Effect of salt feeding on thyroid metabolism of I¹³¹ in the dog

¹ Department of Research Physiology, William H. Singer Memorial Research Laboratory, Allegheny General Hospital, Pittsburgh, Pennsylvania

Six adult male dogs were fed on 5% NaCl added to the same diet on which a group of six dogs were maintained as a control group. At 12 weeks 24-hour I¹³¹ uptake, PBI¹³¹, serum and urine sodium and potassium were measured. Two weeks later, 5-hour Na²⁴ and I¹³¹thyroxine dilution curves were determined from serial blood samples in the anesthetized animals. The salt fed dogs had elevated 24-hour I¹³¹ uptake and PBI¹³¹, decreased serum sodium and increased serum potassium, and both total urine sodium and potassium were increased with salt feeding at 12 weeks. In the salt-fed dog, both Na²⁴ and I¹³¹-thyroxine dilution volumes were increased at 5 hours over the values for the control group, indicating expansion of extravascular volume. It was suggested that alterations of I¹³¹ metabolism were influenced by extrarenal factors of expanded fluid volume and tissue concentration of electrolytes in addition to the dominant factor of renal electrolyte regulation with salt loading.