Phosphaturesis: a Direct Renal Effect of Triiodothyronine

¹ From the Department of Metabolism, Division of Medicine, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington, D.C.

A possible direct renal effect of thyroid hormone was investigated by administering 1.0 mg 3,5,3' l-triiodothyronine (T₃) to normal dogs, and measuring the excretion of calcium, phosphorus, magnesium, creatinine and nitrogen for 4 1/2 hours thereafter. In contrast to controls, a pronounced rise in urinary phosphorus regularly followed T₃. Renal clearance of phosphorus increased, and tubular reabsorption fell to a mean of 68% of the filtered phosphorus load. A similar response occurred in dogs without parathyroid glands. No increase in calcium, magnesium or nitrogen excretion accompanied the acute phosphaturesis. These results indicate a direct action of triiodothyronine on the renal tubule independent of the level of parathyroid activity.

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