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Summary
Thyroxine glucuronide is actively secreted into bile by the liver, with a high concentration gradient achieved. Bromosulphophthalein inhibits this process, suggesting a shared transport mechanism.
Area of Science:
- Hepatobiliary transport
- Drug metabolism and pharmacokinetics
Background:
- Thyroxine glucuronide is a metabolite of thyroxine.
- Understanding its biliary secretion is crucial for pharmacokinetics.
Purpose of the Study:
- To investigate the mechanism of thyroxine glucuronide secretion into bile.
- To determine if the secretion process is active and identify potential carriers.
Main Methods:
- Isolated perfused rat liver model.
- Intact anesthetized rat model with intravenous injection.
- Use of radiolabeled [(125)I]thyroxine glucuronide.
- Inhibition studies with bromosulphophthalein.
Main Results:
- The isolated liver actively transports thyroxine glucuronide into bile, achieving an 1800x concentration gradient.
- Secretion into bile occurs rapidly after tissue uptake.
- Bromosulphophthalein strongly inhibits thyroxine glucuronide secretion, indicating a common carrier.
- Approximately 77% of intravenously injected thyroxine glucuronide is recovered from bile in intact rats.
Conclusions:
- Biliary secretion of thyroxine glucuronide is an active, carrier-mediated process.
- The transport likely involves two stages: uptake into hepatocytes and active secretion into bile.
- This active transport mechanism plays a significant role in the elimination of thyroxine glucuronide.