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BackgroundThe ACTH stimulation has low sensitivity for the diagnosis of hypercortisolism possibly as a result of biological and analytical variability.Hypothesis/ObjectivesTo report the components of biological and analytical variability in serum cortisol concentration post‐ACTH stimulation ([cortisol]) in healthy dogs.AnimalsFourteen healthy harrier hound dogs.MethodsThe 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.ResultsThe 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 ImportanceFalse‐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.

Male and female rats form a conditioned preference to copulate and/or mate with conspecifics bearing an odor that was paired with either the postejaculatory reward state in males, or paced sexual contact in females, making the odor act as a discrete partner-related cue. Here, we asked whether a somatosensory cue, a rodent jacket, could act as a discrete cue to establish a conditioned partner choice (CPC). In the first study, sexually naïve Long-Evans males and females underwent 14 copulatory conditioning trials for 30 min with their opposite sex partner in unilevel pacing chambers. On the final test, each experimental male or female was placed into an open field with two sexually receptive partners, one jacketed and the other unjacketed. A trend was found for more males to ejaculate first with jacketed females relative to the unjacketed females, whereas the females had no preference. Males and females in the second study were exposed sequentially to jacketed, sexually receptive partners, and unjacketed, sexually nonreceptive partners prior to a final open field test. Both males and females displayed a significant CPC for the jacketed opposite sex partner. This study demonstrates that a somatosensory cue previously used to establish sexual arousal as a contextual cue on rats can be used as a discrete, partner-based cue to establish a CPC for a particular partner wearing the jacket and that stronger conditioning occurs when the jacket is explicitly paired with the sexual reward state.

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