1. Biology of Incretins: GLP-1 and GIP
Laurie L. Baggio, Daniel J. Drucker 
Gastroenterology 
Volume 132, Issue 6, Pages (May 2007)
DOI: /j.gastro
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2. Figure 1
Structures of (A) the proglucagon gene, (B) mRNA, and (C) protein. (D) Tissue-specific posttranslational processing of proglucagon in the pancreas leads to the generation of Glicentin-related polypeptide (grpp), glucagon (gluc), intervening peptide-1 (ip-1), and major proglucagon fragment (mpgf), whereas glicentin, oxyntomodulin (oxm), intervening peptide-2 (ip-2), and GLP-1 and GLP-2 are liberated after proglucagon processing in the intestine and brain.
Gastroenterology  , DOI: ( /j.gastro )
Copyright © 2007 AGA Institute Terms and Conditions

3. Figure 2
Bioactive GLP-1(7-36)amide and GIP (1-42) are released from the small intestine after meal ingestion and enhance glucose-stimulated insulin secretion (incretin action). DPP-4 rapidly converts GLP-1 and GIP to their inactive metabolites GLP-1 (9-36) and GIP (3-42) in vivo. Inhibition of DPP-4 activity prevents GLP-1 and GIP degradation, thereby enhancing incretin action.
Gastroenterology  , DOI: ( /j.gastro )
Copyright © 2007 AGA Institute Terms and Conditions

4. Figure 3
GLP-1 actions in peripheral tissues. The majority of the effects of GLP-1 are mediated by direct interaction with GLP-1Rs on specific tissues. However, the actions of GLP-1 in liver, fat, and muscle most likely occur through indirect mechanisms.
Gastroenterology  , DOI: ( /j.gastro )
Copyright © 2007 AGA Institute Terms and Conditions

5. Figure 4
GLP-1R–dependent intracellular signal transduction pathways in the pancreatic β-cell. Although there is considerable overlap between pathways, the major effectors that couple GLP-1R activation to insulin secretion and biosynthesis (green), β-cell proliferation and neogenesis (blue), inhibition of apoptosis (red), and ER stress reduction (purple) are highlighted.
Gastroenterology  , DOI: ( /j.gastro )
Copyright © 2007 AGA Institute Terms and Conditions

6. Figure 5
(A) ProGIP gene, (B) mRNA, and (C) protein. Bioactive GIP is generated from its proGIP protein precursor by posttranslational cleavage at single arginine residues that flank GIP.
Gastroenterology  , DOI: ( /j.gastro )
Copyright © 2007 AGA Institute Terms and Conditions

7. Figure 6 GIP actions in peripheral tissues.
Gastroenterology  , DOI: ( /j.gastro )
Copyright © 2007 AGA Institute Terms and Conditions

8. Daniel J. Drucker, MD
Gastroenterology  , DOI: ( /j.gastro )
Copyright © 2007 AGA Institute Terms and Conditions