Maintenance of glomerulotubular balance for bicarbonate during carbonic anhydrase inhibition in the dog.

Studies were performed to examine the possible effects of carbonic anhydrase (CA) inhibition on the glomerulotubular balance for bicarbonate in anesthetized dogs. Maximal CA inhibition was achieved by acetazolamide infusion and glomerular filtration rate (GFR) was reduced in a stepwise fashion by progressive clamping of the left renal artery. A close relationship (R equals 0.973) was maintained between the amount of filtered and reabsorbed bicarbonate in normal dogs with CA inhibition. A similar relationship was observed between GFR and bicarbonate reabsorption during CA inhibition in normal dogs (R equals 0.957) as well as in sodium bicarbonate loaded dogs (R equals 0.867). In these two groups, GFR in the clamped kidney was reduced to values ranging respectively from 99 to 5% and from 96 to 3%. Distal tubular blockade with ethacrynic acid and chlorothiazide, performed in normal dogs and in sodium bicarbonate loaded dogs, did not abolish glomerulotubular balance for bicarbonate during CA inhibition. This study demonstrates that the glomerulotubular balance for bicarbonate is maintained during CA inhibition whether or not distal tubular blockade is superimposed. A proportionate decrease in both fractions of bicarbonate reabsorption, either CA dependent or not mediated by CA, or an adaptive increase in the fraction of bicarbonate reabsorption not mediated by CA can explain the maintenance of glomerulotubular balance for bicarbonate.