Add time:08/20/2019         Source:sciencedirect.com

In anesthetized dogs, YM-09538, a new sulfonamide-substituted phenylethylamine, competitively antagonised the phenylephrine-induced vasopressor response with a DR10 of 0.50 mg/kg i.v. and the isoproterenol-induced positive chronotropic response with a DR10 of 0.66 mg/kg, i.v., indicating that YM-09538 blocks both α1- and β1-adrenoceptors almost to the same extent. YM-09538 was 4 times more potent than phentolamine in blocking α1-adrenoceptors and 3 times less potent than propranolol in blocking β1-adrenoceptors. YM-09538 non-selectively blocked cardiac β1- and vascular β2-receptors and was devoid of intrinsic β-sympathominetic and local anesthetic activities. In anesthetized closed-chest dogs, YM-09538 resembled propranolol in reducing heart rate, cardiac output, max. dLVP/dt and left ventricular cardiac work but differed from propranolol in decreasing total peripheral resistance, in increasing femoral blood flow, in causing larger falls in arterial blood pressure and in decreasing pulmonary arterial pressure. In non-ischemic myocardium, transmural flow and coronary vascular resistance were respectively strongly increased and decreased and the endo/epi flow ratio was slightly but not significantly reduced. In ischemic myocardium, YM-09538 also increased transmural flow and since endocardial and epicardial flows were augmented to the same extent, the endo/epi flow ratio remained unchanged. All these hemodynamic and coronary effects of YM-09538 can be accounted for the drug's combined α- and β-adrenoceptors blocking properties.

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