Effects of melatonin an vascular reactivity, catecholamine levels, and blood pressure in healthy men

The cardiovascular system shows a diurnal rhythm of activity, shown by the nocturnal decrease of blood pressure (BP)(1) and catecholamine levels.(2) N octurnal cardiovascular blunting is important for the prevention of cardiov ascular diseases,(3) whereas the morning period is strictly linked to the p eak frequency of cardiovascular accidents.(4) Melatonin, which is secreted almost exclusively at night,(5) influences several endocrine and biologic f unctions.(6) A possible link between melatonin and circulation is suggested by 2 pieces of evidence. First, the nocturnal increase of melatonin seems to show an inverse temporal relation with the decrease of cardiovascular ac tivity.(5,6) Second, in rats, melatonin and the pineal gland are able to pr event ischemia and/or reperfusion-induced heart arrhythmias,(7) influence t he control of BP,(8,9) regulate blood flow to the brain,(10) and modify per ipheral artery responsiveness to norepinephrine.(11) In this study it was i nvestigated whether melatonin may have a direct influence in the control of the cardiovascular sq,stem of healthy men.