractory Phases

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Abstract
Estradiol-17.beta. [E2] biosynthesis was studied by radioimmunoassay during the active phase of ovaries of early bovine fetuses of 5-8 cm crown-rump length (CRL) (n = 40) and during the refractory phase of ovaries of fetuses of 10-20 cm CRL (n = 85). The mean value of E2 secreted by the incubated ovaries of the early active phase was 1.5 .+-. 0.4 ng/ovary/24 h (mean .+-. SEM [standard error of the mean]) and in the presence of bovine LH [luteinizing hormone, lutropin], E2 secretion was significantly enhanced (4.2 .+-. 0.6, P < 0.001). In the presence or absence of LH, E2 was undetectable in the incubated ovaries of the refractory phase. Addition of testosterone to the incubation medium significantly enhanced E2 production (P < 0.001) by ovaries of the active and refractory phase. Neither progesterone, dihydrotestosterone nor 17.alpha.-hydroxyprogesterone affected estradiol secretion. In the time-course studies of E2 production in response to testosterone, the incubated active phase ovaries from fetuses of 5-8 cm CRL responded to testosterone within 30 min; for the refractory phase ovaries, a lag period of 10 h was needed. Addition of 8-Br-cAMP caused a significant stimulation after 5 h of testosterone (P < 0.001) and E2 (P < 0.02) production by the incubated active ovaries; when the inactive ovaries were used, only progesterone secretion was significantly enhanced (P < 0.001). Apparently, the lack of ovarian aromatizable androgens may play a role in the change from the active to the refractory phase. That ovaries from bovine fetuses of 10-20 cm CRL become refractory suggests that the high estrogen level found at the time of the differentiation of the primordial gonad to ovary is of functional significance.

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