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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #149586
Title: ESTRADIOL-INDUCED LH RELEASE IN MALE-ORIENTED RAMS: RELATIONSHIP TO SEXUAL DIFFERENTIAION

Author
item ROSELLI, CHARLES - OREGON HLTH & SCI UNIV
item SCHRUNK, JESSICA - OREGON STATE UNIV
item STORMSHAK, FRED - OREGON STATE UNIV
item RESKO, JOHN - OREGON HLTH & SCI UNIV
item Stellflug, John

Submitted to: Endocrine Society Meeting
Publication Type: Proceedings
Publication Acceptance Date: 5/20/2003
Publication Date: 6/30/2003
Citation: Roselli, C.E., Shrunk, J.N., Stormshak, F., Resko, J.A., Stellflug, J.N. Estradiol-induced LH surge in male-oriented rams: Relationship to sexual differentiation. Endocrine Society. 2003. Abstract #P2-646. p 464.

Interpretive Summary:

Technical Abstract: Adult gonadectomized ewes given an injection of estradiol respond with an initial decline in immunoreactive serum LH concentrations, followed by a subsequent rise, referred to as an LH surge. High prenatal testosterone levels, either endogenous to fetal males or experimentally elevated in females, abolish this response, provided exposure is of sufficient magnitude and duration, and occurs during a critical period of fetal development. This aspect of sexual differentiation has been termed brain androgenization/masculinization. In the current study, we tested whether rams exhibiting variations in sexual partner preference differ in their capacity to respond to estradiol with an LH surge. Adult rams were administered sexual partner preference tests and classified as either female-oriented rams (FORs; n=4) or male-oriented rams (MORs; n=4). Four age-matched ewes were studied for comparison. The sheep were gonadectomized and approximately one month later challenged with an i.m. injection of 17B-estradiol (50 micro/animal). Blood samples (7 ml) were taken at 2 h intervals beginning prior to the injection of estradiol and extending for 48 h thereafter. An LH surge was defined as serum LH concentrations exceeding twice the average pre-estradiol baseline (12.35 ng/ml) for a minimum of 6 h or three consecutive samples. We found that the LH surge mechanism was operational in 4 of 4 ewes, 3 of 4 MORs, and 0 of 4 FORs. Peak serum LH concentrations were not significantly different between ewes (49.0 +/- 12.9 [SEM] ng/ml) and MORs (37.7 +/- 13.0 ng/ml), nor did the latency (approx. 15 h) or duration (approx. 5-10 h) of the surge response differ; p > 0.05. In contrast, two-way repeated measures ANOVA indicated that serum levels of LH in ewes and MORs were greater (p < 0.05) than in FORs during the interval of the surge in the former animals. These results demonstrate that MORs exhibit a neuroendocrine LH response similar to ewes and indirectly support the hypothesis that MORs are incompletely androgenized/masculinized. Supported by NIH grant RR14270.