Changes in TBG Concentration Determine Binding and Influence Ta and T3 Levels ● Increased tbg o Total serumt andt levels increase Free T4(Ft4), and free T,(FT3 )concentrations remain unchanged Decreased tbg e Total serum t andt levels decrease Ft and fta levels remain unchanged
Changes in TBG Concentration Determine Binding and Influence T4 and T3 Levels Increased TBG Total serum T4 and T3 levels increase Free T4 (FT4), and free T3 (FT3) concentrations remain unchanged Decreased TBG Total serum T4 and T3 levels decrease FT4 and FT3 levels remain unchanged
Drugs and Conditions That Increase Serum Ta and T3 Levels by Increasing TBG Drugs that increase TBg. Conditions that increase Oral contraceptives and TBG other sources of estrogen Pregnancy Methadone Infectious/chronic active ● Clofibrate hepatitis 5-Fluorouracil HIV infection Heroin Biliary cirrhosis Tamoxifen acute intermittent porphyria Genetic factors
Drugs and Conditions That Increase Serum T4 and T3 Levels by Increasing TBG Drugs that increase TBG Oral contraceptives and other sources of estrogen Methadone Clofibrate 5-Fluorouracil Heroin Tamoxifen Conditions that increase TBG Pregnancy Infectious/chronic active hepatitis HIV infection Biliary cirrhosis Acute intermittent porphyria Genetic factors
Drugs and Conditions That Decrease Serum T4 and T3 by Decreasing TBG Levels or Binding of Hormone to TBG o drugs that decrease serum Conditions that decrease T and t serum t and t Glucocorticoids Genetic factors Androgens Acute and chronic illness L-asparaginase ● Salicylates Mefenamic acid Antiseizure medications, eg, phenytoin, carbama-zepine ● Furosemide
Drugs and Conditions That Decrease Serum T4 and T3 by Decreasing TBG Levels or Binding of Hormone to TBG Drugs that decrease serum T4 and T3 Glucocorticoids Androgens L-Asparaginase Salicylates Mefenamic acid Antiseizure medications, eg, phenytoin, carbama-zepine Furosemide Conditions that decrease serum T4 and T3 Genetic factors Acute and chronic illness
Thyroid Hormone action
Thyroid Hormone Action
nuclear thyroid hormone receptors ( trs) Isoform: a and f tissue specific different function a: brain, kidney, gonads, muscle, and heart 1: pituitary and liver(feedback control) o T, is bound with io to 15 times greater affinity than t
nuclear thyroid hormone receptors (TRs) Isoform: α and ß tissue specific different function α : brain, kidney, gonads, muscle, and heart ß : pituitary and liver (feedback control) T3 is bound with 10 to 15 times greater affinity than T4