Summary
A reproducible method is described for quantitating either spontaneous or ADP- induced platelet aggregation in circulating dog blood after heparinization. An extra- corporeal shunt containing screen material with openings 53 microns square was placed in the dog’s arterial circulation. The blood pressure was measured proximal to this filter. The blood pressure decreased upon opening the shunt to the circulation and increased when the filter became occluded. The degree and rate of aggregation was determined by means of measuring these blood pressure changes. Phase and electron microscopy demonstrated platelet aggregates occluding the filters. Platelet aggregation on the filter was experimentally accelerated by infusing ADP before the filter. The administration of ADP in concentrations between 0.625 and 10 μg/ml until occlusion, produced a dose response relationship between log of ADP concentration and rate of filter occlusion. Macrodex, a known inhibitor of platelet aggregation was given intravenously and was found to delay filter occlusion. Similar results were obtained with high intravenous doses of phenylbutazone. The method was used to compare the drug effects with their in vitro effects measured photometrically. It would appear that this technique can be used for demonstrating and quantitating the effects of drugs on the process of platelet adhesion and aggregation in vivo.
