Failure of Nocturnal Prolactin Suppression by Methysergide to Entrain Changes in Testosterone in Normal Men*

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Abstract
To investigate further the postulated relationship between the secretion of PRL [prolactin] and testosterone, 10 normal young men were studied during polygraphically recorded sleep. Concentrations of LH [luteinizing hormone] and testosterone were measured in plasma every 20 min, and the results were analyzed in relation to sleep parameters and previously reported concentrations of PRL. All subjects were studied on a control night after placebo administration and on an experimental night after ingestion of the serotonin receptor blocker, methysergide. Analysis of variance revealed that concentrations of testosterone rose gradually during sleep on both nights. Highest LH values occurred during stage 1 sleep, but were only 25% higher than the lowest values, which were seen in stage 4. PRL concentrations were markedly suppressed by methysergide treatment. No significant change in testosterone values were observed on the methysergide nights as compared to the control nights. When the data were analyzed by a correlational approach, again, no significant relation between concentrations of PRL and testosterone was found. Although these data do not support the concept that PRL-stimulated testosterone secretion occurs during the night in normal men, such a mechanism may be operative during daytime hours or under conditions of PRL stimulation rather than PRL suppression.