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Background The ACTH stimulation has low sensitivity for the diagnosis of hypercortisolism possibly as a result of biological and analytical variability. Hypothesis/Objectives To report the components of biological and analytical variability in serum cortisol concentration post- ACTH stimulation ([cortisol]) in healthy dogs. Animals Fourteen healthy harrier hound dogs. Methods The data were extracted from a separate, prospective, randomized, double-blinded, controlled discovery study in which dogs treated with vehicle control and 4 different doses of cortisone acetate ( CA) for 7 days had an ACTH stimulation test performed to confirm the dose-dependent effect of CA. The index of individuality (IoI), the critical difference between sequential measurements ( C D), and the number of measurements required to assess the homeostatic set point ( HSP) of [cortisol] with confidence intervals ( CI) of 90 and 95% were estimated. Results The IoI was equal to 1.1 and the C D was 3.3 μg/ dL (92 nmol/L). The number of measurements required to assess the HSP of [cortisol] with CI of 90 and 95% were 3 and 15, respectively. Additionally, mean [cortisol] was higher in males than in females (13.3 ± 4 μg/ dL [366 ± 114 nmol/L] vs. 11.5 ± 2.5 μg/ dL [318 ± 65 nmol/L], respectively; P = .046). As expected, treatment with CA resulted in a dose-dependent suppression of [cortisol]. Conclusions and Clinical Importance False-negative test results in hypercortisolism could occur when [cortisol] is outside of the individual's HSP and within the reference interval. The large C D emphasizes the importance of assessing clinically relevant parameters in the diagnosis and monitoring of HC. [ABSTRACT FROM AUTHOR]

Background There are breed differences in several blood variables in healthy dogs. Objective Investigate breed variation in plasma endothelin-1 ( ET-1) concentration, plasma renin activity, and serum cortisol concentration. Animals Five-hundred and thirty-one healthy dogs of 9 breeds examined at 5 centers (2-4 breeds/center). Methods Prospective observational study. Circulating concentrations of ET-1 and cortisol, and renin activity, were measured using commercially available assays. Absence of organ-related or systemic disease was ensured by thorough clinical investigations, including blood pressure measurement, echocardiography, ECG, blood and urine analysis. Results Median ET-1 concentration was 1.29 (interquartile range [ IQR], 0.97-1.82) pg/mL, median cortisol concentration 46.0 ( IQR, 29.0-80.8) nmol/L, and median renin activity 0.73 ( IQR, 0.48-1.10) ng/ mL/h in all dogs. Overall, breed differences were found in ET-1 and cortisol concentrations, and renin activity ( P < .0001 for all). Pair-wise comparisons between breeds differed in 67% of comparisons for ET-1, 22% for cortisol, and 19% for renin activity, respectively. Within centers, breed differences were found at 5/5 centers for ET-1, 4/5 centers for cortisol, and 2/5 centers for renin activity. Newfoundlands had highest median ET-1 concentration, 3 times higher than Cavalier King Charles Spaniels, Doberman Pinschers, and Dachshunds. Median renin activity was highest in Dachshunds, twice the median value in Newfoundlands and Boxers. Median cortisol concentration was highest in Finnish Lapphunds, almost 3 times higher than in Boxers. Conclusions and Clinical Importance Breed variation might be important to take into consideration when interpreting test results in clinical studies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]