EFFECT OF AMILORIDE ON ISOLATED GUINEA-PIG ATRIUM

  • 1 January 1979
    • journal article
    • research article
    • Vol. 242  (2) , 222-229
Abstract
The effect of high concentrations (62.5-500 .mu.g/ml) of amiloride [AM], a K sparing diuretic, was investigated in the isolated guinea-pig atrium. AM decreased the frequency of contractions of the spontaneously beating right atrium in a time-dependent fashion. The inotropic effect of AM was frequency-dependent. It increased the peak developed tension of the electrically paced left atrium with 1 Hz stimulation. This was dose and time-dependent. Stimulation at 0.35 and 0.1 Hz resulted in no effect and a negative inotropic effect respectively. The effects of AM were not prevented by the autonomic drugs atropine, propranolol, phenoxybenzamine, metiamide, tetrodotoxin or by pretreatment of animals with reserpine. The positive inotropic effect (at 1 Hz) was inhibited by Ca antagonists verapamil or chlorpromazine. The negative inotropic effect (at 0.1 Hz) was prevented by doubling Ca concentration of the medium. AM had no significant effect on Na, K and Ca content of the tissue. High concentrations of AM apparently decreases the frequency and changes the peak developed tension of the guinea-pig atrium possibly by decreasing Na entry and altering the availability of Ca to the contractile elements.

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