Serum testosterone response in Holstein bulls after administration of luteinizing hormone

Seven yearling Holstein bulls were given 0, 20, 40, 60, 80, 100 and 200 micrograms 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 wer measured in serum by radioimmunoassay. Area under the LH and testosterone response curves, expressed as nanograms per milliliter x hours, increased (P less than .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 micrograms 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 micrograms exogenous LH, respectively. The LH area response to exogenous LH was linear (Y = .4717 + .0352X; P less than .001), with testosterone concentration reaching maximum level in response to 100 micrograms LH (Y = 1.0279 + .1041X + .0001X(2); P less than .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.