this increase in cardiac output is probably brought about by effects of phenylephrine on the capacitance vessels rather than by an effect on the heart.4 evidence is presented to show that the effects of phenylephrine are mediated largely by alpha-adrenoceptors , but that beta-adrenoceptors which affect tpr are also stimulated by the amine.5 isoprenaline produces a dose-dependent fall in mabp that is due entirely to a fall in tpr since the cardiac output increases.6 unlike phenylephrine , the increase in cardiac output obtained with isoprenaline was achieved by an increase in heart rate while stroke volume remained close to control values .
C0020649
fall in mabp
C0031469
phenylephrine