Hypothalamic-pituitary-adrenal axis function in pony foals after neonatal ACTH-induced glucocorticoid overexposure.

The research investigates the effects of overexposure to glucocorticoids, induced by ACTH, in the early life of foals on their hypothalamic-pituitary-adrenal axis, revealing that it does not notably affect the programming of the HPA axis function at 13 weeks, indicating that stressful conditions that raise plasma cortisol concentrations in early life are less likely to program cardiovascular and metabolic function in the short term in horses.

Research Methodology

• The test involved the use of foals as test subjects, which were separated into two groups. For a period of five days starting from Day 1, one group received saline (n = 9) while the other group received a long-acting ACTH treatment (n = 6).
• The purpose of the ACTH injection was to increase endogenous cortisol concentrations in the test subjects. Long-term indwelling catheters were employed, and, under local anesthesia, inserted into the jugular veins of foals aged two and twelve weeks.
• Post-recovery, short-acting ACTH1-24 was given as a single intravenous injection and blood samples were periodically taken in 5 – 30-minute intervals before and after ACTH administration. This was done to monitor plasma cortisol concentrations.

Results

• The results indicated that, at three weeks of age, ACTH-treated foals exhibited higher basal plasma cortisol concentrations in comparison to the saline-treated cohort. However, this disparity was not shown when comparing 13-week-old foals in the same groups.
• There were no statistically significant variations in either the time profile or the area under the cortisol curve in response to ACTH between the two groups.

Conclusion

• The data suggests that overexposure to glucocorticoids during the early postnatal life of a foal doesn’t influence the function of the hypothalamic-pituitary-adrenal axis at 13 weeks.
• The study concluded that the potential effects of ACTH-induced overexposure to glucocorticoids, if any, are likely to manifest much later in life. Furthermore, it points out that in short-lived species such as the horse, the impacts of ACTH-induced overexposure to glucocorticoids may not be easily detected in the early stages of life.
• Additionally, this research suggests that conditions inducing stress that result in raised plasma cortisol concentrations during early life are not likely to affect the programming of cardiovascular and metabolic function in the short term in horses.