Possible Errors in the Use of P³² Orthophosphate for the Estimation of Platelet Life Span

Specific activities of platelet lecithin, plasma lecithin, and plasma inorganic phosphate were followed in patients for 4-5 weeks following a single therapeutic injection of P³² orthophosphate, and were found to be of the same order of magnitude at any one specific time. Platelets labeled in vivo with P³² orthophosphate were incubated with non-radioactive plasma, and lost some of the labeled phosphatides to the plasma. Platelets incubated in vitro with P³² orthophosphate incorporated the label into some phosphatides. The findings suggest there is some intrinsic platelet metabolism, and that this must be considered when estimates of platelet life span are made using a P³² orthophosphate label.