Factors other than Light Affecting the Pineal Gland: Hypophysectomy, Testosterone, Dihydrotestosterone, Estradiol, Cryptorchidism, and Stress

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Abstract
This article reviews those factors other than light that affect the activity of the pineal gland. Both testosterone and dihydrotestosterone were shown to have tissue specific inhibitory effects on pineal MAO activity concomitant with an increased activity of the gland. Estradiol stimulated pineal MAO activity and decreased the activity of this gland. This effect also was tissue-specific. Bilateral and unilateral experimental cryptorchidism also decreased pineal MAO activity 3 to 4 weeks after surgery. Acute stresses appear to increase adrenal catecholamine output (epinephrine and norepinephrine) as well as to stimulate local adrenergic pathways, while chronic stress, such as starvation, appears to act through the adrenal corticosteroids by decreasing pineal MAO activity thereby indirectly increasing melatonin synthesis. Thusly, both components of the adrenal gland appear to act in concert to increase effectively melatonin synthesis by the pineal gland. Irradiation and histamine have also been reported to affect pineal function—the latter specifically inhibits HIOMT activity. These observations indicate that many factors other than light affect pineal morphology and melatonin synthesis. The pineal appears to be a true neuroendocrine organ that is affected by hypophysectomy and is responsive to feedback and control from other organs within the mammalian organism.
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