1. The influence of thyroparathyroidectomy on renal function and specifically on acid excretion was studied in rats with or without oral supplementation of calcium.

2. Thyroparathyroidectomy caused a significant decrease in glomerular filtration rate, in the urinary/ plasma inulin ratio and in overall acid excretion. These changes were not corrected by calcium supplementation.

3. Rates of proximal tubular acidification were studied by means of double-barrelled resin/reference microelectrodes. Acidification half-time was significantly increased in both thyroparathyroidectomized and calcium-supplemented thyroparathyroidectomized rats (838 s and 7.40 s, respectively) compared with control rats (5.44 s).

4. When 10−6 mol/l A23187, a calcium ionophore, was added to the luminal bicarbonate solution, the acidification half-time returned to 3.97 s in the thyroparathyroidectomized rats, whereas no significant changes were detected in the properties of acidification in the control rats.

5. These data show that parathyroid hormone and cellular calcium are important factors involved in proximal tubular H+ secretion, which appears to be largely dependent on a well-defined concentration range of these agents.

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