Lithium inhibits adenylate cyclase of human platelets

The ADP-induced aggregation of human platelets is markedly increased after preincubation with lithium chloride, whereas lithium has the opposite effect on rabbit platelets. Since this phenomenon might be related to cAMP metabolism, the influence of lithium on total cAMP content and adenylate cyclase activity was investigated. Lithium does not significantly change the total cAMP content of human platelets neither during incubation nor during ADP-induced aggregation. Basal adenylate cyclase activity, however, was slightly inhibited by lithium in human platelets. The inhibition of adenylate cyclase by ADP appeared to be enhanced by lithium. Prostacyclin induced stimulation of adenylate cyclase is counteracted by this ion. In rabbit platelets the prostacyclin stimulated adenylate cyclase activity is not affected by lithium. These data suggest that a correlation exists between the influence of lithium on the aggregation of human and rabbit platelets and the sensitivity of their adenylate cyclase for this ion.