Reduction in testicular function in rats. I. Reduction by a specific gonadotropin-releasing hormone antagonist in fetal rats.

A gonadotropin-releasing hormone (GnRH) antagonist, when injected 24 h before sacrifice to rat fetuses, did not modify plasma testosterone concentrations in males on day 18 of gestation but it did on days 19, 20 and 21. This GnRH antagonist reduced plasma luteinizing hormone (LH) levels and increased pituitary LH content in both male and female 19-day-old fetuses from mothers adrenalectomized on day 14 of gestation. An inverse relationship between plasma testosterone and LH levels was noted in males and females, on days 19 and 21. These data suggest that the hypothalamic control of gonadotropic function is operating by day 19 of fetal life and that a negative feedback of testosterone on LH and probably GnRH release is also operating in rat fetuses on days 19 and 21 of gestation.