Epinephrine and the carotid sinus baroreceptor reflex. Influence on capacitive and resistive properties of the total systemic vascular bed of the dog

To quantify the interaction between epinephrine infusion and cartoid sinus baroreceptor reflex control of vascular capacity and resistance, we have simultaneously measured total systemic compliance, Ct, arterial compliance, Ca, changes in 'unstressed vascular volume', ΔVo, and resistance, R, in nine dogs whose carotid tissues were isolated and cardiac output fixed by a perfusion pump. In response to intrasinus pressures (ISP) of 50, 125, and 200 mm Hg without epinephrine infusion, total systemic compliance (Ct) was 1.00, and 1.10, and 1.22 ml/mm Hg per kg, whereas arterial compliance showed no change and averaged 0.0984 ml/mm Hg per kg for all ISP's. Resistance was 1.45, 0.88, and 0.57 mm Hg/(ml per min per kg) for intrasinus pressure of 50, 125, and 200 mm Hg. The change in unstressed vascular volume from ISP of 50 to 125 was 7.32 ml/kg and 5.03 ml/kg for an ISP change from 125 to 200 mm Hg. When epinephrine was infused at a constant rate of 1.2 μg/min per kg at a fixed ISP of 125 mm Hg, arterial pressure rose by 69.1 mm Hg, the change in unstressed vascular volume was 8.02 ml/kg, and resistance increased from 0.89 to 1.54 mm Hg/(ml per min per kg), an increase of 73% of control. At the same infusion rate and at each ISP of 50, 125 and 200 mm Hg, compliances, Ct and Ca, and resistance were measured. In contrast to the control data, Ct showed no increase with changes in ISP (0.92, 0.94, and 0.92 ml/mm Hg per kg), whereas Ca measured 0.081 Ml/mm Hg per kg. Resistance was 1.71, 1.46, and 1.19 mm Hg/min per kg for intrasinus pressures of 50, 125, and 200 mm Hg. The change in unstressed vascular volume caused by an ISP change of 50-125 mm Hg was 1.78 ml/kg and for an ISP change of 125-200 mm Hg was 1.30 ml/kg. The data indicate that epinephrine greatly attenuates the reflex control of the vascular properties by mechanisms other than the modification of the carotid sinus receptor characteristics.