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Changes in LH secretion in response to an estradiol challenge in male- and female-oriented rams and in ewes

F Stormshak, Animal Sciences, Oregon State University, Portland, United States
C Estill, College of Veterinary Medicine, Oregon State University, Portland, United States
J Resko, Physiology and Pharmacology, Oregon Health and Science University, Portland, United States
C Roselli, Physiology and Pharmacology, Oregon Health and Science University, Portland, 97239-3098, United States

Correspondence: Charles Roselli, Email: rosellic{at}ohsu.edu

Abstract

Two experiments were conducted to determine whether an estradiol challenge could cause a female type LH surge in castrated male- and female-oriented rams. Administration of estradiol-17β to castrated male- and female-oriented rams and ovariectomized ewes caused an initial reduction in LH secretion followed in 12 to 20 h by a surge release of LH in the ewes. No surge release of LH occurred in the male- and female-oriented rams. The pattern of changes in LH secretion within rams and ewes did not differ between the breeding and nonbreeding season. Treatment failed to elicit female typical receptive sexual behaviors in the rams but did stimulate increased sexual receptivity in the ewes as determined by measures of responsiveness to the teaser ram. Overall, no differences were found in hypothalamus-hypophyseal function in response to exogenous estradiol between male- and female-oriented rams. These data are interpreted to suggest that in contrast to sexual attraction, the neural mechanisms controlling the LH surge and female receptivity are defeminized in male-oriented rams.