Administration of Antiluteinizing Hormone-Releasing Hormone Serum to Rats: Effects on Periovulatory Secretion of Luteinizing Hormone and Follicle-Stimulating Hormone,*

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Abstract
We investigated the effects of administration of anti-LHRH serum (a-LHRH) from sheep on the periovulatory secretion of LH and FSH in rats. Nonspecific serum from sheep or a-LHRH from sheep was injected through a cannula into the right atrium of the heart at 1100 and 1400 h or at 2000 and 2300 h on proestrus. Rats were bled serially through the cannula. The nonspecific serum had no effect on the plasma concentrations of LH or FSH during proestrus and estrus. The injection of 1.0 ml a-LHRH at 1100 h suppressed plasma LH concentrations but not plasma FSH concentrations by 1400 h. Injections of 1.0 ml a-LHRH at 1100 and 1400 h blocked the preovulatory surge of LH during the afternoon and early evening of proestrus, the associated increase in plasma FSH concentration (first phase of FSH release), the second or selective phase of FSH release, which starts during the late evening of proestrus and continues through the morning of estrus, and ovulation. In additional rats, the injection of 1.0 ml a-LHRH at 2000 and 2300 h on proestrus was without effect on the second phase of elevated plasma FSH concentration. The administration of exogenous rat FSH on the afternoon (1600 h) of proestrus to a-LHRH-blocked rats caused plasma FSH to rise rapidly, then to fall by 2200 h on proestrus to values similar to the elevated levels observed in control rats at 2200 h on proestrus, and remain at these elevated levels through 1000 h on estrus. The results indicate that the entire preovulatory LH surge and first phase of FSH release require LHRH release during the afternoon of proestrus; LHRH is not significantly involved in causing the second phase of FSH release after the first phase has occurred; and injection of rat FSH to a- LHRH-blocked rats on proestrus appears to cause endogenous FSH release during the morning of estrus.