Plasma testosterone during bicycle ergometer exercise without and after L-dopa pretreatment.

The level of testosterone in plasma during submaximal, prolonged submaximal and maximal exercise on a bicycle ergometer was measured in healthy untrained men. To evaluate the possible involvement of prolactin in the regulation of testosterone secretion during exercise, the influence of prolactin inhibition by oral L-dopa (1 g) pretreatment was also studied. The exercise evoked a small but significant rise of testosterone concentration with peak levels immediately at the end of work performance or 10 min after that. No substantial difference between the response to submaximal and maximal exercise was noted. In these experiments the findings by others on a lack of plasma LH changes and significant increase of plasma prolactin were confirmed. Pharmacological blockade of prolactin release by L-dopa pretreatment failed to modify the response of testosterone to bicycle ergometer exercise. It may be suggested that prolactin is not involved in the induction of plasma testosterone increase during physical exercise.