title: Endothelial function is not changed during short-term withdrawal of thyroxine in patients with differentiated thyroid cancer and low cardiovascular risk.
abstract: OBJECTIVE
  The incidence of differentiated thyroid cancer is increasing in young adults and females in Korea. Some of them experience short-term hypothyroidism in preparation for radioiodine (RAI) therapy, which can have a deleterious effect on the cardiovascular system. However, it is not clear if short-term hypothyroidism induces endothelial dysfunction in patients with low cardiovascular risk. Therefore, the aim of this study was to investigate whether short-term hypothyroidism is associated with endothelial dysfunction in patients with low cardiovascular risk.
  
  
  METHODS
  To evaluate the effect of short-term hypothyroidism on endothelial function in this group, we recruited fifteen female patients with low cardiovascular risk. We analyzed clinical, biochemical, and cardiovascular parameters at four time points: the last day on levothyroxine (LT4) at their usual thyroid-stimulating hormone (TSH)-suppressive doses (P1), 7 days (P2) and 4 weeks (P3) after withdrawal of LT4, and 8 weeks (P4) after replacement of the previous dose of LT4. A high resolution ultrasound was used to measure brachial artery diameter at rest, after reactive hyperemia, and after sublingual nitroglycerin.
  
  
  RESULTS
  During short-term hypothyroidism (P3), serum concentrations of total cholesterol and low-density lipoprotein (LDL)-cholesterol were increased (p < 0.001 for each period). In spite of having worsened lipid states, serum high sensitivity C-reactive protein or flow-mediated vasodilatation, which is one of the surrogate markers of the endothelial function, did not change during short-term hypothyroidism.
  
  
  CONCLUSIONS
  Short-term hypothyroidism induced worsening of metabolic parameters, but not enough to induce the endothelial dysfunction in patients with low cardiovascular risk.
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Hyuk-Jae
authors.initials: HJ
authors.lastname: Chang
authors.forename: Kyung Won
authors.initials: KW
authors.lastname: Kim
authors.forename: Sung Hee
authors.initials: SH
authors.lastname: Choi
authors.forename: Soo
authors.initials: S
authors.lastname: Lim
authors.forename: Kyoung Un
authors.initials: KU
authors.lastname: Park
authors.forename: Do Joon
authors.initials: DJ
authors.lastname: Park
authors.forename: Dong Joo
authors.initials: DJ
authors.lastname: Choi
authors.forename: Hak C
authors.initials: HC
authors.lastname: Jang
authors.forename: Bo Youn
authors.initials: BY
authors.lastname: Cho
authors.forename: Young Joo
authors.initials: YJ
authors.lastname: Park
mesh_terms: D000328:Adult; D002318:Cardiovascular Diseases / Q000209:etiology*; D004730:Endothelium, Vascular / Q000503:physiopathology*; D005260:Female; D006339:Heart Rate; D006801:Humans; D007037:Hypothyroidism / Q000503:physiopathology*; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008055:Lipids / Q000097:blood; D008875:Middle Aged; D013961:Thyroid Gland / Q000503:physiopathology; D013964:Thyroid Neoplasms / Q000503:physiopathology* / Q000532:radiotherapy; D013974:Thyroxine / Q000627:therapeutic use*
chemical_list: D007457:Iodine Radioisotopes; D008055:Lipids; D013974:Thyroxine