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

¹ Department of Animal Sciences² College of Veterinary Medicine, Oregon State University, Corvallis, Oregon 97331-4501 USA³ Department of Physiology and Pharmacology L334, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97201-3098, USA

Correspondence should be addressed to C E Roselli; Email: rosellic{at}ohsu.edu

Two experiments were conducted to determine whether an estradiol challenge could cause a female-type LH surge in castrated male- and female-oriented rams (MORs and FORs). Administration of 17β-estradiol to castrated MORs and FORs and ovariectomized ewes caused an initial reduction in LH secretion followed for 12–20 h by a surge release of LH in the ewes. No surge release of LH occurred in the MORs and FORs. The pattern of changes in LH secretion within rams and ewes did not differ between the breeding and nonbreeding seasons. Treatment failed to elicit female-typical receptive sexual behaviors in the rams but did stimulate increased sexual receptivity in the ewes as determined by the measures of responsiveness to the teaser ram. Overall, no differences were found in hypothalamic–hypophyseal function in response to exogenous estradiol between MORs and FORs. 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 MORs.