Some Clinical, Biochemical, and Physiological Actions of the Pineal Gland

Abstract

Pineal tumors may be associated with 2 endocrine syndromes: destructive, nonparenchymal lesions frequently produce precocious puberty in young boys, while true parenchymatous tumors have been found in children with delayed sexual development. Patients with each of these syndromes are described. The pineal gland contains a hormone, melatonin (5-methoxy N-acetyltryptamine) which inhibits ovarian growth and the incidence of estrus in rats. Only the pineal has been shown to have the enzymatic capacity to synthesize melatonin and other methoxyindoles from serotonin, which it contains in large quantities. The activity of the melatonin-forming enzyme varies diurnally: it is highest at night, when rats are in darkness. Environmental lighting controls the activity of this enzyme, light inhibiting and dark stimulating melatonin synthesis. Information about lighting is transmitted to the pineal gland via a neural route, involving its sympathetic nerves. Since melatonin inhibits ovary growth and the incidence of vaginal estrus in rats, and since these aspects of gonad function are both stimulated by light, it is suggested that light exerts part of its neuroendo-crine effect by modifying the synthesis of pineal melatonin. When the sympathetic nerves to the pineal are destroyed, both the pineal and the gonads lose their capacity to respond to light. Light increases the activity of the pineal enzyme which synthesizes serotonin, also by a neural route. Tumor tissue from a patient with a metastatic parenchy-mal pinealoma was examined and was found to contain serotonin, melatonin, and the melatonin-forming enzyme. This constitutes the 1st description of this enzyme in tissue other than normal pineal.