Inhibitory effects of atropine and hexamethonium on the angiotensin II-induced contractions of rat anococcygeus smooth muscles

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Abstract
We have evaluated the interaction between angiotensin II (Ang II) and the cholinergic transmission in anococcygeus smooth muscles isolated from rats treated (sympathectomised group) or not (vehicle group) with reserpine and α-methyl-p-tyrosine. For this, we contracted the tissues with Ang II in the presence and absence of atropine and hexamethonium. Ang II induced concentration-dependent contractions, which did not undergo temporal changes in tissues isolated from both groups of rats. In the vehicle group, Ang II induced more potent contractions than in the sympathectomised group. In the sympathectomised rat group, atropine inhibited the contractions induced by Ang II in a concentration-dependent fashion with no decrease in Emax. Additionally, hexamethonium inhibited the contraction induced by Ang II in a concentration-dependent fashion with a decrease in Emax. Association of atropine and hexamethonium produced Ang II-induced curves with rightward shifts from the control curve with a decrease in Emax. Incubation with NG-nitro-L-arginine methyl ester (L-NAME) reversed the effects of atropine and hexamethonium association. Conversely, in the vehicle group of rats, atropine and hexamethonium did not produce any significant effect. However, in the presence of yohimbine, atropine shifted the Ang II-induced curves to the right of the control curve with no Emax decrease. Results suggest that there is a positive interaction between Ang II and cholinergic transmission in the rat anococcygeus smooth muscle mediated by angiotensin receptors located on pre-ganglionic cells.

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