Hormone Implants for Pet Ferrets with Adrenal Disease
Charlotte Hitch (Vet News Exotics Editor)
Hyperadrenocorticism is arguably one of the most serious and prevalent diseases in pet ferrets in the USA and United Kingdom. There is a particularly high rate of incidence in neutered individuals; studies show that 50-75% of neutered ferrets develop the condition at some point in their lives. Although the prognoses may differ depending on how early in its development intervention occurs, the condition can potentially be life threatening in some cases if inflamed tissue causes anuria. The animal is then unable to remove waste and toxins from its body through urination.
Neutering the animal is considered to be one of the main causes of the onset of the disease, aside from excessive artificial light exposure and genetic predisposition. In the endocrine system, hormones work antagonistically against each other, and the presence of high levels of one hormone in the blood can stimulate the release of a different hormone to counteract the effects of the first. After neutering, there is no negative feedback from the gonads to the pituitary gland, so the pituitary gland continually releases a hormone called Gonadotrophin Releasing Hormone (GnRH) which in turn stimulates the overproduction of gonadotrophins (sex steroids) from the adrenal glands, situated beside each kidney.
One hormone produced in great quantities is Luteinizing Hormone (LH), which stimulates ovulation. The gonads are no longer present to respond to high blood LH levels, so negative feedback does not occur and the levels continue to rise in an unregulated manner. Hyperplasia occurs in the adrenal cortices, and this can lead to adenoma or carcinoma formation.
The main symptoms of the disease include severe alopecia, pruritus (itchiness), polydipsia (excessive drinking), aggressive behaviour, swollen or enlarged vulva/prostate tissue, and muscular atrophy. Adrenocortical hyperplasia may cause malignant tumours to develop; in this case the condition is often life threatening.
Current treatment options include surgery to remove the affected gland, inhibition of the release of GnRH using melatonin, and desensitisation of the pituitary gland using Lupron Depot injections, again stopping the production of GnRH. Unfortunately, surgery has limitations in that only the left gland can be removed safely because ferrets with both adrenal glands absent are likely to develop Addison’s disease, and the right gland is extremely close to the vena cava. Melatonin and Lupron only work to relieve the symptoms; they do not remove the tumour (although Lupron may shrink it).
Recently, subcutaneous deslorelin implants manufactured by Virbac have been legally marketed in the UK. Over the period of about 8 months, the implant releases hormones which antagonise the release of GnRHs, removing the stimulus for the overproduction of sex hormones by the adrenal glands. This treatment is multifunctional because not only can it be used to reduce the effects or prevent the onset of adrenal disease, but it can even be used as an alternative to neutering, saving the ferret the pain and risk associated with surgery. The implants are not yet approved in the USA, but with further research they may have great potential in the treatment of this highly prevalent condition.