Chapter 5 Studies on Melatonin and Other Pineal Factors

This chapter describes the effects of melatonin and other pineal agents in humans. The pineal gland is an actively secreting endocrine gland that affects diverse aspects of brain and endocrine physiology. A common feature of these glands is that they are usually solid and well-vascularized parenchymatous organs containing characteristic cells termed pinealocytes that have a secretory function. The mammalian pineal gland differs from the saccular pineals of submammalian species that consist of photoreceptor and sensory nerve cells. The pineal contains all the enzymes necessary for catecholamine synthesis and noradrenaline. Studies suggest that in schizophrenia pineal, HIOMT may be out of phase with its normal substrate and may thus act on abnormal substrates to produce the dimethylated metabolites responsible for the disease. Depression, as suggested by many researchers, may result from a deficiency of serotonin or catecholamines or both. Melatonin secretion has been examined in manic and depressive patients because of evidence linking these disorders with derangements in biological rhythms and with an altered noradrenergic activity. Many investigations in the pineal's role in human and mammalian physiology need to provide a better understanding of the same; principal among these are the effects of the gland in brain and endocrine function and the mechanisms involved. The role of the pineal in human circadian periodicity, sleep, and behavior also await elucidation.