The binding of thyroxine and tri-iodothyronine to plasma proteins in the chicken at the physiological pH.

Amounts of 125I-labelled thyroxine (T4) and triiodothyronine (T3), representing approximately 50 per cent of the plasma concentration, were incubated with chicken plasma or serum, the proteins were separated by polyacrylamide gel electrophoresis at pH 7.4 and the distribution of the hormones determined. Seventy to 75 per cent of T4 migrated with albumin, about 10 per cent with the alpha-globulin and most of the remainder with a pre-albumin fraction. The percentage attached to the pre-albumin tended to increase with age. Neither barbiturate nor 8-anilino-1-naphthalene sulphonic acid (ANS) affected the distribution. About 50 per cent of T3 was associated with albumin, 30 to 40 per cent with the main alpha-globulin and most of the remainder with an adjacent globulin band. ANS reduced the percentage attached to albumin and increased that associated with the alpha-globulin. Barbiturate had no effect.