GIP Does Not Potentiate the Antidiabetic Effects of GLP-1 in Hyperglycemic Patients With Type 2 Diabetes

  1. Michael A. Nauck1
  1. 1Diabeteszentrum Bad Lauterberg, Bad Lauterberg im Harz, Germany
  2. 2Department of Biomedical Sciences, Panum Institute, Copenhagen, Denmark
  3. 3Department of Clinical Therapeutics, University of Athens Medical School, Athens, Greece
  4. 4Medizinische Klinik I, St. Josef-Hospital, Klinikum der Ruhr-Universität Bochum, Bochum, Germany
  1. Corresponding author: Michael A. Nauck, nauck{at}diabeteszentrum.de.
  1. N.M. and I.V. contributed equally to this study.

Abstract

OBJECTIVE The incretin glucagon-like peptide 1 (GLP-1) exerts insulinotropic activity in type 2 diabetic patients, whereas glucose-dependent insulinotropic polypeptide (GIP) no longer does. We studied whether GIP can alter the insulinotropic or glucagonostatic activity of GLP-1 in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS Twelve patients with type 2 diabetes (nine men and three women; 61 ± 10 years; BMI 30.0 ± 3.7 kg/m2; HbA1c 7.3 ± 1.5%) were studied. In randomized order, intravenous infusions of GLP-1(7-36)-amide (1.2 pmol · kg−1 · min−1), GIP (4 pmol · kg−1 · min−1), GLP-1 plus GIP, and placebo were administered over 360 min after an overnight fast (≥1 day wash-out period between experiments). Capillary blood glucose, plasma insulin, C-peptide, glucagon, GIP, GLP-1, and free fatty acids (FFA) were determined.

RESULTS Exogenous GLP-1 alone reduced glycemia from 10.3 to 5.1 ± 0.2 mmol/L. Insulin secretion was stimulated (insulin, C-peptide, P < 0.0001), and glucagon was suppressed (P = 0.009). With GIP alone, glucose was lowered slightly (P = 0.0021); insulin and C-peptide were stimulated to a lesser degree than with GLP-1 (P < 0.001). Adding GIP to GLP-1 did not further enhance the insulinotropic activity of GLP-1 (insulin, P = 0.90; C-peptide, P = 0.85). Rather, the suppression of glucagon elicited by GLP-1 was antagonized by the addition of GIP (P = 0.008). FFA were suppressed by GLP-1 (P < 0.0001) and hardly affected by GIP (P = 0.07).

CONCLUSIONS GIP is unable to further amplify the insulinotropic and glucose-lowering effects of GLP-1 in type 2 diabetes. Rather, the suppression of glucagon by GLP-1 is antagonized by GIP.

Footnotes

    • Received September 18, 2010.
    • Accepted January 7, 2011.

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    1. Diabetes vol. 60 no. 4 1270-1276
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