Validation of a low-dose ACTH stimulation test in healthy adult horses.

The research article describes an evaluation study undertaken to identify the smallest dose of ACTH (cosyntropin) that could cause a significant increase in serum cortisol level in healthy adult horses, and the time at which the cortisol concentration peaks.

Understanding the Study

In this study, the researchers sought to find out the lowest dose of ACTH, a hormone that effectively stimulates the adrenal glands to produce cortisol, that would induce the maximal increase in serum cortisol concentration (the amount of cortisol present in the blood) in healthy adult horses.

• The study involved a total of 8 adult horses, each of which received 5 treatments.
• Four different doses (0.02, 0.1, 0.25, and 0.5 μg/kg) of cosyntropin, a synthetic form of ACTH, or a saline solution were injected into each horse.
• The amount of cortisol in the horse’s blood was then measured at various intervals over a period of 240 minutes post-injection.
• The researchers also conducted complete blood counts (CBCs) at specific times following the injection.

Results of the Study

The results showed a significant increase in serum cortisol concentration as early as 30 minutes after the administration of all doses of cosyntropin, as compared to the baseline values.

• The maximum increase in serum cortisol concentration was triggered by the administration of doses of 0.1, 0.25, and 0.5 μg/kg, and there were no significant differences among the outcomes produced by these dosages.
• The cortisol concentration reached its peak 30 minutes after the administration of 0.02 or 0.1 μg/kg doses, with the peak concentrations being 1.5 and 1.9 times the baseline concentrations, respectively.
• The cortisol concentration peaked 90 minutes after the administration of 0.25 or 0.5 μg/kg doses, with peak concentrations being 2.0 and 2.3 times the baseline concentrations, respectively.
• The administration of cosyntropin significantly influenced white blood cell (WBC), neutrophil, and eosinophil counts, as well as the neutrophil-to-lymphocyte ratio.

Conclusion

The findings of this research suggested that in healthy horses, an administration of cosyntropin at a dose of 0.1 μg/kg creates maximum adrenal stimulation, with the peak cortisol concentration occurring 30 minutes after injection. These outcomes are valuable in providing a better understanding of cosyntropin dosing for veterinary use in horses.