ANTAGONISM OF THE EFFECT OF ISOPRENALINE ON HEART RATE BY PILOCARPINE

Abstract

The interaction of pilocarpine and isoprenaline on heart rate was investigated in the spontaneously beating, right isolated atrium of the rat. The log dose‐effect curve of isoprenaline, measured in the presence of various concentrations of pilocarpine, was not modified when the concentration of the latter did not exceed 10−6 m even though significant slowing of the heart had occurred. At concentrations higher than 10−6 m a rapid but graded shift to the right of isoprenaline response curves occurred so that at pilocarpine 10−5 m the pD2 of isoprenaline was reduced from 11 to 3.3; cocaine slightly reduced this antagonism. It is concluded that pilocarpine antagonizes isoprenaline by some mechanism which is not of the simple competitive type. 1974 British Pharmacological Society