Independence of the acute acid-buffering response from endogenous parathyroid hormone

Two recent reports have made the provocative suggestion that parathyroid hormone (PTH) and, by implication, bone play a critical role in the early phase of acid buffering. The purpose of the present study was to investigate the effect of PTH on the acute buffering process by examining the influence of thyroparathyroidectomy (TPTX) on acid-base parameters in nephrectomized rats following infusion of hydrochloric acid at two differing doses. To ensure hemodynamic and physiologic stability of the animals, the required surgical procedures were staged over several days. Additionally, the experimental protocol was carried out in awake and unrestrained animals. Non-TPTX (sham) animals underwent a sham operation to equalize the surgical stresses between the two groups. The decrements in plasma [HCO-3] observed following infusion of 3.5 mmol/kg HCl over 1 h did not differ between TPTX vs. sham animals at 1 h (-9.4 vs. -9.9 meq/liter), 3 h (-8.6 vs. 8.6 meq/liter), or 6 h (-8.6 vs. -8.5 meq/liter) from the start of the infusion. Similarly, virtually identical falls in plasma [HCO-3] were observed between TPTX vs. sham rats after infusion of 5 mmol/kg HCl over 30 min at 30 min (-13.6 vs. -14.2 meq/liter) and 3 h (-10.9 vs. -11.4 meq/liter) after the start of the infusion. At both doses, the resultant changes in plasma [H+] and PaCO2 were not different in the two groups. The observed mortality was comparable in both TPTX and sham groups. The data demonstrate that endogenous PTH is not necessary in the early phase of buffering of a mineral acid load.