MELATONIN, PITUITARY-FUNCTION AND STRESS IN HUMANS

(1) The nocturnal rise in plasma melatonin concentration continued through two cycles with continuous light occlusion by blindfolds in normal subjects. A daytime nap did not disturb the rhythm. (2) The plasma melatonin rhythm was present in patients with pituitary-adrenal and pituitary-gonadal failure, but appeared diminished or absent in patients bearing lesions at different points in the pineal afferent pathway. (3) In other patients and subjects who showed normal response of cortisol, growth hormone or prolactin after stimuli including hypoglycemia, pneumoencephalography, exercise or administration of l-dopa during the daytime, there was no stimulation of plasma melatonin concentration. (4) Melatonin was not correlated with prolactin in blood or cerebrospinal fluid of patients with a wide range of plasma prolactin levels. (5) The adult human melatonin rhythm is relatively independent from pituitary, gonadal, and adrenal function, but may rely on a neural pathway similar to that controlling the rhythm in lower animals. The human melatonin rhythm may represent the output of a stable oscillator with a signal relatively free from acute perturbation by sleep, darkness, or stress sufficient to cause changes in other hormones. © 1979.