Short-term effect of ovariectomy on measures of insulin sensitivity and response to dexamethasone administration in horses.

The research at hand investigates the impact of ovariectomy (removal of ovaries) on insulin sensitivity in horses, and whether this process affects the responses of the hypothalamo-pituitary-adrenal (HPA) axis to suppression.

Methodology

The study included six health mares. Several tests were carried out before and after the mares underwent an ovariectomy, including:

• An IV glucose tolerance test (IVGTT), which measures how fast glucose is cleared from the blood.
• An insulin sensitivity test, which investigates the body’s response to insulin.
• A dexamethasone suppression test, a procedure to assess adrenal gland function by measuring how cortisol levels change in response to an injection of dexamethasone.

Other variables, such as body weight, serum cortisol levels, plasma ACTH concentrations, serum insulin-to-blood glucose concentration ratios, and the shifts in blood glucose concentration following glucose or insulin injection, were also evaluated.

Results

The study found that while a dexamethasone injection led to a decrease in serum cortisol concentration in all horses, this did not differ noticeably before and after the ovariectomy. Similarly, the researchers discovered that plasma ACTH concentrations were within the normal range both prior to and after the surgery.

The results of the IVGTT were deemed normal for all horses both before and after the procedure. Further, no substantial difference was observed in factors such as basal blood glucose concentration or the time needed to return to baseline glucose concentration after the IV glucose test. Basal serum insulin concentration, as well as serum insulin-to-blood glucose concentration ratios, did not vary significantly either. Similarly, the average time it took to achieve a 50% reduction in blood glucose concentration following an insulin injection remained unchanged.

Conclusions

Based on these findings, the study concluded that ovariectomy in horses does not appear to alter responses to dexamethasone or modify short-term measures of insulin sensitivity. This suggests that mares that undergo ovariectomy are not at an increased risk of developing equine metabolic syndrome or dysfunction in the HPA axis. These are positive results from a veterinary health perspective, as they suggest such procedures do not negatively impact key metabolic or hormonal functions in horses.