Role of the lung in the development of cardiovascular modifications during ADP infusion in the rat

We investigated the role played by platelet aggregates in cardiovascular alterations induced by ADP in the rat by following the localization of Cr⁵¹-platelets in different circulatory districts. An intravenous infusion of ADP (3 mg/kg/5min ) caused cardiovascular collapse accompanied by a 50% fall in platelet count and Cr⁵¹ blood radioactivity. Cr⁵¹-platelet content increased five fold in the lung. When ADP was infused into the left ventricle only a moderate decrease in systemic blood pressure was observed although the platelet fall was similar to that observed after i.v. infusion. Significantly higher radioactivity than controls was found in the heart, kidney, femoral muscle and brain, but not in the lung. It is suggested that selective platelet trapping in the pulmonary circulation in addition to the direct vasodilating activity of ADP were the major causes of cardiovascular shock during ADP infusion in the rat.