Platelet aggregation induced by ADP in vivo: Continuous and quantitative measurements in different vascular beds

Abstract

Platelet aggregates induced by infusion of ADP are recorded in arteries and veins by a previously described photoelectric technique. Two parameters are mainly responsible for the degree of aggregation, (1) the concentration of ADP and (2) the platelet count. The lower the concentration of ADP, the lower the number of aggregates counted. Maximum effect was achieved at 0.35 mg ADP/kg body wt/min. Larger doses of ADP proved to be impractical because of the vasodilatory action with extreme fall in arterial blood pressure. There is a correlation between platelet count in the range from 180,000 to 260,000/mm 3 and the number of aggregates formed, however, beyond 300,000/mm 3 the degree of aggregation seems to be independent of the number of platelets. When blood containing a well-defined number of aggregates passes the minute vessels of kidney, lung, brain, mesentery, and hind leg the aggregate count is reduced significantly. The reduction in aggregate count seems to be most marked in the renal and pulmonary system. This could be due to anatomical and/or hemodynamical differences in the microvascular systems of the organs investigated.