A Study on Plasma Renin Activity in Hyper- and Hypothyroidism

Abstract

In order to investigate the relationship between thyroid function and renin the angiotensin system, plasma renin activity (PRA) was determined under normal diet in 23 hyper-and 13 hypothyroid patients. The effect of beta-adrenergic receptor blocker on the PRA was studied in 9 hyperthyroid patients, especially in view of the cardiovascular dynamics.The blood samples were drawn with a syringe containing EDTA-2Na after maintaining supine and upright positions for 2 hours. The separated plasma was immediately frozen in a deep freezer. The PRA values were determined by the method of Haber, and the others by radioimmunoassay within 2 weeks after taking blood samples. The cardiac in-dices were determined by the dye-dilution method.It was observed that the mean PRA values in supine and upright positions were 0.52±0.15 ng/ml/hr and 1.04±0.24 ng/ml/hr in euthyroid volunteers, 1.14±0.52 ng/ml/hr and 2.72±1.28 ng/ml/hr in non-treated hyperthyroid patients and 0.17±0.11 ng/ml/hr and 0.33±0.17 ng/ml/hr in non-treated hypothyroid patients, respectively. The difference between hyper-thyroid or hypothyroid patients and euthyroid volunteers either in supine or upright positions was statistically significant with p<0.001. The mean PRA values tended to be normalized after achieving euthyroid status with treatment.The PRA values were positively correlated with BMR, serum thyroid hormone levels, creatinine clearance and excreted urinary potassium levels, but were not correlated with blood pressure.The elevated PRA values observed in hyperthyroid patients were suppressed (1.22±0.57 to 0.61±0.44 ng/ml/hr) (p<0.05) after intravenous single administration of beta-adrenergic receptor blocker, YB-2, although the cardiac index was somewhat decreased (4.72±0.94 to 3.02±0.71 1/min/m2) (P<0.02) and serum thyroid hormone levels were unchanged.From these data, it was concluded that the PRA values were elevated in hyperthyroid patients and lowered in hypothyroid patients and that the elevated PRA values observed in hyperthyroid patients were suppressed by the administration of beta-adrenergic receptor blocker. It was therefore indicated that the elevated or lowered PRA values observed in the patients with thyroid dysfunction were not due to the direct action of thyroid hormones, but probably due to the secondary effect of the hormones on the juxtaglomerular apparatus via the sympathetic nervous system.