Glucagon increases plasma levels of cyclic AMP responses in mice and humans, and this may be independent of MASLD

Glucagon resistance impairs amino acid metabolism in individuals with metabolic dysfunction-associated steatotic liver disease (MASLD), but the underlying mechanism remains unclear. Given that glucagon mediates its effects through cyclic adenosine monophosphate (cAMP), impaired cAMP responses have been proposed as the molecular center of glucagon resistance. In this study, we investigated if the glucagon-induced cAMP response is impaired by metabolic dysfunction, thereby contributing to glucagon resistance. Plasma cAMP responses to an intravenous bolus injection of glucagon were analyzed in 64 individuals with or without MASLD and type 1 diabetes. In parallel, hepatic cAMP secretion during glucagon stimulation was determined using in situ liver perfusion in lean and diet-induced obese (DIO) mice with hepatic steatosis. Participants with obesity and MASLD showed higher baseline plasma cAMP, but neither glucagon, insulin, steatosis, nor BMI could explain this. Across all groups, glucagon-induced cAMP responses were similar. Similarly, DIO mice displayed preserved hepatic cAMP release in response to glucagon compared with lean controls. These findings suggest that the glucagon-induced cAMP response is maintained in MASLD independently of insulin. Thus, hepatic glucagon resistance in MASLD may be due to non-cAMP-dependent signaling.<b>NEW & NOTEWORTHY</b> Here, we investigate the molecular cause for hepatic glucagon resistance in MASLD. We demonstrate that cAMP responses to glucagon are preserved in both humans and mice with liver steatosis, suggesting that the defect lies downstream of cAMP production. These findings redefine the understanding of glucagon resistance and point toward alternative mechanisms beyond second messenger activation.