Effects of dexamethasone, glucose infusion, adrenocorticotropin, and propylthiouracil on plasma leptin concentrations in horses.

This study investigated how substances such as dexamethasone, glucose infusion, adrenocorticotropin, and propylthiouracil affect the plasma leptin concentrations in horses, concluding that each treatment resulted in increased levels of leptin.

Introduction and Methodology

• The study was conducted using a set of experiments on light horse geldings and mares, treated with different substances and conditions to study their effects on plasma leptin concentrations.
• In the first experiment, nine geldings were subjected to treatments using dexamethasone (DEX), glucose, or no substances (control) for a duration of four days.
• The second experiment mirrored the first except that the subjects were mares and some received vehicle apart from DEX.
• The third experiment involved six geldings being treated with adrenocorticotropin (ACTH) or vehicle twice daily for four days.
• In the fourth experiment, plasma samples from four stallions fed with 6-n-propyl-2-thiouracil (PTU) were compared to control samples over a 60 day period to induce hypothyroidism.

Results

• DEX and glucose treatments resulted in significantly increased glucose, insulin, and leptin concentrations in both geldings and mares.
• Interestingly, an increase in IGF-I concentrations, albeit delayed, was observed after DEX treatment, suggesting a possible link between DEX and IGF-I.
• ACTH treatment resulted in increased levels of cortisol, glucose, insulin, and leptin. While the cortisol increase was significant, the increase in glucose, insulin, and leptin was lesser.
• In the fourth experiment, stallions fed with PTU showed lower concentrations of thyroxine and triiodothyronine, but higher concentrations of TSH. This hinted towards an induced hypothyroidism state. Leptin concentrations were also significantly higher in these stallions from day 10 to 52.

Conclusion

• The study concluded that leptin levels in the plasma of horses were increased when administered with DEX, ACTH, or induced hypothyroidism conditions using PTU feeding.
• However, the increase in leptin concentrations was found to be lesser in horses treated with ACTH or PTU when compared to DEX treatment.
• This suggests that these substances and conditions have the potential to influence the leptin concentrations in horses, thus opening up future research areas around these findings and their implications.