title: Glucose-dependent insulinotropic polypeptide: a bifunctional glucose-dependent regulator of glucagon and insulin secretion in humans.
abstract: OBJECTIVE
  To evaluate the glucose dependency of glucose-dependent insulinotropic polypeptide (GIP) effects on insulin and glucagon release in 10 healthy male subjects ([means ± SEM] aged 23 ± 1 years, BMI 23 ± 1 kg/m(2), and HbA(1c) 5.5 ± 0.1%).
  
  
  METHODS
  Saline or physiological doses of GIP were administered intravenously (randomized and double blinded) during 90 min of insulin-induced hypoglycemia, euglycemia, or hyperglycemia.
  
  
  RESULTS
  During hypoglycemia, GIP infusion caused greater glucagon responses during the first 30 min compared with saline (76 ± 17 vs. 28 ± 16 pmol/L per 30 min, P < 0.008), with similar peak levels of glucagon reached after 60 min. During euglycemia, GIP infusion elicited larger glucagon responses (62 ± 18 vs. -11 ± 8 pmol/L per 90 min, P < 0.005). During hyperglycemia, comparable suppression of plasma glucagon (-461 ± 81 vs. -371 ± 50 pmol/L per 90 min, P = 0.26) was observed with GIP and saline infusions. In addition, during hyperglycemia, GIP more than doubled the insulin secretion rate (P < 0.0001).
  
  
  CONCLUSIONS
  In healthy subjects, GIP has no effect on glucagon responses during hyperglycemia while strongly potentiating insulin secretion. In contrast, GIP increases glucagon levels during fasting and hypoglycemic conditions, where it has little or no effect on insulin secretion. Thus, GIP seems to be a physiological bifunctional blood glucose stabilizer with diverging glucose-dependent effects on the two main pancreatic glucoregulatory hormones.
authors: Diabetes Research Division, Department of Internal Medicine F, Gentofte Hospital, Copenhagen, Denmark. mch@dadlnet.dk
authors: Mikkel
authors: M
authors: Christensen
authors: Louise
authors: L
authors: Vedtofte
authors: Jens J
authors: JJ
authors: Holst
authors: Tina
authors: T
authors: Vilsbøll
authors: Filip K
authors: FK
authors: Knop
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000187:drug effects*; D005749:Gastric Inhibitory Polypeptide / Q000008:administration & dosage / Q000494:pharmacology*; D005934:Glucagon / Q000378:metabolism*; D006801:Humans; D006943:Hyperglycemia / Q000097:blood / Q000139:chemically induced / Q000378:metabolism; D007003:Hypoglycemia / Q000097:blood / Q000139:chemically induced / Q000378:metabolism; D007276:Injections, Intraventricular; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008297:Male; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D007328:Insulin; D005749:Gastric Inhibitory Polypeptide; D005934:Glucagon