Abstract presented at the Equine Endocrinology Summit, March 2011.
Comparison of Cortisol and ACTH Responses after Administration of Thyrotropin Releasing Hormone in Normal Horses and Those with Pituitary Pars Intermedia Dysfunction
Article first published online: 7 OCT 2011
Copyright © 2011 by the American College of Veterinary Internal Medicine
Journal of Veterinary Internal Medicine
Volume 25, Issue 6, pages 1431–1438, November-December 2011
How to Cite
Beech, J., Boston, R. and Lindborg, S. (2011), Comparison of Cortisol and ACTH Responses after Administration of Thyrotropin Releasing Hormone in Normal Horses and Those with Pituitary Pars Intermedia Dysfunction. Journal of Veterinary Internal Medicine, 25: 1431–1438. doi: 10.1111/j.1939-1676.2011.00810.x
- Issue published online: 16 NOV 2011
- Article first published online: 7 OCT 2011
- Manuscript Accepted: 22 AUG 2011
- Manuscript Revised: 9 AUG 2011
- Manuscript Received: 20 OCT 2010
- Adrenal responses;
Changes in both adrenocorticotropin (ACTH) and cortisol concentration in response to thyrotropin releasing hormone (TRH) administration have been used to diagnose equine pituitary pars intermedia dysfunction (PPID), but the use of the 2 hormones has not been compared.
Measuring ACTH concentration is superior to measuring cortisol concentration after TRH administration in differentiating between normal horses and those with PPID, and the 2 hormone concentrations are disassociated in PPID horses.
Eleven horses and 2 ponies with PPID and 19 normal horses.
A study evaluating cortisol and ACTH concentrations before and at 14, 30, and 60 minutes after TRH administration.
At 14 and 30 minutes after TRH administration, cortisol concentration increased in PPID horses, and ACTH increased in all groups; ACTH, but not cortisol concentration, was significantly higher in PPID horses compared with normal horses. A relationship between cortisol concentration and ACTH concentration was seen in normal horses, but not in horses with PPID. Compared with normal castrated males, normal female horses had a greater change in cortisol concentration per unit change of ACTH concentration.
Conclusions and Clinical Importance
ACTH and cortisol concentrations are disassociated in horses with PPID. Measuring ACTH concentration after TRH administration appears superior to measuring cortisol concentration as a diagnostic test for PPID.