Inositol cyclic triphosphate [inositol 1,2-(cyclic)-4,5-triphosphate] is formed upon thrombin stimulation of human platelets.

Abstract
Cleavage of polyphosphoinositides in vitro by phospholipase C results in formation of both cyclic and noncyclic phosphates. We have now isolated the cyclic product of phosphatidylinositol 4,5-bisphosphate cleavage, inositol 1,2-(cyclic)-4,5-trisphosphate [cIns(1:2,4,5)P3], from thrombin-treated platelets. We found 0.2-0.4 nmol of cIns(1:2,4,5)P3 per 109 platelets at 10 sec after thrombin; none was found in unstimulated platelets or in platelets 10 min after thrombin addition. We conclude that cIns(1:2,4,5)P3 is a major product of polyphosphoinositide metabolism in thrombin-stimulated platelets.