Release of immunoreactive-neuropeptide by rat platelets.

Neuropeptide Y, a potent vasoconstrictor and cardiac depressant, is re-leased from sympathetic nerve endings. Its presence in megakaryocytes suggests this peptide might be stored in platelet granules and released during aggregation. Immunoreactive-neuropeptide Y was measured in platelet rich and platelet poor plasma, and was substantially greater in the former. Addition of collagen to platelets resulted in release of neuropeptide Y which paralleled, in a concentration-dependent manner, the degree of platelet aggregation. Adenosine diphosphate, at concentrations which induce only the first phase of aggregation and not the release reaction, caused only a minor release of neuropeptide Y. These results suggest that platelet release could be a major source of circulating neuropeptide Y and could contribute to hemodynamics of pathophysiological states involving platelet activation.