ADP METABOLISM IN VASCULAR TISSUE, A POSSIBLE THROMBO-REGULATORY MECHANISM

An investigation for adenosine diphosphatase (ADP-ase) activity in various vascular preparations was carried out. Such activity was found in the intact cell preparations derived from digested rabbit aorta, and from cultured pig smooth muscle cells. It was also found in the following isolated vascular preparations: rabbit aortic rings; trickled rabbit aorta; rat lung and guinea-pig heart. All the preparations degraded ADP to AMP. Smooth muscle cells further degraded AMP to adenosine on prolonged incubation (30-120 min). Rat lung and guinea-pig heart considered to be representative of endothelial cell preparations primarily produced AMP with minimum formation of adenosine and inosine. All the rabbit preparations produced a mixture of AMP, adenosine and inosine. It is considered that this is not a species difference but is due to the probable mixed cell population in these preparations. AMP and adenosine are known inhibitors of platelet aggregation and our results suggest that the amounts formed on degradation of ADP are sufficient to produce such inhibition. Finally, it is suggested that vessel wall ADP-ase could regulate haemostasis and thrombosis both by removal of pro-aggregatory ADP and by the production of anti-aggregatory metabolites. © 1979.