DIURETIC, NATRIURETIC AND HYPOTENSIVE EFFECTS OF SYNTHETIC ATRIAL NATRIURETIC FACTOR IN CONSCIOUS NEWBORN CALVES

The effects of synthetic Atrial Natriuretic Factor (ANF) on urine flow rate, sodium excretion, potassium excretion and arterial blood pressure were studied in 10-12 days-old female calves. In four female calves fitted with a Foley catheter, an intravenous administration of ANF (Ile-ANF 26; 1.6 .mu.g/kg body wt during 30 min) induced an increase (P < 0.01) in urine flow rate (from 1.8 .+-. 0.2 to 12.8 .+-. 1.1 ml/min), sodium excretion (from 0.15 .+-. 0.02 to 0.81 .+-. 0.06 mmol/min) and free water clearance (from 0.13 .+-. 0.9 to 5.16 .+-. 0.5 ml/min). It had no significant effect on potassium excretion. In four calves chronically-instrumented with a carotid catheter, an intravenous administration of synthetic ANF alone (1.6 .mu.g/kg body wt during 30 min) induced a gradual decrease (P < 0.01) in systolic, diastolic and mean arterial blood pressure (from 112 .+-. 4 to 72, from 72 .+-. 2 to 61 .+-. 1 and from 90 .+-. 2 to 65 .+-. 2 mmHg respectively, at the end of ANF infusion). An intravenous administration of angiotensin II (AII) (0.5 .mu.g/kg body wet during 45 min) induced a significant increase in systolic, diastolic and mean arterial blood pressure which was antagonized by an i.v. bolus injection of ANF (0.125 .mu.g/kg body wt). However, during a simultaneous administration of AII (0,3 ug/kg body wt during 30 min) and ANF (1.6 .mu.g/kg body wt. during 30 min), the atrial peptide did not influence the pressure action of AII. These findings indicate that the conscious newborn calf is sensitive to diuretic, natriuretic and hypotensive effects of synthetic ANF.