Effects of (-)-phenylephrine on force of contraction in the presence of cocaine and hydrocortisone in cat papillary muscle.

The positive inotropic effect of (-)-phenylephrine, in the presence of propranolol, was studied after inhibition of neuronal and extraneuronal uptake in isolated papillary muscles from reserpine-pretreated cats. An inhibition of extraneuronal uptake with hydrocortisone influenced the effect of (-)-phenylephrine neither when present alone nor in the presence of cocaine (additional inhibition of neuronal uptake). An inhibition of neuronal uptake with cocaine caused a small but significant increase in the potency of (-)-phenylephrine. We conclude that in cat ventricular cardiac muscle the extraneuronal compartment is apparently neither a "site of loss" nor a "site of gain" for (-)-phenylephrine with respect to force of contraction.