Pulsatile Secretion of Gonadotropins and Prolactin in Male Marathon Runners Relation to the Endogenous Opiate System

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Abstract
We tested the hypothesis that sustained, strenuous physical training alters the neuroendocrine regulation of pulsatile gonadotropin and/or prolactin secretion in men. Blood was sampled at 20-minute intervals over 8 flours in five endurance-trained men after a 10–15 mile run in the middle of the active training season, and in 11 nonendurance trained normal controls. In these two groups, basal patterns of physiologically pulsatile secretion of LH, FSH, and prolactin (PRL) were not significantly different in relation to the following parameters: mean serum concentration of each of the three tiormones (N = 25 samples); areas under the hormone concentration vs. time curves; fractional, incremental, ind absolute pulse amplitudes; and pulse frequency, or periodicity. To test for enhanced suppressive effects of endogenous opiates in trained male marathon runners, subjects were administered the potent opiate-receptor antagonist, naltrexone (1 mg/kg). This antagonist significantly stimulated pulsatile LH secretion by increasing mean serum LH values from 10.94 to 13.58 mIU/ml (P = 0.007); area under the LH concentration vs. time curve increased from 5370 to 6510 mIU/ml ± 3 hours (P = 0.05) and, pulse frequency rose from 2.8 to 4.9 pulses/8 hours (P = 0.006). Naltrexone also enhanced pulse frequency of FSH secretion from 3.4 to 5.4 pulses/8 hours (P = 0.009), but did not alter serum prolactin concentrations. None of these responses differed significantly from those in normal sedentary controls. We concluded that 1) detailed parameters of physiologically pulsatile LH and FSH secretion, even in men pf endurance training, are not distinguishable from those of normal sedentary controls; 2) secretion of PRL basally and in response to opiate-receptor blockade is not significantly perturbed; and 3) LH release in male athletes appears to be under tonic inhibitory control by endogenous opiate systems, but the inhibitory influence of these opiates is not markedly exerted.