Cortisol

Cortisol – that sounds like dry biology class at first. In fact, this steroid hormone is one of the most important conductors in a dog’s body: it regulates metabolism, curbs excessive immune reactions and ensures that the organism remains capable of action in stressful situations. Belonging to the group of glucocorticoids, cortisol is formed in the adrenal cortex – and has long been an indispensable marker in veterinary diagnostics.

Biochemical Basics

• Production: Cortisol is produced in the zona fasciculata of the adrenal cortex.
• Regulation: Release occurs via a three-stage hormonal axis: CRH (corticotropin-releasing hormone) signals the pituitary gland to release ACTH – and only then does this prompt the adrenal gland to produce cortisol. This so-called HPA axis (hypothalamic-pituitary-adrenal axis) can be understood as the body’s own feedback system.
• Transport: In the blood, cortisol travels partly bound to the protein CBG (corticosteroid-binding globulin) and partly in free form – and only the free fraction is biologically active.

What Cortisol Does in the Body

Cortisol is not just a “stress hormone” – it acts at several places simultaneously:

• Metabolism: It increases glucose availability via gluconeogenesis and promotes the breakdown of fat and protein.
• Immune System: Excessive immune responses and inflammation are dampened.
• Circulation: Cortisol supports blood pressure regulation and contributes to circulatory stability.
• Stress Response: In acute stress situations, cortisol helps the organism remain capable of action and survival.
• Behaviour: Attention, fear responses, and learning processes – such as so-called stress learning – are influenced by cortisol levels.

Cortisol and Stress in Dogs

Separation from the owner, loud noises, the vet visit, conflicts with other dogs – all of this causes cortisol levels to rise. In the short term, this is exactly sensible, as the body needs this reaction to adapt. It becomes problematic if the level remains permanently elevated. Chronic excess cortisol can lead to the following problems:

• weakened immune system,
• slowed wound healing,
• muscle loss and weight gain,
• fearful or aggressive behaviour.

When the Hormonal Axis Goes Out of Balance

• Cushing’s Disease (Hyperadrenocorticism): The adrenal gland produces too much cortisol. Typical signs include excessive thirst, frequent urination, hair loss, muscle weakness, and a pot-bellied appearance.
• Addison’s Disease (Hypoadrenocorticism): The opposite: too little cortisol. Dogs appear lethargic, have diarrhoea, and can enter acute, life-threatening crises.
• Chronic Stress: Even without clinical disease, persistently elevated cortisol levels can have a lasting negative impact on the dog’s behaviour and health.

Diagnostic Approaches

• ACTH Stimulation Test: Checks whether the adrenal glands can release sufficient cortisol in response to a hormonal stimulus.
• Dexamethasone Suppression Test: Used primarily for diagnosing Cushing’s disease.
• Saliva or Hair Cortisol: Increasingly popular in research because it allows non-invasive measurement of chronic stress in dogs.

Treatment Approaches

• Hyperadrenocorticism: Drugs such as trilostan inhibit the body’s own cortisol production.
• Hypoadrenocorticism: Here, missing hormone production is replaced by administering glucocorticoids and mineralocorticoids.
• Stress Management: Targeted training, sufficient rest periods, and adapted living conditions can significantly reduce chronically elevated cortisol levels.

What Research Shows

Some findings from current science deserve special attention:

• Hair cortisol is now considered a reliable marker for chronic stress in dogs – this is evidenced, among others, by studies from Accorsi et al. (2008) and Roth et al. (2016).
• A close human-dog bond can lower cortisol levels in both parties. Schöberl et al. (2017) were able to demonstrate that this mutual stress buffering is actually measurable – not just felt.
• Cortisol levels vary considerably from dog to dog: genetics, temperament, and environment all play a role.