The exaggerated natriuresis of hypothyroid rats receiving a 5% saline infusion was studied to determine the mechanism and the site within the nephron responsible for this increase in sodium excretion. Sodium clearance (CNa) and fractional sodium excretion were both demonstrated to be greater in hypothyroid rats for any amount of sodium infused. The rate of increase in fractional sodium excretion in response to saline loading was 3.4 times greater in hypothyroid animals. At the conclusion of the diuresis some of the hypothyroid animals excreted greater than 45% of the filtered sodium load, while no control animal excreted more than 12% of the filtered sodium load.
Edward W. Holmes Jr., Vincent A. DiScala