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Evidence for downregulation of hypothalamic 5‐hydroxytryptamine receptor function in endurance‐trained athletes

Serum prolactin (PRL) was used as a hormone marker of serotoninergic function following oral administration of an acute dose of a serotoninergic agonist. Five male endurance‐trained athletes (ET) and five healthy non‐endurance‐trained controls (NT) were studied. The peak PRL concentration was lower (P = 0.031) for the ET athletes (486 +/‐ 208 mU l‐1; mean +/‐ S.D.) than for the NT controls (1000 +/‐ 385 mU l‐1); the total release of PRL was also lower (P = 0.042) for the ET subjects. The lower neuroendocrine response to a serotoninergic agonist in the endurance‐trained athletes suggests a downregulation of central serotoninergic receptor function in response to endurance training in man.