Nocturnal increase of plasma testosterone in men: relation to gonadotropins and prolactin

The nocturnal increase of plasma testosterone (T) in adult men has been well established. Luteinizing hormone (LH) does not show a similar increase throughout the night, whereas prolactin (PRL) does, suggesting the possibility of other hormone influence on T secretion. To investigate this possibility, 8 young adult men were studied for 4 consecutive nights in the sleep laboratory (2 nights adaptation, 2 nights blood sampling), by blood samples taken every 30 min during the 8-h sleep period, for measurement of LH, follicle stimulating hormone (FSH), PRL, and T. LH and FSH were secreted episodically, with little or no change in baseline levels during the night. PRL and T also were secreted episodically, but their baseline levels increased as the night progressed. Both LH and PRL had maximum within-subject correlations (averages equal +0.35 and +0.48 respectively) with T when they led T by 60 min. Within-subject correlations done on first differences (to remove the effect of slow trends) were near zero. LH and PRL had larger correlations with T than did FSH, for both calculations. These data suggest that both LH and PRL levels precede T levels by about 60 min. PRL thus may participate in the regulation of nocturnal T secretion in adult men.