Potentiation by collagen or epinephrine of platelet responsiveness to aggregation. The possible role of substance(s) released from platelet membranes.

When human platelets in plasma were exposed to a small amount (nonaggregating concentration) of collagen, epinephrine, or arachidonic acid, their responsiveness to aggregating agents was potentiated and they were aggregated by a subsequent addition of nonaggregating concentrations of the stimulants. Otherwise the nonaggregating concentrations of the stimulants were incapable of inducing platelet aggregation. The potentiation of platelet responsiveness to aggregating agents was also caused by collagen- or epinephrine-treated platelet membranes. Furthermore, the soluble fraction of collagen- or epinephrine-treated membranes contained some material responsible for platelet potentiation, indicating that the responsible material was released from platelet membranes by collagen or epinephrine. It is suggested that the material may be arachidonic acid or its derivatives related to prostaglandins, since the soluble fraction of collagen- or epinephrine-treated membranes contained a larger amount of the precursor(s) of prostaglandin Falpha than the untreated membranes.