This article is just a discussion of terminology.
The phrase “inactive cortisol” was coined by Dr. Plechner, the veterinarian who first identified the low cortisol/high sex steroid problem in dogs. He also called it “bound” and “defective” cortisol in his writings. He used these phrases to explain why lab work could indicate normal or high cortisol levels when a dog was actually producing insufficient cortisol.
And while my work is based on Dr. Plechner’s work, these are not phrases I use. I have two concerns with them. First, Dr. Plechner never defined them in scientific, molecular terms. Second, there is a much more plausible explanation for the low cortisol/elevated sex steroid scenario.
Scientific explanation is important, so years ago I searched the medical literature in an attempt to decipher Dr. Plechner’s phrase, “inactive cortisol”. The best description I could find was a molecule called epi-cortisol. And I have occasionally used it in my own writings. That said, I do not believe it to be an important feature of this disease.
Epi-cortisol
Epi-cortisol is a molecule built with all the same atoms as regular cortisol but built as a mirror image. This is called an isomer. And as an isomer, it can’t do the same work regular cortisol can — can’t create energy, can’t control inflammation, etc.
Is this what Dr. Plechner meant by “inactive cortisol”? I don’t know. But I’ve never found any other explanation for his phrasing. There is no discussion in the human literature of “bound”, “defective” or “inactive” cortisol.
There is, however, much discussion of enzymes and an adrenal hormone called deoxycortisol (dee-ox-ee-kort-ah-zol).
Adrenal Enzyme Failure
A much more likely mechanism in this disease is adrenal enzyme failure. We have known about this scenario in human healthcare for many, many decades. We know what genes cause it. We know how to treat it. It’s well-described in the medical and research literature. Rather than repeat that information, please read more here.
Adrenal enzymes are natural chemicals that convert one hormone into another. When adrenal enzymes can no longer convert deoxycortisols into cortisol, these deoxycortisols accumulate. Almost all lab tests mistakenly include them as part of the cortisol reading. It’s called cross-reactivity. This provides a much more credible explanation of the disease process and the counter-intuitive lab results. Click here and scroll to the Cortisol section.
Perhaps Dr. Plechner did not understand how deoxycortisol levels accumulate in this type of adrenal disease and simply chose to label them “inactive” or “defective cortisol”. In other words, these phrases probably refer to an enzyme failure that raises levels of sex steroids (estrogen) and deoxycortisols.
It’s also probably worth repeating that SARDS dogs are not Cushing’s dogs. Read more here.
I hope this helps you and your dog.
Caroline