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Nitroclycerin (GTN) but not the new nitric oxide donor Ru(bpy) 2 (py)(NO2)](PF6) (RuBPY) induced in vitro cross‐tolerance with acetylcholine

This work aimed to verify if RuBPY induces in vitro tolerance and cross‐tolerance with acetylcholine (ACh) in rat cava vein and to compare this effect with GTN. We have analyzed the maximum effect (ME) induced by GNT, RuBPY and ACh in concentration‐effect curves in veins contracted with endothelin‐1. P values ≤0.05 were considered significant. In vitro tolerance was induced by 60 min‐incubation with GTN (0.1mM or 4 μM) or Rubpy (0.1μM or 2 μM). In vitro cross‐tolerance for ACh was induced by incubating vein with GTN or Rubpy (4 μM) for 60 min. The protein expression of phosphorylated eNOS on Ser1177 and total eNOs was accessed by Western Blot. Our results demonstrate that after incubation with GTN (EC50,EC100) the ME was reduced from 75.3±2.2%, n=6 to 45.4±2.2%, n= 6 and to 39.2±1.4%, n= 6, respectively. Incubation with RuBPY (EC50,EC100) reduced the ME from 92.8±4.2%, n=7 to 48.0±2.3%, n=7 and 30.1±1.2%, n=7, respectively. GTN but not RuBPY, reduced ACh‐induced relaxation (from 100.3±5.3% to 75.1±4.2%, n=7). GTN, but not RuBPY induced eNOS phosphorylation. In conclusion, RuBPy and GTN induce tolerance in both EC50, EC100. Only GTN induces cross‐tolerance to ACh and increased eNOs phosphorylation. Supported by FAPESP and CNP