Abstract

The effects of isoproterenol, phenylephrine, and norepinephrine were studied in an experimental canine preparation in which cardio-pulmonary bypass permitted exclusion of the heart and lungs, and allowed continuous measurement of alterations of intravascular blood volume. In all experiments the beta adrenergic receptor stimulator, isoproterenol, resulted in a decrease in systemic vascular blood volume, similar to that observed with the alpha receptor stimulating agents, phenylephrine and norepinephrine. By the use of appropriate adrenergic blocking agents, it was demonstrated that the systemic venous bed contains both beta and alpha adrenergic receptors. Thus, in contrast to the opposing actions of these receptors in the arterial bed, stimulation of either alpha or beta receptors produces venoconstriction.