Studies on the Relationship Between the Urinary Excretion of Iodide and Other Electrolytes, and the Effect of Oestrogen on their Excretion in the Rat

Abstract

The relationships between the urinary excretion of iodide, sodium, chloride and potassium, and the effect of oestrogens on the urinary excretion of these electrolytes has been studied in the rat. Acute water and saline-loading experiments have been conducted on female rats where renal tubular reabsorbtion of sodium and chloride has been blocked using chlorothiazide and the aldosterone-antagonist SC-14266. Under these conditions a close correlation exists between iodide, sodium and chloride excretion and it is concluded that iodide and chloride are handled in a similar manner by the kidney. In addition it was found that chlorothiazide is a more powerful chloruretic agent than SC-14266, and that SC-14266 has greater ioduretic properties than chlorothiazide. It is suggested that iodide is preferentially reabsorbed in the distal part of the renal tubule linked to the aldosterone controlled Na-K pump. The acute administration of propylthiouracil in water-loaded female rats produced an ioduresis, naturesis and chloruresis similar to that of SC-14266. In female rats given water and saline-loads at intervals following a single subcutaneous injection of 400 ug oestradiol benzoate the urinary sodium, chloride and iodide was reduced on the first day after oestrogen treatment. On the second day the excretion of all these ions was increased, on the fourth day the excretion of these ions became normal but on the sixth day post-oestrogen treatment there was again an increase in the excretion of these ions. However, in similar experiments using male rats there was a continued reduction of sodium, chloride and iodide excretion on these days .Cyclic variations in urinary electrolyte excretion were found to occur in female rats. A reduced , urinary Na:K ratio, sodium, chloride and high potassium excretion occured at proestrous or oestrous indicating an increase in aldosterone activity at these times. Dietary 1131 tagging experiments confirmed that a close correlation between the urinary excretion of iodide and sodium chloride exists. It is suggested that a cyclic variation in iodide excretion occurs in the rat oestrous cycle. A reduction in excretion occuring at proestrous and oestrous and an increased excretion at dioestrous.