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Serum Testosterone Response in Holstein Bulls after Administration of Luteinizing Hormone¹

University of Georgia and Richard B. Russell Research Center, SEA, US Department of Agriculture, Athens 30602

Abstract

Seven yearling Holstein bulls were given 0, 20, 40, 60, 80, 100 and 200 µg NIH-LH-B9 during a 7-day complete Latin square design experiment. Treatments were administered via jugular cannulas at 0900 hr, and blood was collected at 60, 30 and 0 min before treatment, at 15-min intervals for 3 hr after treatment and at 30-min intervals from 3 to 7 hr after treatment. Luteinizing hormone (LH) and testosterone concentrations were measured in serum by radioimmunoassay. Area under the LH and testosterone response curves, expressed as nanograms per milliliter x hours, increased (P<.001) with increasing amounts of exogenous LH. Basal LH in serum averaged 1.4 ± .1 ng/ml, and peaks ranged from 3.8 ± .4 to 13.3 ± .4 ng/ml after 40 and 200 jug of exogenous LH, respectively. Basal testosterone in serum of bulls given saline was 1.8 ±.2 ng/ml, and peak responses ranged from 4.1 ± .3 ng/ml to 5.9 ± .5 ng/ml after 40 and 200 µg exogenous LH, respectively. The LH area response to exogenous LH was linear (Y = .4717 + .0352X; P<.001), with testosterone concentration reaching maximum level in response to 100 µg LH (Y = 1.0279 + .1041X + .0001X²; P<.001). On the basis of these data, we suggest that the magnitude of the pulsatile release of LH quantitatively controls the secretion of testosterone from the testes of yearling bulls.

¹ This research was supported in part by a grant from Select Sires and by state and Hatch funds allocated to the Georgia Agr. Exp. Stations. LH and testosterone antisera was supplied by Dr. E. M. Convey, Michigan State Univ., and pituitary hormones were supplied by the NIH Hormone Distribution Officer and Dr. L. E. Reichert, Albany Medical College.

² Present address: Dept. of Anim. and Dairy Sci., North Carolina State Univ., Raleigh.