[Epiphyseal-thyroid interrelations: effect of calcitonin on indole metabolism in health and in the presence of an excess of thyroid hormones].

A new regularity was established in a study of epiphyseal thyroid interrelationships: the opposite effect of the thyroid hormones (thyroxin and calcitonin) on the formation of methoxyindoles (melatonin, 5-methoxytryptamine) in the epiphysis. Thyroxin was shown to stimulate and calcitonin to inhibit O-methylation of serotonin in the pineal gland, and combined administration of both hormones levelled their action on one another. The inhibitory effect of calcitonin was more marked if a high basal level of melatonin was stimulated by preliminary administration of thyroxin. The authors assume that such a double control of the thyroid is "protective" for the epiphysis, preventing rapid depletion of reserves in case of excessive saturation of the body with thyroid hormones and maintaining its function in case of a sharp rise of the blood level of calcitonin.