Bicarbonaturic effect of acetazolamide in the dog: the Influence of graded volume expansion

Abstract

Studies were performed in anesthetized dogs to characterize the effect of a progressive volume expansion on the acetazolamide-induced bicarbonaturia. A closed system with urine reinfusion was used in all these experiments. In normovolemic dogs, 24% of the filtered bicarbonate was excreted into the urine while this value reached 62% when a 10% expansion was superimposed on a continuous infusion of acetazolamide. When a single dose of acetazolamide was given, fractional bicarbonate excretion increased from 21% in normovolemic dogs to 46% during 10% expansion. Without acetazolamide administration, 13% of the filtered bicarbonate was excreted during a 10% expansion. The continuous infusion of acetazolamide in normovolemic dogs increased fractional bicarbonate excretion in a progressive fashion, from 25 to 40%. This study shows that an acute volume expansion potentiates markedly the bircarbonaturic effect of acetazolamide, fractional bicarbonate excretion exceeding by far the simple additive effect of acetazolamide and expansion. We speculate that volume expansion might prevent a compensatory rise in acetazolamide-insensitive bicarbonate reabsorption in sites other than the superficial proximal convoluted tubules.