Altered adrenocortical response to acute stressors or ACTH(1–24) in intensively housed pigs

In two experiments, the effect of intensive housing on behavior and adrenocortical reactivity was studied in 68 castrated male German Landrace pigs. In both experiments, half of the pigs were tethered on a partially slatted floor without straw and half were kept, as controls, in groups on straw. Prior to the study, 32 of the pigs used in the first experiment were selected according to their reaction to halothane anesthesia; for the second experiment, 36 pigs were selected according to their adrenocortical response to azaperone-metomidate anesthesia. During the 4- to 6-wk experimental period, behavioral activity was observed and adrenocortical reactivity was analyzed after stimulation with synthetic ACTH(1–24), azaperone-metomidate anesthesia, insulin-induced hypoglycemia and neostigmine-atropine. Although no difference was found in general activity between groups, tethered pigs revealed a significantly higher cortisol increase after stimulation with ACTH(1–24) in both experiments and after insulin stimulation in the second experiment. Similarly, the area below the cortisol response curve after ACTH stimulation was significantly larger in tethered pigs in the second experiment. The individual reaction pattern was positively correlated between tests, indicating this pattern is a relatively constant, individual characteristic. In contrast, no correlation was found between behavior or adrenocortical reaction pattern and sensitivity to halothane. The results suggest that tethering on a partially slatted floor constitutes a chronic stressor which changes the adrenocortical response to an additional acute stressor. This increased reactivity is revealed most clearly after stimulation with ACTH(1–24) when individual responsiveness is taken into consideration.     

Adrenocortical Response in Cows after Intramuscular Injection of Long‐Acting Adrenocorticotropic Hormone (Tetracosactide Acetate Zinc Suspension)

The objectives of this study were first to show adrenocortical response to a long‐acting adrenocorticotropic hormone preparation (tetracosactide acetate zinc suspension) (ACTH‐Z) and its effect on adrenocortical function in beef cows ( Experiment 1 ) and second to apply the ACTH‐Z challenge in dairy cows based on cortisol concentrations in milk collected at routine milking ( Experiment 2 ). In Experiment 1 , four beef cows in luteal phase were challenged with ACTH‐Z, and plasma cortisol concentrations were determined for 48 h after the injection at 30‐min to 2‐h intervals. A rapid ACTH test was conducted 3 days before and 2 h after the completion of ACTH‐Z injection for 48 h to investigate the effect on adrenocortical function. Plasma cortisol concentrations increased significantly 30 min after ACTH‐Z injection (p < 0.001), and the high cortisol levels were maintained for approximately 10 h after the injection. In Experiment 2 , eight dairy cows were subjected to ACTH‐Z challenge 1–2 weeks and 4–5 weeks post‐partum. Blood and milk samples were taken at morning and afternoon milking. All the cows showed a significant increase in cortisol concentrations in plasma as well as in skim milk 8 h after ACTH‐Z injection 1–2 weeks and 4–5 weeks post‐partum (p < 0.001). There was a significant correlation between plasma and skim milk cortisol concentrations 8 h after ACTH‐Z challenge (r = 0.74, p < 0.001). The results obtained in this study suggest that elevated levels of plasma cortisol are maintained for approximately 10 h after ACTH‐Z treatment without adverse effect on adrenocortical function and a long‐acting ACTH‐Z challenge based on cortisol concentrations in milk, which were collected at the morning and the afternoon milking, can be a useful tool to monitor adrenocortical function in cows.     

Assessment of adrenocortical activity by non-invasive measurement of faecal cortisol metabolites in dromedary camels (Camelus dromedarius)

The aim of this study was to determine whether glucocorticoid production could be monitored non-invasively in dromedary camels by measuring faecal cortisol metabolites (FCMs). Five Sudanese dromedaries, two males and three females, were injected with a synthetic adrenocorticotropic hormone (ACTH) analogue. Blood samples were collected pre- and post-ACTH injection. Faeces were sampled after spontaneous defecation for five consecutive days (2 days before and 3 days after ACTH injection). Baseline plasma cortisol values ranged from 0.6 to 10.8 ng/ml in males and from 1.1 to 16.6 ng/ml in females, while peak values after ACTH injection were 10.9–41.9 in males and 10–42.2 ng/ml in females. Peak blood cortisol values were reached between 1.5 and 2.0 h after ACTH injection. The concentration of FCMs increased after ACTH injection in the faeces of both sexes, although steroid levels peaked earlier in males [24 h; (286.7–2,559.7 ng/g faeces)] than in females [36–48 h; (1,182.6–5,169.1 ng/g faeces)], reflecting increases of 3.1–8.3- and 4.3–8-fold above baseline levels. To detect chromatographic patterns of immunoreactive FCMs, faecal samples with high FCM concentrations from both sexes were pooled and subjected to reverse phase high performance liquid chromatography (RP-HPLC). RP-HPLC analysis revealed sex differences in the polarity of FCMs, with females showing more polar FCMs than males. We concluded that stimulation of adrenocortical activity by ACTH injection resulted in a measurable increase in blood cortisol that was reliably paralleled by increases in FCM levels. Thus, measurement of FCMs is a powerful tool for monitoring the adrenocortical responses of dromedaries to stressors in field conditions.     

Use of a low dose synthetic ACTH challenge test in normal and prednisone-treated dogs

The utility of a low dose (1 microgram/kg) synthetic ACTH challenge test in detecting moderate reductions in adrenocortical sensitivity in dogs was examined. First, the adrenocortical responses to an intravenous bolus of either 1 microgram/kg or 0.25 mg per dog of synthetic ACTH were compared in two groups of normal dogs. While plasma cortisol concentrations were similar in both groups 60 minutes after ACTH injection, dogs given 0.25 mg ACTH showed continued elevations in plasma cortisol concentrations at 90 and 120 minutes after ACTH injection. Later, the dogs previously tested with the 1 microgram/kg ACTH challenge were given a single intramuscular dose of prednisone (2.2 mg/kg) and retested with 1 microgram/kg of ACTH one week later. Plasma cortisol levels were significantly reduced after ACTH injection in dogs previously given prednisone demonstrating that a single intramuscular prednisone dose causes detectable adrenocortical suppression one week after administration. The 1 microgram/kg synthetic ACTH challenge test provides a sensitive means for evaluating adrenocortical suppression in dogs.     

Plasma cortisol response to exogenous ACTH in 22 dogs with hyperadrenocorticism caused by adrenocortical neoplasia

The plasma cortisol response to exogenous ACTH (ACTH stimulation test) was evaluated in 22 dogs with hyperadrenocorticism caused by adrenocortical neoplasia. The mean basal cortisol concentration (6.3 microgram/dl) was high, but 7 dogs had basal cortisol concentrations that were within normal range. Administration of exogenous ACTH increased the plasma cortisol concentrations in each dog. Normal post-ACTH cortisol concentrations were found in 9 (41%) of the 22 dogs; 13 (59%) had an exaggerated increase in cortisol concentrations after ACTH administration. In 9 of 13 dogs with carcinoma and in 4 of 9 with adenoma, the cortisol response was exaggerated. The mean post-ACTH cortisol concentration in the dogs with carcinoma was approximately 4 times that of the dogs with adenoma; the 7 dogs with the highest concentrations had carcinoma. Repeat studies were performed in 6 dogs 2 to 8 weeks after initial testing. In 5 of the 6 dogs, repeat testing yielded data of similar diagnostic significance. One dog, however, had an abnormally high post-ACTH cortisol concentration at initial evaluation, but had only a minimal response to ACTH administration, with a normal post-ACTH cortisol concentration, at time of resting. Although ACTH stimulation testing is useful in diagnosing hyperadrenocorticism, it can not reliably separate dogs with hyperfunction adrenocortical tumors from clinically normal dogs or from dogs with pituitary-dependent hyperadrenocorticism (bilateral adrenocortical hyperplasia).     

Effects of single intravenous doses of dexamethasone on baseline plasma cortisol concentrations and responses to synthetic ACTH in healthy dogs

The duration of adrenocortical suppression resulting from a single IV dose of dexamethasone or dexamethasone sodium phosphate was determined in dogs. At 0800 hours, 5 groups of dogs (n = 4/group) were treated with 0.01 or 0.1 mg of either agent/kg of body weight or saline solution (controls). Plasma cortisol concentrations were significantly (P less than 0.01) depressed in dogs given either dose of dexamethasone or dexamethasone sodium phosphate by posttreatment hour (PTH) 2 and concentrations remained suppressed for at least 16 hours. However, by PTH 24, plasma cortisol concentrations in all dogs, except those given 0.1 mg of dexamethasone/kg, returned to control values. Adrenocortical suppression was evident in dogs given 0.1 mg of dexamethasone/kg for up to 32 hours. The effect of dexamethasone pretreatment on the adrenocortical response to ACTH was studied in the same dogs 2 weeks later. Two groups of dogs (n = 10/group) were tested with 1 microgram of synthetic ACTH/kg given at 1000 hours or 1400 hours. One week later, half of the dogs in each group were given 0.01 mg of dexamethasone/kg at 0600 hours, whereas the remaining dogs were given 0.1 mg of dexamethasone/kg. The ACTH response test was then repeated so that the interval between dexamethasone treatment and ACTH injection was 4 hours (ACTH given at 1000 hours) or 8 hours (ACTH given at 1400 hours). Base-line plasma cortisol concentrations were reduced in all dogs given dexamethasone 4 or 8 hours previously.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hyperadrenocorticism in cats: seven cases (1978-1987)

Hyperadrenocorticism was diagnosed in 7 cats with concurrent diabetes mellitus. Four cats had pituitary adenoma with bilateral adrenocortical hyperplasia, 1 cat had pituitary carcinoma with bilateral adrenocortical hyperplasia, 1 cat had adrenocortical carcinoma, and 1 cat had adrenocortical adenoma of the left adrenal gland. One year later, adrenocortical adenoma involving the right adrenal gland also was diagnosed in this cat. Clinical signs included polyuria and polydipsia (n = 7), development of pot-bellied appearance (n = 5), dermatologic alterations (n = 5), lethargy (n = 3), weight loss (n = 3), dyspnea/panting (n = 2), and recurrent bacterial infections (n = 2). In 6 cats, the diagnosis of hyperadrenocorticism was established before death on the basis of results of the ACTH stimulation test (n = 3) and the dexamethasone screening test (n = 5). Pituitary-dependent hyperadrenocorticism was differentiated from adrenocortical neoplasia on the basis of results of the dexamethasone suppression test (n = 4), endogenous ACTH concentration (n = 3), results of abdominal radiography and ultrasonography (n = 3), and exploratory celiotomy (n = 1). Four cats died or were euthanatized without treatment attempts. Treatment with mitotane followed by 60Co teletherapy was ineffective in one cat with pituitary adenoma. One cat with pituitary carcinoma died one week after bilateral adrenalectomy. Bilateral adrenocortical adenomas were removed surgically in the affected cat.     

Plasma beta-endorphin and adrenocorticotrophin in young horses in training

A controlled period of submaximal exercise on a treadmill was used as a standardised stress test in 6 young horses to monitor the effects of training. Circulating plasma concentrations of immunoreactive beta-endorphin (IR beta-EP) were measured before, during and after the exercise period. The stress test was conducted on 3 occasions during an intensive training program lasting 14 weeks. In week 3 a marked increase in plasma IR beta-EP (P = 0.003) was demonstrated as a result of training, but by the last exercise test performed in week 9 no significant increase in plasma IR beta-EP concentrations could be detected. During the training period the basal concentrations of plasma IR beta-EP significantly decreased (P = 0.0059). Plasma adrenocorticotrophin (ACTH) did not increase during exercise, although there was a trend of decreasing basal plasma ACTH by the end of the training period. It was concluded that a standardised work test acted as a mild stress to unfit horses, but as the horses' fitness increased the hormonal response to exercise diminished. Basal plasma beta-EP concentrations were decreased with increasing fitness.     

Effects of a program of human interaction and alterations in diet composition on activity of the hypothalamic-pituitary-adrenal axis in dogs housed in a public animal shelter

OBJECTIVE: To determine whether a program of human interaction or alterations in diet composition would alter activity of the hypothalamic-pituitary-adrenal (HPA) axis in dogs housed in an animal shelter. DESIGN: Prospective study. ANIMALS: 40 dogs. PROCEDURE: Dogs were (n = 20) or were not (20) enrolled in a program of regular supplemental human interaction (20 min/d, 5 d/wk, for 8 weeks) involving stroking, massaging, and behavioral training. In addition, half the dogs in each group were fed a typical maintenance-type diet, and the other half were fed a premium diet. Plasma cortisol and ACTH concentrations were measured during weeks 0, 2, 4, and 8 and before and after exposure to a battery of novel situations during weeks 0 and 8. RESULTS: Plasma cortisol concentration was significantly decreased by week 2, but plasma ACTH concentration was not significantly decreased until week 8 and then only in dogs fed the premium diet. Following exposure to novel situations, plasma cortisol and ACTH concentrations were significantly increased. However, during week 8, dogs enrolled in the program of human interaction had significantly lower increases in cortisol concentration than did dogs not enrolled in the program. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that both a program of human interaction and alterations in diet composition have moderating effects on activity of the HPA axis in dogs housed in an animal shelter and that activity of the HPA axis may be increased for a longer period during shelter housing than measurement of plasma cortisol concentration alone would suggest.     

Hypothalamo‐pituitary‐adrenocortical axis in stress‐susceptible and stress‐resistant pigs: endocrine responses to corticotrophin‐releasing factor and vasopressin*

Swiss Landrace pigs selected into genetically well‐characterized low and high tissue fat lines (f and F respectively) react differently to exogenous and endogenous stressors. Response of the hypothalamo‐pituitary‐adrenocortical (HPA) axis to i.v. administered ovine corticotrophin‐releasing factor (oCRF) and lysine vasopressin (LVP) in young females, intact and pretreated with dexamethasone or metyrapone, leads to the conclusion that different stress susceptibility of the two lines correlates with the sensitivity of pituitary corticotrophs to oCRF stimulation. Total amount of ACTH released after stimulation with submaximal oCRF doses was roughly equal in both lines, and cortisol level is even lower in the f‐line, most likely due to the considerably enhanced metabolic clearance rate of cortisol (lower half‐life of plasma cortisol compared with F‐line). LVP‐stimulated ACTH release is comparable with that of oCRF is stronger in the f‐line. Combined effect of oCRF and LVP is rather additive than synergistic but the half‐life ratio cortisol/ACTH after this stimulation is about four times higher than for stimulation by LVP and oCRF separately. In cases of externally stimulated HPA axis, cortisol plasma concentration tightly cross‐correlates with that of ACTH.     

Adrenocortical suppression in the dog after a single dose of methylprednisolone acetate

Adrenal function was assessed in dogs after intramuscular administration of a single dose of methylprednisolone acetate (MPA). Twelve dogs were test challenged with adrenocorticotropic hormone (ACTH) and then assigned randomly to 1 of 3 groups and given MPA. Individual groups were test challenged with ACTH 2, 3, or 4 weeks later. All dogs were rechallenged 5 weeks after MPA administration. Plasma cortisol concentration was determined by radioimmunoassay. Basal plasma cortisol (time 0) was depressed on weeks 2 and 3, but not on weeks 4 and 5. Adrenal response to ACTH (increment of cortisol change) was suppressed on weeks 2, 4, and 5, but not on week 3. It was concluded that a single dose of MPA is capable of altering adrenal cortical function in dogs for at least 5 weeks.     

Presumptive iatrogenic hypoadrenocorticism induced by high‐dose ketoconazole administration in a dog

A 11‐year‐old male neutered Shih Tzu was referred to a tertiary facility with a history of weight loss, decreased appetite, polydipsia, and lethargy. The dog had a 10‐year history of nonspecific allergic dermatitis and was being treated with 16 mg/kg of ketoconazole q12h for Malassezia dermatitis. Vague gastrointestinal signs, hypocholesterolemia, and lack of a stress leukogram increased suspicion for hypoadrenocorticism (HA). An adrenocorticotropic hormone (ACTH) stimulation test identified hypocortisolemia on pre‐ and post‐ACTH samples and ketoconazole was discontinued. After a short course of corticosteroid treatment, an ACTH stimulation test was repeated and pre‐ACTH cortisol concentration was within the reference range, and the post‐ACTH cortisol concentration was mildly increased. The temporal association between return of adequate adrenocortical cortisol production and discontinuation of ketoconazole led to the conclusion that the dog had developed iatrogenic HA secondary to ketoconazole treatment.     

Cortisol secretion after adrenocorticotrophin (ACTH) and Dexamethasone tests in healthy female and male dogs

Background

For the conclusive diagnosis of Cushing''s Syndrome, a stimulating ACTH test or a low suppressive Dexamethasone test is used. Reports in other species than the dog indicate that plasma cortisol concentration after ACTH administration is affected by gender. We investigated the effect of gender on the cortisol response to ACTH and Dexamethasone tests in dogs.

Methods

Seven healthy adult Cocker Spaniels (4 females and 3 males) were assigned to a two by two factorial design: 4 dogs (2 females and 2 males) received IV Dexamethasone 0.01 mg/kg, while the other 3 dogs received an IV saline solution (control group). Two weeks later the treatments were reversed. After one month, ACTH was given IV (250 μg/animal) to 4 dogs (2 female and 2 males) while the rest was treated with saline solution (control group). Cortisol concentrations were determined by a direct solid-phase radioimmunoassay and cholesterol and triglycerides by commercial kits.

Results and Discussion

No effect of treatment was observed in metabolite concentrations, but females presented higher cholesterol concentrations. ACTH-treated dogs showed an increase in cortisol levels in the first hour after sampling until 3 hours post injection. Cortisol concentrations in Dexamethasone-treated dogs decreased one hour post injection and remained low for 3 hours, thereafter cortisol concentrations increased. The increase in cortisol levels from one to two hours post ACTH injection was significantly higher in females than males. In Dexamethasone-treated males cortisol levels decreased one hour post injection up to 3 hours; in females the decrease was more pronounced and prolonged, up to 5 hours post injection.

Conclusion

We have demonstrated that cortisol response to ACTH and Dexamethasone treatment in dogs differs according to sex.     

In vitro study of the function of adrenocortical cells from pigs of differing in vivo response to adrenocorticotropin

A study was conducted to determine whether within-breed differences in adrenocortical response to exogenous adrenocorticotropin (ACTH) might be accounted for by differences in responsiveness of the adrenocortical cells per se. Large White x Landrace male pigs (n = 20) were used; 10 had high adrenocortical response to ACTH administration and 10 had low response. Five high and 5 low responders were euthanatized at 15 weeks of age, and the remaining 5 high and 5 low responders were euthanatized at 21 weeks of age. Adrenal glands were removed and weighed, and adrenocortical cells were dispersed by tryptic digestion and incubated for 2 hours with synthetic ACTH at concentrations ranging from 0.5 to 10,000 pg/ml. Samples were taken at 30-minutes intervals, and cortisol concentration was determined by use of a radioimmunoassay. Results indicate that for pigs of both age groups, high responders had heavier adrenal glands, with higher adrenocortical cell density and higher cell yield than did low responders. Synthetic ACTH had a stimulatory effect on dispersed porcine adrenocortical cells, as indicated by changes in cortisol concentration in vitro. Adrenocortical cells from high responders produced less cortisol, on a per-cell basis, than did those from low responders. However, when corrected for total cell yield, the potential cortisol production by each pair of adrenal glands was significantly (P less than 0.05) higher in the high responders than in the low responders. Thus, high-responding pigs have larger adrenal glands and higher adrenocortical cell density, which may result in higher output of cortisol after ACTH administration or exposure to stressors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic linkage mapping of quantitative trait loci for behavioral and neuroendocrine stress response traits in pigs

A QTL analysis of behavioral and neuroendocrine responses to a "novel environment" stress was conducted in a three-generation experimental cross between Meishan and Large White pig breeds. A total of 186 F2 males and 182 F2 females were studied for their behavioral and neuroendocrine reactivity to a novel environment test at 6 wk of age. Locomotion, vocalization, and defecation rate, as well as exploration time, were measured for 10 min. Blood samples were taken immediately before and after the test to measure plasma levels of ACTH, cortisol, and glucose. Animals were typed for a total of 137 markers covering the entire porcine genome. Analyses were performed using two interval mapping methods: a line-cross regression method, where founder lines were assumed to be fixed for different QTL alleles, and a half-/full-sib maximum likelihood method where allele substitution effects were estimated within each half-/full-sib family. Both methods revealed a highly significant gene effect for poststress cortisol level (P < 0.001) and a significant effect for basal cortisol level (P < 0.05) at the end of the q arm of chromosome 7, explaining, respectively, 20% and 7% of the phenotypic variance. Meishan alleles are associated with higher cortisol levels and are partially dominant (for poststress levels) over Large White alleles. Other significant gene effects on biological measures were detected on chromosomes 1 and 17 (ACTH response to stress), 3, 5, and 8 (glucose levels). The SSC 17 QTL explains 12% of the phenotypic variance of poststress ACTH levels, with a suggestive evidence of imprinting effects. Meishan alleles are associated with lower poststress ACTH levels. Gene effects of low amplitude only were found for behavioral reactivity traits. Considering the effects of stress neuroendocrine systems on energy fluxes and protein deposition, and the importance of stress reactivity for meat quality and animal welfare, these results open new perspectives for pig selection.     

Behavioural and Pituitary-Adrenal Axis Responses of Tethered Cows or Cows Kept in Pens with Slatted Floors

Abstract

The objective was to examine behavioural and physiological reactions of cows in pens with slatted floors, when pretreatment was tethering in stalls. Ten cows were kept tethered (C), whereas 10 other cows were kept loose in pens with slatted flooring (S). Cow behaviour was observed prior to treatment, and after 4 and 8 weeks, and behaviour in two open-field tests was recorded. Serial plasma concentrations of ACTH and cortisol were measured on day 23 during a 7.5 h period. On d 24, cortisol response was measured in serial samples drawn 0.5 h prior to and for 5 h after intravenous ACTH administration. S-cows showed reduced lying duration and frequency and spent less time exploring and more time immobile in the first test. S-cows showed a slightly increased response to ACTH-injection, otherwise pituitary-adrenal axis reactions did not differ between treatment groups.     

Cardiovascular effects of intermittent or continuous treadmill conditioning in horses

Nine mature Quarter Horse mares were trained for ten weeks by continuous (n=4) or intermittent (n=5) treadmill work. Both groups of horses trotted at 3.3m/sec. The continuous work was performed at a 3% incline while the intermittent work was done at a 9% incline. Heart rate, cardiac output and blood lactate concentration were measured during a standard exercise test that included work on both treadmill grades before and after five and ten weeks of training. The two conditioning programs did not produce differences in the measured parameters of the two groups of horses. However, there was an overall conditioning effect observed in both groups of horses throughout the ten weeks of treadmill conditioning. Heart rate decreased (P<.05) during exercise on both treadmill grades after ten weeks of training. Lactate concentration decreased (P<.05) during the 9 percent grade trot after five weeks of training. Only slight further decreases occurred between week five and week ten of conditioning. Cardiac output increased (P<.05) between rest and exercise on both grades but there was no conditioning effect.     

Evaluation of a six-hour combined dexamethasone suppression/ACTH stimulation test in dogs with hyperadrenocorticism

Seventeen dogs with hyperadrenocorticism were studied. Three dogs had functioning adrenocortical tumors and 14 had pituitary-dependent hyperadrenocorticism. Each dog was evaluated by determining the endogenous plasma ACTH concentration and by performing 4 tests: ACTH stimulation, dexamethasone screening, dexamethasone suppression, and a 6-hour combined dexamethasone suppression/ACTH stimulation test. The combined test was less reliable as a screening test in diagnosing hyperadrenocorticism than was the dexamethasone screening test or the ACTH stimulation test. Compared with the endogenous plasma ACTH concentration, results of the dexamethasone suppression portion of the combined test were less reliable in distinguishing dogs with adrenocortical tumors from those with pituitary-dependent hyperadrenocorticism. It was concluded that the combined test cannot be recommended for use.     

Histochemical studies on the zona reticularis of stress-susceptible pigs

During an investigation into the role of the adrenal gland in stress susceptibility of pigs, the large lipid masses in the inner zona reticularis were seen to be particularly related to sex differences, although stress-susceptible castrates had significantly more lipid in this zone than had stress-resistant castrates. Significant histochemical differences were also found in the activity of glucose-6-phosphate dehydrogenase and succinic dehydrogenase between the sexes and between castrates of differing susceptibility to stress. The differences in histochemical activity suggest a different origin for some of the adrenocortical cells in the inner zona reticularis.     

Cyclic estrous-like behavior in a spayed cat associated with excessive sex-hormone production by an adrenocortical carcinoma

A 15-year-old, spayed female domestic shorthair cat was evaluated for 1-year duration of cyclic intermittent estrous behavior. Diagnostic testing performed before referral, including baseline progesterone concentration, human chorionic gonadotropin (hCG) hormone stimulation test and surgical exploratory laparotomy, had remained inconclusive for a remnant ovary. Evaluation of sex hormones before and after adrenocorticotropic hormone (ACTH) administration revealed increased basal concentrations of androstenedione, estradiol, progesterone, and 17α-hydroxyprogesterone and normal ACTH-stimulated hormone concentrations. Enlargement of the right adrenal gland was identified by abdominal ultrasound. The cat underwent an adrenalectomy and histopathology of the excised adrenal gland was consistent with an adrenocortical carcinoma. Clinical signs resolved immediately following surgery, and most hormone concentrations declined to within or below the reference interval (RI) by 2 months after surgery.