The effects of strenuous physical exercise were studied on the pituitary-testicular response to gonadotropin-releasing hormone (GnRH) stimulation 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 21 days. At the time of the first injection (exercise trial) the subjects had been bicycling for 4 h on the road, and at the time of the second injection (rest trial) they had been resting in a sitting 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 testosterone and luteinizing hormone (LH) decreased during the exercise by 18% (p=0.037) and 29% (p=0.0028), respectively, but increased after the GnRH injection by 1.4- and 12.9-fold (p=0.0001 for both). The areas under the testosterone and LH response curves after GnRH were significantly larger in the exercise trial than in the rest trial, threefold (p = 0.013) and 1.3-fold (p=0.0007), respectively. Growth hormone and cortisol increased during the exercise trial. In the rest trial, the GnRH injection increased serum GH concentrations (p = 0.02 7). In conclusion, the diminished hypothalamic GnRH secretion seems to be the major cause of the post-exercise decrease in LH and testosterone, but altered sensitivity of the pituitary to GnRH also may be involved. Apparently, the build-up of pituitary LH stores during exercise explains the enhanced LH and testosterone response to GnRH challenge after exercise in comparison to control GnRH challenge.
Tommi J Vasankari, Urho M Kujala, Simo Taimela and Ilpo T Huhtaniemi
Tommi J Vasankari, Urho M Kujala, Olli J Heinonen and Ilpo T Huhtaniemi
The effect of several years' endurance training on hormonal changes during acute prolonged physical exercise was studied. In trial I, 13 cross-country skiers were studied before and after a 75-km ski race and 3 weeks later on a control day. In trial II, 10 trained and 8 untrained subjects bicycled for 4 h on the road with as high a performance level as possible. Venous blood samples were taken in both trials before and after the exercise. In trial I, serum concentrations of luteinizing hormone (p<0.01) and follicle-stimulating hormone (FSH, p <0.001) decreased more from morning to afternoon samples, and cortisol (p <0.001) and growth hormone (GH, p <0.001) increased more during the ski race when compared to the control day. Serum testosterone decreased during the ski race (p <0.01) but not on the control day. In trial II, a group difference was seen in serum FSH levels which was higher in the trained than untrained subjects at all three time points (F =4.66, p=0.046). A significant trial-group interaction (p =0.020) was seen in GH, the GH being lower before exercise and higher 2 h after exercise in the untrained subjects. There was a significant group contrast between pre- and post-exercise samples in testosterone (p = 0.021) and cortisol (p = 0.022). In conclusion, the higher basal FSH concentration in the trained versus untrained subjects may be a sign of compensated hypogonadism due to intensive chronic training or it may be due to dysfunction of Sertoli cells. Signs of adaptation to resist the hormonal changes caused by acute physical exercise can be seen in the trained subjects when compared to the untrained subjects.