Increase in plasma concentrations of atrial natriuretic peptide during infusion of hypertonic saline in conscious newborn calves

Plasma concentrations of atrial natriuretic peptide (ANP), plasma renin activity (PRA), plasma concentrations of aldosterone, urine flow rate and sodium and potassium excretion were studied in two groups of four conscious 3-day-old male calves, infused with hypertonic saline or vehicle. Hypertonic saline infusion (20 mmol NaCl/kg body weight) was accompanied by a progressive rise in plasma concentrations of ANP (from 16.5 +/- 0.2 pmol/l at time 0 to 29.3 +/- 3.0 pmol/l at 30 min; P less than 0.05) and by a gradual decrease in PRA (from 1.61 +/- 0.23 nmol angiotensin I/l per h at time 0 to 0.54 +/- 15 nmol angiotensin I/l per h at 90 min; P less than 0.05); there was no change in the plasma concentration of aldosterone. Within the first 2 h of the 24-h urine collection period there was a marked rise in urine flow rate and sodium excretion in treated calves when compared with control animals (66.0 +/- 8.3 vs 15.9 +/- 1.2 ml/kg body weight per 2 h (P less than 0.05) and 6.7 +/- 1.3 vs 0.4 +/- 0.02 mmol/kg body weight per 2 h (P less than 0.01) respectively). During the following 22 h, urinary water and sodium excretion remained at significantly high levels. Thus, in the conscious newborn calf, changes in plasma ANP levels and urinary water and sodium excretion during hypertonic saline infusion are compatible with the hypothesis that endogenous ANP participates, at least in part, in the immediate diuretic and natriuretic renal response induced by the sodium overload.