Selective consumption of thyroxine-binding globulin during cardiac bypass surgery

Area of Science:

• Cardiovascular Surgery
• Endocrinology
• Biochemistry

Background:

• Thyroid hormone binding proteins, including thyroxine binding globulin (TBG) and transthyretin (TTR), are crucial for regulating thyroid hormone availability.
• Coronary artery bypass graft (CABG) surgery is a major cardiovascular procedure with potential systemic effects.

Purpose of the Study:

• To investigate the dynamic changes in serum TBG and TTR concentrations during and after CABG surgery.
• To elucidate the mechanisms behind alterations in thyroid hormone binding proteins following CABG.

Main Methods:

• Serum samples were collected from 32 patients undergoing CABG surgery.
• Concentrations of TBG and TTR were measured during the surgery and up to 5 days postoperatively.
• Changes were analyzed in relation to preoperative levels and corrected for surgical dilution.

Main Results:

• Transthyretin (TTR) concentrations showed a gradual decline after surgery, with no significant decrease in the first 24 hours.
• Thyroxine binding globulin (TBG) levels rapidly decreased to approximately 60% of preoperative levels within 12 hours post-surgery.
• The rapid decline in TBG suggests accelerated consumption, potentially due to protease cleavage at inflammatory sites, rather than reduced production.

Conclusions:

• CABG surgery induces distinct responses in TBG and TTR, with TBG exhibiting a rapid decrease.
• The accelerated consumption of TBG may explain the observed decrease in serum thyroxine (T4) levels post-CABG.
• The findings suggest TBG's role in inflammatory processes during major surgery and its potential involvement in thyroxine iodine accumulation at inflammatory sites.