Thyroid hormones and other endogenous anionic molecules undergoing enterohepatic circulation

The target Thyroid hormones and other endogenous anionic molecules undergoing enterohepatic circulation refers to a physiological pathway involving the recycling of substances like thyroxine (T4), triiodothyronine (T3), and bile acids between the liver and the gastrointestinal tract (StatPearls, 2023). These molecules are synthesized or processed in the liver, secreted into the bile, and released into the small intestine, where they are typically reabsorbed into the portal blood to return to the liver (PubMed, 2021). This enterohepatic circulation is vital for maintaining systemic levels of thyroid hormones and facilitating lipid digestion through the continuous availability of bile acids. In clinical practice, this process is targeted by bile acid sequestrants, such as cholestyramine, which are large, positively charged resins that bind these anionic molecules in the gut lumen (NIH, 2022). By preventing the reabsorption of these substances, these drugs increase their fecal excretion, which is useful for treating hypercholesterolemia and managing thyrotoxicosis or thyroid storm by rapidly lowering circulating hormone levels (Journal of Endocrinology and Metabolism, 2020). Additionally, interrupting this circulation can help alleviate pruritus associated with partial biliary obstruction by reducing the accumulation of bile salts in the skin.

Other names

Enterohepatic circulation substratesBiliary excreted anionsEndogenous anionic metabolitesBile acid sequestrant substrates

Bile acid sequestrants act as non-absorbable anion-exchange resins that bind to these molecules in the gastrointestinal tract, forming an insoluble complex that is excreted in the feces, thereby preventing their reabsorption into the portal circulation (StatPearls, 2023).