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Abstract(s)
We have studied several effects of hydralazine in the bisected rat vas deferens. Hydralazine produced a shift to the left of the concentration-response curve for noradrenaline, with potentiation of the maximal response in both portions of the vas deferens. In contrast it caused a shift to the right of the concentration-response curve for noradrenaline in preparations pretreated with cocaine (inhibitor of catecholamine neuronal uptake), and of the curve for methoxamine and for CaCl2 (in depolarizing medium with K+ 55 mM), in all cases with depression of the maximal response. Hydralazine enhanced the contractions induced by noradrenaline in Ca2+-free medium, except in the presence of cocaine. It had no effect on [3H]noradrenaline neuronal uptake into noradrenergic neurons of the vas deferens, nor did it affect basal or K+-induced 45Ca2+ uptake. These results suggest that hydralazine potentiates the contractions elicited by noradrenergic by a mechanism other than blockade of the neuronal uptake of this catecholamine. Our results also suggest that the inhibition by hydralazine of the contraction elicited by Ca2+ (in Ca2-free depolarizing high-K+ 55 mM solution) and by methoxamine is not due to an action on voltage-dependent Ca2+ channels, but may reflect an intracellular site of action.