CARDIOVASCULAR AND MYOCARDIAL METABOLIC EFFECTS OF INFUSIONS OF PHENYLEPHRINE

¹ Department of Pharmacology, Albany Medical College, Albany, New York

The cardiovascular and metabolic effects of phenylephrine were investigated in dogs with particular emphasis on correlations with myocardial oxygen (O₂) uptake. Phenylephrine could be shown to increase myocardial O₂ uptake but only at doses which also caused a significant increase in mean systolic pressure (MSP). The myocardial O₂ uptake was always strongly correlated with the product of MSP and heart rate (HR) in these dogs both before and during infusion of the drug. Reflex bradycardia, which accompanied the rise in MSP, probably had the effect of limiting myocardial O₂ uptake. This was established, in part, by infusion of drug in vagotomized animals with fixed HR and in animals in which the vagus was stimulated directly. The cardiovascular effects of phenylephrine were also accompanied by hyperglycemia, but the plasma levels of nonesterified fatty acids were not changed. The results of these experiments suggest that phenylephrine causes increased myocardial O₂ uptake only in proportion to increased cardiac work and therefore is not an O₂-wasting sympathomimetic amine.