Cortisol In Dogs Research Articles

Total observed error, total allowable error, and QC rules for canine serum and urine cortisol achievable with the Immulite 2000 Xpi cortisol immunoassay.

Determining a simple quality control (QC) rule for daily performance monitoring depends on the desired total allowable error (TEa) for the measurand. When no consensus TEa exists, the classical approach of QC rule validation cannot be used. Using the results of previous canine serum and urine cortisol validation studies on the Immulite 2000 Xpi, we applied a reverse engineering approach to QC rule determination, arbitrarily imposing sigma = 5, and determining the resulting TEa for the QC material (QCM; TEaQCM) and the resulting probability of error detection (Ped) for each QC rule. For the simple QC rule 12.5S with Ped = 0.96 and probability of false rejection (Pfr) = 0.03, the associated TEaQCM were 20% and 35% for serum and 28% and 24% for urine QCM1 and QCM2. If these levels of TEaQCM are acceptable for interpretation of patient sample results, then users can internally validate the 12.5S QC rule, provided that their QCM CVs and biases are similar to ours. Otherwise, more stringent QC rules can be validated by using a lower sigma to lower the TEaQCM. With spiked samples (relevant cortisol concentrations in the veterinary patient matrix) at 38.6 and 552 nmol/L of cortisol, TEaQCM at sigma = 5 were much higher (54% and 40% for serum; 90.3% and 42.8% for urine). Spiked samples generate TEa that is probably too high to be suitable for daily QC monitoring; however, it is crucial to verify spiked sample observed total error (TEo; 26% and 18% for serum, 60% and 30% for urine) < TEaQCM, and to use spiked sample TEo for patient result interpretation. In the absence of consensus TEa for cortisol in dogs, we suggest the use of a 12.5S rule, provided that users accept the associated level of TEaQCM also as clinical TEa for results interpretation.

ONTOGENETIC, BREED, AND SEASONAL FEATURES OF THE SYNTHESIS OF THYROXIN AND CORTISOL IN DOGS AND CATS

The article presents data on the breed and seasonal characteristics of the synthesis of thyroxine and cortisol in dogs of different breeds and cats that do not have a breed. It has been shown that the synthesis of thyroxine in dogs and cats depends on the breed, age and season. The functional activity of the thyroid gland in dogs decreases by 10-12, and in cats by 9-13 years of age. The highest level of thyroxine production throughout the entire research period belongs to the Griffon Petit-Brabancons. The synthesis of cortisol in dogs and cats is stable and does not undergo statistically significant changes. Seasonal dynamics of thyroxine is observed in dogs, but absent in cats. No sea-sonal dependence of cortisol synthesis has been reported in dogs and cats.

Validation study of canine urine cortisol measurement with the Immulite 2000 Xpi cortisol immunoassay.

We report here validation of the Immulite 2000 Xpi cortisol immunoassay (Siemens; with kit lot numbers <550) for measurement of urine cortisol in dogs, with characterization of the precision (CV), accuracy (spiking-recovery [SR] bias), and observed total error (TEo = bias + 2CV) across the reportable range. Linearity assessed by simple linear regression was excellent. Imprecision, SR bias, and TEo increased markedly with decreasing urine cortisol concentration. Interlaboratory comparison studies determined range-based (RB) bias and average bias (AB). The 3 biases (SR, RB, and AB) and resulting TEo differed markedly. At 38.6 and 552 nmol/L (1.4 and 20 μg/dL), between-run CVs were 10% and 4.5%, respectively, and TEoRB were ~30% and 20%, respectively, similar to observations in serum in another validation study. These analytical performance parameters should be considered for urine cortisol:creatinine ratio (UCCR) result interpretation, given that, for any hypothetical errorless urine creatinine measurement, the error % on UCCR mirrors the error % on urine cortisol. Importantly, there is no commonly used interpretation threshold for UCCR, given that UCCR varies greatly depending on measurement methods and threshold computation. To date, there is no manufacturer-provided quality control material (QCM) with target values for urine cortisol with an Immulite; for Liquicheck QCM (Bio-Rad), between-run imprecision was ~5% for both QCM levels. Acceptable QC rules are heavily dependent on the desired total allowable error (TEa) for the QCM system, itself limited by the desired clinical TEa.

Efficacy of Souroubea-Platanus Dietary Supplement Containing Triterpenes in Beagle Dogs Using a Thunderstorm Noise-Induced Model of Fear and Anxiety.

A novel botanical dietary supplement, formulated as a chewable tablet containing a defined mixture of Souroubea spp. vine and Platanus spp. Bark, was tested as a canine anxiolytic for thunderstorm noise-induced stress (noise aversion). The tablet contained five highly stable triterpenes and delivered 10 mg of the active ingredient betulinic acid (BA) for an intended 1 mg/kg dose in a 10 kg dog. BA in tablets was stable for 30 months in storage at 23 °C. Efficacy of the tablets in reducing anxiety in dogs was assessed in a blinded, placebo-controlled study by recording changes in blood cortisol levels and measures of behavioral activity in response to recorded intermittent thunder. Sixty beagles were assigned into groups receiving: placebo, 0.5×, 1×, 2×, and 4× dose, or the positive control (diazepam), for five days. Reduction in anxiety measures was partially dose-dependent and the 1× dose was effective in reducing inactivity time (p = 0.0111) or increased activity time (p = 0.0299) compared with placebo, indicating a decrease in anxiety response. Cortisol measures also showed a dose-dependent reduction in cortisol in dogs treated with the test tablet.

Short-term imepitoin treatment reduces stress level in dogs with generalized anxiety disorder

Dogs with generalized anxiety disorder exhibit constant or almost constant signs of anxiety and fear regardless of the context, impairing quality of life and daily functioning. In addition to behavior therapy, psychopharmacological interventions might be necessary for a satisfactory treatment success. In this study, we aim to characterize the effects of imepitoin compared to placebo as short-term intervention in dogs with generalized anxiety disorder. Sixty privately owned dogs with diagnosed generalized anxiety disorder participated in this trial, with a behavior test and serum cortisol measurement before treatment start and after 3 days of treatment. The treatment consisted of either imepitoin or placebo at a dose of approximately 20 mg/kg orally twice each day. The behavior test comprised 14 everyday situations presented in a standardized way. Observed behavior changes on video footage and serum cortisol were assessed for differences between the groups. After three days of treatment, no difference in anxiety-related behavior was observed between treatment groups. At the same time, the difference in cortisol between day 3 and day 0 decreased in the imepitoin group (−21.1 nmol/l in median) compared to the placebo group (+11.6 nmol/l; Mann-Whitney U, N = 49; P < 0.05). In conclusion, short-term treatment with imepitoin resulted in reduced serum cortisol in dogs with generalized anxiety disorder, indicating a lower stress level. However, it did not result in a change in behavior, which might be explained by the short treatment duration and the absence of concomitant behavior therapy.

Variations of salivary cortisol in dogs exposed to different cognitive and physical activities

Working dogs are gaining popularity for their ability to learn and perform tasks entertaining their human companions. For this reason, dogs are often subjected to various stimuli due to inter- and intra-specific interactions, environmental variations and effort required by different activities. In the present study, salivary cortisol was measured to monitor physiological response to different conditions. The first study was performed to assess the variability of salivary cortisol in dogs in usual environmental conditions. For this, salivary cortisol was measured in 10 dogs at home during three not consecutive days at three different times of the day and not significant variations between days and time of sampling were observed. In the second study, salivary cortisol was measured in dogs before and after Pointing Hunting (No. 5), Tracking for Ungulate Hunting (No. 6), Blood Tracking (No. 4), Agility Training (No. 6) and Animal Assisted Activities (AAA, No. 6). Salivary cortisol concentration significantly increased after the Pointing Hunting activity (p < .05), while salivary cortisol significantly decreased at the end of AAA session (p < .05). No significant differences in cortisol variations were observed for Tracking for Ungulate Hunting, Blood Tracking and Agility Training, before and after the activities. The response of cortisol suggests that the extent of hypothalamus–pituitary–adrenal axis activation varies between short high-intensity activities and endurance exercises. The measurement of salivary cortisol can support the trainers to evaluate the animal response to the stimulations.

TRH-induced secretion of adrenocorticotropin and cortisol in dogs with pituitary-dependent hypercortisolism

Background: In dogs, spontaneous Cushing’s syndrome is most often pituitary-dependent and caused by hypersecretion of adrenocorticotropic hormone (ACTH), resulting in increased adrenocortical glucocorticoid secretion similar to horses. In horses with Cushing’s syndrome (or pituitary pars intermedia dysfunction [PPID]) a thyrotropin-releasing hormone (TRH) stimulation test can be used for diagnosis, as TRH administration results in increased circulating ACTH and cortisol concentrations in affected horses.Objective: The aim of this study was to investigate the effect of TRH administration on the circulating ACTH and cortisol concentrations in dogs with pituitary-dependent hypercortisolism (PDH).Methods: Ten clinically normal control dogs and 10 dogs with PDH, all client owned, underwent a TRH stimulation test with measurement of plasma concentrations of ACTH and cortisol, before and after intravenous administration of 10 μg TRH/kg bodyweight.Results: Plasma ACTH concentration did not rise significantly after TRH stimulation, neither in PDH dogs nor in clinically normal dogs. In contrast, the plasma cortisol concentration did increase significantly after TRH stimulation in both groups (p = .003 in PDH and p < .001 in control). Immunohistochemistry of normal adrenal glands demonstrated the presence of TRH receptors in the whole adrenal cortex.Conclusions: The results of this study demonstrate that the TRH stimulation test should be rejected as a tool to diagnose PDH in dogs. The observed TRH-induced increase in plasma cortisol concentration without a significant rise in plasma ACTH concentration may be explained by a direct effect of TRH on adrenocortical cells mediated by adrenocortical TRH receptors.

Increased Serum and Urinary Oxytocin Concentrations after Nasal Administration in Beagle Dogs.

In recent years more and more studies have revealed the effect of extraneous oxytocin on the social behavior of dogs. The distribution of administered oxytocin in different physiologically relevant compartments is important because this knowledge forms the basis for the timing of behavior tests after the administration. Most behavioral studies rely on the non-invasive intranasal application of oxytocin. The aim of this study was to determine the time course of intranasal administered oxytocin secretion into blood and urine and also establish a connection between intranasal received oxytocin and urinary cortisol in dogs. In our experiment, four dogs received three puffs, 12 IU intranasal oxytocin treatment, two dogs received three puffs intranasal placebo treatment. Blood and urine samples were collected immediately prior to the administration then regularly during 4 h. After nasal oxytocin application, the serum oxytocin concentration increased, reached a maximum 15 min after the treatment and then rapidly returned to baseline levels 45 min later. The peak urinary oxytocin concentration occurred between 45 and 60 min after administration and returned to baseline levels slowly. We found considerable differences among individuals in the secretion of oxytocin in both the serum and the urinary oxytocin concentration measurements. Our results confirm that intranasally administered oxytocin passes into the blood stream. The time course of intranasally administered oxytocin secretion is similar to the time course of intravenously administered oxytocin secretion, and the peak values are also similar in both the serum and the urinary oxytocin concentration measurements, although there are large individual differences.

Collaboration improves dog management and welfare in tiwi islands

s / Journal of Veterinary Behavior 9 (2014) e1ee19 e12 Salivary cortisol is widely used as an indicator of stress and welfare in canine research, but much remains unclear about the basic features of this hormone marker in domestic dogs. This meta-analysis characterized a reference range for salivary cortisol in dogs, and examined population effects and experimental considerations on cortisol concentrations. Literature databases and conference proceedings from 1992-2012 were systematically reviewed and identified 62 peer-reviewed studies utilizing domestic dog salivary cortisol. Researchers were contacted via email and 31 raw data sets with a total of 5,120 samples from 1,196 dogs were shared. Metaanalysis indicated that the cortisol range was 0-33.79 mg/dL (mean 0.66 mg/dL, SEM 0.222). Significant effects were found for gender and neuter status, age, time of day, living environment, time in environment, testing environment, owner presence during testing, and collection media. Significant effects were not found for breed, weight, dog type, coat color, assay type, exercise, eating, or use of salivary stimulant. Care should be takenwhen using cortisol studies on dogs at a group or population level as there is a large amount of intraand inter-individual variability. External variables can influence salivary cortisol concentration. This analysis highlights the importance of carefully controlling experimental design in order to compare samples within and between individual dogs, in addition to establishing and using best practices for saliva collection. Caution should be exercised in comparing different studies, as the results could be to factors other than those studied.

Personality, social behavior, and cortisol in dogs visiting a dog park

Personality, social behavior, and cortisol in dogs visiting a dog park

Configuration of antibodies for assay of urinary cortisol in dogs influences analytic specificity

Whether the variation in the reported urinary corticoid-to-creatinine ratio in dogs is affected by the application of 2 commonly applied anticortisol antibodies was investigated. Free-catch morning urine samples of 50 healthy dogs were analyzed in duplicate with the use of 2 different polyclonal antibodies (antibody A and B) raised in different rabbits. Antibody A was raised against cortisol-3-carboxymethyl-oxime and antibody B against cortisol-21-hemisuccinate linked to BSA. Enzyme immunoassays were applied by using corresponding biotinylated labels. To examine possible cross-reactions with conjugated and nonconjugated cortisol metabolites, EIA measurements were performed with urine samples both before (directly assayed) and after diethyl-ether extraction, as well as after reversed-phase HPLC. Although the results correlated (P < 0.001), urinary corticoid concentrations and accordingly the urinary corticoid-to-creatinine ratios were 8 times higher when using antibody A than when using antibody B (mean ± SD corticoid concentrations, 223 ± 131 vs 29 ± 12 nmol/L; P < 0.001). Irrespective of the antibody used, extraction significantly decreased measured corticoid concentrations (antibody A, 158 ± 120 nmol/L; antibody B, 15 ± 8 nmol/L; P < 0.001), but the decrease was conspicuous when antibody A was used. Antibody A cross-reacted significantly with polar (eg, conjugated) metabolites, clearly depicted in the chromatogram by 3 additional peaks in earlier fractions well separated from cortisol. In contrast the assay that used antibody B was specific, showing only 1 major peak in the fractions eluting authentic cortisol. In summary, the study indicates that the configuration of the antibody considerably influences the analytic specificity of cortisol assays and underlines the pivotal importance of assay validation for each species and sample material.

Measurement of cortisol in dog hair: a noninvasive tool for the diagnosis of hypercortisolism

The clinical signs of hyperadrenocorticism (hypercortisolism) in dogs are known to be caused by chronic overexposure to glucocorticoids. The quantification of cortisol in serum, saliva or urine reflects the cortisol concentration at the time of sample collection, but in suspected hyperadrenocorticism it may be preferable to examine a long-term parameter of cortisol production. There is a need for a noninvasive method to monitor the long-term production of cortisol in dogs. It seems possible that measuring cortisol levels in hair could represent such a method. Hair was collected from 12 dogs with hyperadrenocorticism and from 10 healthy control dogs. Immunoreactive cortisol, cortisone and corticosterone concentrations were determined by enzyme immunoassay. High-performance liquid chromatography was performed to test the validity of the cortisol assay. Levels of immunoreactive cortisol, cortisone and corticosterone were significantly higher in dogs with hyperadrenocorticism than in control dogs. The difference was most pronounced for the cortisol level. The determination of cortisol in hair offers the advantage that sampling is easier and less invasive than taking blood, urine, faeces or saliva. Measuring cortisol in hair may represent a valuable tool for the diagnosis of hyperadrenocorticism in dogs.

Salivary Cortisol Concentrations in Healthy Dogs and Dogs with Hypercortisolism

Measurement of salivary cortisol is a useful diagnostic test for hypercortisolism (HC) in humans. To determine whether measurement of salivary cortisol concentration is a practical alternative to plasma cortisol to diagnose HC, to validate the use of salivary cortisol, and to examine the effect of time of day and sampling location on salivary cortisol. Thirty healthy dogs and 6 dogs with HC. Prospective, observational clinical trial including healthy volunteer dogs and dogs newly diagnosed with HC. Salivary and plasma cortisol concentrations were measured with an immunoassay analyzer. Intra- and interassay variability, linearity, and correlation between salivary and plasma cortisol concentrations were determined. The required 300 microL of saliva could not be obtained in 88/326 samples from healthy dogs and in 15/30 samples from dogs with HC. The intra-assay variability for measurement of salivary cortisol was 5-17.7%, the interassay variability 8.5 and 17.3%, and the observed to expected ratio 89-125%. The correlation (r) between salivary and plasma cortisol was 0.98. The time of day and location of collection did not affect salivary cortisol concentrations. Dogs with HC had significantly higher salivary cortisol values than healthy dogs (10.2 +/- 7.3 nmol/L versus 1.54 +/- 0.97 nmol/L; P < .001). The ROCHE Elecsys immunoassay analyzer correctly measured salivary cortisol in dogs. However, a broad clinical application of the method seems limited, because of the large sample volume required.

Sources of sampling variation in saliva cortisol in dogs

The main advantage of collecting saliva cortisol as opposed to plasma cortisol is that it is non-invasive and therefore it is now widely used in stress measurement studies on farm animals and dogs. Although a plasma cortisol response to handling associated with blood collection generally occurs at 3 min from the commencement of handling, there is no information in the literature on the time course of the response of salivary cortisol concentration to handling. The aims of these experiments were to (1) determine if there is a response to up to 4 min handling that affects cortisol concentration in saliva and (2) determine the main causes of variation in saliva cortisol in dogs over time. In experiment 1, saliva was collected from six Kelpies at 0 min then 2, 3 or 4 min after the commencement of restraint. There was no handling effect found in up to 4 min sampling time. In experiment 2, saliva was collected from six Labrador Retrievers five times in 2 h (14:00–16:00), three days a week for four weeks. Some of the sources of variation in saliva cortisol over time included between dog variation that varied over a period of days and variation between occasions that affected the group of dogs as a whole.

Effects of growth hormone-releasing peptides in healthy dogs and in dogs with pituitary-dependent hyperadrenocorticism

The aim of this study is to investigate the effects of ghrelin and GH-releasing peptide-6 (GHRP-6) on the release of growth hormone (GH), adrenocorticotrophic hormone (ACTH), and cortisol in dogs with pituitary-dependent hyperadrenocorticism (PDH) and in healthy dogs of comparable age. In eight healthy dogs, the responses to ghrelin and GHRP-6 were compared to those of GH-releasing hormone (GHRH) and NaCl 0.9% (control). In seven dogs with PDH, the effects of ghrelin and GHRP-6 were compared with their effects in healthy dogs. In the healthy dogs, GHRH, GHRP-6, and ghrelin caused a significant rise in plasma GH concentrations. GHRH administration elicited significantly higher plasma GH concentrations than administration of ghrelin and GHRP-6. In the dogs with PDH, the GHRP-6-induced release of GH was significantly lower than in healthy dogs. Administration of ghrelin elicited a GH release that did not differ significantly between dogs with PDH and healthy dogs. Ghrelin and GHRP-6 did not cause a significant rise in plasma ACTH and cortisol concentrations in either the healthy dogs or the dogs with PDH. It is concluded that in comparison with GHRH, GHRP-6 and ghrelin have a low GH-releasing potency in healthy dogs. In dogs with PDH, the GH release in response to GHRP-6 is impaired. Neither GHRP-6 nor ghrelin activates the pituitary–adrenocortical axis in healthy elderly dogs and dogs with PDH.

Validation and application of solid-phase chemiluminescent immunoassays for diagnosis of endocrine diseases in animals

Significant progress has been made in the ability of veterinarians to diagnose endocrine diseases since introduction and development of the radioimmunoassay (RIA) in the 1960s. Alternatives to the radioactive label have been commercialised for human diagnostic applications. Because healthy animals have concentrations of several hormones in serum that are lower than in humans, these non-isotopic assays generally lack the sensitivity for measuring hormones in animals. However, the chemiluminescent enzyme immunoassay may provide this needed sensitivity. We validated the DPC-Cirrus Immulite® automated chemiluminescent immunoassay system for measurement of cortisol in dogs, cats and horses. Serial dilutions of serum inhibited binding of alkaline phosphatase-labelled cortisol in a manner that was parallel with inhibition produced by the stored master calibration curve. Six dogs were injected with adrenocorticotropin (ACTH; 2.2 IU/kg i.m.) and five dogs were injected with dexamethasone (0.015 mg/kg i.v.). Changes in cortisol concentrations measured with the Immulite® were as expected based on published results. Similar tests of biological specificity in other species yielded similar results. Accuracy of the Immulite® cortisol assay was evaluated by comparing cortisol concentrations in serum with concentrations obtained by a validated RIA. The regression equations were: y = 14.6 + 0.8χ for dogs (n = 59, r2 = 0.91), y = 13.5 + 0.9χ for horses (n = 23, r2 = 0.90), and y = 29.8 + 1. Oχ for cats (n = 18, r2 = 0.96), where y = Immulite® result (nmol/l) and χ = RIA result (nmol/l). The regression equation for the canine urinary cortisol: creatinine ratio was y = 0.43 + 1.55χ, where y = ratio calculated from Immulite® cortisol concentrations and χ = ratio using RIA concentrations (n = 35, r2 = 0.93). Initially, the lower limit of the reportable range by the Immulite® was 27.6 nmol/l, a value that was unacceptable for veterinary diagnostics. After consultation with DPC-Cirrus, we adjusted the lower limit to 1.4 nmol/l. Coefficients of variation for two canine, one feline, and two equine quality-control serum samples included in 73 consecutive Immulite® assays ranged from 0.29 (mean = 29.0 nmol/l) to 0.09 (mean = 261.6 nmol/l). We are using the Immulite® routinely for the diagnosis of adrenal disease in animals and have found it to provide diagnostically useful cortisol results for dexamethasone-suppression and ACTH-stimulation tests. Its diagnostic accuracy on single baseline samples is probably less than for the RIA, particularly at concentrations of cortisol less than 27.6 nmol/l.

Effects of synthetic ovine corticotropin-releasing hormone on plasma concentrations of immunoreactive adrenocorticotropin, alpha-melanocyte-stimulating hormone, and cortisol in dogs with naturally acquired adrenocortical insufficiency

Summary We evaluated the effect of ovine corticotropin-releasing hormone (crh) on plasma immunoreactive (ir) concentrations of acth, α-melanocyte-stimulating hormone, and cortisol in 8 dogs with naturally acquired adrenocortical insufficiency. Of the 7 dogs with primary adrenal insufficiency, 6 had markedly high basal plasma ir-acth concentrations and exaggerated acth responses to crh administration, whereas 1 dog that was receiving replacement doses of prednisone at the time of testing had normal basal ir-acth concentrations and a nearly normal response to crh. In contrast, the 1 dog with secondary adrenocortical insufficiency had undetectable basal plasma ir-acth concentrations, which failed to increase after administration of crh. Basal plasma α-melanocyte-stimulating hormone concentrations in the dogs with adrenal insufficiency were within normal range and were unaffected by crh administration. In all 8 dogs with adrenal insufficiency, plasma cortisol concentrations were low and did not increase after administration of crh. Therefore, stimulation with crh produced 2 patterns of plasma ir-acth response when administered to dogs with naturally acquired adrenal insufficiency. Dogs with primary adrenal insufficiency had high basal plasma ir-acth concentrations and exaggerated responses to crh, whereas the dog with secondary adrenal insufficiency had undetectable basal plasma concentrations of ir-acth that did not increase after stimulation with crh.

Effects of age, sex, and body size on serum concentrations of thyroid and adrenocortical hormones in dogs

SUMMARY Thyroxine (T4), 3,5,3′-triiodothyronine (T3), and cortisol frequently are quantified in canine serum or plasma samples to aid in the diagnosis of hypothyroidism, hypoadrenocorticism, and hyperadrenocorticism. Many laboratories have established reliable references values for concentrations of these hormones in blood of clinically normal animals. However, nonpathologic factors that affect thyroidal and adrenocortical secretion may lead to misinterpretation of test results when values for individual animals are compared with reference values. The objective of the study reported here was to identify effects of age, sex, and body size (ie, breed) on serum concentrations of T3, T4, and cortisol in dogs. Blood samples were collected from 1,074 healthy dogs, and serum concentrations of the iodothyronines and cortisol were evaluated for effects of breed/size, sex, and age. Mean (± sem) serum concentration of T4 was greater in small (2.45 ± 0.06 μg/dl)- than in medium (1.94 ± 0.04 μg/dl)- or large (2.03 ± 0.03 μg/dl)-breed dogs, the same in females (2.11 ± 0.04 μg/dl) and males (2.08 ± 0.04 μ/dl), and greater in nursing pups (3.04 ± 0.05 μg/dl) than in weanling pups (1.94 ± 0.05 μg/dl), rapidly growing dogs (1.95 ± 0.04 μg/dl), and young adult (1.90 ± 0.06 μg/dl), middle-aged adult (1.72 ± 0.05 μg/dl), or old adult (1.50 ± 0.05 μg/dl) dogs. Dogs &gt; 6 years old had lower mean serum T4 concentration than did dogs of all other ages, except middle-aged adults. Mean serum T3 concentration in medium-sized dogs (1.00 ± 0.01 ng/ml) was greater than that in small (0.90 ± 0.01 ng/ml)- and large (0.88 ± 0.01 ng/ml)-breed dogs. Serum T3 concentration was lowest in nursing (0.85 ± 0.01 ng/ml) and weanling (0.77 ± 0.02 ng/ml) pups, increased in rapidly growing dogs (0.99 ± 0.01 ng/ml) and young adult dogs (1.10 ± 0.04 ng/ml), and decreased slightly in middleaged (0.98 ± 0.02 ng/ml) and old (1.01 ± 0.03 ng/ml) adult dogs. Serum T3 concentration was unaffected by sex. Mean serum cortisol concentration was greater in small (1.06 ± 0.07 μg/dl)- than in large (0.79 ± 0.03 μg/ dl)-breed dogs. Serum from nursing pups (0.57 ± 0.04 μg/ dl) contained less cortisol than did serum from older dogs (mean values ≥ 0.92 μg/dl). Serum cortisol concentration was not different between males and females. These effects of breed/size and age on serum T3, T4, and cortisol concentrations should be considered when evaluating thyroid and adrenocortical functions in dogs.

Stimulation of κ opiate receptors in intestinal wall affects stress-induced increase of plasma cortisol in dogs

In dogs, an acoustic stress (A.S.) produced by hearing of intense music (⩽90dB) through earpiees for 1 h induced a 520% maximal rise in plasma cortisol 15–30 min after the beginning of stress. Oral administration of the specific κ agonists, U-50488 (0.1 mg/kg) and PD 117302 (0.05 mg/kg), 30 min before the A.S. session reduced significantly (P<0.01) by 71.2% and 80.9% the maximal increase of plasma cortisol but did not affect the increase observed after intracerebroventricular administration of ovineCRF ng/kg). These effects which are not reproduced by intravenous administration of the drugs at similar doses, were blocked by previous treatment with MR 2266 (0.1 mg/kg) or local anesthesia and vagotomy, suggesting that κ opioid agonists inhibit the stress-induced activation of the hypothalamo-pituitary-adrenocortical (HPA) system by acting selectively on specific receptors located in the wall of the proximal gut.

Feedback suppression of ACTH secretion by cortisol in dogs: lags after large signals equal those following very small signals.

Previously, low stepwise infusions of cortisol in resting adrenalectomized dogs (plateaux less than or equal to 6 micrograms/dL) were shown to reduce ACTH secretion only after 20 min. In the present study, large, steep-sloped cortisol signals were used to try to evoke faster feedback. Adrenalectomized male mongrel dogs were maintained on exogenous steroids until 48 h before the experiment. Of the 23 experiments on 15 dogs (under light pentobarbital anesthesia), 12 were on resting dogs, 7 on dogs stressed by variable insulin infusion (keeping plasma glucose at 18-40 mg/dL), and 4 stressed as above but with 4 h of low cortisol infusion (plasma congruent to 5 micrograms/dL) before applying the feedback signal. After a 50-min control period, a 30-min feedback period was initiated by one of two i.v. cortisol signals: (a) injection of 0.3 mg/kg or (b) infusion of 46 micrograms kg-1 min-1. Both raised plasma cortisol above physiological limits (within 2 and 6 min, respectively). In each experiment, 23 timed venous blood samples were assayed for plasma ACTH and cortisol. ACTH secretion rates were calculated continuously using a validated single-compartment method. Results from both types of cortisol signals were indistinguishable, and were thus pooled. In the unstressed dogs, control-period ACTH secretion of 0.97 +/- 0.12 mU kg-1 min-1 showed no significant decline due to the feedback signal for 20.3 +/- 1.4 min.(ABSTRACT TRUNCATED AT 250 WORDS)