LUTEINIZING-HORMONE (LH) AND CORTICOSTERONE IN PROESTROUS AFTERNOON RESTORE THE FOLLICLE-STIMULATING-HORMONE SECRETION AT EARLY ESTRUS IN ADRENALECTOMIZED LH-RELEASING HORMONE ANTAGONIST-TREATED RATS

Administration of the antiprogestagen RU486 in the morning of proestru s abolishes the secondary surge of FSH during early estrus in the rat without preventing the drop in serum inhibin. In addition, the injecti on of an ovulatory dose of LH to RU486-injected rats does not restore the secondary surge of FSH. Since RU486 is a potent antiprogesterone w ith antiglucocorticoid activity, in the first experiment we compared t he effects of RU486 and a specific antiprogesterone serum (APS), admin istered on proestrus, on the secretion of FSH during early estrus. Whi le RU486 and APS reduced the primary surge of LI-I and FSH, only RU486 abolished the secondary secretion of FSH. In the second experiment, r ats injected with LHRH antagonist (LHRHa) and ovine LH (oLH) were adre nalectomized (ADX) or sham-ADX in the morning and injected with cortic osterone (B) or oil in the afternoon of proestrus. LHRHa completely el iminated, and oLH restored, the secretion of FSH at 0200 h in estrus. ADX reduced FSH serum concentration at 0200 h in estrus, and B reverse d this effect in rats injected with LHRHa and oLH. The results of thes e experiments indicate that, in the rat, the LHRH-independent secretio n of FSH during early estrus is evoked by the combined effects of the preovulatory surge of LH and the rise in serum B on proestrous afterno on.