Hyperglycemia and
impaired glucose tolerance are frequently observed in patients with
hyperthyroidism. However, little is known about whether altered
polyol metabolism in
hyperthyroidism is present or not. To examine changes in
polyol metabolism in
hyperthyroidism, we investigated changes in erythrocyte
sorbitol,
glyceraldehyde reductase (GAR) and
sorbitol dehydrogenase (SDH) activities during
hyperthyroid and euthyroid states in patients with
thyrotoxicosis. Mean levels of erythrocyte
sorbitol and GAR were 32.0 +/- 1.6nM/g.Hb and 147.1 +/- 0.3mU/g.Hb, respectively. In thyrotoxic patients in a
hyperthyroid state, these values were significantly higher than those in euthyroid controls. Mean level of erythrocyte SDH in thyrotoxic patients was weak but was significantly increased in comparison with that of euthyroid controls. However, mean levels of erythrocyte
sorbitol and GAR were remarkably reduced to 23.6 +/- 1.4nM/g.Hb and 125.3 +/- 4.6mU/g.Hb in thyrotoxic patients in a euthyroid state
after treatment with anti-thyroid drugs or by subtotal
thyroidectomy. Mean level of SDH, on the other hand, was increased after the treatment. In addition, positive correlations were observed between the level of erythrocyte
sorbitol or GAR, and the level of free
thyroxine(FT4) or free
triiodothyronine(FT3). A negative correlation was observed between the level of erythrocyte SDH and the level of FT4 or FT3. These results suggest that the level of erythrocyte
sorbitol may be increased through direct acceleration of erythrocyte GAR activity by increased
thyroid hormone levels in patients with
thyrotoxicosis.