Dinucleoside polyphosphates, a new group of hormones, are stored in cellular granules and are released into the circulation after the cells have been stimulated. Dinucleoside polyphosphates then bind to specific receptors in other tissues and organs. Dinucleoside polyphosphates may either act as vasoconstrictors or as vasodilators. The type of action of the dinucleoside polyphosphates in various vessels depends on the pattern of purinoceptor expression. In rabbit and guinea pig, cardiac preparations of dinucleoside polyphosphates showed a negative inotropic action. On the other hand, in human cardiac preparations a positive inotropic action of dinucleoside polyphosphates was observed. A great number of enzymes degrading dinucleoside polyphosphates have been isolated from plasma as well as the extracellular surface of plasma membranes, further contributing to the complex picture of metabolism and actions of dinucleoside polyphosphates as cardiovascular hormones. It may be speculated that dinucleoside polyphosphates, especially Ap(5)A, may play a role in the pathogenesis of hypertension. Ap(5)A has been shown to be the most potent agonist of the P-2X receptors mediating vasoconstriction. A P-2X receptor non-desensitized by Ap(5)A may underly the vasoconstriction observed after continuous perfusion of the kidney with Ap(5)A. Potentially, by further characterization of this receptor, an antagonist may be developed which is capable of lowering blood pressure.
