Evidence for a NO synthase in porcine platelets which is stimulated during activation/aggregation

Abstract: We tried to characterize the porcine platelet nitric oxide (NO) synthase and its L-arginine (L-arg)/NO metabolism. Using RT-PCR we could show a constitutive endothelial NOS (ecNOS) and an inducible NOS (iNOS) similar mRNA in platelets. The NOS protein could be evidenced by an ecNOS 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 NADPH-diaphorase staining we could show NO synthase in preactivated platelets but not in resting platelets, indicating that the platelet NOS may be activated during platelet activation/aggregation. Porcine L-arg plasma levels (9.31 × 10^–5 mol/l ± 10%) could be shown to be in the same range as human plasma levels. Moreover, we could show that the NO precursor L-arg and hydroxy-L-arginine (OHarg) concentration dependently inhibited collagen induced platelet aggregation. Summarizing these results confirm the existence of and further characterize porcine platelet NO synthases.