Serum concentrations of cortisol and cortisone in healthy dogs and dogs with pituitary-dependent hyperadrenocorticism treated with trilostane

Treating canine Cushing's syndrome: Current options and future prospects

Naturally occurring hypercortisolism, also known as Cushing's syndrome, is a common endocrine disorder in dogs that can be caused by an adenocorticotrophic hormone (ACTH)-producing pituitary adenoma (pituitary-dependent hypercortisolism, PDH; 80-85% of cases), or by an adrenocortical tumor (ACT; 15-20% of cases). To determine the optimal treatment strategy, differentiating between these two main causes is essential. Good treatment options are surgical removal of the causal tumor, i.e. hypophysectomy for PDH and adrenalectomy for an ACT, or radiotherapy in cases with PDH. Because these options are not without risks, not widely available and not suitable for every patient, pharmacotherapy is often used. In cases with PDH, the steroidogenesis inhibitor trilostane is most often used. In cases with an ACT, either trilostane or the adrenocorticolytic drug mitotane can be used. Although mostly effective, both treatments have disadvantages. This review discusses the current treatment options for canine hypercortisolism, and considers their mechanism of action, efficacy, adverse effects, and effect on survival. In addition, developments in both adrenal-targeting and pituitary-targeting drugs that have the potential to become future treatment options are discussed, as a more selective and preferably also tumor-targeted approach could have many advantages for both PDH and ACTs.

Cortisol Response in Healthy and Diseased Dogs after Stimulation with a Depot Formulation of Synthetic ACTH

Background

The ACTH stimulation test is used to evaluate the adrenocortical reserve. Recently, the availability of the synthetic ACTH formulation was limited, causing major problems in clinical practice.

Objectives

The objective of this study was to evaluate poststimulation peak cortisol concentrations and the duration of the stimulatory effect of a depot ACTH preparation in dogs.

Animals

Twenty‐two healthy dogs, 10 dogs with suspected hypoadrenocorticism (HA) and 15 dogs with suspected hyperadrenocorticism (HC).

Methods

Prospective study. An ACTH stimulation test using a synthetic depot tetracosactide, administered intramuscularly (5 μg/kg or at least 0.1 mL) was performed. Blood samples for determination of cortisol were taken immediately before and 1, 2, 3, 4, 6, and 24 hours after stimulation.

Results

Peak cortisol concentrations were reached after 2–4 hours in all dogs. Cortisol concentrations 1 hour after stimulation were >9 μg/dL in all healthy dogs and >5 μg/dL in all dogs in which HA was excluded. None of the dogs with HA showed a cortisol‐increase above the detection‐limit of the assay. After 6 hours, cortisol concentrations had decreased in the healthy and HC group and were back to baseline after 24 hours.

Conclusions and Clinical Importance

The depot formulation can be used in place of the short‐acting ACTH to evaluate the adrenocortical reserve. Blood for peak cortisol concentrations should be drawn 3 hours after stimulation in cases in which HC is suspected; in HA‐suspected cases, blood sampling can take place after 1 hour. As the stimulatory effect is gone after 24 hours, interference with other hormonal tests is unlikely after that time.

Urinary corticoid concentrations measured by 5 different immunoassays and gas chromatography-mass spectrometry in healthy dogs and dogs with hypercortisolism at home and in the hospital

Background

Determination of the urinary corticoid‐to‐creatinine ratio (UCCR) is an important screening test in the diagnosis of hypercortisolism (HC). However, urinary cortisol metabolites interfere with cortisol measurement in immunoassays, leading to decreased specificity. Gas chromatography‐mass spectrometry (GC‐MS) is considered the gold standard for steroid hormone analysis, because it provides a high level of selectivity and accuracy.

Objectives

To prospectively compare the UCCR of healthy dogs and dogs with HC determined by 5 different immunoassays and by GC‐MS and to evaluate the influence of veterinary care on UCCR.

Animals

Twenty healthy dogs; 18 dogs with HC.

Methods

Urine was collected in the hospital and again after 6 days at home. Three chemiluminescence immunoassays (Access 2, Beckmann; Immulite 2000, DPC Siemens, with and without trichloromethane extraction) and 2 RIAs (Utrecht in house; Access Beckmann) were used. GC‐MS analyses were performed with Agilent 6890N/5973N. Urinary corticoid concentrations were related to urinary creatinine concentrations.

Results

Immunoassay results were significantly higher compared to GC‐MS results. Evaluation of bias plots and clinical assessment made on the basis of the assay results of each dog indicated substantial disagreement among the assays. Sensitivity varied from 37.5 to 75% and with selected assays was lower in samples from day 6 compared to day 0. GC‐MS was not superior to the immunoassays in discriminating healthy from HC dogs.

Conclusions and Clinical Importance

Considerable variation must be anticipated comparing different urinary cortisol assays. Establishing an assay‐ and laboratory‐specific reference range is critical when using UCCR.

Expression of 11β-hydroxysteroid dehydrogenase isoforms in canine adrenal glands treated with trilostane

Trilostane, a competitive inhibitor of 3β-hydroxysteroid dehydrogenase, is often used to treat canine hyperadrenocorticism. In some species, trilostane has been shown to have additional effects on steroid biosynthesis, and it has been postulated that trilostane might have effects on 11β-hydroxysteroid dehydrogenase (11β-HSD) in dogs. To investigate the effect of trilostane on 11β-HSD in canine adrenal glands, healthy Beagle dogs were treated with trilostane for 8 weeks. Trilostane treatment resulted in a significant decrease of the cortisol/cortisone ratio in the serum. The adrenal gland mRNA and protein expression levels of 11β-HSD type 1 and 11β-HSD type 2 were significantly higher and significantly lower respectively in dogs treated with trilostane compared to those in control healthy Beagle dogs. These findings suggest that trilostane may have an effect on 11β-HSD activity in canine adrenal glands.

Interpretation of laboratory tests for canine Cushing's syndrome

Hypercortisolism (HC) is a common disease in dogs. This article will review the laboratory tests that are available for diagnosis of HC and laboratory tests for differentiating between causes of HC. An emphasis will be made on the clinical process that leads to the decision to perform those tests and common misconceptions and issues that arise when performing them. To choose between the adrenocorticotropic hormone (ACTH)-stimulation test and the low-dose dexamethasone suppression test (LDDST), the advantages and disadvantages of both tests should be considered, as well as the clinical presentation. If the index of suspicion of HC is high and other diseases have been appropriately ruled out, the specificity of the ACTH stimulation test is reasonably high with an expected high positive predictive value. Because of the low sensitivity, a negative result in the ACTH stimulation test should not be used to rule out the diagnosis of HC. The LDDST is more sensitive but also less specific and affected more by stress. A positive result on the urine cortisol:creatinine ratio does not help to differentiate HC from other diseases. A negative result on the urine cortisol:creatinine ratio indicates that the diagnosis of HC is very unlikely. The LDDST is useful in differentiating pituitary-dependent HC from an adrenal tumor in about two thirds of all dogs with HC. Differentiation of HC from diabetes mellitus, liver diseases, and hypothyroidism cannot be based solely on endocrine tests. Clinical signs, imaging studies, histopathology, and response to treatment should all be considered.

Trilostane in dogs

Over the last 10 years, trilostane, a competitive inhibitor of steroid synthesis, is being widely used for the treatment of canine hyperadrenocorticism. Trilostane causes a significant but reversible decrease in cortisol production and a concomitant improvement in clinical signs in most dogs with this common condition. Side effects, though infrequent, can be serious: dogs treated with this drug require regular monitoring. This review summarizes current knowledge of the use of this drug with particular emphasis on its efficacy, safety, adverse reactions, and effects on endocrine parameters. Brief mention is made of its other uses in dogs and other species.

Corticotroph adenoma in the dog: pathogenesis and new therapeutic possibilities

The corticotrophinoma, causing pituitary dependent hypercortisolism, represents the highest percentage of pituitary tumours in the dog. The mechanism by which it develops is currently unknown and two theories are postulated: the hypothalamic and the monoclonal. It is not clear either what factors are involved in the tumour genesis; nevertheless, firm candidates are the Rb1 gene, proteins p27, p21 and p16, as are also defects in the glucocorticoid receptor and Nur77/Nurr1. The role of BMPs remains to be evaluated in greater depth. Although at present the chosen treatment in human is surgical, there are various pharmacological treatments already in use that have favourable results and others, still under research, also showing promising results.