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Effect of Intracarotid Infusion of Prostaglandin F₂ on Plasma Luteinizing Hormone, Testosterone and Glucocorticoid Concentrations in Bulls¹

Michigan State University⁴, East Lansing 48824

Abstract

This experiment was designed to investigate the site(s) of action of systemically administered prostaglandin F₂ (PGF₂) in causing increased plasma testosterone and glucocorticoid in bulls. Six bulls 18 months old were each given PGF₂ at 0 (saline), 20, 200 and 2,000 ng/min into a carotid artery or 2,000 ng/min and .2 mg/min into a jugular vein for 3 hours. The high dose into a jugular vein was calculated to provide approximately 2,000 ng/min reaching the head. The design was a latin square with 9 hr between infusion treatments. Jugular blood was sampled at least every 30 min throughout. Infusion of .2 mg PGF₂/min into the jugular vein increased plasma luteinizing hormone (LH), glucocorticoid and testosterone concentrations or prolonged the periods when hormone concentrations were elevated when compared with those in controls. The 2,000 ng/min dose given via the carotid artery also caused increased blood plasma LH, testosterone and glucocorticoids. By contrast, a dose of 2,000 ng/min into the jugular vein was without effect. It is concluded that the major effect of systemically administered PGF₂ in elevating blood plasma testosterone and glucocorticoid is through LH and presumably adrenocorticotropin release from the pituitary and not directly on the adrenal or testis.

¹ Published with approval of Director of the Agriculture Experiment Station as Paper no. 7899. This research was supported in part by USPH Research Grant no. 06948. PGF₂ Tham (Tromethamine) salt was kindly provided by Dr. J. W. Lauderdale, The Upjohn Co.

² Present address: Department of Physiology and Environmental Studies, University of Nottingham School of Agriculture, Sutton Bonington, Nr. Loughborough, Leicestershire, England.

³ Present address: Department of Animal and Dairy Science, University of Georgia, Athens.

⁴ Animal Reproduction Laboratory, Department of Dairy Science.