Mechanism for decrease in cardiac output with atrial natriuretic peptide in dogs

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Abstract
To examine the mechanism by which atrial natriuretic peptide (ANP) decreases cardiac output, we studied changes in the heart, peripheral circulation, and blood flow distribution in eight dogs. ANP was given as a bolus (3.0 .mu.g/kg) followed by an infusion of 0.3 .mu.g .cntdot. kg-1 .cntdot. min-1. ANP did not change heart rate, total peripheral vascular resistance, and the first derivative of left ventricular pressure but decreased mean aortic pressure from 91 .+-. 4 to 76 .+-. 3 mmHg (P < 0.001) and cardiac output from 153 .+-. 15 to 130 .+-. 9 ml .cntdot. kg-1 .cntdot. min-1 (P < 0.02). Right atrial pressure and left ventricular end-diastolic pressure also decreased. Mean circulatory filling pressure decreased from 7.1 .+-. 0.3 to 6.0 .+-. 0.3 mmHg (P < 0.001), but venous compliance and unstressed vascular volume did not change. Resistance to venous return increased from 0.056 .+-. 0.008 to 0.063 .+-. 0.010 mmHg .cntdot. ml-1 .cntdot. kg .cntdot. min (P < 0.05). Arterial compliance increased from 0.060 .+-. 0.003 to 0.072 .+-. 0.004 ml .cntdot. mmHg-1 .cntdot. kg-1 (P < 0.02). Total blood volume and central blood volume decreased from 82.2 .+-. 3.1 to 76.2 .+-. 4.6 and from 19.8 .+-. 0.8 to 17.6 .+-. 0.6 ml/kg (P < 0.02), respectively. Blood flow increased to the kidneys. We conclude that ANP decreases cardiac output by decreasing total blood volume. This results in a lower operating pressure and volume in the venous capacitance system with no significant venodilating effects. Cardiac factors and a redistribution of flow to the splanchnic organs are not important mechanisms to explain the decrease in cardiac output with ANP.