1. The effect of the intravenous injection of synthetic atrial natriuretic peptide (ANP, 2 μg) on systemic haemodynamics and blood flow to several organs has been studied in conscious rats by the radioactive microsphere technique.
2. ANP induced a 540% increase in sodium excretion and a 310% increase in urine flow. Mean arterial pressure decreased by 21 mmHg and the peripheral resistances decreased by 26%, without significant changes in cardiac output.
3. Renal blood flow increased by 37.7% and small intestine and portal blood flow increased by 39% and by 28% respectively. No other alterations in organ blood flows were observed.
4. From these data it can be concluded that atrial natriuretic peptide shows acute vascular relaxant properties, which seem to be specific for renal and mesenteric territories.