Melatonin is a steroid hormone secreted mainly by the pineal gland. It is also secreted in the retina, the lacrimal gland of the orbital cavity, the salivary glands, the chromaffin cells of the intestine, and red blood cells. The process of synthesizing melatonin in the pineal gland is as follows:
- Tryptophan is converted to 5-hydroxytryptophan by tryptophan hydroxylase (TPH).
2.25-hydroxytryptophan decarboxylase (25-HT-POC) catalyzed into serotonin.
- Under the action of serotonin-N-acetyltransferase (NAT) and hydroxy oxime methyltransferase (HIMOT), 5-hydroxytryptamine is converted to melatonin by N-acetyl serotonin (N-acetyl- 5-methoxytryptamine).
In animals, the secretion of melatonin in the pineal gland has obvious circadian rhythm fluctuations, daytime secretion is reduced, and nighttime secretion is increased. Studies have shown that the circadian rhythm of pineal melatonin fluctuates, with light and vision on the pineal gland. The impact has a very important relationship and is also related to sympathetic innervation.
- Regulating biological rhythms
Melatonin regulates biological rhythms and synchronizes rhythms in and out of the body. Melatonin has a light-to-energy conversion of the neuro-endocrine system, thereby maintaining the consistency of endogenous rhythms and environmental cycles in the body. Melatonin is the "hormone of the hormone", which acts on the hypothalamus and promotes the secretion of hormones in the body by secreting various hormones. The effect of melatonin is affected by light. Experiments show that the light intensity of 2500 LX can completely inhibit the action of melatonin. The commonly used illumination lamps can be partially suppressed, but the illumination can be completely suppressed by the illumination for more than 12 hours. The role of the pigment, continuous light can reduce melatonin in the body, the nucleus of the nucleus receives light and so on, which affects the secretion of melatonin and affects the physiological rhythm of human beings. Melatonin can inhibit spontaneous or evoked discharges in the cerebral cortex and hippocampal neurons, and promote the inhibition of neuronal function in the cerebral cortex. Comparison of melatonin and placebo showed that the melatonin group was in a sleep state, and the cycle was basically synchronized with the nighttime tense, while the placebo group showed no significant change. The diurnal variation rhythm of melatonin is not affected by age and gender. The secretion of melatonin is also rhythmic, which is short in summer and short in winter. Melatonin changes physiological rhythms, causing many endogenous substances to also produce physiological rhythmic changes.
- Regulating the immune system
Melatonin is closely related to immune function. As early as 1981, Maestroni has found that melatonin synthesis inhibition is associated with decreased humoral and cellular immune effects in mice. In recent years, a large number of studies have shown that melatonin is an immunomodulator that can improve the body's immune function, including increasing the weight of the thymus, increasing the lymphocyte proliferation response, and activating Th cells to release interleukin-2 (IL-2). And interferons further increase the activity of NK cells and other immune components. Recent studies have also shown that exogenous melatonin can improve immune function caused by aging. The immunomodulatory function of melatonin can be achieved in a variety of ways: (1) melatonin receptors are present in the thymus, spleen, lymph nodes and lymphocytes, and melatonin can directly regulate immune regulation through its receptors. effect. (2) Opioid receptor network. Experiments have shown that melatonin's immune enhancement can be reversed by opioid receptor antagonists; endorphins mimic the immune enhancement of melatonin; melatonin stimulates Th cells to release opioid peptides, so Maestroni considers melatonin Modulation of immune function may be achieved primarily through the endogenous opioid peptide system. (3) Melatonin may also exert immunomodulatory effects through other endocrine systems, such as the thalamus-pituitary-gonadal axis and adrenal gland.
Free radicals may be produced in the enzymatic and non-enzymatic reactions in the body, and free radicals are closely related to aging. Melatonin not only has obvious anti-oxidation effect, but also has multi-stage metabolites with strong antioxidant function, and also has the dual effects of simultaneously removing oxygen and nitrogen radicals and up-regulating various antioxidant enzymes. Active function. Melatonin protects cell structure by scavenging free radicals, anti-oxidation and inhibiting lipid peroxidation, preventing DNA damage and reducing peroxide levels in the body. Melatonin has obvious antagonistic effects on tissue damage caused by peroxidation caused by exogenous toxicants (such as paraquat) and free radicals produced by it.