RELAXIN SECRETION INTO HUMAN SEMEN IS INDEPENDENT OF GONADOTROPIN STIMULATION

To investigate the control of relaxin (Rlx) secretion in men, we studi ed seminal plasma Rlx concentrations after physiologic and supraphysio logic gonadal stimulation. In the first experiment, 14 men with idiopa thic hypogonadotropic hypogonadism provided semen samples at various t ime points before and during therapy with pulsatile GnRH. These data w ere compared to seminal plasma Rlx values in 5 normal men. In a second experiment, pharmacologic doses of hCG were administered in a fashion similar to that previously shown to have stimulated Rlx secretion fro m the CL of women. In men with idiopathic hypogonadotropic hypogonadis m, no relationship was detected by Linear regression analysis between seminal plasma Rlx and testosterone, testicular volume, ejaculate volu me, or the appearance of sperm in the ejaculate. Rlx concentrations va ried considerably between subjects (6-120 ng/ml) but remained fairly c onsistent within the same individual over time. Supraphysiologic gonad al stimulation with hCG similarly failed to alter seminal plasma Rlx ( n = 5, mean +/- SEM; 48 +/- 9 ng/ml, 42 +/- 7 ng/ml, and 56 +/- 9 ng/m l on Days 1, 3, and 6, respectively; p > 0.05) in normal men despite d ramatic increases in serum testosterone (763 +/- 25 ng/dl, 1702 +/- 13 6 ng/dl, and 1494 +/- 97 ng/dl on Days 1, 3, and 6, respectively; p < 0.05 vs. Day 1). Taken together, these data suggest that Rlx in men is secreted independently from direct gonadotropin control.