Insulin Resistance and Sensitivity, Causes and Management

Insulin sensitivity and insulin resistance in horses have become increasingly important areas of research in equine medicine over the past several years, as evidenced by the timely and popular presentations at this year's American College of Veterinary Internal Medicine (ACVIM) Forum, held June 4-7 in San Antonio, Texas.

Rebecca Carter, a PhD candidate from Virginia Tech, and co-author of the research abstract, "Increased adiposity in horses is associated with decreased insulin sensitivity but unchanged inflammatory cytokine expression in subcutaneous adipose tissue," described their study of obesity, insulin sensitivity, and inflammation in horses.

Researchers fed 12 Arabian geldings 200% of their energy requirements for four months to induce weight gain. Various parameter evaluating adiposity, glucose, and insulin dynamics, and inflammation were assessed before and after weight gain.

At the end of the study, body weight, subcutaneous fat, resting insulin levels, and insulin responses were all significantly increased while insulin sensitivity was significantly decreased. No changes in the expression of the measured markers of inflammation were noted.

Together, these results indicate that overweight horses have decreased insulin sensitivity and experience a compensatory increase in insulin secretion.

In the abstract, "Effects of pretreatment with dexamethasone or levothyroxine on endotoxin-induced insulin resistance in horses," Ferenc Toth, DVM, PhD and colleagues evaluated whether resting insulin sensitivity could affect the degree of insulin resistance caused by endotoxins. Endotoxemia, which is caused by release of toxins produced by gram negative bacteria (such as Escherichia coli), is associated with laminitis and is a life-threatening condition in horses.

Twenty adult mares were included in the study and randomly divided into the control (n=8), dexamethasone pre-treatment (n=4), or the levothyroxine pre-treatment group (n=8). While 14 days of dexamethasone administration exacerbated insulin resistance and potentially decreased insulin sensitivity, 14 days of levothyroxine treatment prevented the endotoxin-induced insulin resistance.

Toth explained that together, these results suggest that insulin resistant horses that develop endotoxemia might experience marked alterations in insulin sensitivity, but vets might be able to reduce these changes with levothyroxine pretreatment.

Research in the field of insulin sensitivity and resistance is ongoing.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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