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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 #101967
Title: GNRH ANTAGONIST INHIBITION OF GONADOTROPIN AND STEROID SECRETION IN BOARS IN VIVO AND STEROID PRODUCTION IN VITRO

Author
item ZANELLA, ERALDO - UNIVERSITY OF NEBRASKA
item Lunstra, Donald
item Wise, Thomas
item KINDER, JAMES - UNIVERSITY OF NEBRASKA
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: Zanella, E.L., Lunstra, D.D., Wise, T.H., Kinder, J.E., Ford, J.J. 2000. GnRH antagonist inhibition of gonadotropin and steroid secretion in boars in vivo and steroid production in vitro. Journal of Animal Science. 78(6):1591-1597.

Interpretive Summary: Boars were treated with a gonadotropin-releasing hormone (GnRH) antagonist to determine if the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) would be affected. Both FSH and LH secretion declined immediately followed by a decline in testosterone secretion. Unexpectedly, LH secretion returned to pretreatment concentrations as treatment with antagonist continued, but FSH and testosterone secretion remained suppressed. These observations implied a direct effect of the antagonist within the testes. This prediction was confirmed by incubation of testicular tissue in the presence of the antagonist and observing a reduction in testosterone secretion relative to control incubations. These findings are useful to investigators who are developing an understanding of the mechanisms that regulate testicular steroid production.

Technical Abstract: The objective of the first study was to evaluate concentrations of FSH and LH in plasma of boars after successive treatment with SB75, a GnRH antagonist. Boars were injected once a day with SB75 for 4 d. Plasma concentrations of LH and T decreased after 1 h from the first dose of SB75. After 12 h of treatment, LH gradually returned to pretreatment concentrations, but T remained suppressed (< 2 ng/mL) until after the last injection of SB75. There was a modest, but significant, reduction in FSH during treatment with SB75. The prolonged inhibitory effect of SB75 on suppression of plasma T concentrations, in the presence of pretreatment concentrations of LH, implied direct effects of SB75 at the testis. In the second experiment, testicular tissue from adult boars was incubated in the presence of three doses of human chorionic gonadotropin (hCG) with SB75 or with Deslorelin, a GnRH agonist. Concentrations of T and E1 increased with time in response to treatment with hCG. Co-treatment with SB75 decreased media concentrations of T (P < .01) and E1 (P < .03) compared to controls. In contrast, treatment with Deslorelin had no effect on the amount of T (P > .50) or E1 (P > .26) released with all dosages of hCG. These results indicate that GnRH antagonist has a direct effect on the testis decreasing amounts of T and E1; however, treatment with GnRH agonist had no direct effect on release of these gonadal steroids.