Intrarenal pressures during direct inhibition of sodium transport

Renal interstitial hydrostatic pressure (RIHP) has been implicated in the regulation of sodium excretion. Studies using vasodilators and other maneuvers to increase RIHP have found a significant correlation between RIHP and sodium excretion. Since correlative studies do not prove a cause-and-effect relationship, it is not known whether the rise in sodium excretion in these studies is the result of increases in RIHP or if RIHP is elevated as a result of decreases in sodium and water reabsorption and increases in intratubular pressure. Therefore, the purpose of the present study was to determine whether elevation of intratubular hydrostatic pressures in response to direct inhibition of tubule transport with loop diuretics results in increases in RIHP in dogs and rats. Intrarenal hydrostatic pressures, renal hemodynamics, and sodium and water excretion were examined in dogs during intravenous administration of furosemide (3 mg/kg bolus followed by 0.03 mg.kg-1 x min-1) or bumetanide (60 micrograms/kg bolus followed by 1 microgram.kg-1 x min-1). Furosemide administration increased urinary flow rate (V; 0.10 +/- 0.02 to 4.6 +/- 0.97 ml/min), urinary sodium excretion (UNaV; 16 +/- 5 to 549 +/- 123 mu eq/min), and proximal tubule hydrostatic pressure (PT; 21 +/- 1 to 28 +/- 1 mmHg) but had no effect on RIHP (7.2 +/- 0.6 to 7.4 +/- 0.7 mmHg) or peritubular capillary hydrostatic pressure (14 +/- 1 to 14 +/- 1 mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)