Effect of Hypothyroidism on Antidiuretic Action of Pressor Principle of Posterior Pituitary

Abstract

The effects of total ablation of the normal thyroid gland in man on the action of injected adrenalin and of insulin have been reported previously., Studies of the effect of total thyroidectomy on the action of injected pressor principle of the posterior lobe of the pituitary are presented below. The antidiuretic effect, and blood pressure and heart rate following the subcutaneous injection of pitressin have been studied. Several observations support the idea that the thyroid gland is a factor in maintaining water balance. Whether the antidiuretic action of pitressin is altered after thyroidectomy has not been established. We have compared the effect of pitressin in postoperative hypothyroidism with its effect in subjects with normal thyroid function. Studies were made in 3 subjects with normal thyroid function, in 3 subjects with clinical and laboratory evidence of hypothyroidism which developed after total thyroidectomy, and in 1 additional subject both before operation and subsequently when hypothyroidism had developed. The elapsed time between operation and the pitressin studies varied from 1 to 9 months. Thyroidectomy in 2 of the 4 patients operated was performed for the relief of congestive heart failure, in the other 2 for angina pectoris, in accord with considerations outlined elsewhere by Blumgart and his associates., The basal metabolic rates of the 4 hypothyroid patients studied ranged between —19 and —36% and averaged —27%, clinical signs varying from those of mild hypothyroidism to rather marked myxedema were present. The antidiuretic effect of pitressin in each instance was evaluated by studying the urine output after a liter of water, both on a control day and on a day when pitressin was administered. The following regimen of study was utilized: at 7:00 A. M., the patient received a standard light breakfast with no coffee or added salt. At 9:00 A. M., with the patient in the recumbent position, blood pressure and heart rate measurements were made at 5-minute intervals until constant readings were obtained. The patient then emptied his bladder, and either 0.10 or 0.15 cc. of pitressin was administered subcutaneously, the site of injection being massaged. (On the control day pitressin was omitted.) The patient then ingested 1000 cc. of water. The urine voided between 9 A. M. and 2:00 P. M. was collected at hourly intervals: the volume, specific gravity, and chloride content of the 5 specimens were measured. The chloride contents of the urine were measured by the method of Folin. Blood pressure and heart rate measurements were made every 15 minutes for the first hour following pitressin injection, and at 1 1/2 and 2 hours after injection. The results were compared with those obtained on a control day. Basal metabolic rate measurements were made with a Benedict-Roth apparatus, the results being calculated with reference to the Aub-DuBois normal standards.