PITUITARY-GONADAL RESPONSE TO GONADOTROPIN-RELEASING-HORMONE STIMULATION IS ENHANCED IN MEN AFTER STRENUOUS PHYSICAL EXERCISE

The effects of strenuous physical exercise were studied on the pituita ry-testicular response to gonadotropin-releasing hormone (GnRH) stimul ation and on growth hormone (GH) and cortisol secretion. Eight healthy adult males were injected twice intravenously with 0.1 mg of GnRH at intervals of 2 1 days. At the time of the first injection (exercise tr ial) the subjects had been bicycling for 4 h on the road, and at the t ime of the second injection (rest trial) they had been resting in a si tting position for 4 h. Blood samples were taken before and after the 4-h period and 30, 60 and 120 min after the GnRH injection. Both testo sterone and luteinizing hormone (LH) decreased during the exercise by 18% (p=0.037) and 29% (p=0.0028), respectively, but increased after th e GnRH injection by 1.4- and 12.9-fold (p = 0.0001 for both). The area s under the testosterone and LH response curves after GnRH were signif icantly larger in the exercise trial than in the rest trial, threefold (p = 0.013) and 1.3-fold (p = 0.000 7), respectively. Growth hormone and cortisol increased during the exercise trial. In the rest trial, t he GnRH injection increased serum GH concentrations (p = 0.027). In co nclusion, the diminished hypothalamic GnRH secretion seems to be the m ajor cause of the post-exercise decrease in LH and testosterone, but a ltered sensitivity of the pituitary to GnRH also may be involved. Appa rently, the build-up of pituitary LH stores during exercise explains t he enhanced LH and testosterone response to GnRH challenge after exerc ise in comparison to control GnRH challenge.