GCG and aortic stenosis: Further, the total concentrations of GLP-1 reported (non-diabetic; 23.3 ± 3.2 pmol/l, diabetic; 48 ± 4.5 pmol/l) are in agreement with a rapid degradation of the peptide and only approximately 10–15% of intact GLP-1 reaching the circulation A comparison of fasting plasma GLP-1 levels between diabetic and non-diabetic patients with disease of the aortic valve [aortic stenosis or aortic insufficiency (AI)] revealed significantly higher levels of fasting plasma total and active GLP-1 in diabetic subjects as compared to non-diabetic subjects (Fig. 1a, b).