EFFECT OF NORADRENALINE ON RENAL SODIUM AND WATER HANDLING IN EUHYDRATED AND OVERHYDRATED MAN

1. The renal effects of incremental doses of intravenously infused nor adrenaline were evaluated in normal subjects during two different wate r loads, 5 ml/kg (n=6) and 20 ml/kg (n=9), producing conditions of euh ydration and overhydration, respectively. 2. Noradrenaline infusion ra tes ranged from 0.015 to 0.075 mug min-1 kg-1. In the euhydrated subje cts, noradrenaline caused a dose-dependent fall in urinary sodium excr etion and an increase in urinary flow rate. During overhydration simil ar doses of noradrenaline caused a fall in urinary sodium excretion bu t a decrease in urinary flow rate. 3. Although there was no detectable change in glomerular filtration rate, a dose-dependent fall in effect ive renal plasma flow was observed in both hydration states during nor adrenaline infusion. 4. Noradrenaline infusion was associated with a d ose-dependent increase in proximal tubular sodium reabsorption as asse ssed by the lithium clearance method. Fractional reabsorption of sodiu m by the distal nephron was, however, unchanged by noradrenaline in bo th hydration states. 5. Plasma vasopressin concentration was unchanged by noradrenaline in euhydrated subjects. The renin-angiotensin-aldost erone axis was stimulated by noradrenaline in both euhydrated and over hydrated subjects. 6. Thus we conclude that plasma circulating noradre naline has a dose-dependent antinatriuretic effect in man. The antinat riuretic effect of noradrenaline is mediated mainly at the proximal tu bule in man. We have also shown that during overhydration, noradrenali ne decreased urinary flow rate. In contrast, in euhydrated subjects, n oradrenaline increased urinary flow rate with no accompanying changes in plasma vasopressin concentration, which suggests a direct effect of noradrenaline on the renal tubular permeability to water.