Figure 1.

Glucagon-like peptide 1 (GLP-1) ligand and receptor system super-axis are shown. The expression of the ligand and receptor components of the GLP-1 system spans the whole human body. The repetitive expression of this GPCR system in multiple tissue types reinforces the importance of maintaining energy balance across the whole organism with an easily coordinated mechanism. The physical and hormonal connection between these multiple sites of GPCR functionality therefore can represent a “super-axis” of signaling connectivity that spreads across and over more classically defined tissue–tissue axes, such as the hypothalamic–pituitary– gonadotropic axis.