Thursday, May 2, 2013

Cortisol: What Happens In A Dog’s Body When It Goes Awry?

by Jennifer Coates, DVM

Cortisol is an extremely important hormone from the glucocorticoid family of steroid hormones. 

It is primarily produced by a dog’s adrenal glands. In health, cortisol plays an extremely important role in the ability of dog’s to cope with stress by stimulating the production of glucose and the breakdown of fats, proteins, and carbohydrates to provide fuel for the body. Cortisol also suppresses the immune system.

These physiological changes help animals deal with both physical and psychological stress, giving priority to body processes that are needed in the moment and putting others on the back shelf until times are better.

Under normal circumstances, this system works beautifully. Stress arrives (as it always will), cortisol helps the dog deal with it thereby reducing the stress, and everything returns to normal.

Problems can develop either when cortisol levels remain too high for too long or when the body cannot secrete enough cortisol to deal with normal life events.

Too Much Cortisol

Dogs can develop abnormally high levels of cortisol in their bodies for several reasons:
  • unrelenting stress
  • a tumor in the pituitary gland that over-stimulates the adrenal glands to produce cortisol
  • a hormone-secreting tumor within an adrenal gland
  • the use of corticosteroid drugs like prednisone that have similar effects to cortisol

Long term excessive cortisol production or supplementation has a profound, negative impact on the body. 

Immunosuppression can lead to infection. The effects the hormone has on glucose metabolism can play a role in the development of diabetes mellitus. By breaking down proteins, cortisol can lead to muscle wasting, weakness, and thin, inelastic skin.

Cortisol also encourages the kidneys to excrete water producing the classic symptoms of increase thirst and urination. Dogs under the influence of high levels of cortisol have a ravenous appetite and increase gastric acid secretion (probably to deal with the intake of such large amounts of food) but this also raises their risk for gastrointestinal ulcers.

Too Little Cortisol

As bad as too much cortisol sounds, too little can be even worse. Abnormally low levels of circulating cortisol can develop because of
  • an abnormal immune response that destroys adrenal tissue. Cortisol and/or mineralocorticoid hormones that are essential for fluid and electrolyte balance may be affected.
  • the sudden withdrawal of high doses of corticosteroid drugs that suppress normal adrenal function

Low levels of cortisol prevent many body systems from working as they should. Glucose, electrolyte, and water regulation is impaired, which leads to weakness, tremors, dehydration, and increased thirst. The gastrointestinal tract is particularly affected producing symptoms such as vomiting, diarrhea, poor appetite, and weight loss.

Without the ability to increase cortisol production (often combined with an equivalent drop in mineralocorticoids) during times of stress, dogs become physiologically unable to deal with even the most common of situations. 

Exercise, kenneling, trips to the veterinary clinic… anything that increases a dog’s stress level can result in a life threatening crisis characterized by an extremely slow and irregular heart rate, low blood sugar levels, altered sodium and potassium levels, low blood pressure, collapse, and sometimes death.

Like many things in life, cortisol is part of a goldilocks scenario. The levels in a dog’s body need to be not too low, not too high, but just right to promote health.

***

Jennifer Coates, DVM graduated with honors from the Virginia-Maryland Regional College of Veterinary Medicine in 1999.  In the years since, she has practiced veterinary medicine in Virginia, Wyoming, and Colorado.  She is the author of several books about veterinary medicine and animal care, including the Dictionary of Veterinary Terms: Vet-speak Deciphered for the Non-veterinarian

Dr. Coates has recently joined the PetMD team and she is now writing for the Fully Vetted column; great blog, do check it out.

Jennifer also writes short stories that focus on the strength and importance of the human-animal bond and freelance articles relating to a variety of animal care and veterinary topics.  Dr. Coates lives in Fort Collins, Colorado with her husband, daughter, and pets.


Articles by Dr. Coates:
Kidney Disease – Say What? 
What Happens In The Dog's Body When The Kidneys Fail To Function Properly? 
Heat Stroke: What Happens In The Dog's Body?  
The Perplexities of Pancreatitis
The Other Side Of The Coin: The Cost Of Defensive Medicine
To Neuter Or Not To Neuter… That Is The Question
Don’t Forget the Physical Therapy
Common Misdiagnoses (Part 1)
Common Misdiagnoses (Part 2)
Picking the Right Dog to Breed
When Is It An Emergency?
Dog Allergies: Common, Commonly Misdiagnosed, or Both? 
Why Does The Spleen Get No Respect?
Protect Your Dog From Snake Bites 
More Creepy Crawlies
Why I Dislike Inflammatory Bowel Disease
Salmonella – A Significant Problem, Or Not? 
What’s In the Vomit? 

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