Toborinone and olprinone, phosphodiesterase III inhibitors, inhibit human platelet aggregation due to the inhibition of both calcium release from intracellular stores and calcium entry.

Purpose: We investigated the inhibitory effects of toborinone and olprinone on human platelet aggregation and calcium mobilization.Abstract Copyright:

Methods: Washed human platelets were preincubated with toborinone or olprinone, then exposed to 0.015 U.ml-1 of thrombin. Aggregation curves were measured using an aggregometer. Effects of toborinone or olprinone on changes in intracellular calcium concentration ([Ca2+]i) were measured fluorometrically using fura-2 acetoxymethyl ester (fura-2). Levels of intracellular cyclic 3",5"-adenosine monophosphate concentration ([cAMP]i) were also measured, using enzyme-linked immunosorbent assay (ELISA) techniques.

Results: The concentrations required to cause 50% inhibition of aggregation (IC50) induced by thrombin were 9.7 +/- 0.9 micro M for toborinone and 3.6 +/- 0.2 micro M for olprinone. Both drugs at IC50 significantly elevated [cAMP]i levels and significantly inhibited Ca2+ release from intracellular stores. Release of [Ca2+]i induced by thrombin was 272.9 +/- 87.1 nM, 153.3 +/- 28.7 nM, and 138.9 +/- 58.2 nM in the control, toborinone, and olprinone groups, respectively ( P < 0.02). Calcium influx through calcium channels in the plasma membrane was also suppressed by toborinone and olprinone.

Conclusion: Toborinone (9.7 micro M) and olprinone (3.6 micro M) inhibit human platelet aggregation, though these concentrations are higher than their therapeutic plasma concentrations. The inhibitory effects of both drugs are related to the inhibition of both Ca2+ release and Ca2+ entry through [cAMP]i elevation.