Neuroendocrine regulation of growth hormone and androgen axes by selective estrogen receptor modulators in healthy men.

Abstract

In men, the stimulation of GH and inhibition of LH secretion by testosterone requires aromatization to estradiol. Tamoxifen, a selective estrogen receptor modulator (SERM), possesses central estrogen antagonistic effect but peripheral hepatic agonist effect, lowering IGF-I. Thus, tamoxifen is likely to perturb the neuroendocrine regulation of GH and gonadal axes. Raloxifene, a SERM, is used for therapy of osteoporosis in both sexes. Its neuroendocrine effects in men are poorly understood. The aim was to compare the impact of raloxifene and tamoxifen on GH-IGF-I and gonadal axes in healthy men. We conducted a randomized, open-label crossover study. Ten healthy men were randomized to 2-wk sequential treatment with tamoxifen (10 and 20 mg/d) and raloxifene (60 and 120 mg/d), with a 2-wk intervening washout period. We measured the GH response to arginine and circulating levels of IGF-I, LH, FSH, testosterone, and SHBG. Tamoxifen, but not raloxifene, significantly reduced IGF-I levels by 25±6% (P<0.01) and increased SHBG levels by 20±7% (P<0.05) at the higher therapeutic dose. There was a nonstatistically significant trend toward a reduction in the GH response to arginine with both SERMs. Both drugs significantly increased LH, FSH, and testosterone concentrations. The mean increase in testosterone (40 vs. 25%; P<0.05) and LH (70 vs. 30%; P<0.01) was significantly greater with tamoxifen than with raloxifene treatment. Tamoxifen, but not raloxifene, reduces IGF-I levels. Both SERMs stimulate the gonadal axis, with tamoxifen imparting a greater effect. We conclude that in therapeutic doses, raloxifene perturbs the GH and gonadal axes to a lesser degree than tamoxifen.