Sex Difference in Human Growth Hormone (GH) Response to Intravenous Human Pancreatic GH Releasing Hormone Administration in Young Adults

Abstract

Intravenous administration of a 100-μg dose of human pancreatic GH-releasing hormone (human pancreatic GHRH_1-44, indicated by GHRH) disclosed a sex difference in GH responsiveriess. The maximum GH increments [41 ± 11 (SEM) vs. 15 ± 4 ng/ml, P^* < 0.05]and the areds under the curves (419 ± 105 vs. 148 ± 53 area U, P^* < 0.05) were significantly higher in 12 men than in 10 women. No significant correlation was found in either group between the basal plasma estradiol or testosterone levels and the maximum or integratedGH response to GHRH. Serum PRL levels significantly increased in both groups within 5 min after GHRH injection (men, P < 0.001 vs. t = 0; women, P < 0.05 vs. t = 0). The areas under the curves of the PRL responses (355 ± 184 vs. 189 ± 73 area U) and the maximum PRL increments (58 ± 18 vs. 36 ± 6 mU/1, P^* > 0.10) were similar. In conclusion, a sex difference in GH responsiveness to GHRH was found between young adult men and women. Recent in vivo and in vitro data reveal a similar sex difference in rodents and an enhancing effect of androgens, but not estrogens, on the GH response to GHRH. These findings support the theory that in humans testosterone also plays a key role in the genesis of this sex difference.