Hemodynamic effects of atrial natriuretic peptide in conscious sheep

The present study examines the effects of intravenous infusion of atrial natriuretic peptide (ANP) on blood pressure, heart rate, cardiac output, sodium excretion and urine output in conscious, chronically instrumented sheep. Human ANP (1-28) was infused into the jugular vein (I.V.) for 60 min at 20, 50, 100 and 500 micrograms/h. ANP caused a decrease in blood pressure at all doses which was associated with a reduction in stroke volume and cardiac output. There was also a decrease in right atrial pressure. At the two higher rates of infusion an increase in both heart rate and calculated total peripheral resistance was observed. These data are consistent with ANP acting on the venous side of the circulation to produce venodilatation, and a reduction in venous return, stroke volume and cardiac output. The increases in urinary sodium excretion and urine output observed when ANP was infused I.V. at 100 micrograms/h for 60 min were small. The data suggest that the minimum dose for effects on the cardiovascular system (20 micrograms/h) is less than that required to produce renal effects (100 micrograms/h). ANP has potent effects on the cardiovascular system in conscious sheep, exerting its effect on blood pressure primarily by its action on the venous circulation and on cardiac output.