Calcium-stimulated vasopressin secretion in uremic patients: an effect mediated via parathyroid hormone?

The effect of whole blood ionized calcium levels on vasopressin (AVP) secretion has been studied in 12 uremic hemodialysis patients (6 nephrectomized and 6 nonnephrectomized), 6 healthy subjects, and a sprue patient, first while she was hypocalcemic and again after her blood calcium had normalized. Changes in whole blood ionized calcium were induced by calcium infusion (3.15 mg Ca/kg BW h-1). In uremic patients, an increase in plasma AVP took place during infusion, and the changes in AVP were correlated to the changes in whole blood ionized calcium. In normals, no changes in AVP were found. In the sprue patient, an increase in plasma AVP correlated to whole blood ionized calcium was found in the hypocalcemic state, but this could not be demonstrated after treatment. Parathyroid hormone has been shown to facilitate calcium entry into cells, and it is proposed that the pathophysiological effect of calcium on AVP secretion in uremic patients is caused by the elevated parathyroid hormone level found in these patients.