Effects of long-term oral administration of levothyroxine sodium on glucose dynamics in healthy adult horses.

The research investigates how long-term use of levothyroxine sodium (L-T(4)) impacts glucose dynamics in adult horses. It found that L-T(4) administration was associated with weight loss and increased insulin sensitivity (SI), indicating potential use in treating obesity and insulin resistance in horses.

Study Design and Methodology

• This study involved six healthy adult mares. The horses were given L-T(4) orally at a dose of 48 mg/day for 48 weeks.
• The frequently sampled intravenous glucose tolerance test procedures were carried out at 24-hour intervals before and at 16, 32, and 48 weeks during the treatment period.
• To analyze the obtained data, minimal model analysis was used. The repeatability of measurements was evaluated, to ensure the reliability of results.

Results

• As a result of L-T(4) treatment, the body weight of the horses significantly decreased from the pretreatment value. The mean weight decreased at weeks 16, 32, and 48 respectively.
• Compared to pretreatment findings, insulin sensitivity (SI) increased 1.8-, 2.4-, and 1.9-fold at weeks 16, 32, and 48 respectively. SI was found to be negatively correlated with body weight, i.e., as the body weight decreased, the insulin sensitivity increased.
• Glucose effectiveness also increased during the treatment period, and the acute insulin response to glucose decreased.
• The coefficients of variation for plasma glucose and serum insulin concentrations, as well as for SI, glucose effectiveness, and the acute insulin response to glucose, were calculated to assess the repeatability of results.

Conclusions

• The study concluded that long-term administration of L-T(4) was linked with weight loss and increased insulin sensitivity in adult euthyroid horses.
• However, it is important to note that other factors may have influenced the results, potentially confounding them.
• Nevertheless, levothyroxine sodium may be a promising solution for the treatment of obesity and insulin resistance in horses. Further studies are required to confirm these findings and determine optimal treatment plans.