Effect of parathyroid hormone on bicarbonate absorption by proximal tubules in vitro

1979.~The effect of parathyroid hormone on bicarbonate ab-sorption was tested in rabbit proximal renal tubules perfused in vitro. In proximal straight tubules 0.05 U/ml of parathyroid hormone caused a large and reversible increase in the steady-state bicarbonate concentration in tubule fluid. Further, the rates of bicarbonate and fluid absorption (measured at faster flow rates) were inhibited approximately 50 % by the hormone. We conclude that parathyroid hormone directly inhibits fluid and bicarbonate absorption by proximal straight tubules, caus-ing an increase in the bicarbonate concentration in the tubule fluid, and we suggest that this action of the hormone contributes to the increase in renal bicarbonate excretion that is generally caused by the hormone. In proximal convoluted tubules, para-thyroid hormone was previously demonstrated by other inves-tigators to inhibit fluid and bicarbonate absorption approxi