Cortisol, aldosterone, cortisol precursor, androgen and endogenous ACTH concentrations in dogs with pituitary-dependant hyperadrenocorticism treated with trilostane

Trilostane: Beyond Cushing's Syndrome

Trilostane is a drug able to block the synthesis of progesterone from pregnenolone, dependent on the enzyme 3β-hydroxysteroid dehydrogenase/Δ5-4 isomerase. As a consequence of this effect, it is used to treat endocrinological diseases such as Cushing's syndrome, especially in dogs. Because of the modulatory effects of trilostane on the hypothalamic-pituitary-adrenal axis, trilostane administration causes an increase in brain levels of neurosteroids with anticonvulsant properties, as in the case of allopregnanolone. Allopregnanolone is also of interest in curing depression, suggesting that trilostane might represent a tool to address neurological and psychiatric disorders. In this review, we investigated the historical development of this drug and its current use, mechanisms, and possible developments. By searching the literature from 1978 to 2025, we identified 101 papers describing studies with trilostane. Precisely, 55 were about dogs and trilostane, 3 were on cats, and 23 were with other animals. Some studies (15) were also designed with human patients. The main disease treatment with trilostane was hyperadrenocorticism. However, we also found two preclinical papers on trilostane's potential use in psychiatric diseases and three on trilostane's potential use in neurological disorders. Moreover, few clinical and preclinical studies suggested the involvement of neurosteroids modulated by trilostane in different neurological disorders, thus opening a possible new perspective for the use of this drug.

Serum Bile Acids Concentrations and Liver Enzyme Activities after Low-Dose Trilostane in Dogs with Hyperadrenocorticism

Hyperadrenocorticism (HAC) often leads to vacuolar hepatopathy. The impact of trilostane treatment on serum total bile acids (SBAs) concentrations in dogs with HAC remains unknown. This study investigated SBAs concentrations in healthy dogs and those with HAC following trilostane therapy. Ten healthy dogs and fifteen dogs with HAC were prospectively enrolled. A biochemistry profile and pre- and post-prandial SBAs concentrations were determined in each dog. Dogs with HAC were reassessed at 1 and 3 months after the initiation of trilostane treatment. Dogs with HAC had significantly higher serum ALT, ALP, and GGT activities, and cholesterol, triglyceride, and pre-prandial SBAs concentrations compared to healthy dogs. After 3 months of trilostane treatment, polyuria/polydipsia and polyphagia were completely resolved in 42.8% and 35.7%, respectively. Significant improvements in serum ALT and ALP activities and cholesterol concentrations were observed within 1-3 months of trilostane treatment. However, pre- and post-prandial SBAs concentrations did not significantly decrease. These findings suggest that treatment with low-dose trilostane for 3 months appears to reduce serum liver enzyme activities, but not SBAs concentrations. Further investigation is warranted to explore the effects of low-dose trilostane treatment on SBAs concentrations for a longer duration or after achieving appropriate post-ACTH cortisol levels.

Clinical features of muscle stiffness in 37 dogs with concurrent naturally occurring hypercortisolism

BACKGROUND

Severe muscle stiffness (SMS) in dogs with hypercortisolism (HC) is uncommon.

OBJECTIVES

To evaluate signalment, presentation, treatments, and long-term outcomes of dogs with concurrent HC and SMS.

ANIMALS

Thirty-seven dogs.

METHODS

Medical records of dogs with HC and concurrent SMS were recruited from 10 institutions. Clinical information, test results, therapeutic responses, and survival times were reviewed.

RESULTS

All 37 dogs with HC and SMS had pituitary-dependent hypercortisolism (PDH); 36/37 weighed <20 kg. Signs and test results were typical of PDH aside from SMS, initially diagnosed in all 4 limbs in 9, pelvic limbs of 22, and thoracic limbs of 6 dogs. Hypercortisolism and SMS were diagnosed together in 3 dogs; HC 1-36 months before SMS in 23; SMS 1-12 months before HC in 11. Mitotane or trilostane, given to control HC in 36/37 dogs, improved or resolved HC signs in 28; SMS did not resolve, remaining static or worsening in 31/36 dogs, mildly improving in 5/19 dogs given additional therapies. Progression of SMS included additional limbs in 10 dogs and the masticatory muscles of 2. The median survival time from diagnosis of SMS was 965 days (range, 8-1188).

CONCLUSIONS AND CLINICAL IMPORTANCE

Concurrent SMS and HC is uncommon, possibly affecting only dogs with PDH. Development of SMS might occur before or after diagnosis of HC. Apart from SMS, the clinical picture and survival time of these dogs seem indistinguishable from those of dogs with HC in general. However, while muscle weakness usually resolves with HC treatment SMS does not.

Comparison of methods to monitor dogs with hypercortisolism treated with trilostane

Background

The use of adrenocorticotropic hormone stimulation test as method to monitor efficacy of trilostane treatment of hypercortisolism (HC) in dogs has been questioned.

Objectives

To evaluate and compare 12 methods with which to monitor efficacy of trilostane treatment in dogs with HC.

Animals

Forty‐five client‐owned dogs with HC treated with trilostane q12h.

Methods

Prospective cross‐sectional observational study. The dogs were categorized as well‐controlled, undercontrolled, and unwell through a clinical score obtained from an owner questionnaire. The ability to correctly identify trilostane‐treatment control of dogs with HC with the following variables was evaluated: before trilostane serum cortisol (prepill), before‐ACTH serum cortisol, post‐ACTH serum cortisol, plasma endogenous ACTH concentrations, prepill/eACTH ratio, serum haptoglobin (Hp) concentration, serum alanine aminotransferase (ALT), gamma‐glutamyl transferase (γGT) and alkaline phosphatase activity, urine specific gravity, and urinary cortisol : creatinine ratio.

Results

Ninety‐four re‐evaluations of 44 dogs were included; 5 re‐evaluations of 5 unwell dogs were excluded. Haptoglobin was significantly associated with the clinical score (P < .001) and in the receiver operating characteristic analysis, Hp cutoff of 151 mg/dL correctly identified 90.0% of well‐controlled dogs (specificity) and 65.6% of undercontrolled dogs (sensitivity). Alanine aminotransferase (P = .01) and γGT (P = .009) were significantly higher in undercontrolled dogs. Cutoff of ALT and γGT greater than or equal to 86 U/L and 5.8 U/L, respectively, were significantly associated with poor control of HC by trilostane.

Conclusions and Clinical Importance

Of all the 12 variables, Hp, and to a lesser degree ALT and γGT, could be considered additional tools to the clinical picture to identify well‐controlled and undercontrolled trilostane‐treated dogs.

Evaluation of Iatrogenic Hypocortisolemia Following Trilostane Therapy in 48 Dogs with Pituitary-Dependent Hyperadrenocorticism

This study aimed to retrospectively describe the clinical progression following diagnosis of iatrogenic hypocortisolemia (iHC) in 48 dogs receiving trilostane for pituitary-dependent hyperadrenocorticism. Cortisol concentrations were ≥1.5 mg/dL within 6 mo following diagnosis of iHC in 76.3% of dogs (95% confidence interval [CI] 59.8-88.6%). At the time of study completion, 25% of dogs (95% CI 13.6-39.6%) were receiving either glucocorticoids or mineralocorticoids or both; 42% of dogs (95% CI 27.6-56.8%) were on no adrenal-related medications; and the remaining 33% of dogs (95% CI 20.4-48.4%) were receiving trilostane. No patient-, clinicopathologic-, or trilostane-associated factors were identified to influence adrenal recovery following diagnosis of iHC, and it remains difficult to predict the clinical progression in this population of dogs.

Changes in systolic blood pressure in dogs with pituitary dependent hyperadrenocorticism during the first year of trilostane treatment

Background

Systemic hypertension (SH) is common in dogs and humans with hypercortisolism and can persist after treatment.

Objectives

To evaluate changes in prevalence of SH and systolic blood pressure (SBP) in dogs with pituitary‐dependent hyperadrenocorticism (PDH) during the first year of trilostane treatment, its relationship with disease control and selected laboratory variables, and their response to antihypertensive treatment.

Animals

Fifty‐one dogs with PDH treated with trilostane Q12h.

Methods

Prospective case series study. Dogs were evaluated at diagnosis (T0) and 1, 3, 6, and 12 months (T12). Dogs were classified as nonhypertensive (SBP < 160 mm Hg) or hypertensive (SBP≥160 mm Hg) and subclassified according to target organ damage (TOD) risk. Hypertensive dogs were treated with benazepril and, if control of SH was not achieved, amlodipine was added.

Results

Prevalence of SH decreased from T0 (36/51) to T12 (17/37; P = .01). Changes in SBP during the study were influenced by the risk of TOD at T0. In severely hypertensive (SBP ≥ 180 mm Hg) dogs, the decrease in SBP was more pronounced whereas in normotensive (SBP < 140 mm Hg) dogs SBP increased slightly (P = .00). Blood pressure was not associated with disease control. Antihypertensive treatment was needed in 31/51 dogs, and in 13/31 dogs additional SH control with amlodipine was required. One third of nonhypertensive dogs at T0 required treatment with benazepril because SH developed during follow‐up.

Conclusions and Clinical Importance

In dogs with PDH, SBP should be measured at every visit, regardless of disease control or SBP at diagnosis. More than 1 drug may be necessary to manage SH in affected dogs.

Laboratory assessment of trilostane treatment in dogs with pituitary-dependent hyperadrenocorticism

Background

Results of ACTH stimulation test (ACTHst), pre‐ and post‐trilostane serum cortisol concentrations (SCCs), urine concentration (urine‐specific gravity [USG]), and urine cortisol : creatinine ratios (UCCRs) are common variables used to monitor trilostane treatment of dogs with pituitary‐dependent hyperadrenocorticism (PDH). However, none has consistently discriminated dogs receiving an adequate dose (A) from those overdosed (O) or underdosed (U).

Objectives

To assess and compare recommended monitoring variables, including serial SCCs in a cohort of dogs with PDH treated with trilostane.

Animals

Privately owned dogs with PDH (n = 22) and 3 healthy dogs (controls).

Methods

Prospective, multicenter, 2‐day study. On day “a” (randomized): ACTHst was completed. Day “b” (>2 to <7 days later): SCCs were assessed −0.5 hours, immediately before, and 1, 2, 2.5, 3, 3.5, 4, 6, 8, and 12 hours after trilostane administration. On the first study day, urine collected at home was assessed for USG, UCCR and owner opinions regarding PDH were categorized as: A (clinical signs resolved), U (remains symptomatic), or ill (possible O).

Results

At 27 pairs of evaluations, 7 dogs were categorized as A, 19 U, and 1 possible O (excluded from the study). There was overlap in SCC results from the A and U dogs at every time point. Results of USG, UCCR, and ACTHst did not discriminate A from U dogs. Trilostane suppresses SCC within 1 hour of administration and its duration of action in most PDH dogs is <8 hours.

Conclusions and Clinical Importance

No single variable or group of variables reliably discriminated A dogs from U dogs during trilostane treatment for PDH.

Attempts to downregulate ovarian function in the bitch by applying a GnRH agonist implant in combination with a 3ß-hydroxysteroid-dehydrogenase blocker; a pilot study

Approaches to downregulate ovarian function in the sexually mature bitch by applying slow release GnRH agonist implants are hampered by the initial stimulation of folliculogenesis (flare up) and the resulting side effects. The present pilot study was designed to test to what extent these effects can be suppressed by simultaneous treatment with the 3ß-hydroxysteroid-dehydrogenase (HSD3B) blocker trilostane (T). Treatment with T in 6-h intervals completely blocked adrenal cortisol production. However, in parallel and concomitant with the increase of LH, progesterone and estradiol levels increased, ending up in pro-estric steroid levels in two of the three dogs. Hormonal changes were reflected in the respective clinical symptoms. During the whole observation period the course of LH concentrations did not indicate downregulation of pituitary function as a result of treatment with the GnRH-agonist Suprelorin®, 4.7 mg. The incomplete inhibitory effect of T on the follicular production of sex steroids could be explained by an insufficient transfer of T into the follicular compartment or the existence of a HSD3B isoform in the dog ovary different from the adrenal enzyme. Concerning the lack of downregulation and when accounting for published data different pharmacodynamics/pharmacokinetic activities of GnRH-agonists should be taken into account.

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.

[Atypical Cushing's syndrome in a dog. A case report]

In a 12-year-old male Labrador Retriever, presented due to other disease symptoms, clinical signs of hyperadrenocorticism (polyuria, polydipsia, abdominal distention, muscle atrophy) were an incidental finding. Abnormal laboratory results and sonographic findings of the adrenal glands, but negative low-dose dexamethasone suppression tests with low basal cortisol concentrations, a negative andrenocorticotropic hormone (ACTH)-stimulation test and exclusion of iatrogenic hyperadrenocorticism, suggested an atypical hyperadrenocorticism (AHAC). Results of further examinations, particularly stimulation of progesterone production by ACTH (0 h value: 0.21 ng/ml; 1 h value: 4.9 ng/ml) and good response to therapy with trilostane, supported this diagnosis. However, it has to be critically considered, whether and to what extent additionally present diseases (arthroses, testicular tumour) played a role regarding the symptoms and laboratory results in this dog. This case illustrates the difficulties with the diagnosis of AHAC.

Uso de baixa dose de ACTH sintético no teste de estimulação da função adrenal para o diagnóstico e controle do hiperadrenocorticismo canino: avaliação da eficácia diagnóstica

RESUMO: O teste de estimulação com ACTH é o teste de escolha para realizar o controle dos valores de cortisol endógeno em pacientes sob tratamento para o hiperadrenocorticismo canino, podendo ser utilizado também para diagnosticar a doença. Os protocolos atuais utilizam doses que variam entre 5ug/kg a 250ug/animal por administração intravenosa ou intramuscular. Não se constatam estudos com doses menores que as de 5ug/kg em pacientes portadores de hiperadrenocorticismo. No presente estudo, foi testada a dose de 1ug/kg/IV; comparada à dose consagrada de 5ug/kg/IV, em grupos de animais suspeitos de HAC (HAC Diag), animais portadores de HAC e em tratamento (HAC Control) e animais sadios (Sadios). Na dose de 1ug/kg/IV, os valores basais de cortisol dos Sadios foram iguais à média 2,40ug/dL(+/-1,57ug/dL), dos HAC control foi de média 1,53ug/dL(+/-0,93,ug/dL) e dos HAC diag foi média 3,37ug/dL(+/-1,57ug/dL). Os valores pós-ACTH na dose de 1ug/kg foram de média 11,43ug/dL(+/-2,46ug/dL) para animais sadios, 2,67ug/dL(+/-1,39ug/dL) para o grupo HAC Control e média 16,56ug/dL(+/-7,62ug/dL) para o grupo HAC Diag. Os valores basais de cortisol na dose de 5ug/kg foram 0,89ug/dL(+/-0,23ug/dL) para o grupo HAC Control; média 3,08ug/dL(+/-1,99 ug/dL) para o grupo HAC Diag. Os valores pós-ACTH na dose de 5ug/kg foram de média 3,71ug/dL(+/-1,57ug/dL), para o grupo HAC control e média 22,52ug/dL (+/-8,75ug/dL) para o grupo HAC diag. Analisando-se os resultados obtidos, constatou-se que as doses 1 e 5ug/kg de ACTH sintético não diferem entre si, promovendo o mesmo tipo de variação nos valores de cortisol (ANOVA; p=0,225). Também, que a dose de 1ug/kg de ACTH foi igualmente eficaz na elevação dos níveis de cortisol nos três grupo testados (Sadios, HAC Control e HAC Diag; ANOVA, p<0,05). E, pelo teste de Dunn observamos que o grupo HAC control apresenta Δ-cortisol (delta =diferença entre cortisol após estimulo e o cortisol basal) significativamente menor que o dos grupos diagnóstico (p<0,05) e animais sadios (p<0,05). Concluiu-se que a dose de 1ug/kg de ACTH sintético pode ser utilizada com eficácia para a realização do teste de estimulação com ACTH.

Comparison of adrenocorticotropic hormone stimulation test results started 2 versus 4 hours after trilostane administration in dogs with naturally occurring hyperadrenocorticism

Background

Trilostane medical treatment of naturally occurring hyperadrenocorticism (NOH) in dogs is common, as is use of the adrenocorticotropic hormone (ACTH) stimulation test (ACTHst) in monitoring response to treatment. There is uncertainty regarding when the ACTHst should be started relative to time of trilostane administration.

Objective

To compare ACTHst results in dogs being treated for NOH with trilostane when the test is begun 2 versus 4 hours after trilostane administration.

Animals

Twenty‐one privately owned dogs with NOH, each treated with trilostane for at least 30 days.

Methods

Each dog had 2 ACTHst completed, 1 started 2 hours and the other 4 hours after trilostane administration. The second test was started no sooner than 46 hours and no later than 74 hours after the first.

Results

For all 21 dogs, the mean post‐ACTH serum cortisol concentration from tests started 2 hours after trilostane administration (5.4 ± 3.7 μg/dL) was significantly lower (P = .03) as compared with results from the tests started 4 hours after administration (6.5 ± 4.5 μg/dL).

Conclusions

Results of ACTHst started at different times yield significantly different results. Dogs with NOH, treated with trilostane, and monitored with ACTHst results should have all of their subsequent ACTHst tests begun at or about the same time after trilostane administration.

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.

Effect of trilostane and mitotane on aldosterone secretory reserve in dogs with pituitary-dependent hyperadrenocorticism

Background

Maximal aldosterone secretion in healthy dogs occurs 30 minutes postadrenocorticotropin (ACTH; 5 μg/kg IV) stimulation. The effect of trilostane and mitotane on aldosterone at that time is unknown.

Objectives

To assess the effect of trilostane and mitotane in dogs with pituitary‐dependent hyperadrenocorticism on aldosterone secretory reserve. To determine if aldosterone concentration correlates with electrolyte concentrations.

Animals

Serum collected from 79 client‐owned dogs and 33 stored samples.

Methods

Client‐owned dogs had ACTH stimulation tests with cortisol concentrations measured at 0 and 60 minutes and aldosterone concentrations measured at 0, 30, and 60 minutes. Stored samples had aldosterone concentrations measured at 0 and 60 minutes. Ten historical clinically healthy controls were included. All had basal sodium and potassium concentrations measured.

Results

The aldosterone concentrations in the mitotane‐ and trilostane‐treated dogs at 30 and 60 minutes post‐ACTH were significantly lower than in clinically healthy dogs; no significant difference was detected in aldosterone concentration between 30 and 60 minutes in treated dogs. However, a significantly higher percentage of dogs had decreased aldosterone secretory reserve detected at 30 minutes than at 60 minutes. At 30 minutes, decreased secretory reserve was detected in 49% and 78% of trilostane‐ and mitotane‐treated dogs, respectively. No correlation was detected between aldosterone and serum electrolyte concentrations.

Conclusions and Clinical Importance

Decreased aldosterone secretory reserve is common in trilostane‐ and mitotane‐treated dogs; it cannot be predicted by measurement of serum electrolyte concentrations. Aldosterone concentration at 30 minutes post‐ACTH stimulation identifies more dogs with decreased aldosterone secretory reserve than conventional testing at 60 minutes.

Effect of trilostane on hormone and serum electrolyte concentrations in dogs with pituitary-dependent hyperadrenocorticism

Background

The effects of trilostane on key hormones and electrolytes over 24 hours in dogs with pituitary‐dependent hyperadrenocorticism (PDH) are unknown.

Objectives

To determine the plasma concentration of cortisol, endogenous adrenocorticotropic hormone (ACTH), aldosterone, sodium, potassium, and ionized calcium concentrations, and plasma renin activity over a 24‐hour period after administration of trilostane to dogs with well‐controlled PDH.

Animals

Nine dogs (mean age 9.3 ± 0.67 years, mean weight 31.9 ± 6.4 kg) with confirmed PDH.

Methods

Prospective study. Thirty days after the first administration of trilostane, blood samples were taken at −30, 0 (baseline), 15, 30, 60, and 90 minutes, and 2, 3, 4, 6, 8, 12, 16, 20, and 24 hours after administration of trilostane and plasma concentration of cortisol, endogenous ACTH, aldosterone, sodium, potassium, ionized calcium, and renin activity were determined.

Results

Cortisol concentrations decreased significantly (P < .001) 2–4 hours after trilostane administration. From baseline, there was a significant (P < .001) increase in endogenous ACTH concentrations between hours 3–12, a significant increase (P < .001) in aldosterone concentration between hours 16–20, and a significant (P < .001) increase in renin activity between hours 6–20. Potassium concentration decreased significantly (P < .05) between hours 0.5–2.

Conclusion and Clinical Importance

Treatment with trilostane did not cause clinically relevant alterations in plasma aldosterone and potassium concentration. Results suggest that in dogs with PDH, the optimal time point for an ACTH‐stimulation test to be performed is 2–4 hours after trilostane dosing. Future studies are necessary to establish interpretation criteria for a 2‐ to 4‐hour postpill ACTH‐stimulation test.

Evaluation of aldosterone concentrations in dogs with hypoadrenocorticism

BACKGROUND

Some dogs with primary hypoadrenocorticism (HA) have normal sodium and potassium concentrations, a phenomenon called atypical Addison's disease. The assumption that the zona glomerulosa and aldosterone secretion in these dogs are normal seems widely accepted; however, aldosterone measurements are missing in most published cases.

OBJECTIVES

To measure aldosterone in dogs with HA with and without electrolyte abnormalities and to determine the time point of aldosterone peak concentrations during ACTH stimulation.

ANIMALS

Seventy dogs with HA, 22 dogs with diseases mimicking HA, and 19 healthy dogs.

METHODS

Prospective study. Blood samples were taken before and 60 minutes after injection of 250 μg ACTH in all dogs. Additional blood samples were taken 15, 30, and 45 minutes after ACTH in 7 dogs with HA and in 22 with diseases mimicking HA.

RESULTS

Baseline and ACTH-stimulated aldosterone was significantly lower in dogs with HA than in the other groups. Aldosterone was low or undetectable in 67/70 dogs with HA independently of sodium and potassium levels. In 3 dogs, sodium/potassium concentrations were normal; in 1 dog, sodium was normal and potassium decreased. In all 4, ACTH-stimulated aldosterone concentrations were below the detection limit of the assay. Aldosterone concentrations were not different at 30, 45, or 60 minutes after ACTH administration.

CONCLUSION AND CLINICAL IMPORTANCE

Cortisol and aldosterone secretion is compromised in dogs with HA with and without electrolyte abnormalities. The term atypical Addison's disease, used for dogs with primary HA and normal electrolytes, must be reconsidered; other mechanisms allowing normal electrolyte balance without aldosterone should be evaluated in these dogs.

Evaluation of baseline cortisol, endogenous ACTH, and cortisol/ACTH ratio to monitor trilostane treatment in dogs with pituitary-dependent hypercortisolism

BACKGROUND

The effectiveness of trilostane treatment is currently monitored by regular ACTH stimulation tests, which are time-consuming and expensive. Therefore, a monitoring system without a stimulation protocol and with less client expense would be preferable.

HYPOTHESIS/OBJECTIVES

The aim of our study was to evaluate if baseline cortisol, endogenous ACTH (ACTH) concentration or the baseline cortisol to ACTH ratio (cortisol/ACTH ratio) could replace the ACTH stimulation test.

ANIMALS

Forty trilostane-treated dogs with pituitary-dependent hypercortisolism (PDH) were included in this prospective study.

METHODS

A total of 148 ACTH stimulation tests and 77 ACTH concentrations and cortisol/ACTH ratios were analyzed. Control of cortisol release was classified according to cortisol concentration after ACTH administration as excessive (<1.5 μg/dL; group 1), adequate (1.5-5.4 μg/dL; group 2), or inadequate (>5.4 μg/dL; group 3).

RESULTS

Baseline cortisol concentrations had considerable overlap between excessively, adequately, and inadequately controlled dogs. Only baseline cortisol >4.4 μg/dL (in 12% of tests) was a reliable diagnosis of inadequate control. Endogenous ACTH concentrations did not differ between groups. The overlap of the cortisol/ACTH ratio between groups was large. Correct classification was only possible if the cortisol/ACTH ratio was >15, which occurred in 4% of tests.

CONCLUSIONS AND CLINICAL IMPORTANCE

To monitor trilostane treatment the ACTH stimulation test cannot be replaced by baseline cortisol, ACTH concentration, or the cortisol/ACTH ratio.

Determination of the concentrations of trilostane and ketotrilostane that inhibit ex vivo canine adrenal gland synthesis of cortisol, corticosterone, and aldosterone

OBJECTIVE

To determine whether trilostane or ketotrilostane is more potent in dogs and determine the trilostane and ketotrilostane concentrations that inhibit adrenal gland cortisol, corticosterone, and aldosterone secretion by 50%.

SAMPLE

24 adrenal glands from 18 mixed-breed dogs.

PROCEDURES

Adrenal gland tissues were sliced, placed in tissue culture, and stimulated with 100 pg of ACTH/mL alone or with 5 concentrations of trilostane or ketotrilostane. Trials were performed independently 4 times. In each trial, 6 samples (1 for each time point) were collected for each of the 5 concentrations of trilostane and ketotrilostane tested as well as a single negative control samples. At the end of 0, 1, 2, 3, 5, and 7 hours, tubes were harvested and media and tissue slices were assayed for cortisol, corticosterone, aldosterone, and potassium concentrations. Data were analyzed via pharmacodynamic modeling. One adrenal slice exposed to each concentration of trilostane or ketotrilostane was submitted for histologic examination to assess tissue viability.

RESULTS

Ketotrilostane was 4.9 and 2.4 times as potent in inhibiting cortisol and corticosterone secretion, respectively, as its parent compound trilostane. For trilostane and ketotrilostane, the concentrations that inhibited secretion of cortisol or corticosterone secretion by 50% were 480 and 98.4 ng/mL, respectively, and 95.0 and 39.6 ng/mL, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Ketotrilostane was more potent than trilostane with respect to inhibition of cortisol and corticosterone secretion. The data should be useful in developing future studies to evaluate in vivo serum concentrations of trilostane and ketotrilostane for efficacy in the treatment of hyperadrenocorticism.

Adrenocorticotropic hormone, but not trilostane, causes severe adrenal hemorrhage, vacuolization, and apoptosis in rats

Adrenal necrosis has been reported as a complication of trilostane application in dogs with hyperadrenocorticism. One suspicion was that necrosis results from the increase of adrenocorticotropic hormone (ACTH) during trilostane therapy. The aim of the current study was to assess the effects of ACTH and trilostane on adrenal glands of rats. For experiment 1, 36 rats were divided into 6 groups. Groups 1.1 to 1.4 received ACTH in different doses (60, 40, 20, and 10 μg/d) infused subcutaneously with osmotic minipumps for 16 wk. Group 1.5 received saline, and group 1.6 received no therapy. For experiment 2, 24 rats were divided into 3 groups. Group 2.1 and 2.2 received 5 and 50 mg/kg trilostane/d orally mixed into chocolate pudding for 16 wk. Eight control rats received pudding alone. At the end of the experiments, adrenal glands were assessed for necrosis by histology and immunohistochemistry; levels of endogenous ACTH and nucleosomes were assessed in the blood. Rats treated with 60 μg ACTH/d showed more hemorrhage and vacuolization and increased numbers of apoptotic cells in the adrenal glands than rats treated with 20 or 10 μg ACTH/d, trilostane, or control rats. Rats treated with 60 μg ACTH/d had a higher amount of nucleosomes in the blood compared with rats treated with 10 μg ACTH/d, trilostane, or saline. We conclude that in healthy rats ACTH, but not trilostane, causes adrenal degeneration in a dose-dependent manner. Results of this study support the hypothesis that adrenal gland lesions seen in trilostane-treated dogs are caused by ACTH and not by trilostane.

Monitoring the response of canine hyperadrenocorticism to trilostane treatment by assessment of acute phase protein concentrations

BACKGROUND

Acute phase proteins (APPS) include haptoglobin (Hp), C-reactive protein (CRP) and serum amyloid A (SAA). Increased Hp concentrations may be induced by endogenous or exogenous glucocorticoids in dogs.

OBJECTIVES

To assess whether control of hyperadrenocorticism (HAC) affects the concentrations of Hp, CRP, SAA, alkaline phosphatase (ALKP) and cholesterol, to determine whether these analytes can be used to assess control of HAC following trilostane treatment, and whether a combination of these tests offers a valid method of assessing disease control.

METHODS

Hp, CRP, SAA, ALKP and cholesterol were assessed in 11 dogs with spontaneous HAC before and after treatment with trilostane. Adequate control of HAC was defined as post-ACTH cortisol less than 150 nmol/l.

RESULTS

Significant reductions in Hp, ALKP, cholesterol and SAA (P<0.05) but not of CRP were found after control of HAC. Only Hp, cholesterol and ALKP were moderately informative (Se & Sp>0.7) of disease control when compared to adrenocorticotropin or corticotropin (ACTH) stimulation test. SAA and CRP were unhelpful (Se & Sp<0.7). The analysis of the combination of the analytes did not improve the correlation with ACTH stimulation test.

CLINICAL RELEVANCE

Relying on these analytes does not provide additional information over ACTH stimulation test results when assessing control of HAC treated with trilostane.

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.

Serum 17alpha-hydroxyprogesterone concentrations during the reproductive cycle in healthy dogs and dogs with hyperadrenocorticism

OBJECTIVE

To determine concentrations of 17alpha-hydroxyprogesterone (17OHP) in serum of healthy bitches during various stages of the reproductive cycle and in bitches with hyperadrenocorticism and to compare the dynamics of 17OHP with those of progesterone.

DESIGN

Prospective evaluation study.

ANIMALS

15 healthy sexually intact bitches and 28 spayed bitches with hyperadrenocorticism.

PROCEDURES

11 healthy bitches were evaluated during estrus, nonpregnant diestrus, and anestrus (group 1); 4 other healthy bitches were evaluated during pregnancy and after ovariohysterectomy (group 2). Cycle stages were determined via physical examination, vaginal cytologic evaluation, and serum progesterone concentration. Bitches with hyperadrenocorticism were evaluated once at the time of diagnosis (group 3). Serum hormone concentrations were determined with immunoassays.

RESULTS

In group 1, the serum 17OHP concentration was significantly higher in diestrus (median, 1.8 ng/mL) than in estrus (median, 1.1 ng/mL) and anestrus (median, 0.2 ng/mL) and higher in estrus than in anestrus. Changes in serum progesterone concentrations accounted for 22% (estrus) or 23% (diestrus) of the variation in serum 17OHP concentrations. In group 2, 17OHP and progesterone concentrations were significantly higher during pregnancy than after ovariohysterectomy. The serum 17OHP concentration in group 3 was significantly lower (median, 0.2 ng/mL) than in group 1 in estrus and diestrus and in group 2 during pregnancy (median, 0.7 ng/mL) but was not different from 17OHP concentrations in anestrus or after ovariohysterectomy (median, 0.2 ng/mL).

CONCLUSIONS AND CLINICAL RELEVANCE

Serum 17OHP concentrations in healthy bitches increased during estrus, diestrus, and pregnancy and at those times were higher than in spayed bitches with hyperadrenocorticism.

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.

Urinary corticoid: creatinine ratios in dogs with pituitary-dependent hypercortisolism during trilostane treatment

BACKGROUND

The adrenocorticotropic hormone (ACTH) stimulation test is used to evaluate trilostane treatment in dogs with hypercortisolism.

HYPOTHESIS

The urinary corticoid : creatinine ratio (UCCR) is a good alternative to the ACTH stimulation test to determine optimal trilostane dose.

ANIMALS

Eighteen dogs with pituitary-dependent hypercortisolism.

METHODS

In this prospective study, the dose of trilostane was judged to be optimal on the basis of resolution of clinical signs of hypercortisolism and results of an ACTH stimulation test. The owners collected urine for determination of UCCR at 2-week intervals for at least 8 weeks after achieving the optimal trilostane dose.

RESULTS

The UCCRs were significantly higher before treatment (11.5-202.0 x 10(-6); median, 42.0 x 10(-6)) than at rechecks 2 months after optimal dosing, but they did not decrease below the upper limit of the reference range in the majority of dogs. The UCCRs of 11 dogs that initially were dosed insufficiently (range, 7.5-79.0 x 10(-6); median, 31.0 x 10(-6)) did not differ significantly from UCCRs when the dosage was optimal (8.2-72.0 x 10(-6); median, 33.0 x 10(-6)). Post-ACTH cortisol concentrations did not correlate significantly with UCCRs at rechecks during trilostane treatment. Long-term follow-up indicated that the decrease in UCCR below the upper limit of the reference was associated with hypocortisolism.

CONCLUSION AND CLINICAL IMPORTANCE

The UCCR cannot be used as an alternative to the ACTH stimulation test to determine the optimal dose of trilostane, but might be helpful in detecting dogs at risk for developing hypocortisolism during trilostane treatment.

Trilostane-induced inhibition of cortisol secretion results in reduced negative feedback at the hypothalamic-pituitary axis

Cushing's disease caused by pituitary corticotroph adenoma in dogs is usually treated by medical treatment, and the efficacy of this treatment has been reported. However, controversy remains as to whether reduced negative feedback through the inhibition of cortisol secretion, similar to Nelson's syndrome, may appear as an adverse effect. The purpose of this study was to investigate the effect of reduced negative feedback through the inhibition of cortisol secretion by daily trilostane administration on the pituitary-adrenal axis in clinically normal dogs. Dogs were administered 5mg/kg trilostane twice a day every day for 8 weeks (n=8) or 16 weeks (n=3). After the initiation of trilostane administration, plasma adrenocorticotropic hormone (ACTH) concentrations were increased remarkably. As assessed by magnetic resonance imaging (MRI) during administration, the pituitary became enlarged. After trilostane administration, the cytoplasmic areas of the pituitary corticotrophs were increased and the ratio of pituitary corticotrophs to all cells in the anterior lobe was greater in the trilostane-treated dogs than that in untreated animals. In addition, histological examinations revealed bilateral adrenal cortical hyperplasia. Using real-time PCR quantification, the expression of proopiomelanocortin (POMC) mRNA in the pituitary and ACTH receptor (ACTH-R) mRNA in the adrenal gland was greater in the dogs treated with trilostane than in untreated dogs. These results indicate that reduced negative feedback induced hyperfunction of the pituitary corticotrophs and pituitary enlargement in healthy dogs. These changes suggest that the inhibition of cortisol secretion by trilostane may increase the risk for accelerating the growth of corticotroph adenomas in dogs with Cushing's disease.

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

The serum concentrations of cortisol and cortisone were measured in 19 healthy dogs and in 13 dogs with pituitary-dependent hyperadrenocorticism (PDH) before and one hour after an injection of synthetic adrenocorticotropic hormone (ACTH). In the dogs with pdh, the cortisol and cortisone concentrations were measured before and after one to two weeks and three to seven weeks of treatment with trilostane. The dogs with PDH had significantly higher baseline and poststimulation concentrations of cortisol and cortisone, and higher baseline cortisol:cortisone ratios than the healthy dogs. During the treatment with trilostane, the poststimulation cortisol, the baseline and poststimulation cortisone concentrations, and the baseline and poststimulation cortisol:cortisone ratios decreased significantly. The decrease in poststimulation cortisone was significantly smaller than the decrease in cortisol.

Effects of trilostane on the pituitary-adrenocortical and renin-aldosterone axis in dogs with pituitary-dependent hypercortisolism

The medical records of 63 dogs with pituitary-dependent hypercortisolism (PDH) before and during treatment with trilostane were reviewed retrospectively. The correct trilostane dosage in dogs with PDH was based on the resolution of clinical signs and the results of an adrenocorticotropic hormone (ACTH) stimulation test. The mean (+/-SD) dose rate of trilostane to achieve good clinical control was 2.8+/-1.0mg/kg bodyweight. Trilostane treatment resulted in a significant decline in basal plasma cortisol concentrations. The median plasma ACTH concentration (39 pmol/L, range 7-132 pmol/L; n=60) at the optimal trilostane dosage time was significantly higher (P<0.001) than before treatment (13 pmol/L, range 2-102 pmol/L). These values did not overlap with plasma ACTH concentrations (range 212-307 pmol/L) of five PDH dogs with trilostane-induced hypocortisolism. The median cortisol/ACTH ratio in well-controlled dogs (0.23, range 0.03-2.5; n=46) was significantly lower (P<0.001) than before treatment (2.59, range 0.27-13.25). Trilostane treatment resulted in an insignificant decrease in plasma aldosterone concentration (PAC), but the median plasma renin activity (PRA) at the time the trilostane dosage was considered optimal (265 fmol/L/s, range 70-3280 fmol/L/s; n=18) was significantly higher (P<0.001) than prior to treatment (115 fmol/L/s, range 15-1330 fmol/L/s). Similarly, the median PAC/PRA ratio during trilostane treatment (0.16, range 0.003-0.92; n=17) was significantly lower (P<0.001) than before treatment (median 0.44, range 0.04-1.33). Trilostane affected both the hypothalamic-pituitary-adrenocortical and the renin-aldosterone axes. The results also suggested that basal plasma ACTH concentration may be used to detect trilostane overdosage.

Cortisol and behavioral responses of working dogs to environmental challenges

This paper's primary objective is to analyse the physiological (cortisol) and behavioral responses of military working dogs (MWD). Dogs (N=27) were submitted twice to environmental challenges (challenge 1 and 2, 20 days in-between) composed of social (training), visual (mobile toy car) and auditory (air blast) stimuli. Cortisol levels decreased back to the baseline after the second challenge. The behavioral observations showed that these MWD were more active, and presented less stereotypic behaviors (pacing, manipulation of the environment) during both visual challenges, whereas half low posture was observed during the first but not during the second visual challenge. The present study shows that this group of MWD still has an adaptation capacity to an environmental challenge (return to baseline of the cortisol levels, a higher posture during the second than at the first challenge). These results are encouraging and indicate that the dogs might have a diminished welfare (i.e. stereotypic behaviors), but are not chronically stressed.

Pharmacological management of Cushing's syndrome: an update

The treatment of choice for Cushing's syndrome remains surgical. The role for medical therapy is twofold. Firstly it is used to control hypercortisolaemia prior to surgery to optimize patient's preoperative state and secondly, it is used where surgery has failed and radiotherapy has not taken effect. The main drugs used inhibit steroidogenesis and include metyrapone, ketoconazole, and mitotane. Drugs targeting the hypothalamic-pituitary axis have been investigated but their roles in clinical practice remain limited although PPAR-gamma agonist and somatostatin analogue som-230 (pasireotide) need further investigation. The only drug acting at the periphery targeting the glucocorticoid receptor remains Mifepristone (RU486). The management of Cushing syndrome may well involve combination therapy acting at different pathways of hypercortisolaemia but monitoring of therapy will remain a challenge.

Cushing's disease in dogs: cabergoline treatment

The treatment of pituitary-dependent hyperadrenocorticism (PDH) in dogs has for a long time been focused on inhibiting the adrenal gland using drugs such as o-p'-DDD, Ketoconazole and Trilostane, without attacking the primary cause: the corticotrophinoma. Corticotroph cells can express the D2 dopaminergic receptor; therefore cabergoline (Cbg) could be effective as a treatment. Follow-up over 4 years was carried out in 40 dogs with PDH that were treated with Cbg (0.07 mg/kg/week. Out of the 40 dogs, 17 responded to Cbg (42.5%). A year after the treatment, there was a significant decrease in ACTH (p<0.0001), alpha-MSH (p<0.01), urinary cortisol/creatinine ratio (p<0.001), and of the tumor size (p<0.0001) evaluated by nuclear magnetic resonance. Dogs responding to Cbg lived significantly longer (p<0.001) than those in the control group. To conclude, Cbg is useful in 42.5% of dogs with PDH, justifying its use as a treatment.

Trilostane in advanced breast cancer

Antiestrogens, principally tamoxifen, and aromatase inhibitors have been used as the first- and second-line therapy in patients with advanced postmenopausal breast cancer for many years. However, some patients acquire resistance to these treatments and, at present, further endocrine treatment is achieved by merely substituting the current medication with a different antiestrogen or aromatase inhibitor. Trilostane offers an alternative endocrine treatment due to its unique mode of action. It is an allosteric modulator of the estrogen receptor and targets both the estrogen- and growth factor-dependent pathways through which estradiol stimulates cell proliferation. In clinical trials, trilostane has been shown to be an effective treatment for breast cancer in patients who have relapsed after receiving treatment with one or more forms of endocrine therapy. Ongoing and future clinical trials are examining the potential for the use of trilostane in premenopausal breast cancer, as well as in other malignancies such as prostate cancer.