title: Serum concentrations of remnant-like particles in hypothyroid patients before and after thyroxine replacement.
abstract: OBJECTIVE
  Remnant-like particles (RLPs) reflect chylomicron remnants and very-low-density lipoprotein remnants, which are most likely to be atherogenic particles. To investigate the effect of thyroxine replacement on the metabolism of RLPs in hypothyroidism, we measured serum concentrations of RLPs during an oral fat-loading test in patients with hypothyroidism before and after thyroxine replacement.
  
  
  METHODS
  Thirteen patients with hypothyroidism, having serum-free thyroxine (FT4) of 4.25 +/- 2.23 pmol/l (mean +/- SD) and TSH of 72.5 +/- 27.7 mU/l, participated in the study. Two-hundred grams of cream containing 32.9% of fat were given to each patient followed by blood draws every 2 h for 8 h. The patients became euthyroid after 3 months of T4 replacement, and the fat-loading tests were then repeated.
  
  
  RESULTS
  Fasting levels of serum total cholesterol and low-density lipoprotein cholesterol were remarkably decreased after T4 therapy (P < 0.0005). Serum high-density lipoprotein cholesterol and triglyceride were also decreased by T4 therapy, not so remarkably but significantly (P < 0.05). Activities of lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) increased 52% and 85%, respectively, from the pretreatment values. Serum concentrations of remnant-like particle cholesterol (RLP-C) and remnant-like particle triglyceride (RLP-TG), measured by immunoseparation assays, significantly decreased from 0.14 +/- 0.03 to 0.09 +/- 0.03 mmol/l (P < 0.0005) and from 0.19 +/- 0.11-0.11 +/- 0.07 mmol/l (P < 0.01), respectively. In the fat-loading test, serum low-density lipoprotein cholesterol concentrations were not changed, while serum RLPs concentrations were increased and remained high throughout the test, with the peak value at 6 h in a hypothyroid condition. In an euthyroid condition after T4 therapy, the peak values of RLPs were obtained at 4 h, and the concentrations were decreased rapidly. As the result, areas under the curve of serum RLPs were decreased remarkably after T4 therapy.
  
  
  CONCLUSIONS
  Hypothyroidism seems to be associated with a decrease in metabolism of serum RLPs. Such altered metabolism of RLPs may be related to the decreased activities of LPL and HTGL and can be corrected by T4 replacement therapy.
authors.affiliation: The Kuma Hospital, Kobe, Hyogo, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Ito
authors.forename: Junta
authors.initials: J
authors.lastname: Takamatsu
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsuo
authors.forename: Keiichi
authors.initials: K
authors.lastname: Kameoka
authors.forename: Sumihisa
authors.initials: S
authors.lastname: Kubota
authors.forename: Shuji
authors.initials: S
authors.lastname: Fukata
authors.forename: Hajime
authors.initials: H
authors.lastname: Tamai
authors.forename: Akira
authors.initials: A
authors.lastname: Miyauchi
authors.forename: Kanji
authors.initials: K
authors.lastname: Kuma
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Hanafusa
mesh_terms: D019540:Area Under Curve; D002784:Cholesterol / Q000097:blood*; D008076:Cholesterol, HDL / Q000097:blood; D053298:Chylomicron Remnants; D002914:Chylomicrons / Q000097:blood*; D020249:Hormone Replacement Therapy / Q000379:methods*; D006801:Humans; D007037:Hypothyroidism / Q000097:blood* / Q000188:drug therapy; D008074:Lipoproteins / Q000097:blood*; D008079:Lipoproteins, VLDL / Q000097:blood; D008875:Middle Aged; D013960:Thyroid Function Tests; D013974:Thyroxine / Q000627:therapeutic use*; D014280:Triglycerides / Q000097:blood*
chemical_list: D008076:Cholesterol, HDL; D053298:Chylomicron Remnants; D002914:Chylomicrons; D008074:Lipoproteins; D008079:Lipoproteins, VLDL; D014280:Triglycerides; C030104:lipoprotein cholesterol; C112017:remnant-like particle cholesterol; D002784:Cholesterol; D013974:Thyroxine