Preparation of I-131-labeled human serum prealbumin and its metabolism in normal and sick patients.

Despite some early doubts concerning its presence in plasma and its physiological function (1-4), the thyroxine-binding prealbumin of human serum (TBPA) is now known to play a significant role in the transport of thyroxine (T4) (5-8). Nor- mally, as assessed by in vitro techniques, TBPA appears to bind at least 25 to 35%o of T4 in serum (5, 6). In the serum of many patients with se- vere acute or chronic illness, however, the propor- tion of endogenous T4 in serum bound by TBPA and the T4-binding capacity of TBPA decline The recent availability of substantial quanti- ties of a highly purified preparation of TBPA has made possible an investigation of the in vivo me- tabolism of this protein in normal patients and in patients with a variety of disorders that lead to de- creased binding of T4 by TBPA in serum. In ad- dition, the cause of this decrease in T4 binding in the serum of such "sick" patients has been evalu- ated. A portion of the findings has been presented in abstract form While these studies were in progress, Oppenheimer, Surks, Bernstein, and Smith reported similar studies in abstract form (11, 12).