Role of the Nitric Oxide on Relaxation of the Human Umbilical Artery during Cooling

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In the present study, the effects of cooling (to 28°C) on the vasodilatation induced by diazoxide (10−9−3×10−4 M), isoproterenol (10−9−3×10−4 M) and magnesium sulphate (0.1-30 mM) on serotonin-pre-contracted human umbilical artery and the role of nitric oxide in these effects were analyzed. Diazoxide, isoproterenol and magnesium produced concentration-dependent relaxation of human umbilical artery precontracted with serotonin (10−6 M). During cooling, the pIC50 values and maximal responses to these agents were significantly lower than at 37°C. Cooling to 28°C in the presence of NG-nitro-L-arginine methyl ester (L-NAME, 10−4 M) did not modify the effects of temperature on diazoxide, isoproterenol and magnesium-induced relaxations. These results suggest that cooling-induced changes of diazoxide, isoproterenol, and magnesium sulphate in human umbilical artery are independent of nitric oxide.