This chapter discusses the involvement of pineal indoles and polypeptides with the neuroendocrine axis. The number of endocrine organs that the pineal gland influences is truly remarkable. Most, if not all, of the hormones derived from the anterior pituitary gland are modulated by pineal secretions. Furthermore, many of the extra-pituitary regulated endocrine glands are also under control of this multipotent epithalamic structure. Because of its profuse blood supply, several investigators predicted an endocrine role for the pineal gland at a time during which it was unpopular to do so. The question of the specific pineal substance(s) responsible for the gonad-regulating capability of the pineal obviously remains unanswered. The indoles may act on the brain where they modify monoamine or catecholamine metabolism while the polypeptides may act on the anterior pituitary in a manner similar to the action of other polypeptides, the hypothalamic releasing factors.
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