Kinetics, distribution, and sites of destruction of canine blood platelets with In-111 oxine.

In five normal dogs we have studied the survival, tissue distribution, and fate of autologous platelets labeled with indium- 111 oxine. The methods include blood sampling, computer-assisted scintigraphy, and whole-body profile scanning. Mean In- 111-platelet recovery in the circulation was 45 +/- 22.5 (s.d.) and survival 124.6 +/- 10.5 hr. Platelet survival curves fitted a linear function best. Initially platelets pooled rapidly in the spleen with a single exponential function, and at zero-time equilibrium (35 +/- 4)% of the injected In- 111 was located in this organ. Early hepatic uptake was also significant, and constituted (20 +/- 4)% of total-body radioactivity. As labeled platelets disappeared from the circulation, In- 111 activity in the spleen increased progressively and linearly to reach (59 +/- 9)% of the body activity at 120 hr. Hepatic radioactivity decreased with time but to a lesser extent than that of the heart. The results indicate that in the dog the major site of destruction of platelets is the spleen, with the liver playing a less important role.