Effects and interactions of furosemide and acetazolamide on tubular function in rat kidney.

Furosemide and acetazolamide effects on tubular function in rat kidney have been studied by micropuncture. Furosemide produced a marked rise in fractional proximal fluid reabsorption when urine loss was not replaced, and sodium excretion rose significantly indicating a distal effect. If urinary losses were replaced proximal fractional reabsorption was depressed and fractional sodium excretion increased more than 60%. After replacing urinary losses, acetazolamide had a greater depressive effect on proximal tubular fluid reabsorption than furosemide but sodium excretion values were about 1/3 of those obtained with furosemide. Superimposition of one drug during the action of the other resulted in potentiation of proximal inhibition, suggesting a different mechanism of action. The changes observed in potassium excretion are of great interest. Separately, furosemide or acetazolamide produced kaliuresis. When furosemide was administered during acetazolamide diuresis, however, potassium excretion was reduced despite the sharp rise in sodium excretion.