Influence of neuropeptide Y on regional vascular capacitance in dogs

To determine the effect of neuropeptide Y (NPY) on regional vascular capacitances, we measured the regional blood volume (Vb), unstressed volume (V0), blood flow distribution, venous compliance (Cv), venous resistance (Rv), and the time constant of venous drainage (tau v) in the splanchnic and extrasplanchnic circulation of 13 dogs anesthetized with chloralose. Cardiac output was kept constant with circulatory bypass. The extrasplanchnic region was further divided into superior vena caval (SVC) and inferior vena caval (IVC) regions. Vb was measured in the splanchnic and SVC regions using indicator dilution curves and the mean transit times. Changes in venous outflow pressures were used to change regional volumes, and a stop-flow procedure was used to obtain the regional venous filling pressures. This allowed construction of pressure-volume (P-V) curves and the calculation of Cv, Rv, and tau v. Hexamethonium chloride was infused throughout the experiment to prevent autonomic reflexes. Sham injections had no effects on four dogs. In nine dogs, NPY (bolus of 7.4 x 10(-8) or 14.8 x 10(-8) mol and 0.37 mol/min infusion) increased arterial blood pressure from 98.4 +/- 4.2 to 121.3 +/- 6.9 mmHg (P < 0.001), decreased splanchnic Vb from 31.6 +/- 2.1 to 24.9 +/- 1.8 ml/kg (P < 0.01), and decreased splanchnic V0 from 21.8 +/- 2.6 to 12.1 +/- 2.2 ml/kg (P < 0.001). SVC volumes were not affected by NPY. Extrasplanchnic Cv increased with NPY, but splanchnic Cv did not change. Thus exogenous NPY infusion decreases splanchnic capacitance, which could potentially increase venous return and cardiac output.