Serum testosterone responses to continuous and intermittent exercise training in male rats.

Serum testosterone (T) were investigated at rest and following exercise during 6 weeks of continuous and intermittent swimming training in male rats, and the regulatory mechanisms of the changes were discussed by evaluating serum luteinizing hormone (LH), and conducting GnRH (gonadotropin releasing hormone, 1.5 microg/kg body weight) or hCG (human chorionic gonadotropin, 25 IU/kg body weight) challenge tests. Relative to the resting level, serum T increased after intermittent exercise (6.47 +/- 1.58 vs 3.08 +/- 2.85 nmol/l), which was followed with the same changes in LH (12.81 +/- 4.21 vs 5.70 +/- 1.56 nmol/l). Serum T was lower after continuous exercise compared to the resting level (2.02 +/- 0.53 vs 10.96 +/- 3.11 nmol/l), while LH level was higher than that in sedentary group (11.23 +/- 5.61 vs 5.00 +/- 1.61 nmol/l). No significant changes were observed in resting T during and after intermittent training. A lower resting T level was shown at the end of 3 weeks of continuous training as compared to the sedentary group (1.88 +/- 0.69 vs 12.36 +/- 2.10 nmol/l), but it increased after 6 weeks of training. Serum T increased significantly in the intermittent training group after hCG treatment as compared to the saline treatment (52.42 +/- 12.10 vs 6.81 +/- 6.22 nmol/l), but insignificantly in the continuous training group. The similar increases in serum LH were observed in all the groups after GnRH treatment.