Effects of metabolic alkalosis on calcium excretion in the conscious dog

The tubular reabsorption of calcium has been studied in chronic metabolic alkalosis and acidosis. Clearance studies were performed in five conscious mongrel dogs during control periods and during alkalosis and acidosis both before and after thyroparathyroidectomy. After thyroparathyroidectomy, normocalcemia was maintained with oral dihydrotachysterol, and thyroxine was replaced. An initial control study was followed by the induction of chronic metabolic alkalosis by repeated gastric drainage for 4 days through a previously implanted gastric fistula. A second control study 1 week after alkalosis was followed by the induction of acidosis by feeding ammonium chloride, 10 gm daily for 3 days. A final control study was performed 1 week later. Serum proteins, GFR, and filtered calcium load were not significantly different in control, alkalosis, or acidosis. Alkalosis, in both intact and TPTX dogs, was associated with no change in TRNa in comparison with controls (94.6% vs. 95.4 in intact, p greater than 0.05; 95.0% vs. 96.3% in TPTX, p greater than 0.05). By contrast, TRCa increased significantly (97.2% vs. 95.5, p less than 0.05 in intact; 98.0% vs. 95.0, p less than 0.05 in TPTX). In acidosis, TRNa in both intact and TPTX dogs was unchanged in comparison with control (96.4%, p greater than 0.05 and 96.6%, p greater than 0.05, respectively), and TRCa was significantly decreased (to 91.9%, p less than 0.01 and 83.3%, p less than 0.001, respectively). These data indicate that chronic metabolic alkalosis increases the TRCa independently of changes in TRNa, filtered calcium load, or parathyroid activity.