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Induced Gonadotropin Release in Adrenocorticotropin-Treated Bulls and Steers^1,2,

Clemson University, Clemson, SC 29631

Abstract

The effect of adrenocorticotropin hormone (ACTH) on plasma Cortisol and on gonadotropin releasing hormone (GnRH)-induced release of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone was determined in nine Holstein bulls and 12 Holstein steers. Treatments consisted of animals receiving either GnRH (200 µg, Group G), ACTH (.45 IU/kg BW, Group A) or a combination of ACTH followed 2 h later by GnRH (Group AG). Group G steers and bulls had elevated plasma LH and FSH within .5 h after GnRH injection and plasma testosterone was increased by 1 h after GnRH injection in bulls. In Group A, plasma Cortisol was elevated by .5 h after ACTH injection in both steers and bulls, but plasma LH and FSH were unaffected. In Group A bulls, testosterone was reduced after ACTH injection. In Group AG, ACTH caused an immediate increase in plasma Cortisol in both steers and bulls, but did not affect the increase in either plasma LH or FSH in response to GnRH in steers. In Group AG bulls, ACTH did not prevent an increase in either plasma LH, FSH or testosterone in response to GnRH compared with basal concentrations. However, magnitude of systemic FSH response was reduced compared with response in Group G bulls, but plasma LH and testosterone were not reduced. The results indicate that ACTH caused an increase in plasma Cortisol, but did not adversely affect LH or FSH response to GnRH in steers and bulls. Further, while testosterone was decreased after ACTH alone, neither ACTH nor resulting increased plasma Cortisol resulted in decreased testosterone production in the bull after GnRH stimulation.

¹ Technical Contribution No. 1863 of the South Carolina Agr. Exp. Sta., Clemson Univ.

² The authors are indebted to K. W. Cheng, Univ. of Manitoba, Winnipeg, Manitoba, Canada, for purified bovine FSH and specific bovine FSH antiserum; L. E. Reichert for purified bovine LH (LER-1072); T. E. Kiser, Univ. of Georgia, for specific bovine LH antiserum; G. D. Niswender, Colorado State Univ. for testosterone antiserum (S250); the Endocrine Study Section, NIH, Bethesda, MD, for pituitary hormones, and S. T. Bierley for technical assistance.

³ Dept. of Dairy Sci., Virginia Tech, Blacksburg, 24061; Reprints.

⁴ Dept. of Poul Sci.

⁵ Dept. of Exp. Stat.