The circadian rhythm of melatonin in hypothyroidism and hyperthyroidism

UNLABELLED: In order to determine the influence of thyroid function on the pineal gland in humans, the circadian rhythm of the serum melatonin concentration was estimated in 16 women with thyroid disorders: 8 with hypothyroidism and 8 with hyperthyroidism, as well as in 5 healthy controls. A significant melatonin circadian rhythm was observed in all the three groups studied. The melatonin rhythm parameters derived from cosinor analysis: mesor (controls: 0.163 +/- 0.03 nmol/l (+/- SEM), hypothyroid patients: 0.176 +/- 0.22 nmol/l, and hyperthyroid patients: 0.167 +/- 0.04 nmol), amplitude (0.155, 0.145 and 0.138 nmol/l, respectively), acrophase (1:38, 2:22 and 1:51 h, respectively) did not differ significantly in the three groups studied. Integrated 24-h melatonin secretion was also similar in patients and controls. The melatonin concentrations were positively correlated with TSH levels in hypothyroidism, and negatively correlated with T3 in hyperthyroidism. IN CONCLUSION: in patients with hypo- and hyperthyroidism the circadian rhythm of melatonin secretion is not altered.