Cardiovascular Effects of Melatonin

In the course of aging, the incidence of both acute and chronic heart diseases, systematically increases. Concentrations of some hormones decrease in the course of aging, e.g., melatonin concentrations in serum and urinary levels of its main metabolite, 6-sulphatoxymelatonin, are lower in older, when compared to values observed in younger population. The evidence obtained during the last 10 years suggests that melatonin exerts certain effects upon the cardiovascular system. The presence of vascular melatoninergic receptors (binding sites) has been demonstrated; these receptors are functionally associated with either vasoconstrictor or vasodilatory effects of melatonin. Melatonin clearly indicates a certain contribution in general cardioprotection of the rat heart, following myocardial ischemia-reperfusion and adriamycin-induced cardiotoxicity. It has been shown that patients with coronary heart disease have a low melatonin production rate, especially those with higher risk of cardiac infarction and/or of sudden death. There are clinical data, reporting alterations of melatonin concentrations in serum in coronary heart disease. The suprachiasmatic nucleus and, possibly, the melatoninergic system may also modulate cardiovascular rhythmicity. Other problems, related to age, include hypercholesterolemia and hypertension. People with high levels of LDL-cholesterol have low levels of melatonin. It has been shown that melatonin suppresses the formation of cholesterol, reduces LDL accumulation in serum and modifies fatty acid composition of rat plasma and liver lipids. People with hypertension demonstrate lower melatonin levels vs. those with normal blood pressure. The administration of the hormone in question declines blood pressure to normal range. This chapter summarizes the actual knowledge of the relationships between the cardiovascular system and melatonin.