Effects of two models of hypercalcemia on renal acid base metabolism

Effects of two models of hypercalcemia on renal acid base metabolism. The effects of two models of chronic hypercalcemia on renal acid-base metabolism were studied in rats. In the first series of experiments, rats were rendered hyperparathyroid by the autologous grafting of 20 to 24 parathyroid glands into a single recipient. Hypercalcemia (5.48 ± 0.03 mEq/liter in high PTH animals, 4.96 ± 0.06 mEq/liter in pair-fed controls, P < 0.001) occurred as did metabolic alkalosis (plasma total carbon dioxide 25.44 ± 0.47 mEq/liter vs. 23.84 ± 0.57 in controls, P < 0.05). The rise in total carbon dioxide was in part a renal tubular effect since urine pH was lower (6.77 ± 0.04 vs. 6.95 ± 0.04, day 5, P < 0.01) bicarbonaturia less (165 ± 26 vs. 283 ± 28 µmoles/24 hr, day 5, P < 0.01) and titratable acid (TA) excretion increased (164 ± 43.4 vs. 48.2 ± 2.53 mEq/24 hr, day 5, P < 0.01) in hyperparathyroid animals vs. pairfed controls. To test the specific role of hypercalcemia versus PTH in this effect, normoparathyroid animals were treated with 1,25 (OH)2 vitamin D3 or SHAM injected. Urinary cAMP was reduced in these animals (0.030 ± 0.004 µmoles/8hr) compared to hyperparathyroid rats (0.055 ± 0.01 µmoles/8hr P < 0.05) suggesting differences in PTH levels. Hypercalcemia occurred in 1,25(OH)2 vitamin D treated animals as did increased plasma total carbon dioxide and urinary TA while urinary bicarbonate excretion and urine pH were reduced. Because hypercalcemia was associated with elevated total carbon dioxide in both models, it is proposed that chronic hypercalcemia stimulated renal acid excretion and in a sustained manner results in metabolic alkalosis, at least in part, on a renal basis. Effets de deux modéles d'hypercalcémie sur le métabolisme acidobasique rénal. Les effets de deux modèles d'hypercalcémie chronique sur le métabolisme acido-basique rénal ont été étudié chez des rats. Dans une première série d'expériences, des rats ont été rendus hyperparathyroïdiens par la greffe autologue de 20 à 24 glandes parathyroïdes chez un seul receveur. Une hypercalcémie (5,48 ± 0,03 mEq/litre chez les animaux à PTH élevée, 4,96 ± 0,06 mEq/litre chez les contrôles nourris de façon apariée, P < 0,001) est apparue en même temps qu'une alcalose métabolique (carbonique plasmatique total 25,44 ± 0,47 mEq/litre, contre 23,84 ± 0,57 chez les contrôles, P < 0,05). L'élévation du carbonique total était en partie due à un effet tubulaire rénal puisque le pH urinaire était plus bas (6,77