Renin and aldosterone in hypothyroidism: relation to excretion of sodium and potassium.

Changes in plasma renin activity (PRA) and plasma aldosterone (PA) were studied together with the urinary excretion of sodium and potassium in patients with hypothyroidism. The basal levels of PRA and PA were significantly less than those in normal subjects. However, there was no significant relationship between PRA and PA. The response of PRA after administration of 40 mg of frusemide in patients with hypothyroidism was significantly less than that in normal subjects, although the excretion of sodium was slightly higher than that in normal subjects. On the other hand, the excretion of potassium in patients with hypothyroidism was significantly lower than that in normal subjects. The responses of PA to various stimulations, such as ACTH, angiotensin II, potassium and frusemide, were equally suppressed. These results suggest that PRA and PA may be suppressed independently in hypothyroidism ,probably due to dysfunction of juxtaglomerular cells and glomerulosa cells, respectively, and the possibility that suppression of PRA and PA in patients with hypothyroidism is related to exaggerated sodium excretion and a decrease in potassium excretion cannot be ruled out.