Hypothalamic-pituitary-adrenal axis assessment in healthy term neonatal foals utilizing a paired low dose/high dose ACTH stimulation test.
BACKGROUND
Hypothalamic-pituitary-adrenal (HPA) axis function is dynamic in the neonatal foal. The paired low dose/high dose cosyntropin (ACTH) stimulation test allows comprehensive HPA axis assessment, but has not been evaluated in neonatal foals.


OBJECTIVE
Foal age will significantly affect cortisol responses to a paired 10 and 100 microg dose cosyntropin stimulation test in healthy neonatal foals.


METHODS
Twenty healthy neonatal foals.


METHODS
HPA axis function was assessed in 12 foals at birth and at 12-24, 36-48 hours, and 5-7 days of age. At each age, basal cortisol and ACTH concentrations were measured and cortisol responses to 10 and 100 microg cosyntropin were assessed with a paired ACTH stimulation test protocol. Eight additional 36-48-hour-old foals received saline instead of 10 microg cosyntropin in the same-paired ACTH stimulation test design.


RESULTS
At birth, foals had significantly higher basal cortisol and ACTH concentrations and higher basal ACTH : cortisol ratios compared with foals in all other age groups. A significant cortisol response to both the 10 and 100 microg doses of cosyntropin was observed in all foals. The magnitude of the cortisol response to both doses of cosyntropin was significantly different across age groups, with the most marked responses in younger foals. There was no effect of the paired ACTH stimulation test design itself on cortisol responses.


CONCLUSIONS
A paired 10 and 100 microg cosyntropin stimulation test can be used to evaluate HPA axis function in neonatal foals. Consideration of foal age is important in interpretation of HPA axis assessment.
Hart
K A
KA
Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA. khart4@uga.edu
Heusner
G L
GL
Norton
N A
NA
Barton
M H
MH
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D003366:Cosyntropin / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006736:Horses / Q000097:blood / Q000502:physiology*; D006854:Hydrocortisone / Q000097:blood; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000502:physiology*
D003366:Cosyntropin; D006854:Hydrocortisone