effect of verapamil and nitrendipine on noradrenaline induced contraction of the isolated rabbit acritic strip

The possibility of the involvement of the alpha-adrenoceptors in the mechanism of calcium channel blockers inducing vasodilatation was investigated. The effects of verapamil, nifedipine and phentolamine have been compared on the contractions of the rabbit aortic strips produced by different concentrations of noradrenaline [NA] [10-7 - 10-4 M]. Results showed that preincubation of the rabbit aortic strip with a low concentration of verapamil [10-6 M] caused a parallel rightward shift of NA dose response curve, with significant depression of the minimal response induced by NA. A highly marked rightward shift of the NA dose response curve, with significant depression of the minimal response induced by NA. A highly marked rightward shift of the NA dose response curve was noticed with a higher concentration of verapamil [10-5 M]. This was accompanied by a highly significant depression of the minimal [P <0.001] and maximal [P <0.005] responses of NA. Similarly, phentolamine [10-7 M] produced a parallel rightward shift of the NA dose response curve with a highly significant inhibition of the responses induced by lower concentrations of NA [P <0.001]. On the other hand, nifedipine [10-6, 10-5 M] shifted the NA dose response curve to the right in a nonparallel manner and depressed only the maximal responses induced by NA. These observations suggested an alpha-antagonistic property of verapamil on the rabbit aortic strip which was not demonstrated with the other calcium channel blocker, nifedipine

effect of verapamil on brain monoamines of rats pretreated with nialamide and reserpine

The present work investigated the acute effect of verapamil on the brain levels of 5-hydroxytryptamine [5HT], dopamine [DA] and noradrenaline [NA] in nialamide and reserpine pretreated rats. Results showed that treatment of rats with verapamil [5 mug/kg] one hour prior to sacrifice significantly increased brain 5HT and decreased DA brain level. However, brain NA level showed no significant difference compared to control values. Treatment of rats with nialamide, significantly increased brain 5HT, DA and NA levels. In nialamide pretreated rats, verapamil [5 mug/kg] revealed a highly significant increase was slightly higher than that produced by either verapamil or nialamide alone, it did not reach statistical significance. Moreover, pretreatment of rats with nialamide completely blocked the verapamil-induced decrease in brain DA level. On the other hand, the treatment of rats with reserpine, significantly depleted brain 5HT, DA and NA levels. The verapamil-induced increase in brain 5HT was blocked by the pretreatment of rats with reserpine. However, reserpine pretreatment revealed a synergistic effect with the calcium antagonist on brain DA level, where a highly significant depletion was evident. The possible mechanisms by which verapamil induced these changes in brain monoamines was discussed

Verapamil: a calcium channel blocker and its effect on brain monoamines in the rat

The present work is an attempt to investigate the effect of verapamil, a calcium channel blocker, on brain 5 hydroxytryptamine [5 HT], dopamine [DA] and noradrenaline [NA]. Results showed that the intraperitoneal [i.p.] injection of verapamil in doses of 1, 5, 25 and 50 mug/kg, one hour prior to sacrifice, significantly increased brain 5 HT level. A significant decrease in brain DA was detected with doses of 5, 25 and 50 mug/kg of verapamil, while 1 mug/kg caused no significant change in this parameter. Brain NA level, however, was not significantly changed with all the doses of verapamil previously mentioned when measured one hour from the injection of the drug. The mechanism of action of verapamil in the management of affective disorders and the possibility of the involvement of brain 5 HT and DA was discussed