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.