Postoperative Changes in the concentration of Thyroxine-Binding Prealbumin and Serum Free Thyroxine

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Abstract
Six patients subjected to various surgical procedures [mitral commissurtomy (two), herniorrhaphy, below-knee amputation, hysterectomy, and thoracotomy] demonstrated marked postoperative changes in the binding of thyroxine by serum proteins. Sera obtained before and at intervals after the surgical procedures were analyzed for free thyroxine concentration, protein-bound iodine (PBI), and the maximal binding capacity of thyroxine-binding prealbumin (TBPA) and thyroxine-binding globulin (TBG). The concentration of prealbumin-1 (PA-1) was determined densitometrically from starch gel elec-trophoretic patterns. The mean increase in free thyroxine concentration above preoperative levels was 63% (range 37[long dash]125%). There was a concomitant mean decrease of 54% (range: 36[long dash]63%) in the binding capacity of TBPA and a similar fall in the concentration of PA-1. These effects, which commenced on the day of surgery in all patients, were maximal on the 2nd to 5th postoperative days. All values returned to or nearly to preoperative levels by the 8th to 28th postoperative days. There was no consistent change in either PBI or the binding capacity of TBG. These findings indicated that the fall in the concentration of PA-1 is largely responsible for the observed rise in free thyroxine concentration. The data also provide further evidence that PA-1 and TBPA are the same protein. It is suggested that TBPA may play an important role in the regulation of the serum free thyroxine concentration in response to varying physiological requirements.

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