The hormonal response to a d-fenfluramine challenge in trained and sedentary men

Purpose: The purpose of the present study was to examine the responsiveness of serotonergic receptors in endurance trained and sedentary men. Methods: The serum prolactin and cortisol responses to the oral administration of 3 0 mg of the serotonin releaser and reuptake inhibitor d-fenfluramine were d etermined in eight male endurance-trained subjects and seven male sedentary controls. Results: A Friedman's repeated-measures test for both the endura nce-trained (P = 0.006) and sedentary (P = 0.018) prolactin results demonst rated a change in the mean prolactin concentration over time, but no differ ence in prolactin response was observed between the subject groups (P = 0.8 1). In both subject groups, the serum cortisol concentration remained uncha nged. However, the mean serum concentration of cortisol for the endurance-t rained subjects at each time point tended to be lower than at the correspon ding time point for the sedentary subject group and was significantly lower at 180 min (P = 0.04). Conclusion: The present study suggests that, in con trast to an earlier report of down-regulation of 5-HT1A receptor function i n endurance-trained subjects in response to a nonspecific challenge, postsy naptic 5-HT2 function as determined by the d-fenfluramine-evoked alteration in the plasma concentration of prolactin is not altered by endurance train ing.