Active metabolite of GLP-1 mediates myocardial glucose uptake and improves left ventricular performance in conscious dogs with dilated cardiomyopathy

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Abstract
We have shown previously that the glucagon-like peptide-1 (GLP-1)-(7–36) amide increases myocardial glucose uptake and improves left ventricular (LV) and systemic hemodynamics in both conscious dogs with pacing-induced dilated cardiomyopathy (DCM) and humans with LV systolic dysfunction after acute myocardial infarction. However, GLP-1-(7–36) is rapidly degraded in the plasma to GLP-1-(9–36) by dipeptidyl peptidase IV (DPP IV), raising the issue of which peptide is the active moiety. By way of methodology, we compared the efficacy of a 48-h continuous intravenous infusion of GLP-1-(7–36) (1.5 pmol·kg−1·min−1) to GLP-1-(9–36) (1.5 pmol·kg−1·min−1) in 28 conscious, chronically instrumented dogs with pacing-induced DCM by measuring LV function and transmyocardial substrate uptake under basal and insulin-stimulated conditions using hyperinsulinemic-euglycemic clamps. As a result, dogs with DCM demonstrated myocardial insulin resistance under basal and insulin-stimulated conditions. Both GLP-1-(7–36) and GLP-1-(9–36) significantly reduced ( P < 0.01) LV end-diastolic pressure [GLP-1-(7–36), 28 ± 1 to 15 ± 2 mmHg; GLP-1-(9–36), 29 ± 2 to 16 ± 1 mmHg] and significantly increased ( P < 0.01) the first derivative of LV pressure [GLP-1-(7–36), 1,315 ± 81 to 2,195 ± 102 mmHg/s; GLP-1-(9–36), 1,336 ± 77 to 2,208 ± 68 mmHg] and cardiac output [GLP-1-(7–36), 1.5 ± 0.1 to 1.9 ± 0.1 l/min; GLP-1-(9–36), 2.0 ± 0.1 to 2.4 ± 0.05 l/min], whereas an equivolume infusion of saline had no effect. Both peptides increased myocardial glucose uptake but without a significant increase in plasma insulin. During the GLP-1-(9–36) infusion, negligible active (NH2-terminal) peptide was measured in the plasma. In conclusion, in DCM, GLP-1-(9–36) mimics the effects of GLP-1-(7–36) in stimulating myocardial glucose uptake and improving LV and systemic hemodynamics through insulinomimetic as opposed to insulinotropic effects. These data suggest that GLP-1-(9–36) amide is an active peptide.

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