Nitrovasodilator induced relaxation of isolated porcine basilar artery segments. The vasodilator activity of S-nitroso-N-acetyl-D,L-penicillamine (SNAP), glyceryl trinitrate (GTN), isosorbide-5-nitrate (ISMN) and pentaerythritol tetranitrate (PETN) was assessed in the presence (intact) and absence (denuded) of intact endothelium. Each concentration-response curve is plotted by taking the respective mean values of 6 – 9 individual experiments (s.e.mean indicated by bars, *P<0.05 compared to intact endothelium, halfmaximal effective concentrations, see Table 1).