Abstract
Effects of β-adrenergic blocking drugs (β-blockers) on monoamine oxidase (MAO) and their membrane stabilizing and local anesthetic effects were studied. MAO activities were determined by the radioisotopic assay using 14C-5-hydroxytryptamine (5-HT) 14C-β.phenylethylamine (β-PEA) as substrates. Inhibition of hypotonic hemolysis of rat erythrocytes was measured as hemoglobin concentration in the supernatant. Local anesthetic effects were tested by the rabbit's cornea method. β-blockers at concentrations of 1×10-4M to 1×10-3M except for atenolol inhibited MAO in rat brain homogenate and liver mitochondria with 5-HT as substrate. The order of potency was propranolol> pindolol>oxpreonolol. Propranolol and pindolol inhibited 5-HT oxidation much more than β-PEA oxidation. Inhibition of MAO activity by β-blockers was reversible. Propranolol inhibited 5-HT oxidation by liver mitochondrial MAO competitively while pindolol and oxprenolol inhibited 5-HT oxidation non-competitively. Membrane stabilizing effects of β-blockers except for oxprenolol on erythrocytes were observed from concentration of 6×10-5M. The order of potency was propranolol>pindolol>atenolol. Local anesthetic effects of β-blockers on cornea were observed from concentration of 2×10-4M. The surface anesthetic potency of β-blockers was higher order of propranolol>pindolol>oxpren-olol>atenolol. These results suggest that inhibitions of MAO (type A) activities by β-blockers are correlated to their local anesthetic effects. Possible mechanism of hypotensive effect of β-blockers will be discussed in this respect.
