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Increased awareness of metabolic disorders in horses has brought new lingo into the industry. Quite frankly, some of it can be confusing to horse owners trying to do what’s best for their horses. Case in point: insulin dysregulation and insulin resistance. Are these terms synonymous?

Let’s begin with insulin. “The hormone insulin is secreted systemically in response to elevated blood glucose and is used to control blood glucose concentrations in the blood and glucose utilization in the body,” said Laura Petroski, B.V.M.S., a veterinarian at Kentucky Equine Research. “Insulin communicates with cells, via receptors, to facilitate glucose uptake into the cells.”

Insulin dysregulation is abnormal insulin metabolism in response to a normal physiologic process, such as eating. “Simply put, insulin is released in response to circulating glucose molecules stimulating receptors on the membranes of pancreatic cells,” explained Petroski. Beta cells of the pancreas release insulin in response to this stimulation, and gastric-emptying signals and small intestine signals also promote insulin secretion.

Excessive insulin release occurs in insulin resistance, beta-cell hyperplasia (unusual increase in volume of normal pancreatic cells that produce insulin), insulinoma (pancreatic tumor that generates insulin), and liver damage. Liver disease could result in hyperinsulinemia, or excessive insulin, as the liver is responsible for removing insulin from the bloodstream. Certain hormones, like incretin and glucagon, also accelerate insulin secretion from the pancreas, so hormonal imbalances could affect insulin secretion.

In short, any abnormality in insulin metabolism can be referred to as insulin dysregulation, and is therefore an important element of equine metabolic syndrome, said Petroski.

In regard to insulin resistance, cells become less sensitive to insulin, thus resulting in impaired glucose uptake, increased release of glucose from the liver, and increased levels of fatty acids in the blood. Certain structures are affected by this more than others, such as the liver, skeletal muscle, and fat cells.

“When cells become resistant to insulin, more insulin is secreted in order to keep blood glucose concentrations within normal limits. In severe cases, insulin is ineffective in clearing glucose from the blood, and glucose remains abnormally high. Prolonged hyperinsulinemia influences long-term health,” explained Petroski.

Particular attention has been paid to the fact that pastured horses can eat nearly continuously and thus may be secreting insulin constantly. Near-constant secretion of insulin could cause horses to develop some level of insulin resistance during their lifetime. In horses with a genetic predisposition to high insulin secretion, insulin resistance would raise these insulin levels further.

Frank, N., and E.M. Tadros. 2014. Insulin dysregulation. Equine Veterinary Journal 46:103-112.

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