The aim of the current study was to identify
associations between pituitary lesions, body condition scores, and mesenteric
lipomas in horses with insulin resistance. Necropsy examinations were performed
following euthanasia in 30 adult horses designated as insulin resistant (n =
11) or insulin sensitive (n = 19). Insulin sensitivity was determined using the
insulin-modified frequently sampled intravenous glucose tolerance test and
resting insulin concentrations. At necropsy, mesenteric lipomas were measured.
The pituitary and adrenal glands, pancreas, and liver were evaluated
histologically; pituitary glands were scored based on published criteria.
Insulin-resistant horses had significantly higher pituitary scores (p = 0.0035)
and body condition scores (p = 0.0001), even when adjusting for age, and a
greater frequency of mesenteric lipomas (p = 0.014) and greater lipoma area (p
= 0.0332) than insulin-sensitive horses. Regardless of insulin status, horses
with pituitary scores ≥3 (diffuse hyperplasia; n = 25) had higher body
condition scores (p = 0.0313) and a greater frequency of mesenteric lipomas (p
< 0.0002) than those with lower pituitary scores. High body condition score
was not correlated to an increased frequency of mesenteric lipomas. Detection
of higher pituitary scores in insulin-resistant horses suggested an association
between insulin resistance and pituitary morphology. Horses in the
insulin-resistant group and those with high pituitary scores had higher body
condition scores and a greater frequency of mesenteric lipomas. These horses might
be at increased risk for lipoma-associated colic.
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