Thyrocalcitonin and the jejunal absorption of calcium, water, and electrolytes in normal subjects.

Jejunal absorption of calcium, water, and electrolytes was measured in 10 normal subjects by the triple-lumen perfusion method. During the control period, water and electrolyte movements were minimal when a bicarbonate-free test solution was infused. By contrast, bicarbonate-containing solutions were readily absorbed in the control period. Intravenous infusion of synthetic salmon calcitonin (SCT) (1 Medical Research Council U/kg wt/h) over 110-120 min resulted in a marked jejunal secretion of water, sodium, potassium, and chloride in 8 of the 10 subjects. This jejunal secretion occurred with both the bicarbonate-free and the bicarbonate-containing test solutions. Calcium absorption was not affected by SCT, and the serum calcium concentration did not fall during SCT infusion. These results suggest that diarrhea in patients with medullary carcinoma of the thyroid may be due to intestinal secretion secondary to high blood concentrations of thyrocalcitonin.