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Calcium-induced natriuresis: physiologic and clinical implications.
1Istituto Semeiotica e Nefrologia Medica, University of Verona, Italy.
Calcified Tissue International
|May 24, 2000
Summary
Calcium infusion causes significant sodium excretion in humans, potentially leading to volume depletion. Patients with hypercalcemia, like primary hyperparathyroidism, may have mild sodium depletion and are more prone to volume loss.
Area of Science:
- Nephrology
- Endocrinology
- Human Physiology
Background:
- Assessing tubular calcium reabsorption is complex due to parathyroid hormone (PTH) suppression and calcium-sensing receptor activation.
- The natriuretic effect of calcium in humans is not well understood.
Purpose of the Study:
- To reanalyze the relationship between serum calcium and urinary calcium and sodium excretion.
- To investigate the magnitude of calcium's natriuretic effect in healthy volunteers and patients with primary hyperparathyroidism.
Main Methods:
- Standard calcium infusion in 14 healthy volunteers and 8 primary hyperparathyroid patients.
- Analysis of urine calcium and sodium excretion per unit of creatinine clearance (CaE and NaE) and per unit of time (UCa and UNa).
Main Results:
- Healthy subjects showed a large natriuretic effect of calcium infusion, increasing NaE up to 8 mmol/liter GFR.
- Patients with primary hyperparathyroidism had significantly lower CaE and NaE during calcium infusion compared to controls.
- Both serum calcium and sodium excretion explained the variance in calcium excretion in both groups.
Conclusions:
- Hypercalcemia has a surprisingly large natriuretic effect, potentially causing extracellular fluid depletion.
- Chronic hypercalcemia patients may experience mild sodium depletion and increased susceptibility to volume depletion.
- Calcium reabsorption is influenced by PTH suppression and sodium depletion-induced volume contraction, which can create a detrimental cycle in severe hypercalcemia.