Biology of Reproduction, Vol 22, 197-201, Copyright © 1980 by Society for the Study of Reproduction

Effect of Exogenous Prolactin on Peripheral Luteinizing Hormone Levels in Ovariectomized Cows

¹ Animal Science Department, The Texas Agricultural Experiment Station, Texas A&M University, College Station, Texas 77843

Peripheral levels of luteinizing hormone (LH) and prolactin (PRL) were determined in mature chronically ovariectomized beef cows during i.v. infusion of either saline (0.9% NaCl) (SAL), or 30 mg bovine PRL in SAL (PRL) over a 3 h period. Each cow was infused once in the morning and once in the afternoon with either SAL or PRL (sequence alternated) for 4 consecutive days. Jugular vein blood samples were obtained at 10 min intervals. Thirty min following the initiation of PRL infusion, plasma PRL levels were maintained above 200 ng/ml, while plasma PRL concentrations remained well below 50 ng/ml during SAL infusion. A pulsatile fluctuation in plasma LH was observed in all cows, with each pulse being characterized by a rapid increase in LH followed by a more gradual decline to basal levels. This pulsatile pattern was consistent within cows over the 4 day period but varied significantly among cows. There were no differences in the pattern of plasma LH between SAL and PRL infusions. The results suggest that short term elevations in plasma PRL do not influence the pulsatile pattern of plasma LH in ovariectomized cows.

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ACKNOWLEDGMENTS The authors acknowledge the gift of bovine prolactin (NIH-P-B4) and luteinizing hormone (NIH-LH-B9) from the Endocrinology Study Section, NIH, Bethesda, MD. Gratitude is expressed to Dr. L. E. Reichert, Jr., Emory University, Atlanta, Georgia, for purified bovine LH (LER-1072-2) and to Dr. G. D. Niswender, Colorado State University, Fort Collins, CO and Dr. D. J. Bolt, USDA-SEA-AR for antiserum to LH and prolactin, respectively. We thank Martha Wright for her technical help and Nancy Howard for her editorial and secretarial assistance.