Tirzepatide increased force of contraction in the isolated human atrium

Tirzepatide is an approved drug that is used to treat type 2 diabetes. Tirzepatide is a peptide comprised of 39 amino acids and activates glucose-dependent insulinotropic polypeptide receptors (GIPR) and glucagon-like peptide-1 receptors (GLP-1R). Via GIPR and GLP-1R, tirzepatide stimulated in cell culture adenylyl cyclases (AC) and thereby elevated the cellular content of 3':5' cyclic adenosine monophosphate (cAMP). We tested the hypothesis that tirzepatide augmented the force of contraction (FOC) in isolated electrically driven (1 Hz) human right atrial preparations (HAP) obtained during open heart surgery from adult patients. Cumulatively applied tirzepatide, starting at nanomolar concentrations, raised FOC in a concentration-dependent manner and a time-dependent manner (p < 0.05). The positive inotropic effects (PIE) of tirzepatide were attenuated by about a quarter by a GIPR antagonist (100 nM, Pro3-GIP) and by about three quarters by a GLP-1R antagonist (100 nM, exendin9-39) in HAP. Tirzepatide (1 µM) was less effective than 1 µM isoprenaline in raising FOC in HAP. The inhibitor of the cAMP-dependent protein kinase called H89 reversed the PIE of tirzepatide. We suggest that tirzepatide probably acts via stimulation of GIPR and GLP-1R to exert a PIE in HAP.