Renal Response to Sodium Restriction in Myxedema 1

Summary

The renal response to dietary Na restriction after initial equilibration on a liberal salt intake was studied under carefully controlled conditions in 6 patients with myxedema and four euthyroid control subjects. In 4 patients with mild to moderate hypothyroidism, the time required to reduce Na excretion by 50% (Na t _1/2) and the cumulative urinary Na losses were comparable to those of the euthyroid controls. In 2 patients with clinically severe myxedema, however, renal Na conservation was clearly abnormal, with delayed achievement of sodium balance, prolonged Na t _1/2 and increased cumulative sodium losses. Improvement in the ability to conserve Na was demonstrated upon restudy of one patient after partial correction of his myxedema-tous state. Available evidence suggests that the basis for the impairment in sodium conservation in hypothyroidism is a decrease in renal tubular sodium reabsorption.

The authors are grateful to Dr. Lawrence Fish-man for the many helpful suggestions and criticisms. The invaluable assistance of Marcella Farmer, Patricia Whelton and Robert Rubin is appreciated.