Action of adrenergic agonists on resistance v capacitance vessels during cardiopulmonary bypass

The peripheral vascular effects of three different adrenergic agonists were investigated in 13 patients undergoing valve replacement during cardiopulmonary bypass (CPB). The venous reservoir (RV) and mean arterial pressure (MAP) were used as indices of the changes in venous capacitance and arterial resistance, respectively, produced by the adrenergic agonists. Isoproterenol, a pure beta-adrenergic agonist, decreased both MAP and RV. Norepinephrine (NE), which activates both alpha 1- and alpha 2-receptors in humans, increased both MAP and RV, while phenylephrine (PH) a selective alpha 1-adrenergic agonist, increased only MAP with no significant change in RV. It is concluded that in humans during hypothermic CPB, beta-agonists dilate both the resistance and capacitance vessels, selective alpha 1-adrenergic agonists preferentially constrict the resistance vessels, and non-selective alpha 1- and alpha 2-adrenergic agonists constrict both the resistance and capacitance vessels.