Characterization of -adrenoceptors in the myocardium.

1. In the driven rabbit left atrium alpha-adrenoceptors mediate the inotropic effect of phenylephrine and the prolongation of functional refractory period by sympathomimetic amines.2. These receptors are highly sensitive to blockade by phentolamine and phenoxybenzamine.3. Prolongation of functional refractory period is greater with the secondary amines, phenylephrine, adrenaline and epinine, than with the primary amines, norphenylephrine, noradrenaline and dopamine.