Polyacrylamide gel electrophoretic study on the effect of estrogen on human thyroxine-binding prealbumin.

Ethinyl estradiol was administered orally in a daily dose of 0.18-0.3mg for seven days to subjects with normal and abnormal thyroid function, and the changes of several parameters of the thyroid function during estrogen admin istration were investigated. The concentration and maximum T4 binding capacity of thyroxine-binding prealbumin (TBPA) were estimated by polyacrylamide gel electrophoresis. Estrogen increased the serum PBI value and the binding capacity of thyroxinebinding globulin (TBG), while it lowered Triosorb test value, elutable fraction and the concentration and binding capacity of TBPA. However, free T, value, BMR, thyroidal 24-hour uptake of 1311 and thyroidal effective half-life of 1311 did not change . T4 half-life in serum was prolonged. These results show that ethinyl estradiol may have an effect at first on the metabolism of thyroxine-binding proteins. The concentration and binding capacity of thyroxine-binding proteins may increase as a whole. The fact that T4 half-life is prolonged and free T, level stays as before in spite of the rise of PBI in estrogen administration might be due to suppressed decomposition of free T4. These results are observed equally in subjects with intact and abnormal thy roid functions, and it is concluded that these phenomena have no relation to the pituitary-thyroid system.