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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #102407
Title: RELATIONSHIPS OF GONADOTROPINS, TESTOSTERONE, AND CORTISOL IN RESPONSE TO GNRH AND GNRH ANTAGONIST IN BOARS SELECTED FOR HIGH AND LOW FOLLICLE STIMULATING HORMONE LEVELS

Author
item Wise, Thomas
item ZANELLA, ERALDO - UNIV NEBRASKA, LINCOLN
item Lunstra, Donald
item Ford, Johny

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2000
Publication Date: 6/1/2000
Citation: Wise, T.H., Zanella, E.L., Lunstra, D.D., Ford, J.J. 2000. Relationships of gonadotropins, testosterone, and cortisol in response to GnRH and GnRH antagonist in boars selected for high and low follicle-stimulating hormone levels. Journal of Animal Science. 78(6):1577-1590.

Interpretive Summary: Chinese Meishan boars have considerably higher circulating FSH concentrations and smaller testis than boars of European breeds. The mechanism by which certain boars have high circulating FSH concentrations is unknown, and this study did not show any altered sensitivity to effects of GnRH or GnRH antagonist on circulating FSH concentrations. Boars selected for increased circulating FSH concentrations did have steeper declines of LH after GnRH challenge. The important point of the identification of high FSH boars is that these boars have smaller testis and thus lower sperm production, which is particularly relevant in artificial insemination studs. Identification of endocrine mechanisms that have a major impact on gonadal function in the male may also aid in the understanding of increased ovarian function, thus leading the way to understanding mechanisms of increased ovulation rates.

Technical Abstract: Considerable variation exists in the serum levels of gonadotropins in boars; this results in differential testicular function. Boars (Chinese Meishan, European White composite, and crosses of the two breeds) selected for high- and low-circulating FSH concentrations were used to define possible differences in pituitary sensitivity to GnRH and GnRH antagonist and gonadal and adrenal responses. After a 2-h pretreatment sampling period, boars were injected with GnRH or GnRH antagonist and repetitively sampled via jugular cannula for changes in serum concentrations of FSH, LH, testosterone and cortisol. In response to varying doses of GnRH or GnRH antagonist, no major differences were detected in relation to pituitary release of gonadotropins or testicular testosterone secretion in high- or low-circulating FSH boars. Declines in LH after GnRH stimulation were consistently quicker in boars selected for high FSH. Chinese Meishan boars shad considerably higher cortisol concentrations than White composite boars (132.2 +/- 28.5 vs 67.4 +/- 26.8 ng/ml, respectively; P < .01). When select high- and low-gonadotropin Meishan:White composite crossbreds were sampled, cortisol levels were elevated but comparable between the two groups (126.5 +/- 13.7 vs 131.4 +/- 13.4 ng/ml, respectively). After GnRH antagonist lowered LH concentrations, administration of hCG resulted in increased testosterone and cortisol concentrations. Although testosterone concentrations remained high for 30 h, cortisol concentrations returned to normal levels within 10 h post hCG injection. The mechanism by which boars selected for high gonadotropins achieve increased levels of LH and FSH may not be due to differences in pituitary sensitivity to GnRH but to differences in clearance from the circulation.