Equine intravenous glucose tolerance test: glucose and insulin responses of healthy horses fed grain or hay and of horses with pituitary adenoma.

This study explores the glucose and insulin responses in healthy horses, those fed with different diets and horses diagnosed with pituitary adenoma using an intravenous glucose tolerance test. It reveals that horses with pituitary adenomas demonstrate decreased tissue sensitivity to insulin, resting hyperglycemia and a slow return of glucose levels to baseline.

Research Objective

• The research aimed to characterise and compare the glucose and insulin responses to an intravenous glucose tolerance test among three different groups of horses.

Methodology

• The intravenous glucose tolerance test was administered to three different groups of horses – one group who were fed with hay (5 horses), another group with a diet of hay supplemented with grain (5 horses), and a group diagnosed with pituitary adenoma (10 horses).

Findings

• Healthy horses showed a rapid increase in plasma glucose levels following an intravenous glucose injection, and the levels returned to their baseline within an hour.
• The horses diagnosed with pituitary adenoma demonstrated resting hyperglycemia, which is unusually high levels of glucose in the blood while at rest and a delay in the return of blood glucose levels to the base line, taking about 3 hours for the levels to normalise.
• The same group of horses also displayed hyperinsulinemia, or abnormally high levels of insulin in the blood, and a non-significant reaction to the glycemic stimulus with insulin levels decreasing gradually to the base line. This indicates a reduced tissue sensitivity to insulin in these horses.
• Further evidence for the reduced insulin sensitivity is found in the protracted glucose and insulin curves and the initial decrease in the ratio of insulin to glucose following acute IV glucose loading, suggesting a secretory deficiency in insulin response among the horses diagnosed with pituitary adenoma.