Defective amplification of the late phase insulin response to glucose by GIP in obese Type II diabetic patients.
OBJECTIVE
Glucagon-like-peptide-1 (GLP-1) is strongly insulinotropic in patients with Type II (non-insulin-dependent) diabetes mellitus, whereas glucose-dependent insulinotropic polypeptide (GIP) is less effective. Our investigation evaluated "early" (protocol 1) - and "late phase" (protocol 2) insulin and C-peptide responses to GLP-1 and GIP stimulation in patients with Type II diabetes.


METHODS
Protocol 1: eight Type II diabetic patients and eight matched healthy subjects received i.v. bolus injections of GLP-1(2.5 nmol) or GIP(7.5 nmol) concomitant with an increase of plasma glucose to 15 mmol/l. Protocol 2: eight Type II diabetic patients underwent a hyperglycaemic clamp (15 mmol/l) with infusion (per kg body weight/min) of either: 1 pmol GLP-1 (7-36) amide (n=8), 4 pmol GIP (n=8), 16 pmol GIP (n=4) or no incretin hormone (n=5). For comparison, six matched healthy subjects were examined.


RESULTS
Protocol 1: Type II diabetic patients were characterised by a decreased "early phase" response to both stimuli, but their relative response to GIP versus GLP-1 stimulation was exactly the same as in healthy subjects [insulin (C-peptide): patients 59+/-9% (74+/-6%) and healthy subjects 62+/-5% (71+/-9%)]. Protocol 2, "Early phase" (0-20 min) insulin response to glucose was delayed and reduced in the patients, but enhanced slightly and similarly by GIP and GLP-1. GLP-1 augmented the "late phase" (20-120 min) insulin secretion to levels similar to those observed in healthy subjects. In contrast, the "late phase" responses to both doses of GIP were not different from those obtained with glucose alone. Accordingly, glucose infusion rates required to maintain the hyperglycaemic clamp in the "late phase" period (20-120 min) were similar with glucose alone and glucose plus GIP, whereas a doubling of the infusion rate was required during GLP-1 stimulation.


CONCLUSIONS
Lack of GIP amplification of the late phase insulin response to glucose, which contrasts markedly to the normalising effect of GLP-1, could be a key defect in insulin secretion in Type II diabetic patients.
Department of Internal Medicine F, Gentofte Hospital, University of Copenhagen, Niels Andersens Vej 65, 2900 Hellerup, Denmark. tivi@gentoftehosp.kbhamt.dk
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Vilsbøll
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Krarup
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Madsbad
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Holst
D000368:Aged; D001786:Blood Glucose / Q000032:analysis; D002096:C-Peptide / Q000097:blood; D003920:Diabetes Mellitus / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D004357:Drug Synergism; D005260:Female; D005934:Glucagon / Q000008:administration & dosage / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D005947:Glucose / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D007004:Hypoglycemic Agents / Q000097:blood*; D007275:Injections, Intravenous; D007328:Insulin / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009765:Obesity; D010446:Peptide Fragments / Q000008:administration & dosage / Q000494:pharmacology*; D011498:Protein Precursors / Q000008:administration & dosage / Q000494:pharmacology*; D012016:Reference Values; D013997:Time Factors
D001786:Blood Glucose; D002096:C-Peptide; D007004:Hypoglycemic Agents; D007328:Insulin; D010446:Peptide Fragments; D011498:Protein Precursors; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D005947:Glucose