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Selective consumption of thyroxine-binding globulin during cardiac bypass surgery
B Afandi1, G C Schussler, A H Arafeh
1Department of Medicine, State University of New York Health Science Center at Brooklyn, 11203-2098, USA.
Insights
Coronary artery bypass graft surgery significantly impacts thyroid hormone binding proteins. Thyroxine binding globulin (TBG) rapidly decreases, suggesting accelerated consumption, while transthyretin (TTR) declines gradually after 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.
Abstract:
A study of serum thyroid hormone binding proteins and thyroid hormone concentrations during and after coronary artery bypass graft (CABG) surgery shows a marked difference in the response of thyroxine binding globulin (TBG) and transthyretin (TTR). The effects of CABG on TBG and TTR were compared in 32 patients during the day of surgery. In a few of these patients, additional determinations were performed to 5 days. When corrected for dilution, TTR concentrations decline gradually after surgery, with no significant decrease over the first 24 hours. In contrast, a rapid decrease of TBG to a mean level of 60% of the preoperative control at 12 hours after the start of surgery appears to account for the concomitant decrease of serum T4. The rate at which the TBG concentration decreased far exceeds the reported fractional clearance of TBG and therefore implies accelerated consumption rather than inhibition of production. TBG is a member of the serine protease inhibitor (SERPIN) superfamily. We propose that its rapid consumption is due to protease cleavage at inflammatory sites. This may explain the previously observed accumulation of thyroxine iodine at such sites.
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