Biology of Reproduction, Vol 23, 577-582, Copyright © 1980 by Society for the Study of Reproduction

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

¹ Department of Hormone Research, Kimron Veterinary Institute, P.O.B. 12, Beit-Dagan, Israel

Estradiol-17 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 estradiol-17 secreted by the incubated ovaries of the early active phase was 1.5 ± 0.4 ng/ovary/24 h (mean ± SEM), and in the presence of bovine LH estradiol-17 secretion was significantly enhanced (4.2 ± 0.6, P<0.001). In the presence or absence of LH, estradiol-17 was undetectable in the incubated ovaries of the refractory phase. Addition of testosterone to the incubation medium significantly enhanced estradiol-17 production (P<0.001) by ovaries of both the active and refractory phase. In contrast, neither progesterone, DHT, nor 17-hydroxyprogesterone affected estradiol secretion. In the time-course studies of estradiol-17 production in response to testosterone, the incubated active phase ovaries from fetuses of 5-8 cm CRL responded to testosterone within 30 min, whereas 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 both testosterone (P<0.001) and estradiol (P<0.02) production by the incubated active ovaries, whereas when the inactive ovaries were used only progesterone secretion was significantly enhanced (P<0.001). The data suggest that 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.

Note:
ACKNOWLEDGMENTS The author wishes to thank the National Pituitary Agency, NIH, NIAMDD for the generous supply of bovine LH (NIH-LH-B10). I also thank F. Mileguir and M. Ailenberg for excellent technical assistance.

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