NITRIC-OXIDE DONORS INDUCE EXTRUSION OF CYCLIC-GMP FROM ISOLATED HUMAN BLOOD-PLATELETS BY A MECHANISM WHICH MAY BE MODULATED BY PROSTAGLANDINS

In the presence of 3-isobutyl-methylxanthine (IBMX), induction of cycl ic 3',5'-guanosine monophosphate (GMP) production in human washed plat elets (HWP) by nitric oxide donors (NOD) is followed by its accumulati on in the surrounding medium in a time- and concentration-dependent ma nner. Thirty minutes incubation of HWP with 3-morphoiino-sydonimine (S IN-1, 10 mu M) at 37 degrees C resulted in a 4.6-fold increase of cycl ic GMP in platelets, whereas in the extracellular medium the increase was 17.6-fold, Similar results were obtained when other NOD such as S- nitroso-N-acetylpenicyllamine (SNAP) and 3-(2-metoxy-5-chlorophenyl)ox atriazol-5-imine (GEA 3184) and the selective phosphodiesterase inhibi tor, zaprinast (M&B 22948, 10 mu M), were used. Probenecid (1-300 mu M ), an inhibitor of organic anion transport, or ouabain (1-300 mu M), a n inhibitor of Na+/K+ adenine triphosphate (ATP)-ase had no effect on cyclic GMP production or extrusion after stimulation with SIN-1. Signi ficantly, prostaglandin A(1) (PGA(1)) and prostaglandin D-2 (PGD(2)) i nhibited the efflux of cyclic GMP from platelets induced by SNAP (10 m u M) in a concentration-dependent fashion, with an IC50 of 63 +/- 16 a nd 143 +/- 17 mu M, respectively. These studies suggest that the extru sion of cyclic GMP from human platelets after activation of soluble gu anylate cyclase by NOD may contribute to the control of cyclic GMP lev els in platelets with potential physiological and therapeutic conseque nces.