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Effect of Intracarotid Infusion of Prostaglandin F₂ on Plasma Prolactin and Growth Hormone in Bulls¹

Michigan State University^,5, East Lansing 48824

Abstract

Two experiments were designed to localize the action of systemically administered PGF₂ in causing increased plasma prolactin and growth hormone in bulls. Five bulls approximately 18 months old were each given 3-hr infusions of PGF₂ at 0 (saline), 20, 200, and 2,000 ng/min into a carotid artery, and 2,000 ng/min and .2 mg/min into a jugular vein. Administration of PGF₂ at .2 mg/min into a jugular vein was calculated to represent a dose of about 2,000 ng/min reaching the head. The design was a Latin square with 12 hr between beginning 3-hr infusions. Jugular vein blood was sampled at least every 30 min throughout. The high jugular dose (.2 mg/min) caused significantly increased plasma prolactin and growth hormone concentrations compared to saline controls. The 2,000 ng/min dose given via the carotid artery also was effective in increasing plasma prolactin and growth hormone, whereas a dose of 2,000 ng/min given into the jugular vein and 20 and 200 ng/min into the carotid artery were ineffective. In the second experiment, a 50 µg bolus of PGF₂ given into a carotid artery in four bulls caused release of prolactin within 4 min, but growth hormone was not affected significantly. It is concluded that the major site of systemic PGF₂ in enhancing prolactin and growth hormone secretion is the pituitary or the brain, with no more than minor indirect action at the periphery.

¹ Michigan Agricultural Experiment Station Journal Article No. 8440. This research was supported in part by USPHS Research Grant 06948. PGF₂ Tham salt was kindly provided by Dr. J. W. Lauderdale, the Upjohn Co. We thank Dr. W. D. Oxender and Dr. T. D. Carruthers for performing the surgery. The Milk Marketing Board of England provided a travel grant for N.B.H.

² Present address: Department of Physiology and Environmental Studies, University of Nottingham, School of Agriculture, Sutton Bonington, Loughborough, Leicestershire LEI2 5RD, England.

³ Present address: Department of Animal and Dairy Science, University of Georgia, Athens 30602.

⁴ Animal Reproduction Laboratory, Department of Dairy Science.

⁵ Animal Reproduction Laboratory, Department of Dairy Science.