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  Discussion on Research: Cortisol in Health, Equine Metabolic SynDrOme, and PPID
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Moderator:
DrO

Posted on Thursday, Feb 11, 2016 - 10:07 am:

The message here is total cortisol levels are not beneficial for characterizing endocrine disease but looking for free cortisol fractions may help characterize some endocrine disorders and also play a role in creating hyperinsulinemia. A factor that leads to weakening of the laminae, predisposing to laminitis.
DrO

J Vet Intern Med. 2016 Feb 9.
Effect of Age, Season, Body Condition, and Endocrine Status on Serum Free Cortisol Fraction and Insulin Concentration in Horses.
Hart KA1, Wochele DM1, Norton NA1, McFarlane D2, Wooldridge AA3, Frank N4.

Author information:
1University of Georgia College of Veterinary Medicine, Athens, GA.
2Oklahoma State College of Veterinary Medicine, Stillwater, OK.
3Auburn University College of Veterinary Medicine, Auburn, AL.
4Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA.

Abstract

BACKGROUND:
Increased free cortisol fraction is associated with insulin dysregulation (ID) in people with Metabolic SynDrOme and Cushing's Disease. Free cortisol has not been investigated in equine endocrine disorders.

HYPOTHESES:
(1) In healthy horses, sex, age, body condition score (BCS), and season impact free cortisol; (2) free cortisol is increased in horses with Pituitary Pars Intermedia Dysfunction (PPID) or Equine Metabolic SynDrOme (EMS).

ANIMALS:
Fifty-seven healthy horses; 40 horses and ponies with PPID (n = 20) or EMS (n = 20).

METHODS:
Prospective study. Serum collected seasonally from healthy animals and archived serum from PPID and EMS animals was analyzed for insulin, total and free cortisol concentrations, and free cortisol fraction (FCF). Linear mixed models were used to determine effects of age, sex, season, and BCS on hormones in controls. Hormone measurements were compared between disease groups and age- and season-matched controls with t-tests. EMS and hyperinsulinemic PPID animals were combined in an ID (hyperinsulinemia) group.

RESULTS:
Free cortisol concentrations were increased in overweight/obese controls (0.3 ± 0.1 μg/dL) compared to lean controls (0.2 ± 0.1 μg/dL; P = .017). Mean FCF was significantly higher in animals with PPID (8.8 ± 5.8 μg/dL, P = .005) or ID (8.8 ± 10.2 μg/dL, P = .039) than controls (5.0 ± 0.9 μg/dL), but total cortisol concentrations were similar (P ≥ .350) (PPID: 4.2 ± 4.3 μg/dL; ID: 5.0 ± 4.5 μg/dL; controls: 4.6 ± 1.7 and 5.1 ± 2.1 μg/dL).

CONCLUSIONS AND CLINICAL IMPORTANCE:
Increased FCF is associated with obesity in healthy horses and with ID (hyperinsulinemia) in horses and ponies with endocrine disease. Decreased plasma cortisol-binding capacity could be a component of these endocrine disorders in horses.
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