Micropuncture studies were performed in intact and thyroparathyroidectomized (TPTX) dogs to evaluate the relationship between the absolute level of serum ultrafilterable phosphate concentration (SUFP) and proximal bicarbonate reabsorption. In both groups of animals, a reverse linear relationship was noted between the serum phosphate level and the tubular fluid bicarbonate concentration (TFHCO3). For the intact dogs, TFHCO3 = 32.27 SUFp ± 2.17, r = 0.715, p = 0.02, and for the TPTX dogs, TFHCO3 = 35.68 – 2.39 SUFP ± 2.26; r = 0.619, p < 0.02. Furthermore, when late-proximal tubular values for absolute bicarbonate reabsorptive rate (Thco3)/100 nl single nephron filtrate were plotted against SUFp, a direct relationship was found for both groups; intact dogs: THCO3 = 205 SUFp – 169 ± 136, r = 0.707, p < 0.05; TPTX dogs: THCO3 = 224 SUFp – 882 ± 221, r = 0.625, p < 0.01. Variations in plasma bicarbonate concentration or PCO2 did not contribute to the relationship between SUFP and bicarbonate reabsorption. The data suggest that extracellular fluid phosphate concentration is an important modulator of proximal bicarbonate transport, independent of the action of parathyroid hormone. a number of investigators have documented the fact that alterations in phosphate excretion are accompanied by parallel changes in bicarbonate transport both in the experimental animal [2,3] and in man [4–6]. A characteristic effect of the administration of parathyroid hormone (PTH) is a substantial phosphaturia

Keywords:
Serum phosphate, Bicarbonate reabsorption, Bicarbonate transport, Phosphate transport, Proximal tubule, Micropuncture, Parathyroid hormone
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© 1977 S. Karger AG, Basel
1977
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