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

Adrenal cortex stimulation with hCG in spayed female dogs with Cushing's syndrome: Is the LH-dependent variant possible?

Background:

The expression and overexpression of luteinizing hormone (LH) receptors in the canine adrenal gland cortex have been reported. Therefore, it was hypothesized that a LH-dependent form of Cushing’s syndrome (CS) could exist in dogs.

Aim:

To assess whether the adrenal gland post-ovariectomy (OVx) exhibits a greater response to adrenocorticotrophin (ACTH) stimulation; to evaluate whether the adrenal gland responds to human chorionic gonadotropin (hCG) stimulation by increasing the release of cortisol; and to consider whether hCG stimulus testing would be useful as a diagnosis for possible cases of LH-dependent CS.

Methods:

Cortisol concentrations were measured from healthy female dogs (n=16) at baseline and following ACTH stimulation before and 2 months after gonadectomy (OVx). Cortisol concentrations were also measured for female dogs with CS (n = 14) following administration of hCG (5000 IU). A post-hCG cortisol concentration greater than 140 nmol/l was used to define dogs with LH-dependent Cushing’s syndrome.

Results:

In normal female dogs, both pre- and post-stimulation cortisol concentrations increased following OVx (p = 0.002 and p = 0.0003, respectively). In female dogs with CS, cortisol concentrations increased following stimulation with hCG in 57% (8/14; p = 0.002). Age at the time of OVx was associated (p = 0.015) with the cortisol response to hCG [8 (5–9) years vs. 3.5 (2–6) years, p = 0.0013).

Conclusion:

Based on these results, an LH-dependent form of CS occurs in spayed female dogs, and that it is more likely to occur when female dogs are spayed later in life.

Changes in the Canine Plasma Lipidome after Short- and Long-Term Excess Glucocorticoid Exposure

Glucocorticoids (GCs) are critical regulators of metabolic control in mammals and their aberrant function has been linked to several pathologies. GCs are widely used in human and veterinary clinical practice as potent anti-inflammatory and immune suppressive agents. Dyslipidaemia is a frequently observed consequence of GC treatment, typified by increased lipolysis, lipid mobilization, liponeogenesis, and adipogenesis. Dogs with excess GC show hyperlipidaemia, hypertension, and a higher risk of developing type 2 diabetes mellitus, but the risk of developing atherosclerotic lesions is low as compared to humans. This study aimed to examine alterations in the canine plasma lipidome in a model of experimentally induced short-term and long-term GC excess. Both treatments led to significant plasma lipidome alterations, which were more pronounced after long-term excess steroid exposure. In particular, monohexosylceramides, phosphatidylinositols, ether phosphatidylcholines, acyl phosphatidylcholines, triacylglycerols and sphingosine 1-phosphates showed significant changes. The present study highlights the hitherto unknown effects of GCs on lipid metabolism, which will be important in the further elucidation of the role and function of GCs as drugs and in metabolic and cardiovascular diseases.

Metabolite-inactive etomidate analogues alleviating suppression on adrenal function in Beagle dogs

Owing to rapid generation in body, the metabolites of etomidate softdrug are able to accumulate in either the brain or periphery and subsequently affect the recovery from anaesthesia or cause corticosteroid suppression. This study was designed to investigate the ability of two etomidate analogues (ET-26, ET-42) with inactive metabolites to provide anaesthesia with lesser corticosteroid suppression. The 50% effective dose (ED₅₀) of ET-26, ET-42, Etomidate, MOC-ET (an etomidate softdrug) and CPMM (an improved etomidate softdrug) required to induce anaesthesia intravenously in Beagle dogs were 1.44mg/kg, 0.72mg/kg, 0.43mg/kg 23.12mg/kg and 0.59mg/kg, respectively. After adrenocorticotropic hormone (ACTH) stimulation, the serum concentrations of cortisol and corticosterone in the ET-26, ET-42 and CPMM groups were similar to those of controls, and significantly higher than those of the etomidate and MOC-etomidate groups (P<0.05). Furthermore, no significant differences in serum concentrations of cortisol and corticosterone after ACTH-stimulation between ET-26, ET-42, CPMM, and blank control groups were observed. In this study, anaesthetic potencies of ET-26 (ED₅₀=1.44mg/kg) and ET-42 (ED₅₀=0.72mg/kg) were determined. Both analogues can significantly reduce the corticosteroid suppression in vivo. Metabolite-inactive etomidate derivatives with slow metabolism might provide a novel strategy to improve Etomidate associated corticosteroid suppression.

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.

Immunohistochemical analysis of the hypothalamic-pituitary-adrenal axis in dogs: Sex-linked and seasonal variation

This study evaluated sexual dimorphism and seasonal variations in corticotrophs and adrenal zona fasciculata in dogs, as well as the expression of oestrogen receptor alpha (ERα). An immunohistochemical analysis was conducted in pituitaries for ACTH and in adrenal glands for ERα and for the melanocortin-2-receptor (MC2R) in winter and summer. Double immunofluorescence was performed to identify ERα in corticotrophs. Females had a greater proportion of corticotrophs per field (p<0.01), with a greater cellular area and optical density (p<0.001) than males. Optical density of corticotrophs was greater in winter for both sexes (p<0.001). In zona fasciculata, ERα and MC2R expression was greater in females (p<0.001) and was greater in winter (p<0.001). ERα was identified in corticotrophs. This study is the first to demonstrate ERα expression in corticotrophs and the adrenal cortex in dogs, providing evidence for sexual dimorphism and seasonal variations.

Effects of continuous infusion of etomidate at various dose rates on adrenal function in dogs

BACKGROUND

Etomidate is a commonly used sedative in intravenous anesthesia. The aim of this study was to compare the effects of various etomidate doses administered by continuous infusion on adrenal function in dogs under general anesthesia.

METHODS

Thirty-six healthy adult male dogs were randomly divided into six groups. Sodium pentobarbital alone was administered to the control group (group C); five experimental groups (E1, E2, E3, E4, and E5) were also given etomidate at doses of 10, 15, 20, 25, and 30 μg · kg(-1) · min(-1), respectively, to maintain anesthesia. Heart rate (HR), mean arterial pressure (MAP), and bispectral index (BIS) were monitored. Serum cortisol, aldosterone, adrenaline, and noradrenaline levels were measured, and HR, MAP, and BIS values recorded, before intubation (T0), and at 1 h, 2 h, and 3 h after intubation (T1-3).

RESULTS

Cortisol and aldosterone levels in groups E1-5 decreased as the doses and times of continuous infusion of etomidate increased. The cortisol level was significantly decreased compared with baseline at T3 in group E1 and at T1-3 in groups E2-5 (P < 0.05). Compared with the corresponding levels in group C, cortisol levels were significantly lower than T0 values at T3 in group E1 and at T1-3 in groups E2-5 (P < 0.05). The aldosterone level was significantly lower at T3 in group E2 and at T1-3 in groups E3-5 (P < 0.05). Significant reductions in cortisol levels at T2-3 in group E2 and at T1-3 in groups E3-5 compared with group C were also observed (P < 0.05). The plasma adrenaline and noradrenaline levels, HR, MAP, and BIS in groups E1-5 were within the normal range at the different times and with the different doses (P > 0.05).

CONCLUSIONS

Cortisol and aldosterone levels decreased with time and continuous infusion of etomidate; there were no significant changes in adrenaline and noradrenaline levels, HR, MAP, and BIS in any group.

Tailored reference limits for urine corticoid:creatinine ratio in dogs to answer distinct clinical questions

To establish reference intervals for the urinary corticoid:creatinine ratio (UCCR) determined by chemiluminometric immunoassay, UCCR was measured by this method in 50 healthy dogs. To assess the diagnostic performance of different cut-off levels, the UCCR of 66 dogs with hyperadrenocorticism and 87 dogs with diseases mimicking hyperadrenocorticism were used to construct a receiver operating characteristic (ROC) curve. The upper reference limit derived from morning samples in healthy dogs was 30.81 × 10(-6). The area under the ROC curve was 0.94. The diagnostic cut-off with the highest negative likelihood ratio was 26.5 × 10(-6) (sensitivity 1, specificity 0.54), whereas the cut-off with the highest positive likelihood ratio was 161.2 × 10(-6) (specificity 0.988, sensitivity 0.515). The application of these two different diagnostic cut-offs eliminated the necessity to perform additional tests in 53 per cent of the patient population.