Effects of pretreatment with dexamethasone or levothyroxine sodium on endotoxin-induced alterations in glucose and insulin dynamics in horses.

The study aims to understand the impact of two different drugs, dexamethasone and levothyroxine sodium, on disruptions in glucose and insulin responses caused by endotoxins in horses. The researchers found that while both dexamethasone and hospitalization lowered insulin sensitivity, levothyroxine sodium seemed to prevent this reaction in response to endotoxin exposure.

Methodology

• Twenty-four horses were subjected to the study and were randomly assigned into three groups.
• One group was given 48 mg of levothyroxine mixed with 200 g of oats, another group received 20 mg of dexamethasone with oats, and the third (control) group was given oats alone.
• The treatment lasted for 15 days, after which, the horses were given an IV infusion of lipopolysaccharide, an endotoxin, at a dose of 20 ng/kg.
• Frequent IV glucose tolerance tests were conducted before the treatment, after treatment, and 20 hours following the endotoxin administration.
• The scientists also measured the area under the curve (AUC) for the plasma glucose and serum insulin concentrations and performed minimal model analyses.

Results

• The results demonstrated significant treatment-by-time effects on insulin sensitivity and glucose and insulin AUC.
• Insulin sensitivity decreased over time in all treatment groups, with the largest drop noticed in the dexamethasone group.
• The infusion of endotoxin reduced mean insulin sensitivity by 71% and 63% in the dexamethasone and control groups, respectively, but did not affect horses in the levothyroxine group.
• The lowest mean insulin sensitivity was noted in the dexamethasone group, however, the percentage reduction was the same in both dexamethasone and control groups.

Conclusions

• In all three groups, insulin sensitivity decreased during the pretreatment period, indicating that the hospitalization process itself interfered with glucose and insulin dynamics.
• The dexamethasone treatment notably diminished insulin sensitivity, and the condition of endotoxemia further intensified this insulin resistance.
• Contrary to dexamethasone, levothyroxine proved to prevent the endotoxin-induced drop in insulin sensitivity. Therefore it can potentially be used as a treatment against endotoxemia-related insulin resistance in horses.