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) Nocturnal cardiovascular blunting is important for the prevention of cardiovascular diseases,(3) whereas the morning period is strictly linked to the peak frequency of cardiovascular accidents.(4) Melatonin, which is secreted almost exclusively at night,(5) influences several endocrine and biologic functions.(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 activity.(5,6) Second, in rats, melatonin and the pineal gland are able to prevent ischemia and/or reperfusion-induced heart arrhythmias,(7) influence the control of BP,(8,9) regulate blood flow to the brain,(10) and modify peripheral artery responsiveness to norepinephrine.(11) In this study it was investigated whether melatonin may have a direct influence in the control of the cardiovascular sq,stem of healthy men.