A simplified method for the preparation of rat thyroxine-binding prealbumin. Factors influencing its circulating level.

Rat thyroxine-binding prealbumin (TBPA) was isolated in three simple steps by means of a serum precipitation by a 5% phenol solution and two consecutive semi-preparative polyacrylamide gel electrophoreses. The overall yield was 15% and the TBPA preparation contained less than 1% impurities. In addition a monospecific antiserum was raised in the rabbit. In polyacrylamide gel, rat TBPA, as with its human counterpart, migrated anodally to albumin while in agarose gel, its electrophoretic mobility was similar to that of albumin. Serum TBPA measured in adult male Wistar rats did not exhibit a circadian rhythm. However, a significant 13% decrease was observed between 9 and 15 h, followed by the restoration of the initial value by 21 h. TBPA concentration was measured in 1-, 15- and 28-day-old male and female pups as well as in adult rats. The level of this protein increased from 1 to 28 days of age and did not display any sexual difference. Yet, while TBPA concentrations in adult males were similar to those recorded in the 28-day-old pups, for adult females, they returned to the levels measured in the 1-day-old pups.