NALOXONE INHIBITS EXERCISE-INDUCED RELEASE OF PRL AND GH IN ATHLETES

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Abstract
Opiate peptides stimulate the release of GH [growth hormone] and PRL [prolactin], and such changes were also reported following physical exercise. To investigate opiate involvement in the exercise-induced release of these hormones, 8 professional athletes were exercised to 80% of their maximal heart rate on a bicycle ergometer. This exercise alone induced an increase in circulating mean GH (basal to maximal level, 3.1 .+-. 0.9 ng/ml-27.3 .+-. 5.9 ng/ml) and mean PRL level (6.1 .+-. 1.1 ng/ml-19.5 .+-. 1.9 ng/ml). Infusion of naloxone (0.3 mg/min) antagonized these responses in mean serum GH (5.6 .+-. 1.0 ng/ml to 8.6 .+-. 1.1 ng/ml) and PRL levels (6.4 .+-. 1.1 ng/ml-8.1 .+-. 1.2 ng/ml), which were both significantly less than during the control infusions (P < 0.01). Apparently certain forms of stress stimulate the release of PRL and GH via endogenous opiate peptides.