Furosemide dynamics: influence of dietary sodium and of saralasin

The influence of dietary sodium and saralasin on the natriuretic and diuretic response to furosemide (5 mg/kg i.v.) was studied in three groups of conscious rabbits maintained for 4 weeks on either a normal sodium diet (NSD), or a low sodium diet (LSD) or a high sodium diet (HSD). Neither the sodium content in the diet nor saralasin affected glomerular filtration rate or renal plasma flow. Compared to the NSD, an LSD did not affect the furosemide-induced increment in urinary excretion of sodium (dUNaV) but increased the increment in urinary excretion (dUV) (p less than 0.05). An HSD reduced the furosemide-induced dUNaV and dUV (p less than 0.05). Plasma renin activity (PRA) increased following furosemide administration in animals on an NSD and an LSD, but not in those on an HSD. Independent of diet, a positive correlation occurred between the increment in PRA and the dUNaV (p less than 0.001). Saralasin increased PRA and decreased baseline urinary excretion of sodium (UNaV). In addition, in rabbits on an LSD, saralasin reduced the furosemide-induced dUNaV and dUV by 34 and 27% (p less than 0.05), respectively. It is concluded that furosemide-induced diuresis is increased in rabbits on an LSD and decreased in rabbits on an HSD. In animals on an LSD, the increase in furosemide response appears to be associated with changes in the activity of the renin-angiotensin system and in rabbits on an HSD, the decrease in furosemide effect is probably the net result of several factors.