Parathyroid hormone and extrarenal acid buffering

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Abstract
The role of parathyroid hormone (PTH) on the extrarenal buffering of an acid load was examined during HCl infusion (5 meq x kg-1 x h-1) to bilaterally nephrectomized rats. Thyroparathyroidectomized (TPTX) rats replaced with PTH had significantly higher blood pH and HCO3 values than TPTX rats not infused with PTH. Administration of EDTA, in a dose shown to release PTH, was associated with a significant increase in buffering capacity in intact but not in TPTX rats. Colchicine, given in a dose capable of stimulating PTH release, was also associated with enhanced buffering capacity in intact but not in TPTX rats. In TPTX rats infused with acetazolamide and PTH, the hormone failed to enhance extrarenal buffering of an acid load. Animals with chronic renal failure, induced by infarction of the kidney, also had an enhanced capacity to buffer an acid load. This enhanced buffering capacity in chronic renal failure was abolished by TPTX. Acute renal failure induced by bilateral ureteral ligation was also associated with increased buffering only in the presence of parathyroid glands. These data demonstrated that PTH, from either an exogenous or endogenous source, enhances extrarenal buffering capacity of an acid load. Chronic and acute renal failure are associated with increased buffering capacity, which is dependent on the presence of parathyroid glands. The data suggest that this effect is mediated through carbonic anhydrase.