Reversible alteration of red cell lithium-sodium countertransport in patients with thyroid disease

Thyroid hormones may alter red blood cell (RBC) sodium content and transport. The functional importance of lithium-sodium (Li-Na) countertransport in regulating sodium (Na) transport in vascular smooth muscle and kidney by Na-H countertransport and the potential effect of thyroid hormone on these processes led us to study Li-Na countertransport and other sodium transporters in RBCs of patients with thyroid dysfunction. Patients with untreated hypothyroidism (10) and hyperthyroidism (10) were studied, along with normal subjects (10). The mean value for Li-Na countertransport was significantly higher in the hypothyroid group [0.46 +/- 0.08 (+/- SE) mmol/L cell.h; P less than 0.05] and lower in the hyperthyroid group (0.15 +/- 0.04 mmol/L cell.h; P less than 0.05) compared to that in the normal subjects (0.25 +/- 0.03 mmol/L cell.h). When all groups were combined, significant negative correlations were found between Li-Na countertransport and serum T4 (r = -0.48; P less than 0.01), free T4 index (r = -0.42; P less than 0.05), and serum T3 (r = -0.38; P less than 0.05). Li-Na countertransport was positively correlated with serum triglyceride (r = 0.57; P less than 0.01), but not with serum cholesterol levels (r = 0.28; P = NS). The values became normal in subsets of the hypothyroid (n = 5) and hyperthyroid groups (n = 5) during treatment. We found a bidirectional effect of thyroid status on RBC Li-Na countertransport, which was reversible when serum thyroid hormone levels became normal. Changes in Li-Na countertransport, a pathway of Na-H exchange, may influence renal sodium handling and vascular tone in patients with thyroid disease and contribute to abnormalities such as hypertension that occur in patients with hypothyroidism.