Following the induction of IR, administration of metformin was associated with significant differences in peak glucose concentration (P<0.001), the percentage increase in glucose concentration (P = 0.010), the area under the glucose curve (P<0.001) and insulin concentration at 120min (P = 0.034) and 150min after dextrose administration (P = 0.014). Conclusions: Metformin resulted in reduced glycaemic and insulinaemic responses both in healthy horses and in horses with experimentally induced IR. Potential relevance: Metformin may benefit horses with naturally acquired IR by reducing glycaemic and insulinaemic responses to dietary nonstructural carbohydrates. Further investigations into the mechanisms of action of metformin in horses and controlled clinical trials are warranted.Reasons for performing study: Metformin is a potential therapeutic agent for the treatment of insulin resistance (IR). In laboratory animals, orally administered metformin reduces intestinal glucose absorption and may therefore affect insulinaemic responses to oral carbohydrate ingestion. Objectives: To determine whether pretreatment with metformin reduces plasma glucose concentration and insulin responses following consumption of dextrose in horses. Study design: Therapeutic cross-over study. Methods: Seven healthy Standardbred and Thoroughbred geldings were subjected to an oral dextrose challenge test on 4 occasions: with and without metformin, before and after induction of IR with dexamethasone. Metformin was administered by nasogastric tube at 30mg/kgbwt 1h before administration of dextrose. Glucose and insulin concentrations in plasma/serum were measured at regular intervals during each test. Linear mixed models were specified for each predetermined outcome variable, and for each model the 'treatment' was included as a fixed effect with 4 categorical levels (none, metformin, dexamethasone and dexamethasone with metformin) and horse accounted for as a random effect. Results: In healthy horses, the administration of metformin resulted in a statistically significant reduction in peak glucose concentration (P = 0.002), area under the glucose curve (P<0.001) and insulin concentration 120min after dextrose administration (P = 0.011).
Rendle, D., Rutledge, F., Hughes, K., Heller, J., & Durham, A. (2013). Effects of metformin hydrochloride on blood glucose and insulin responses to oral dextrose in horses. Equine Veterinary Journal, 45(6), 751-754. https://doi.org/10.1111/evj.12068