title: Effect of chronic metabolic acidosis on thyroid hormone homeostasis in humans.
abstract: The effects of metabolic acidosis on thyroid function are unknown. We investigated the effects of chronic extrarenal acidosis on the hypothalamic-pituitary-thyroid axis. Chronic metabolic acidosis was induced by administering NH4Cl (4.2 mmol.kg body wt-1.day-1) to six normal male volunteers during metabolic balance conditions. Plasma bicarbonate concentration decreased from 25.0 +/- 0.4 to 15.5 +/- 0.9 mmol/l (P < 0.001). Metabolic acidosis significantly decreased serum-free 3,5,3'-triiodothyronine (T3) concentrations from 373 +/- 18 (control) to 251 +/- 13 pg/dl (P < 0.001) and decreased serum-free L-thyroxine (T4) from 1.55 +/- 0.42 to 1.25 +/- 0.37 ng/dl (P < 0.002), whereas serum total reverse T3 did not change significantly. Consequently, the reverse T3-to-free T4 ratio increased. Serum thyroid-stimulating hormone (TSH) levels increased significantly from 0.70 +/- 0.07 during control to 1.30 +/- 0.12 mU/l during acidosis (P < 0.003). The TSH response to thyrotropin (TRH, 2 mg intranasally) was exaggerated in acidosis: the partial area under the concentration curve for the TSH response (210 min post-TRH) was 902 +/- 167 during control compared with 1.394 +/- 209 mU.min.l-1 during acidosis (P = 0.0139). Chronic metabolic acidosis, as produced by the model employed here, induces a decrease in thyroid hormone secretion and might exert additional effects on thyroid hormone metabolism in humans. The acidosis-induced decrease in thyroid function might modulate some of the reported effects of metabolic acidosis, such as on nitrogen balance, protein synthesis, lean body mass, insulin-like growth factor I levels, renal acidification, and cardiac contractile function.
authors.affiliation: Klinik B für Innere Medizin, Kantonsspital, St. Gallen, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Brüngger
authors.forename: H N
authors.initials: HN
authors.lastname: Hulter
authors.forename: R
authors.initials: R
authors.lastname: Krapf
mesh_terms: D000138:Acidosis / Q000378:metabolism*; D000643:Ammonium Chloride / Q000494:pharmacology; D001835:Body Weight; D002908:Chronic Disease; D003404:Creatinine / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D013961:Thyroid Gland / Q000503:physiopathology*; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014882:Water-Electrolyte Balance
chemical_list: D013963:Thyroid Hormones; D000643:Ammonium Chloride; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D003404:Creatinine