Ovarian hCG and FSH receptor content was measured at different postnatal ages (days 4–32), at 4-day intervals, and expressed as counts per min l25I-labeled hormone bound /μg DNA. Specific FSH binding was minimal at day 4 and increased to a maximum at day 28, with the greatest rate of increase between day 4 and 16. hCG receptor content increased 6-fold between day 4 and 32, but contrasting with FSH, its greatest rate of increase occurred between day 16 and 28. The effectiveness of in vivo treatment with LH in inducing ovarian ornithine decarboxylase (ODC) activity, measured in 20, 000 × g supernatants by the in vitro formation of l4CO2 from labeled ornithine, increased significantly during prepubertal development (days 21–33), paralleling the changes in hCG receptors.Ovarian hCG and FSH receptor content was also measured during the time of puberty. Specific hCG binding increased from anestrus (juvenile 32-day-old animals) to 1300 h of the first proestrus. The levels declined significantly by 1600 h of first proestrus and reached minimal values by the morning of estrus. Specific FSH binding also increased from anestrus to first proestrus, but to a much lesser degree, the levels showing only minor fluctuations during the rest of the cycle. hCG receptors measured in granulosa cells during puberty increased to an even greater extent than in the whole ovary; binding exhibited an 8-fold increase from anestrus to 1300 h of first proestrus and then declined to much lower values on estrus and the first diestrus. The capacity of LH to induce ovarian ODC activity increased markedly between anestrus and first proestrus, declining thereafter, and again paralleled the changes in LH receptor content.Evaluation of the kinetics of binding of hCG and FSH with their respective receptors in ovaries of 28-day-old rats revealed that the binding of hCG reached equilibrium within 4–8 h, whereas the binding of FSH attained equilibrium between 12–24 h. In both cases, however, the labeled hormones were clearly dissociable from their respective receptors by addition of an excess of unlabeled hormone. Moreover, although the ovarian receptor content of both hCG and FSH increased during prepubertal development, the equilibrium association constant of ither hormone with its receptor remained unchanged.The results suggest that the infantile increase in FSH receptors may be induced by the high serum FSH levels present at that age and that, as shown by others in hypophysectomized rats, the subsequent increase in hCG receptors is, at least in part, an FSH-dependent phenomenon. The parallel changes in hCG receptors and LH-induced ODC activity during pre- and peripubertal development strongly suggest that an increase in LH binding capacity plays a fundamental role in the process of ovarian growth. It is also suggested that the changes in the steroidogenic ovarian response to hCG previously observed in peripubertal rats are, at least in part, determined by changes in ovarian LH receptor content.
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