ROLE OF CATECHOLAMINES IN PLATELET-FUNCTION - PATHOPHYSIOLOGICAL AND CLINICAL-SIGNIFICANCE

Platelets are involved in the pathogenesis of vascular damage in both atherosclerosis and arterial hypertension. Their reactivity in vivo is influenced by different factors, including sympathoadrenal activation , plasma levels of atherogenic lipoproteins and haemorrheological chan ges. In the present review, we examine the modulation of platelet func tion by the sympathoadrenal system and concentrate on the role of circ ulating catecholamines in the control of platelet responses. Human pla telets exhibit both adrenergic and dopaminergic receptors that are inf luenced by different catecholamines. alpha(2)-Adrenoceptors of alpha(2 A) subtype prevail on platelet membrane; through their stimulation, ca techolamines potentiate the effects of other agonists and, at higher c oncentrations, initiate platelet responses, including aggregation, sec retion and arachidonate pathway activation. Physiological and patholog ical conditions causing sympathoadrenal activation in vivo, i.e. physi cal activity, mental stress, insulin-induced hypoglycaemia, acute coro nary ischaemia and heart failure, modify the circulating platelet popu lations and modulate platelet reactivity through an increase in circul ating catecholamines. A sympathoadrenal hyperactivation modifies the f unction of circulating platelets through direct catecholamine effects, catecholamine-induced changes of haemodynamic factors and lipid patte rn and inhibition of the vascular eicosanoid synthesis. The catecholam ine effects on platelet function can be involved in the interplay amon g stress, adrenomedullary system activation and cardiovascular disease s.