Plasma free cortisol concentrations in dogs with hyperadrenocorticism

Area of Science:

• Veterinary Endocrinology
• Glucocorticoid Metabolism
• Canine Health

Background:

• Free cortisol, not total cortisol, is the biologically active form.
• Hyperadrenocorticism in dogs may involve altered free cortisol levels.
• Understanding free cortisol is crucial for assessing glucocorticoid activity.

Purpose of the Study:

• To test if the percentage of free cortisol differs in dogs with hyperadrenocorticism.
• To compare free cortisol levels between healthy dogs and those with hyperadrenocorticism.
• To investigate the relationship between total and free cortisol in canine plasma.

Main Methods:

• Plasma samples from humans, healthy dogs, and dogs with hyperadrenocorticism were analyzed.
• Centrifugal ultrafiltration-dialysis was used to estimate percentage free cortisol.
• Radioimmunoassay determined total cortisol concentrations.

Main Results:

• Dogs with hyperadrenocorticism had significantly higher total plasma cortisol than healthy dogs.
• The percentage of free cortisol was not significantly different between healthy dogs and those with hyperadrenocorticism.
• Plasma free cortisol concentrations were significantly higher in dogs with hyperadrenocorticism compared to healthy dogs.

Conclusions:

• Elevated plasma free cortisol concentrations in dogs with hyperadrenocorticism likely contribute to increased target tissue response.
• The percentage of free cortisol may not be the primary factor altered in canine hyperadrenocorticism.
• A positive linear relationship exists between total and free cortisol levels in dogs.