Effects of endotoxaemia and carbohydrate overload on glucose and insulin dynamics and the development of laminitis in horses.

Abstract

REASONS FOR PERFORMING STUDY: Insulin resistance (IR) is a risk factor for pasture-associated laminitis in equids and alimentary carbohydrate overload may trigger laminitis. Whether glucose metabolism responses to carbohydrate overload are more pronounced in insulin-resistant horses requires further study. HYPOTHESIS: Horses pretreated with endotoxin to alter insulin sensitivity differ significantly in their glucose and insulin responses to carbohydrate overload. METHODS: Horses (n=24) were divided into 3 groups. A lipopolysaccharide (LPS; n=8) group that received endotoxin as an 8 h 7.5 ng/kg bwt/h i.v. continuous rate infusion, an oligofructose (OF; n=8) group that received an infusion of saline followed by 5 g/kg bwt OF via nasogastric intubation, and a LPS/OF (n=8) group that received LPS followed 16 h later by OF. Glucose and insulin dynamics were evaluated at -24 h and 48 h using the frequently sampled i.v. glucose tolerance test and minimal model analysis. Physical examinations and haematology were performed and the severity of laminitis assessed. RESULTS: Horses receiving LPS developed leucopenia and both LPS and OF induced clinical signs consistent with systemic inflammation. Insulin sensitivity significantly decreased (P < 0.001) over time, but responses did not differ significantly among groups. Time (P < 0.001) and treatment x time (P = 0.038) effects were detected for the acute insulin response to glucose, with mean values significantly increasing in LPS and LPS/OF groups, but not the OF group. Five horses in the LPS/OF group developed clinical laminitis compared with 0 and 2 horses in the LPS and OF groups, respectively. CONCLUSIONS: Endotoxaemia and carbohydrate overload reduce insulin sensitivity in horses. Endotoxin pretreatment does not affect the alterations in glucose metabolism induced by carbohydrate overload. POTENTIAL RELEVANCE: Insulin sensitivity decreases after carbohydrate overload in horses, which may be relevant to the development of pasture-associated laminitis.