Adrenal gland function in the horse: effects of cosyntropin (synthetic) and corticotropin (natural) stimulation.

The research focuses on the effects of cosyntropin and corticotropin, on hydrocortisone levels in the blood. The results suggest that while both substances can stimulate hydrocortisone release in horses, cosyntropin delivers a prompt and predictable response. This makes cosyntropin a useful substance for testing adrenal function in horses.

Methods and Materials

• The researchers tested two substances, cosyntropin and corticotropin, for their effect on the adrenal gland in horses.
• Cosyntropin (100 IU) was administered intravenously and corticotropin (200 IU) was given intramuscularly.
• The plasma hydrocortisone levels were then measured at various time intervals after the administration of these substances.

Results

• In mares treated with cosyntropin, plasma hydrocortisone concentrations increased significantly for up to 120 minutes after administration compared to the base-line values. These levels then returned to the base-line value at 240 minutes.
• In mares treated with corticotropin, mean plasma hydrocortisone concentrations also rose above the base-line values, but the increase continued even at 240 minutes.
• There were no significant differences in total leukocyte count, total eosinophil count, and plasma concentrations of electrolytes (calcium, sodium, magnesium, potassium) between cosyntropin- and corticotropin-treated mares, and control animals.

Conclusion

• The study concluded that the horse responds to small dosages of cosyntropin (IV) in a predictable and reproducible manner as determined by plasma hydrocortisone values.
• The response to corticotropin, however, was slow and less consistent.
• Therefore, administration of cosyntropin to the horse, according to test results with paired samples collected before administration and again at 2 hours after injection, is a useful and reliable test of adrenal gland function.