title: Changes in renal tri-iodothyronine and thyroxine handling during fasting.
abstract: OBJECTIVE
  Liver handling of thyroid hormones (TH) has been known to alter significantly during fasting. This study investigates whether renal handling of TH is also changed during fasting.
  
  
  METHODS
  We measured urinary excretion rates and clearances of free tri-iodothyronine (T(3)) and free thyroxine (T(4)) in healthy subjects prior to and on the third day of fasting.
  
  
  RESULTS
  During fasting, both mean T(3) and T(4) urinary excretion decreased significantly to a mean value of 42% of control. Also, total and free (F) serum T(3) concentrations declined significantly, but serum T(4) did not change. Both FT(3) and FT(4) clearance decreased significantly during fasting (62% and 42% of control). The fasting-induced decrease in uric acid clearance correlated well with the decrease in FT(3) clearance (r=0.94; P<0.001). Serum concentrations of non-esterified fatty acids (NEFA) were significantly elevated during fasting.
  
  
  CONCLUSIONS
  The findings cannot be fully explained by the fasting-induced decrease in serum T(3), and are in accordance with inhibition of uptake of T(3) and T(4) at the basolateral membrane of the tubular cell. This inhibition may be caused by a decreased energy state of the tubular cell and by other factors such as ketoacidosis and/or increased NEFA concentrations during fasting.
authors.affiliation: Department of Internal Medicine III, Academic University Hospital Dijkzigt and Erasmus Medical School, Rotterdam, The Netherlands.
authors.forename: E J
authors.initials: EJ
authors.lastname: Rolleman
authors.forename: G
authors.initials: G
authors.lastname: Hennemann
authors.forename: H
authors.initials: H
authors.lastname: van Toor
authors.forename: C H
authors.initials: CH
authors.lastname: Schoenmakers
authors.forename: E P
authors.initials: EP
authors.lastname: Krenning
authors.forename: M
authors.initials: M
authors.lastname: de Jong
mesh_terms: D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology; D003404:Creatinine / Q000097:blood; D005215:Fasting / Q000097:blood / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008297:Male; D013974:Thyroxine / Q000097:blood / Q000378:metabolism* / Q000652:urine; D013997:Time Factors; D014284:Triiodothyronine / Q000097:blood / Q000378:metabolism* / Q000652:urine; D014527:Uric Acid / Q000097:blood / Q000652:urine
chemical_list: D005230:Fatty Acids, Nonesterified; D014284:Triiodothyronine; D014527:Uric Acid; D003404:Creatinine; D013974:Thyroxine