[Effect of atenolol on MAO activities in SHR]

The effects of atenolol on monoamine oxidase (MAO) activities in the heart, liver, kidney and mesenteric artery in spontaneously hypertensive rats (SHR) were studied. Male SHR (5-weeks-old) were given 20 and 100 mg/kg/day of atenolol by gavage for 10 weeks. The MAO activities were determined once every 2 weeks. Atenolol produced a hypotensive effect and bradycardia in SHR. The heart weight/body weight ratio in SHR was suppressed from 4 weeks of atenolol treatment. Though atenolol induced MAO activities in the 2 weeks treated heart and 4-6 weeks treated liver, it inhibited the increase of MAO activities in all prepared organs after 10 weeks treatment. The MAO activities of the heart were more markedly inhibited than in the other organs by the treatment of atenolol. Atenolol did not lower the Km value, but reduced significantly the Vmax value of the 10 weeks treated heart MAO. Atenolol had no effect on the MAO activities in vitro. These results suggest that the changes of the MAO activities in the organs of SHR by the treatment of atenolol may be relative to the hypotensive and bradycardic effects of the cardioselective beta-adrenoceptor blocking agent.