Regulation of the Second Surge of Follicle-Stimulating Hormone; Effects of Antiluteinizing Hormone-Releasing Hormone Serum and Pentobarbital*

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Abstract
The blockade in the rat of the estrous FSH surge was investigated by the injection of anti-LHRH serum in order to clarify whether LHRH controls this postovulatory surge as well as the preovulatory LH-FSH surge. A single iv injection of anti-LHRH serum at 1300 h on proestrus not only inhibited ovulation but also eliminated both the preovulatory LH-FSH surge and the second FSH surge in estrus. A single iv injection of anti-LHRH serum at 2200 h on proestrus after the LH-FSH surge did not inhibit either the estrous FSH surge or ovulation, although plasma LH was lowered, and the number of ova ovulated was reduced. Depression of plasma FSH and LH levels was also observed after a single iv injection of pentobarbital sodium (Nembutal; 35 mg/kg BW) at 1300 h on proestrus, but no such effect was observed when pentobarbital was injected at 2200 h on proestrus. A single injection of 10 IU hCG at 1800 h on diestrous II induced precocious ovulation and a concomitant increase in FSH secretion. It was not possible to inhibit the induced secretion of FSH and ovulation by a simultaneous injection of anti-LHRH serum, but plasma LH was completely suppressed. These results demonstrate that the second FSH surge is not controlled by LHRH.