Effects of thyroid hormone on erythrocyte carbonic anhydrase-I and zinc concentrations in vivo and in vitro: clinical usefulness of carbonic anhydrase-I and zinc concentrations in erythrocytes.

Red blood cell (RBC) carbonic anhydrase-I isozyme (CAI) and zinc concentrations were measured in patients with various thyroid diseases. Both concentrations were decreased in patients with hyperthyroid Graves' disease, and the RBC CAI concentration significantly (r = 0.95) correlated with the RBC zinc concentration. After treatment, the normalization of RBC CAI and zinc lagged 2 months behind normalization of plasma T4 and T3 levels. Furthermore, the highest correlation coefficients were observed between RBC CAI and zinc levels and plasma thyroid hormone levels measured 8 weeks earlier. These results indicate that both RBC CAI and zinc levels reflect the integrated plasma thyroid hormone levels over the previous few months. Transient thyrotoxicosis due to destructive (subacute or painless) thyroiditis did not cause significant changes in the RBC CAI and zinc concentrations. Therefore, the measurement of RBC CAI and zinc concentrations may be useful in differentiating patients with Graves' disease from those with transient thyrotoxicosis. T3 at a physiological free concentration significantly decreased CAI concentration in erythroleukemic YN-1 cells and burst forming unit-erythroid-derived cells obtained by culturing peripheral blood mononuclear cells. These cells may be useful in vitro models for investigations of thyroid hormone action in human erythroid cells.