Topic:Cortisol
Cortisol is a steroid hormone produced by the adrenal glands in horses, playing a significant role in the regulation of metabolism, immune response, and stress management. As a glucocorticoid, cortisol influences various physiological processes, including glucose metabolism, inflammation modulation, and the maintenance of homeostasis during stress. Its levels in horses can vary due to factors such as exercise, environmental changes, and psychological stressors. Cortisol is often measured to assess stress responses and overall well-being in equine health management. This page compiles peer-reviewed research studies and scholarly articles that explore the production, regulation, and implications of cortisol in equine physiology and health.
Dietary protein and(or) energy restriction in mares: plasma growth hormone, IGF-I, prolactin, cortisol, and thyroid hormone responses to feeding, glucose, and epinephrine. Sixteen light horse mares were fed diets of bermudagrass hay and a corn/cottonseed hull-based supplement formulated to contain either 100% (control) or 50% (restricted) of the protein and(or) energy requirements for maintenance in a 2 x 2 factorial arrangement of treatments. Plasma IGF-I, prolactin, cortisol, triiodothyronine, and thyroxine were monitored for 33 d. On the 27th d, frequent blood samples were drawn throughout the day for the measurement of growth hormone (GH), and on the 29th d, an epinephrine challenge and an i.v. glucose tolerance test (IVGTT) were performed in the morning and...
Lipid metabolism in horses with hyperadrenocorticism. Lipid metabolism was studied in 21 horses with hyperadrenocorticism. To be included in the study, horses had to have histologic evidence of a pars intermedia adenoma found at necropsy (n = 9), a baseline ACTH concentration greater than 400 pg/ml (n = 6), or a plasma cortisol concentration 2 hours after i.v. administration of 25 IU of ACTH greater than 413 nmol/L (n = 16). Mean +/- SD baseline plasma cortisol concentration was 338 +/- 261 nmol/L (n = 20), mean +/- SD plasma insulin concentration was 97 +/- 54 microU/ml (n = 15), mean +/- SD plasma beta-hydroxybutyrate concentration was 1.8 +/- ...
Problems in the diagnosis of pituitary adenoma (Cushing’s syndrome) in horses. Thyrotropin releasing hormone (TRH) stimulation tests were carried out on a number of horses, including one clinically affected horse whose age and clinical signs suggested that a pituitary adenoma was most unlikely. The results of these tests indicated that, according to criteria published overseas, the majority of these horses had pituitary adenomas. The fact that clinically normal or affected horses may have marked increases in cortisol concentrations indicates that the TRH stimulation test is not suitable for the diagnosis of pituitary adenoma. Other tests, including alterations in glucose...
Immunohistochemical localisation of steroidogenic enzymes and phenylethanolamine-N-methyl-transferase (PNMT) in the adrenal gland of the fetal and newborn foal. An increase in fetal adrenal cortisol output signals the onset of parturition in many animal species but, in the fetal horse, plasma concentrations of cortisol remain low for much of late pregnancy, with a rise occurring only very close to the time of birth (term 320-360 days). Immunohistochemistry was used to determine the localisation and changes in distribution of key steroidogenic enzymes for cortisol production; P450scc, P450C17 and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) in adrenal tissue from fetal and newborn horses and these findings were correlated with the appearance of imm...
Ontogeny and ultradian rhythms of adrenocorticotropin and cortisol in the late-gestation fetal horse. Fetal maturation and the timing of parturition in both sheep and primates are thought to be controlled by the hypothalamic-pituitary-adrenal axis but little is known about the endocrinology of the equine fetus. We investigated the ontogeny of plasma concentrations of adrenocorticotropic hormone (ACTH), cortisol and corticosteroid binding capacity in the late-gestation fetal horse. We also wished to determine whether there is ultradian rhythmic release of ACTH and cortisol in fetal horses and we compared fetuses to maternal and non-pregnant adult horses. Six fetuses, 278-304 days gestation (ter...
Laboratory diagnosis of equine pituitary pars intermedia adenoma. The objective of the study was to determine the sensitivity with which an adenoma of the pars intermedia of the pituitary gland can be predicted in horses by measuring the basal concentrations of glucose, cortisol, adrenocorticotropin (ACTH), and insulin, the urinary concentration of corticoids, the urinary corticoid:creatinine ratio, and the plasma cortisol concentration after the administration of 25 IU of ACTH intravenously. The records of 24 cases of histologically confirmed equine pituitary pars intermedia adenomas were used. An adenoma of the pars intermedia of the pituitary gland in hor...
A retrospective study of increased plasma progestagen concentrations in compromised neonatal foals. Plasma progestagen concentrations were measured daily by radioimmunoassay (RIA) in 35 sick foals for the duration of their illness. The foals were divided into three groups on the basis of time to stand after birth. Foals were given intensive care treatment according to the severity of their illness. Plasma and urine concentrations of pregnenolone (P5) and pregnenediol (P5 beta beta) were measured by gas chromatography--mass spectrometry; plasma cortisol concentrations were measured by RIA and the foals' renal and respiratory status were assessed by creatinine clearance ratios and arterial oxy...
Pituitary-adrenal activity and opioid release in ponies during thiopentone/halothane anaesthesia. The effect of thiopentone/halothane anaesthesia on the release of endogenous opioid, adrenocorticotrophin, arginine vasopressin, cortisol and catecholamine was investigated in ponies. The contribution made by halothane itself was studied by maintaining six ponies with a constant 1.2 per cent end tidal halothane concentration and five with a concentration ranging between 0.8 and 1.2 per cent. Cardiorespiratory depression was more prolonged in the ponies receiving a constant 1.2 per cent end tidal halothane concentration than in those which received less halothane. Plasma lactate concentration i...
Effect of food deprivation on baseline iodothyronine and cortisol concentrations in healthy, adult horses. Six healthy, adult horses, with normal (mean +/- SEM) baseline serum concentrations of total triiodothyronine (T3, 1.02 +/- 0.16 nmol/L), free T3 (FT3, 2.05 +/- 0.33 pmol/L), total thyroxine (T4, 19.87 +/- 1.74 nmol/L), free T4 (FT4, 11.55 +/- 0.70 pmol/L), total reverse T3 (rT3, 0.68 +/- 0.06 nmol/L), and cortisol (152.75 +/- 17.50 nmol/L), were judged to be euthyroid on the basis of response to a standardized thyroid-stimulating hormone response test. Serum concentrations of T3, FT3, T4, FT4, rT3, and cortisol were determined immediately before and every 24 hours during a 4-day period of foo...
Horse plasma corticotrophin-releasing hormone (CRH): characterisation and lack of a late gestational rise or a plasma CRH-binding protein. Immunoreactive corticotrophin-releasing hormone (irCRH) was present in methanolic extracts of equine peripheral blood and showed no elevation in maternal peripheral serum in late gestation (0.54 +/- 0.25 pmol/l; mean +/- S.D.) compared with control horses (0.41 +/- 0.15 pmol/l). The irCRH of methanolic extracts of pituitary venous plasma had a similar elution position following reverse-phase HPLC to synthetic human CRH(1-41) and to irCRH released from horse stalk-median eminence tissue incubated in vitro. Gel chromatographic studies showed no evidence for a plasma CRH-binding protein (CRHBP) a...
Generic immunoassay of corticosteroids with minimum pre-treatment of urine samples. A generic, rapid and sensitive enzyme linked immunosorbent assay (ELISA) test has been developed which allows large-scale simultaneous testing of synthetic corticosteroids viz., flumethasone, dexamethasone and betamethasone. This assay can be directly applied to diluted urine samples (1 + 9) without hydrolysis of glucuronide or sulfate conjugates or any other treatment of samples. The polyclonal antibody was obtained by immunizing sheep with a flumethasone derivative linked to human serum albumin. This polyclonal antibody displayed high-reactivity with several synthetic corticosteroids whilst ...
Plasma beta-endorphin response of thoroughbred horses to maximal exercise. Ten horses underwent a standardised strenuous treadmill exercise test, before, during and after which measurements were made of plasma beta-endorphin and cortisol concentrations, blood lactate, glucose, haemoglobin and pH, the activities of creatine kinase, lactate dehydrogenase and aspartate amino-transferase, and heart rate, oxygen uptake and expired minute volume. The correlations between the exercise-induced response of beta-endorphin and the changes observed in the other physiological measurements were examined. There was a large variation in the beta-endorphin response of the horses to e...
Effect of increasing work rate on metabolic responses of the donkey (Equus asinus). Oxygen consumption (VO2) and concentration of venous blood metabolites were measured in donkeys trained to run and to pull loads on a treadmill. VO2 in two donkeys running at maximal speed on a 9.8% slope was 110 +/- 2 ml.min-1.kg-1, approximately 22 times preexercise VO2. Average heart rate at maximal VO2 (VO2max) was 223 +/- 2 beats/min, five times the preexercise heart rate. Blood lactate increased 14-fold, and blood glucose did not change (P > 0.05). Animals running up a 4% incline and incremental draft loading of five donkeys walking on the level were also studied. The total energy cost o...
Short-term secretion patterns of corticotropin-releasing hormone, arginine vasopressin and ACTH as shown by intensive sampling of pituitary venous blood from horses. To characterize the short-term ACTH secretion pattern and to investigate factors regulating it, pituitary venous (PV) blood was collected using our nonsurgical method from 8 unperturbed horses every 20 or 30 s for approximately 1 h. In all but 1 horse, sampling occurred during the broad circadian maximum in plasma cortisol concentrations. Concentrations of corticotropin-releasing hormone (CRH; n = 7 horses), arginine vasopressin (AVP), ACTH and cortisol were measured by radioimmunoassay. In all horses, CRH, AVP and ACTH secretion patterns appeared irregular in time and amplitude. The mean (+/-...
Prepartum adrenocortical maturation in the fetal foal: responses to ACTH. The present study was carried out on 19 chronically catheterized mares and fetuses in late gestation (term > 320 days). In six animals which were monitored up to the time of delivery of a live foal, plasma and amniotic fluid cortisol concentrations remained low until 4-5 days before parturition when there was a rapid, significant rise (P < 0.05) which was not accompanied by any corresponding changes in maternal plasma cortisol. Circulating fetal ACTH concentrations became more variable close to delivery and ANOVA revealed no significant increases during this critical period, although a n...
Changes in concentrations of hormones, metabolites, and amino acids in plasma of adult horses relative to overnight feed deprivation followed by a pellet-hay meal fed at noon. Experiment 1 was conducted to characterize the concentrations of prolactin, growth hormone (GH), cortisol, insulin, glucagon, glucose, nonesterified fatty acids (NEFA), urea N, and 10 indispensable amino acids in the plasma of mares (n = 8) and stallions (n = 8) during the last 4 h of a 19-h period of feed deprivation and for 8 h after a noon meal. Experiment 2 was similar to Exp. 1 except that only stallions (n = 8) were used, and they were either fed (n = 4) or not fed (n = 4) at noon in a 2 x 2 Latin square design conducted over two sampling days 7 d apart. In Exp. 1, increases (P < .01)...
Factors affecting the circadian rhythm in plasma cortisol concentrations in the horse. In horses, a circadian rhythm in plasma cortisol concentrations has been reported in some but not all studies. When a rhythm occurred, horses were accustomed to a management routine, comprising stabling, feeding and sometimes exercise, which may entrain a circadian pattern. In this work, we monitored plasma cortisol by collecting jugular blood through indwelling cannulae from four groups: 1): 10 untrained, unperturbed mares grazing excess pasture, bled hourly for 26 hr; 2) 4 mares housed in a barn for 48 hr before sampling every 15 min for 20-24 hr; 3) 5 mares placed in an outdoor yard for sam...
Diagnostic testing for pituitary pars intermedia dysfunction in horses. Pituitary pars intermedia dysfunction is a slowly progressive disorder that afflicts most breeds of horses. Because it shares features with human Cushing disease, it has been referred to as equine Cushing disease. A variety of tests of pituitary-adrenocortical function were performed on horses with evidence of pituitary pars intermediate dysfunction, and results were compared with those in healthy control horses. Diurnal variations in plasma cortisol concentration were not statistically different between control horses and those with pituitary pars intermedia dysfunction. An ACTH stimulation (...
Adrenocortical carcinoma in a 12-year-old mare. A 12-year-old Dutch warmblood mare was examined because it had suffered colic intermittently for a few years and had lost weight in the previous two months. Palpation per rectum revealed a large firm mass in the left sublumbar region; the mass was classified post mortem as an adrenocortical carcinoma. The basal plasma cortisol concentration (at 10.00) of the mare was 94 nmol/litre, within the normal range. As in another case of adrenocortical neoplasm, a functional tumour could not be demonstrated. Only one of the 21 horses with a neoplasm of the pituitary-adrenocortical axis examined by the a...
Urinary concentration of corticoids in normal horses and horses with hyperadrenocorticism. The urinary corticoid:creatinine (c:c) ratio was determined in eight horses with hyperadrenocorticism (HAC). The mean (+/- SD) urinary c:c ratio of the eight horses with HAC (29 +/- 14 x 10(-6)) was significantly (P < 0.05) greater than the ratio in seven control horses (11 +/- 4.3 x 10(-6)). The urinary concentration of corticoids in control horses (201 +/- 60.4 nmol litre-1) was significantly (P 0.05) between both groups. As both false negative and false positive cases were found, it is concluded that a measurement of the urinary c:c ratio in the horse should not be used as the sole test...
Placental progestagens in the sheep and horse and the changes leading to parturition. Placental progestagen production and metabolism during pregnancy, the changes which precede parturition and the extent of fetal involvement in the latter processes are compared in the sheep and the horse. Neither species requires the presence of a corpus luteum for maintenance of the latter part of pregnancy, but the mechanisms involved in placental progesterone/progestagen production are very different in the two species. In sheep the primary product is progesterone (P4), levels of which are high in the maternal but not the fetal circulations. By contrast, in the mare P4 is not detectable in ...
Equine pituitary neoplasia: a clinical report of 21 cases (1990-1992). The records of 21 horses with an adenoma of the pars intermedia of the pituitary gland were reviewed. The animals comprised nine Dutch warmblood horses and 12 ponies. They ranged in age from 12 to 30 years (mean +/- sem 21 +/- 1.3 years) for 20 of the horses, and comprised 13 geldings and eight mares. All the animals showed hirsutism. In 1991, nine horses were diagnosed as having the adenoma, equivalent to 0.5 per cent of the horses examined in 1991. The mean +/- sem survival time of four of the horses (from discharge to the development of complications which required euthanasia) was 192 +/- 5...
Adrenal insufficiency associated with long-term anabolic steroid administration in a horse. Adrenal insufficiency was diagnosed in a 9-year-old American Quarter Horse gelding that had received monthly injections of stanozolol for 8 years. After the injections were abruptly discontinued, the horse developed anorexia, lethargy, weight loss, and bilateral forelimb lameness. Secondary hypoadrenocorticism was diagnosed on the basis of clinical signs, lack of high endogenous plasma ACTH concentration, and lack of cortisol response to administration of ACTH. Because the medical history did not include glucocorticoid administration, the cause was determined to be excessive administration of ...
Effects of triamcinolone acetonide on pulmonary function and bronchoalveolar lavage cytologic features in horses with chronic obstructive pulmonary disease. Effects of triamcinolone acetonide (TA) on pulmonary function, bronchoalveolar lavage cytologic features and serum cortisol concentration, were studied in 5 control horses and 5 horses with chronic obstructive pulmonary disease (COPD). In experiment 1, horses were brought in from pasture 3 weeks before administration of 1 injection of TA (0.09 mg/kg of body weight, IM), and were stabled in dusty conditions throughout the experimental period. Measurements of respiratory rate (f), tidal volume, minute ventilation, expiratory-to-inspiratory time ratio, maximal change in transpulmonary pressure (d...
The acute effect of lowering plasma cortisol on the secretion of corticotropin-releasing hormone, arginine vasopressin, and adrenocorticotropin as revealed by intensive sampling of pituitary venous blood in the normal horse. The effect of an acute fall in plasma cortisol on the secretion of CRH, arginine vasopressin (AVP), and ACTH was studied using our nonsurgical technique for collecting pituitary venous (PV) blood from horses. PV blood from six mares was collected continuously and divided into 30-sec segments for 0.5 h before and during a 3-h infusion of metyrapone, an 11-beta-hydroxylase inhibitor. During treatment, plasma cortisol fell (P < 0.01) to a mean nadir of 15% of pretreatment levels, and 11-deoxy-cortisol rose (P < 0.02). Three mares became mildly agitated during treatment. Mean PV concentratio...
The effect of cortisol on the secretion of ACTH by anterior pituitary cells of the horse in culture. Perifused equine anterior pituitary cells were used to investigate the effect of cortisol on the ACTH response to pulses of corticotrophin-releasing hormone (CRH; 0.01 nmol/l) and arginine vasopressin (AVP; 100 nmol/l), given for 5 min every 30 min for 690 min and ACTH measured in 5-min fractions. At the fourth pulse of secretagogue (0 min), a constant perifusion with cortisol began (0 nmol/l (control), 100, 200, 500, 5000 and 50,000 nmol/l) and continued until the ninth pulse (150 min). For each pulse of secretagogue, the amount of ACTH (pmol) secreted in response to each pulse (ACTH response...
[Anorexia in a pony with Cushing’s disease]. An eighteen-year-old pony gelding was referred to the Faculty of Veterinary Medicine because of colic, due to cecal tympany. His haircoat was dull with long wavy hair. After medical treatment of the colic it was sent home three days later. Just before it had been dismissed the morning plasma glucose concentration measured 10.2 mmol.l-1. The basal plasma cortisol concentration was high (180 nmol.l1) and basal plasma ACTH concentration was highly elevated (> 960 pg.ml1). An ACTH-stimulation test was performed by intravenous administering of 0.25 mg synthetic ACTH 1 24 at 9.00 hours showing ad...
Foetal endocrine maturation. In domestic ruminants such as the sheep, birth is effected through sequential maturation of the foetal hypothalamic-pituitary-adrenal (HPA) axis, leading to the increased output of cortisol. Factors regulating foetal pituitary adrenocorticotrophin (ACTH) secretion have been delineated, and these include corticotrophin releasing hormone (CRH), arginine vasopressin, prostaglandin (PG) E2 and endogenous opioids. The pre-partum increase in foetal plasma ACTH is associated with a rise in pro-opiomelanocortin (POMC) mRNA in the foetal pars distalis, and with an altered pattern of POMC post-translati...