The
metyrapone-test was used to study the influence of pituitary-adrenal activity on the pineal function in man. We recorded in blood the circadian rhythmicity of
melatonin,
ACTH and
cortisol and the excretion of
melatonin,
cortisol and
Porter-Silber chromogens in urine before, during and after the administration of 750 mg
metyrapone every 4 h during 24 h in two healthy volunteers and in two patients with asymptomatic, moderate
hyperparathyroidism and a
prolactin-secreting microadenoma, respectively. The present study confirmed our previous report on an increased excretion of
melatonin per 24 h and per mmol
creatinine during the administration of
metyrapone. The excretory maximum preceded the maximal
ACTH-adrenal response. Serum
melatonin remained unchanged during the administration of
metyrapone. A second finding was depressed serum
melatonin the night after the test in the subjects with the most marked
ACTH-
cortisol response following the
metyrapone-test indicating suppression of
melatonin secretion when
ACTH-
cortisol secretions were increased. A third finding was a late increase in diuresis appearing the day after
metyrapone-administration while glomerular filtration rates did not show significant alterations. Thus, it is shown that the
metyrapone-induced
cortisol inhibition stimulates both
ACTH and
melatonin secretion, while high
ACTH and
cortisol levels are accompanied by reduced S-
melatonin levels.