Effects of dermal dexamethasone application on ACTH and both basal and ACTH-stimulated cortisol concentration in normal horses

Systemic absorption of triamcinolone acetonide is increased from intrasynovial versus extrasynovial sites and induces hyperglycemia, hyperinsulinemia, and suppression of the hypothalamic-pituitary-adrenal axis

Steroid-associated laminitis remains a major concern with use of corticosteroids in horses. Individual case factors such as joint pathology, pre-existing endocrinopathies, or corticosteroid type, dose, and timing influencing steroid-induced laminitis risk have not been investigated. This study aimed to determine if systemic absorption of triamcinolone acetonide (TA) varies between intrasynovial (antebrachiocarpal) and extrasynovial (sacroiliac) injection sites, and to determine the effects of TA absorption on glucose, insulin, cortisol, and adrenocorticotropic hormone (ACTH). Twenty adult horses were randomized into antebrachiocarpal or sacroiliac joint injection groups, and each horse received bilateral injections with a total dose of 18 mg triamcinolone. Blood was collected prior to injection and at 1, 2, 4, 6, 8, 10, 12, 16, 20, 24, 36, 48, 60, and 72 h post-injection. Peak TA absorption occurred at 8 h in both groups, and was significantly higher in the intrasynovial group compared to the extrasynovial group (1.397 ng/mL, 0.672 ng/mL, p < 0.05). Plasma TA levels were significantly higher in the intrasynovial group from 8 to 36 h post-injection (p < 0.05). There was no difference in glucose, insulin, cortisol, or ACTH between groups at any time point. Insulin and glucose were significantly increased from baseline at all timepoints from 10-72 h and 1-72 h post-injection, respectively. Horses with elevated baseline insulin values (>20 μU/mL) from both groups experienced a more marked hyperinsulinemia, reaching a mean peak insulin of 197.5 μU/mL as compared to 90.06 μU/mL in those with normal baseline insulin. Cortisol and ACTH were significantly decreased from baseline at timepoints from 4-72 h post-injection in both groups. This study is the first to evaluate drug absorption from the sacroiliac site and demonstrates that drug absorption varies between intrasynovial and extrasynovial injection sites. TA absorption causes metabolic derangements, most notably a marked hyperinsulinemia that is more severe in horses with elevated baseline insulin values. The influence of baseline endocrinopathies on response to corticosteroid administration as well as the effect of corticosteroid-induced metabolic derangements warrant further investigation as risk factors for corticosteroid-associated laminitis.

Factors affecting measurement of basal adrenocorticotropic hormone in adult domestic equids: A scoping review

Measurement of basal adrenocorticotropic hormone (ACTH) concentration is the most commonly used diagnostic test for pituitary pars intermedia dysfunction (PPID). Although several pre-analytical and analytical factors have been reported to affect basal ACTH concentrations in equids, the extent to which these have been evaluated in the context of PPID diagnosis is unclear. The objectives of this scoping review were to identify and systematically chart current evidence about pre-analytical and analytical factors affecting basal ACTH concentrations in adult domestic equids. Systematic searches of electronic databases and conference proceedings were undertaken in June 2022, repeated in October 2022 and updated in August 2023. English language publications published prior to these dates were included. Screening and data extraction were undertaken individually by the authors, using predefined criteria and a modified scoping review data extraction template. After removal of duplicates, 903 publications were identified, of which 235 abstracts were screened for eligibility and 134 publications met inclusion criteria. Time of year, exercise, breed/type and transportation were the factors most frequently associated with significant increases in ACTH concentration (n = 26, 16, 13 and 10 publications, respectively). Only 25 publications reported inclusion of PPID cases in the study population, therefore the relationship between many factors affecting basal ACTH concentration and diagnostic accuracy for PPID remains undefined. However, several factors were identified that could impact interpretation of basal ACTH results. Findings also highlight the need for detailed reporting of pre-analytical and analytical conditions in future research to facilitate translation of evidence to practice.

Contribution of Hemogram Plan in the Horse's Clinical Evaluation

The interpretation of the blood count is essential to help the equine clinician in the diagnosis, prognosis, patient management, and control of equine diseases. Hematologic alterations often reflect the condition of the individual or an overall response to a pathological situation. A thorough clinical examination of the patient is essential to correctly interpret the hematological results. The most common abnormalities in the erythrogram are mainly anemia and polycythemia. The frequent causes of anemia in horses are acute and chronic blood loss, hemolytic anemia, and anemia caused by chronic disease. Evaluation of leukogram, including a total white cell count, a differential cell count, absolute numbers of specific leukocytes can help identify abnormalities that may suggest specific diseases such as a viral or bacterial infection, inflammatory disorders or even a neoplastic process. The platelet count is most often used to monitor or diagnose conditions that cause too much bleeding related with thrombocytopenia; it can be due to multiple mechanisms such as reduction of thrombopoiesis (myeloptisis, myelofibrosis, myeloproliferative disease, and idiopathic medullary aplasias or due to the effect of mielosuppresive drugs), increased peripheral destruction of platelets (immune mediated thrombocytopenia), consumption (dissemined intravascular coagulation) sequestration of the spleen and loss of platelets by idiopathic origin.

Relationship between glucocorticoids and prolactin during mammary gland stimulation in dairy cows

The objectives of this study were to determine the role of glucocorticoids in the regulation of prolactin (PRL) release induced by mammary gland stimulation and to investigate whether the milk depression induced by glucocorticoids in dairy cows is due to a decrease in PRL release. In experiment 1, 8 dairy cows were used in a 4 × 4 Latin square design. Four hours after the morning milking, the cows received 1 of the following treatments: (1) a 5-min manual stimulation of the mammary gland; (2) an i.v. injection of 1 mg of dexamethasone; (3) 2 infusions of 2.5 g of metyrapone (an inhibitor of cortisol biosynthesis) in the omasum 4 and 2 h before a 5-min stimulation of the mammary gland; or (4) no treatment. Sixty minutes later, the mammary gland of each cow was stimulated for 5 min. Blood samples were collected from 20 min before to 120 min after the start of the treatment. When the mammary gland was stimulated twice in 60 min, less PRL and cortisol were released during the second stimulation. Metyrapone did not affect PRL or cortisol release. Dexamethasone decreased serum cortisol concentration but did not affect PRL concentration. In experiment 2, 16 cows were used in a crossover experimental design consisting of 2 experimental weeks separated by 1 resting week. During the first week, cows were treated as follows: (1) 4 cows were injected with 0.5 g of domperidone (a PRL secretagogue) in canola oil on d 1 and 2 and 20 mg of dexamethasone on d 1; (2) 4 cows were injected with 0.5 g of domperidone on d 1 and 2; (3) 4 cows were injected with canola oil on d 1 and 2 and with 20 mg of dexamethasone on d 1; and (4) 4 cows were injected with canola oil on d 1 and 2. During the second experimental week, the same 4 treatments were repeated, except the cows that did not receive dexamethasone in the first week received it on d 1 of the second week, and cows that did receive it in the first week did not receive it in the second week. On d 1 and 2 of each week, blood samples were collected during morning milking for PRL determination. Dexamethasone reduced milk production and decreased both basal and milking-induced PRL release. It also increased milk fat and protein percentages and decreased milk lactose content. Domperidone increased basal PRL levels in serum and milk but did not affect milk yield. Although we cannot rule out the possibility that inhibition of PRL secretion or reduction of mammary gland PRL responsiveness play a role in the inhibition of milk production by glucocorticoids, the fact that enhancement of PRL secretion by domperidone could not prevent the depression of milk yield suggests that other mechanisms are involved.

Influence of external factors on hair cortisol concentrations

Measuring hair cortisol has attracted interest as a long term parameter for chronic stress evaluation. However, some studies support the hypothesis that locally produced cortisol, originating from the hair follicle or skin cells, affects concentrations in the hair. In an animal model the influence of different treatments (extensive brushing, administration of a hyperemising fluid that enhances blood circulation or a synthetic glucocorticoid) on the local cortisol production of hair was evaluated. Therefore eight sheep were sheared and the area of the skin surface of the back was quartered, with three quarters being daily subjected to a certain treatment and one quarter remaining untreated. The skin areas were sheared again after three weeks and cortisol concentrations of all wool samples were determined by immunoassay. Systemic cortisol concentrations were additionally monitored with faecal samples, indicating a significant decline in concentrations of glucocorticoid metabolites between week 1 and 2 or 3, respectively. We found no significant difference in hair cortisol concentrations between fields before treatment (p=0.310). Comparing matched fields before and after treatment, we found no significant differences in wool cortisol concentrations for fields treated with hyperemising fluid as well as for the control fields (p=0.329, p=0.097). Hairs exposed to either extensive brushing or dexamethasone fluid had significantly higher immunoreactive cortisol concentrations after three weeks of treatment (p=0.016, p=0.01). We therefore advise cautious interpretation when measuring hair cortisol concentrations as a parameter for chronic stress, because external factors may have a significant influence on the results.

Evaluation of thymus morphology and serum cortisol concentration as indirect biomarkers to detect low-dose dexamethasone illegal treatment in beef cattle

Background

Corticosteroids are illegally used in several countries as growth promoters in veal calves and beef cattle, either alone or in association with sex steroids and β-agonists, especially at low dosages and primarily through oral administration, in order to enhance carcasses and meat quality traits. The aim of the present study is to evaluate the reliability of the histological evaluation of the thymus, as well as the serum cortisol determination, in identifying beef cattle, treated with two different dexamethasone-based growth-promoting protocols and the application of different withdrawal times before slaughter.

Results

Our findings demonstrate that low dosages of dexamethasone (DXM), administered alone or in association with clenbuterol as growth promoter in beef cattle, induce morphologic changes in the thymus, resulting in increase fat infiltration with concurrent cortical atrophy and reduction of the cortex/medulla ratio (C/M). In fact, the C/M value was significantly lower in treated animals than in control ones, with both the protocols applied. The cut off value of 0.93 for the cortex/medulla ratio resulted to be highly effective to distinguish control and treated animals. The animals treated with DXM showed inhibition of cortisol secretion during the treatment period, as well as at the slaughterhouse, 3 days after treatment suspension. The animals treated with lower doses of DXM in association with clenbuterol, showed inhibition of cortisol secretion during the treatment period, but serum cortisol concentration was restored to physiological levels at slaughterhouse, 8 days after treatment suspension.

Conclusions

The histological evaluation of thymus morphology, and particularly of the C/M may represent a valuable and reproducible method applicable to large-scale screening programs, due to the easy sampling procedures at slaughterhouse, as well as time and cost-saving of the analysis. Serum cortisol determination could be considered as an useful in vivo biomarker of dexamethasone illegal treatment in beef cattle during the fattening period, whilst it does not appear to be a good biomarker at the slaughterhouse, since the protocol of DXM administration, as well as the withdrawal period could affect the reliability of the method.