Differences in the vascular selectivity and tolerance between the NO donor/beta-blocker PF9404C and nitroglycerin

The vascular selectivity of PF9404C ((2'S),(2S)-3-isopropylamine,1-[4-(2,3-dinitroxy)propoxymethyl]-phenoxy-2'-propanol), a new beta-blocker with nitric oxide (NO)-donor and vasodilator properties, was studied in different rabbit arteries and veins. Phenylephrine (10(-6) M) or 35 mM K+ were used to pre-contract the arteries and veins prior to study the relaxant effects of PF9404C and nitroglycerin. The potency of both drugs to depress the phenylephrine-induced contraction was greater than that shown in the blockade of the K(+)-evoked contraction in most of the vessels studied, with the exception of the central ear artery. PF9404C exhibited about three-fold higher potency than nitroglycerin to relax the majority of the vessels studied, especially when they were contracted with K+, and showed a certain selectivity of action for the renal artery. PF9404C produced autotolerance but this effect was about 20-fold less pronounced than that observed with nitroglycerin. Cross-tolerance in those preparations pre-exposed to PF9404C that were relaxed later on with nitroglycerin was much greater than autotolerance. The tolerance for nitroglycerin was practically abolished in the presence of N-acetylcysteine. However, this was not the case for PF9404C. These results indicate that, although sharing the property of being NO donors, PF9404C and nitroglycerin show a different profile in causing vasodilation; furthermore, the tolerance to this effect is lesser for PF9404C and seems to be mediated by a mechanism different to that of nitrates. This makes PF9404C a nice pharmacological tool to further develop novel NO-donor compounds with a lesser degree of vascular tolerance than those now available.