Serum Levels of Gonadotropin-Releasing Hormone (Gn-RH) During the Estrous Cycle and in Pentobarbital-Treated Rats

Abstract
4-day cycling rats were sacrificed by decapitationduring the estrous cycle from 08.00 through 18.00 h. Additional rats were given i.p. pentobarbital injections at 13.30 on proestrus and were then sacrificed between 14.00 and 18.00. Serum levels of LH and Gn-RH were quantitated by radioimmunoassay. A peak in serum Gn-RH levels was observed between 08.00 and 16.00 on each day of the estrous cycle. Pentobarbital treatment blocked the pre-ovulatory LH surge on proestrus and significantly reduced (p<0.05) serum Gn-RH levels between 14.00 and 16.00. However, the major portion of Gn-RH release had already occurred prior to pentobarbital administration.

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