| pubmed-article:2566129 | pubmed:abstractText | The present study was performed to gain more information on the nature of the opioid peptide(s) involved in the mechanism of action of alpha-methyldopa. Conscious, normotensive Wistar rats were used and all treatments were given intracisternally. For blood pressure and heart rate, pretreatment with a midportion beta-endorphin antiserum resulted in a parallel shift to the right of the dose-response curve for alpha-methyldopa. In addition, when rats were pretreated with various dilutions of this antiserum and treated with a constant dose of alpha-methyldopa, the antiserum dose-dependently inhibited alpha-methyldopa-induced hypotension and bradycardia. Using antisera specifically recognizing the C-terminus of beta-, gamma- and alpha-endorphin, respectively, revealed that only the beta-endorphin antiserum inhibited the decrease in blood pressure seen after administration of alpha-methyldopa. An antiserum against [Met5]enkephalin did not influence the cardiovascular responses following alpha-methyldopa. On the other hand, a dynorphin(1-13) antiserum also inhibited in a dose-dependent manner the hypotension induced by alpha-methyldopa. When administered 3 h after the injection of alpha-methyldopa, the beta-endorphin and dynorphin(1-13) antisera failed to reverse the hypotension induced by alpha-methyldopa. The results favor a role for beta-endorphin(1-31) and dynorphin(1-13) in the hypotension centrally mediated by alpha-methyldopa. | lld:pubmed |
