Comparative physiology: pineal gland.

Literature on the endocrinologic function of the pineal gland is reviewed. The pineal gland appears to have an inhibitory effect on gonadtoropin release. It is possible, since no hypothalamic inhibiting factors have been indentified with the control of luteinizing hormone (LH) and follicle stimulating hormone synthesis and release by the anterior pituitary, that the pineal gland provides the necessary inhibitory principles. The antigonadotropic activity of pineal polypeptides may be of importance in this regard. In that these polypeptides are not present in the urine of pinealectomized rats, it is assumed that they are secreted by the pineal gland. Although the effects of the pineal gland on sexual physiology in animal experiments performed under phototropic conditions are barely detectable, it is incorrect to assume that the organ has no function. Exposure to artificial light for 12-16 hours may severely bias or negate the effect of the pineal gland. In that the pineal gland influences brain constituents and, possibly, synaptic transmission, it is likely that it may control the peripheral organs of internal secretion by a mechanism involving corticol indoleamine and catecholamine concentrations.