1. Diadenosine phosphates were isolated from platelets, adrenal gland and autonomic nerves. The presence of diadenosine phosphates in storage pools releasable into the circulation suggests an important role in the control of blood pressure, and potentially to a modulation of the actions of catecholamines. 2. Besides a role of the diadenosine phosphates in platelet aggregation, these agents have potent vasoactive properties. Vasoactive actions of the diadenosine phosphates were demonstrated in numerous vascular models including most of the physiologically important elements of blood pressure regulation. Mostly, the vasoactive action depends on the number of phosphates in the diadenosine phosphates. Vasodilation can be observed in intact vessels after administration of Ap2A, Ap3A and Ap4A whereas contraction is affected by Ap5A and Ap5A and Ap6A. Vasocontraction induced by the diadenosine phosphates in vascular smooth muscle cells is mediated by an increase in intracellular free Ca2+. 3. In vivo, intravenous injection of Ap4A lowers blood pressure whereas injections of Ap5A and Ap6A caused a prolonged increase in blood pressure. In blood, in contrast to ATP, diadenosine phosphates are relatively long-lived molecules, suggesting that the action of the latter is of intermediate time span. In a similar manner to the vasoconstrictor angiotensin II, diadenosine phosphates also act as mitogens. It can be assumed that diadenosine phosphates may be involved in pathophysiological events of circulation including hypertension and atherosclerosis.
