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The EflFects of Gonadal Steroids on Plasma Gonadotropins and Prolactin in the Rat¹

University of Texas Southwestern Medical School, Department of Physiology Dallas, Texas 75235

Abstract

The effects of single sc injections of various doses of estradiol benzoate (Eb) and testosterone propionate (Tp) on plasma levels of LH, FSH and prolactin have been reinvestigated in castrate rats of both sexes. Our results indicate that Eb or Tp inhibited release of LH in castrate rats of both sexes. Males were more sensitive to the inhibitor effect of the low dose of Tp than females. The steroids also lowered plasma FSH levels in spayed females; however, in castrated males Eb stimulated FSH release and a decrease in FSH followed the injection of only the highest dose (2 mg) of Tp. Eb and Tp had a synergistic effect in inhibiting FSH release in the male. Both steroids stimulated release of prolactin in castrate males and females (no sex difference in release of prolactin in response to Eb was observed; however, males appeared more sensitive to Tp treatment). Single injections of progesterone (P) in spayed females produced variable results. High doses inhibited LH release and elevated prolactin levels.

Effects of ovarian steroids during the estrous cycle were also studied. The proestrous surge of FSH and LH could be enhanced as well as advanced by P in intact rats. Eb was also effective in stimulating release of gonadotropins and prolactin if administered at estrus but was ineffective on diestrus day 1. In rats, spayed on diestrus day 2, the proestrous surge could be induced by treatment with Eb or Eb plus P. (Endocrinology 92: 1256, 1973)

Footnotes

¹ Presented in part at the 52nd meeting of the Endocrine Society, St. Louis, p. 126, 1970.

² Postdoctoral Fellow of the Ford Foundation. Present address: Institute of Food and Agricultural Sciences, Department of Dairy Science, University of Florida, Gainesville, Florida.

³ Supported by Grant #AM 1073 from the USPHS, by a Ford Foundation Grant and by a Grant from the Texas Population Crisis Foundation.

Received August 3, 1972.

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