EVIDENCE FOR A NO SYNTHASE IN PORCINE PLATELETS WHICH IS STIMULATED DURING ACTIVATION AGGREGATION/

We tried to characterize the porcine platelet nitric oxide (NO) syntha se and its L-arginine (L-arg)/NO metabolism. Using RT-PCR we could sho w a constitutive endothelial NOS (ecNOS) and an inducible NOS (iNOS) s imilar mRNA in platelets. The NOS protein could be evidenced by an ecN OS specific antibody which also bound in platelets. This finding could be confirmed by Western blot showing an ecNOS in the membrane but not the cytosolic fraction; iNOS protein could not be detected. Using NAD PH-diaphorase staining we could show NO synthase in preactivated plate lets but not in resting platelets, indicating that the platelet NOS ma y be activated during platelet activation/aggregation. Porcine L-arg p lasma levels (9.31x10(-5) mol/l+/-10%) could be shown to be in the sam e range as human plasma levels. Moreover, we could show that the NO pr ecursor L-arg and hydroxy-L-arginine (OHarg) concentration dependently inhibited collagen induced platelet aggregation. Summarizing these re sults confirm the existence of and further characterize porcine platel et NO synthases.