PROTECTIVE ACTION OF METHYLDOPA AGAINST OUABAIN-INDUCED CARDIAC-ARRHYTHMIAS AND LETHALITY

Methyldopa (25, 50 and 100 mg/kg, i.p.) was studied for its effect on cardiac arrhythmias and lethality induced by slow intravenous infusion of ouabain in guinea-pigs. Methyldopa increased the dose of ouabain r equired to elicit the arrhythmic stages and lethality. However, it did not provide any protection in reserpinized guinea-pigs. Methyldopa al so inhibited the rate of the ouabain-induced rise in blood pressure an d the peak pressor response. Yohimbine significantly antagonized the p rotective action of methyldopa. It is concluded that the protective ac tion of methyldopa against the arrhythmogenic and lethal effects of ou abain may be due to its action on the indirect neural components of ou abain toxicity, mediated through stimulation of alpha2-adrenoceptors.