Chronic Sex Steroid Exposure Increases Mean Plasma Growth Hormone Concentration and Pulse Amplitude in Men with Isolated Hypogonadotropic Hypogonadism

Sex steroid administration can increase the GH response to provocative stimuli, but the relationship of sex steroids to spontaneous GH secretion is still controversial. We sought to characterize the effect of sex steroids on the plasma GH concentration by examining the 24-h pattern of episodic GH secretion in nine previously untreated adult men with isolated hypogonadotropic hypogonadism before and during long term testosterone, gonadotropin, or pulsatile GnRH treatment. After chronic sex steroid exposure, the mean 24-h plasma GH level, mean GH pulse amplitude, and mean area under the curve of pulses were significantly increased compared to pretreatment values 3.2 +/- 1.8 ( +/- SD) vs. 1.8 +/- 1.2 ng/mL (P less than 0.01); 11.4 +/- 7.2 vs. 5.5 +/- 4.4 ng/mL (P less than 0.05); and 720 +/- 547 vs. 316 +/- 371 ng/mL X 20 min (P less than 0.05), respectively, while mean 24-h pre- and posttreatment GH pulse frequencies were indistinguishable (5.7 +/- 2.1 posttreatment vs. 5.0 +/- 3.2 pretreatment; P = NS). The mean posttreatment plasma somatomedin-C level also rose significantly during treatment (1.89 +/- 0.65 vs. 1.28 +/- 0.48 U/mL; P less than 0.01). We conclude that the increase in the mean plasma GH level during chronic sex steroid exposure is due mainly to augmentation of GH pulse amplitude, and that sex steroids probably increase spontaneous GH secretion.