How Oxyntomodulin Burns Calories: It's the Glucagon Receptor, Not GLP-1

Animal study in rats using a sustained-release oxyntomodulin analogue (OX-SR). Energy expenditure was measured by indirect calorimetry (oxygen consumption). The GLP-1 receptor was blocked using Exendin 9-39 to test whether energy expenditure still occurred. Separately, glucagon receptor activity was eliminated to test whether it was required. This receptor-specific blocking approach allowed researchers to dissect which receptor drives each metabolic effect.

Oxyntomodulin is a natural gut hormone that activates both GLP-1 and glucagon receptors — making it a natural 'dual agonist.' This study is critical for drug design because it shows that the two receptors contribute different benefits: GLP-1 for appetite suppression, glucagon for increased energy expenditure. Drugs like survodutide and other GLP-1/glucagon dual agonists in development are designed based on this principle, and this study provides the mechanistic proof for why balancing both receptor activities matters.

This study provides the scientific rationale for the 'dual agonist' drug development strategy that has produced some of the most promising obesity drugs in the pipeline — including survodutide (GLP-1/glucagon) and retatrutide (GLP-1/GIP/glucagon). By understanding that GLP-1 and glucagon receptors contribute different weight-loss mechanisms, drug developers can fine-tune the ratio of receptor activities to maximize both appetite suppression and calorie burning while minimizing glucagon's side effects (like raising blood sugar).

Rat study — the receptor pharmacology may not translate identically to humans. The specific OX-SR analogue used is a research tool, not a clinical drug candidate. The study focused on energy expenditure and did not measure appetite or food intake effects in parallel. Glucagon receptor activation also carries risks (e.g., hepatic glucose output), which were not assessed in this short-term study.