title: Effect of hypothyroidism on insulin sensitivity and glucose tolerance in dogs.
abstract: OBJECTIVE
  To determine the effects of hypothyroidism on insulin sensitivity, glucose tolerance, and concentrations of hormones counter-regulatory to insulin in dogs.
  
  
  METHODS
  8 anestrous mixed-breed bitches with experimentally induced hypothyroidism and 8 euthyroid control dogs.
  
  
  METHODS
  The insulin-modified frequently sampled IV glucose tolerance test and minimal model analysis were used to determine basal plasma insulin and glucose concentrations, acute insulin response to glucose, insulin sensitivity, glucose effectiveness, and disposition index. Growth hormone response was assessed by stimulation and suppression tests. Additionally, basal serum growth hormone (GH) and insulin-like growth factor-1 (IGF-1) concentrations and urine cortisol-to-creatinine concentration ratios were measured and dual energy x-ray absorptiometry was performed to evaluate body composition.
  
  
  RESULTS
  Insulin sensitivity was lower in the hypothyroid group than in the euthyroid group, whereas acute insulin response to glucose was higher. Glucose effectiveness and disposition index were not different between groups. Basal serum GH and IGF-1 concentrations as well as abdominal fat content were high in hypothyroid dogs, but urine cortisol-to-creatinine concentration ratios were unchanged.
  
  
  CONCLUSIONS
  Hypothyroidism appeared to negatively affect glucose homeostasis by inducing insulin resistance, but overall glucose tolerance was maintained by increased insulin secretion in hypothyroid dogs. Possible factors affecting insulin sensitivity are high serum GH and IGF-1 concentrations and an increase in abdominal fat. In dogs with diseases involving impaired insulin secretion such as diabetes mellitus, concurrent hypothyroidism can have important clinical implications.
authors.affiliation: Department of Small Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Natalie
authors.initials: N
authors.lastname: Hofer-Inteeworn
authors.forename: David L
authors.initials: DL
authors.lastname: Panciera
authors.forename: William E
authors.initials: WE
authors.lastname: Monroe
authors.forename: Korinn E
authors.initials: KE
authors.lastname: Saker
authors.forename: Rebecca Hegstad
authors.initials: RH
authors.lastname: Davies
authors.forename: Kent R
authors.initials: KR
authors.lastname: Refsal
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Kemnitz
mesh_terms: D015502:Absorptiometry, Photon; D000818:Animals; D001786:Blood Glucose; D001823:Body Composition; D004283:Dog Diseases / Q000209:etiology*; D004285:Dogs; D005260:Female; D018149:Glucose Intolerance / Q000209:etiology / Q000662:veterinary*; D013006:Growth Hormone / Q000378:metabolism / Q000494:pharmacology; D006854:Hydrocortisone / Q000652:urine; D007037:Hypothyroidism / Q000139:chemically induced / Q000150:complications / Q000662:veterinary*; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007457:Iodine Radioisotopes / Q000633:toxicity
chemical_list: D001786:Blood Glucose; D007328:Insulin; D007457:Iodine Radioisotopes; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D006854:Hydrocortisone