Abstract

In an attempt to investigate the possibility that both alpha and beta adrenergic receptors are of importance in the myocardium, the response of the atrial functional refractory period to norepinephrine, epinephrine and isoproterenol has been analyzed by the use of phenoxybenzamine and pronethalol. It was found that the response consists of two opposing components, one tending to decrease the refractory period, the other increasing it. The order of potency of the three amines in producing the decrease is isoproterenol > epinephrine > norepinephrine. The decrease is also specifically blocked by pronethalol, and is, therefore, considered to be mediated through beta adrenergic receptors. The increase in refractory period is produced with the order of potency epinephrine > norepinephrine > isoproterenol, and is specifically blocked by phenoxybenzamine. The increase is, therefore, considered to be a function of alpha adrenergic receptors. It is concluded that both alpha and beta adrenergic receptors are present and have a function in the myocardium.