[Effects of acid-base changes upon the chronotropic response to norepinephrine (author's transl)]

The effect of changes in pH produced by changing NaHCO2 at constant pCO2 and by changing pCO2 at constant NaHCO2 concentration was studied in the spontaneous beating rat atrium. Alkalosis produced either by changes in pCO2 or in NaHCO2 concentration increased basal heart rate shifting dose-response curves to norepinephrine upwards. When these dose-response curves were analysed for a horizontal shift, it was found that the necessary dose to produce a given effect was lesser in alkalosis than in acidosis. This shift was significant at the ED10 and at ED30 when the pCO2 was lowered and at ED30, ED50 and ED70 when the NaHCO2 concentration was increased. Beta-adrenergic blockade did not prevent the rate increasing effect of alkalosis. Our results suggest that there is a sensitizing effect to norepinephrine in alkalosis superimposed to a direct effect of pH upon heart rate.