Topic:Adrenal
The adrenal glands in horses are small endocrine organs located near the kidneys, responsible for producing a variety of hormones essential for physiological regulation. These hormones include cortisol, adrenaline, and aldosterone, which are involved in stress response, metabolism, and electrolyte balance. The functioning of the adrenal glands is integral to the horse's ability to respond to stressors and maintain homeostasis. Research in equine endocrinology often focuses on understanding the regulation of adrenal hormones, their role in equine health, and the impact of disorders such as equine Cushing's disease and adrenal insufficiency. This page compiles peer-reviewed research studies and scholarly articles that explore the anatomy, function, and clinical implications of adrenal gland activity in horses.
Catecholamine affects acetylcholine release in trachea: alpha 2-mediated inhibition and beta 2-mediated augmentation. We investigated the effects of catecholamines on acetylcholine (ACh) release from equine airway parasympathetic nerves. Trachealis strips were suspended in 2-ml tissue baths with Krebs-Henseleit solution containing atropine (10(-7) M), neostigmine (10(-6) M), and guanethidine (10(-5) M). Electrical field stimulation (20 V, 0.5 ms, 0.5 Hz, for 15 min) was applied, and ACh was measured by high-performance liquid chromatography with electrochemical detection. Epinephrine (Epi) and norepinephrine (NE) inhibited ACh release in a concentration-dependent manner. Inhibition was attenuated by the alpha...
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...
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...
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...
Participation of alpha 1- and beta 1-adrenoceptors in norepinephrine-induced contraction and relaxation of isolated equine coronary artery in vitro. In coronary arterial rings isolated from horse, norepinephrine (NE)(10(-7) - 10(-5) M) induced concentration-dependent contractions which were not influenced by endothelial denudation. Prazosin (alpha 1-antagonist) inhibited the contraction, but yohimbine (alpha 2-antagonist) did not, and propranolol (beta-antagonist) enhanced the contraction. Pretreatment with phentolamine (10(-5) M) (alpha-antagonist) converted the contraction induced by NE to relaxation in coronary rings precontracted with ONO11113 (thromboxane A2 derivative). The relaxation was not influenced by removal of the endothelium,...
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...
Prejunctional alpha 2-adrenoceptors inhibit acetylcholine release from cholinergic nerves in equine airways. To determine the presence and function of alpha 2-adrenoceptors on cholinergic nerves innervating horse airway smooth muscle, the effects of some alpha 2-adrenoceptor agents on contractions of and acetylcholine (ACh) release from equine airway smooth muscle preparations were studied. Muscle contractions were elicited by either electrical field stimulation (EFS) or exogenous ACh. ACh release was induced by EFS and measured by high-pressure liquid chromatography and electrochemical detection. The alpha 2-adrenoceptor agonists clonidine (10(-7) to 10(-5) M) and UK-14,304 (10(-8) to 10(-6) M) conc...
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 ...
Investigation of stimulus-secretion coupling in equine sweat gland epithelia using cell culture techniques. When sweat glands isolated from samples of horse skin were explanted and cultured under favourable conditions, they could exhibit cellular outgrowth. This growth could be maintained for 2-4 weeks and these primary cultures were then disaggregated and the resultant cell suspensions used to initiate epithelial cell lines. Secretion from intact equine sweat glands is regulated by beta 2-adrenoceptors and appears to be mediated by cyclic AMP, but there is evidence that calcium may also play a role. Adrenaline could increase the cyclic AMP content of the cultured cells and this response was mediate...
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...
Effects of clenbuterol hydrochloride on pulmonary gas exchange and hemodynamics in anesthetized horses. We evaluated the effects of clenbuterol HCl (0.8 micrograms/kg, of body weight, IV), a beta 2 agonist, on ventilation-perfusion matching and hemodynamic variables in anesthetized (by IV route), laterally recumbent horses. The multiple inert gas elimination technique was used to assess pulmonary gas exchange. Clenbuterol HCl induced a decrease in arterial oxygen tension (from 57.0 +/- 1.8 to 49.3 +/- 1.2 mm of Hg; mean +/- SEM) as a result of increased shunt fraction (from 6.6 +/- 2.1 to 14.4 +/- 3.1%) and ventilation to regions with high ventilation-perfusion ratios. In contrast, no changes in...
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...
Synovial and serum levels of triamcinolone following intra-articular administration of triamcinolone acetonide in the horse. Seven mature thoroughbred horses, weighing between 400 and 541 kg, were each injected intra-articularly into three joints with 6 mg/joint of triamcinolone acetonide (Vetalog). The fourth joint, the control, was injected with saline. Synovial fluid was taken from all four legs of the horses on days 1, 2, 3, 4, 5, 6, 7, 8, 11, and 15 following the injections. Triamcinolone acetonide was assayed by a radioimmunoassay. Blood was collected at 1, 2, 4, 6, 12 h and on days 1, 2, 3, 4, 5, 6, 7, 8, 11, and 15 following injection of either triamcinolone or saline. Both cortisol and triamcinolone were as...
Inotropic mechanisms of dopexamine hydrochloride in horses. Mechanisms responsible for the positive inotropic effects of dopexamine were investigated in 8 halothane-anesthetized horses. The hemodynamic effects of increasing infusions of dopexamine (5, 10, 15 micrograms/kg of body weight/min) were determined before and after sequential administration of specific antagonists. Using glycopyrrolate and chlorisondamine, and atenolol and ICI 118,551, muscarinic and nicotinic ganglionic, and beta 1, and beta 2-adrenergic receptor blockade, respectively, was induced. Dopexamine infusions induced increase in heart rate, cardiac output, systolic and mean arteria...
A comparison of the sedative effects of three alpha 2-adrenoceptor agonists (romifidine, detomidine and xylazine) in the horse. The sedative effects of a new alpha 2-adrenoceptor agonist, romifidine, were compared with those of xylazine and detomidine. Five horses were treated with two doses of romifidine (40 micrograms/kg body weight and 80 micrograms/kg body weight), two doses of detomidine (10 micrograms/kg body weight and 20 micrograms/kg body weight) and one dose of xylazine (1 mg/kg body weight) given by intravenous injection using a Latin-square design. The dose of 80 micrograms/kg romifidine appeared equipotent to 1 mg/kg xylazine and 20 micrograms/kg detomidine, although at these doses both xylazine and detomi...
Ejaculation. Physiology and dysfunction. In summary, important events of ejaculation include emission of sperm and the accessory gland fluids into the urethra, simultaneous closure of the bladder neck, and forceful ejaculation of the combined semen through the urethra. Emission and bladder neck closure are primarily alpha-adrenergically mediated thoracolumbar sympathetic reflex events with supraspinal modulation. Ejaculation is a sacralspinal reflex mediated by the pudendal nerve. In stallions, the most common ejaculation disorders are emission and ejaculation failure, and urine contamination of semen. Rare disorders are azoospermia ...
Sympatho-adrenal activity and the clinical sedative effect of detomidine in horses. Thirty-nine horses were given detomidine 10 micrograms/kg bodyweight (bwt) intravenously (iv) and six horses were given a corresponding volume of saline solution before minor procedures. Venous blood samples were collected for catecholamine and cortisol determination immediately before the detomidine or saline injection and 20 mins after it. The behaviour of the horse at the time of detomidine injection and the extent of sedation were evaluated. Plasma adrenaline, noradrenaline and the catecholamine metabolites, 3,4-dihydroxyphenylglycol (DHPG) and 3,4-dihydroxyphenylacetic acid (DOPAC), and c...
Relaxant effects of theophylline and clenbuterol on tracheal smooth muscle from horse and rat in vitro. A comparison between the relaxant effects of clenbuterol and theophylline on horse tracheal smooth muscle has been made in vitro. Rat tracheal smooth muscle was also investigated as a reference. The tracheal preparations were initially contracted with carbachol since the smooth muscle did not spontaneously develop tone. The response of the carbachol-contracted preparations to theophylline was the same in the two species. The response to clenbuterol varied. In only five out of eleven horses were the tracheal smooth muscles sensitive to clenbuterol (mean pD2 = 7.92 M). In the remaining six horse...
Beta-adrenergic receptor activity in ponies with recurrent obstructive pulmonary disease. Pulmonary function measurements were made in control ponies and in ponies with recurrent obstructive pulmonary disease (principals) during clinical remission and during an attack of acute airway obstruction. The ponies were given beta-adrenergic antagonists and agonists to determine the role of beta receptors in recurrent obstructive pulmonary disease, and to determine the subtypes of beta receptors mediating bronchodilation in ponies. Aerosol administration of the beta antagonists, propranolol (beta 1 and beta 2), atenolol (beta 1), and butoxamine (beta 2) decreased dynamic compliance (Cdyn) ...
Action of sympathomimetic drugs on the bronchial circulation of the horse. In the quietly standing horse I.V. administration of adrenaline decreased, and of dobutamine increased, bronchial artery flow. These changes paralleled changes in arterial pressure. With phenylephrine and noradrenaline bronchial artery flow decreased while arterial pressure increased, indicating active vasoconstriction in the bronchial circulation. With clenbuterol an increase in bronchial artery flow was accompanied by a decrease in systemic blood pressure, indicating bronchial arterial vasodilatation. We conclude that alpha-constrictor and beta 2-dilator receptors are present in the bronchia...
Hemodynamic effects of atropine, dobutamine, nitroprusside, phenylephrine, and propranolol in conscious horses. The authors investigated the cardiovascular effects of low doses of nitroprusside, dobutamine, and phenylephrine and a beta-adrenergic blocking dose of propranolol in conscious, healthy horses with and without prior atropine administration. A parasympathetic blocking dose of atropine produced significant increases in heart rate and arterial pressures, and decreased stroke volume, ejection fraction, pulse pressure, and right-ventricular end-diastolic pressure and volume. Cardiac output was not changed by atropine administration. Nitroprusside reduced arterial pressures to a greater extent in at...
In vitro responses of airway smooth muscle from horses with recurrent airway obstruction. The in vitro contractile and relaxant responses of tracheal smooth muscle strips (TSM) and third-generation bronchi (3B) of control horses and horses with recurrent obstructive disease (heaves) were compared. Acetylcholine (ACH) sensitivity of the diseased tissues was less than that of tissues from control horses, especially at the level of the third generation (EC50 controls 15 +/- 11 microM vs 81 +/- 17 microM for heaveys). Despite tracheal and bronchial hyporesponsiveness to ACH, these tissues from heavey horses were hyperresponsive to EFS. The inhibitory effect of isoproterenol and electri...
Effects of placental pathology on maternal plasma progestagen and mammary secretion calcium concentrations and on neonatal adrenocortical function in the horse. Between 1985 and 1990, 25 Thoroughbred mares were classified as having an abnormal pregnancy on the basis of precocious signs of impending parturition. Throughout the remainder of their pregnancies, plasma progestagen and mammary secretion calcium concentrations were monitored. After parturition, evidence of placental pathology was recorded and their foals were assessed with regard to adrenocortical function and behaviour. Seven pony mares were used to establish a model of placental pathology and, following induced placental separation, were subjected to the same protocol. Control animals cons...
In vitro responses of equine digital vessels to dopamine and fenoldopam. The in vitro responses of isolated vascular preparations of digital arteries and veins obtained from healthy anaesthetised horses were determined for dopamine and fenoldopam. The digital vessels were harvested, cut into 4 mm vascular segments, suspended in tissue baths and attached to force-displacement transducers. Dose-response studies between 10(-8) and 10(-4)M concentrations were performed for all drugs. The change in tension of each vascular ring was measured in grams of force. The reactivity between palmar and plantar digital vessels and baseline vascular responses were determined for do...
[The diagnosis of adrenal cortical function in animals using hormone analysis]. This paper describes the use of hormone analysis in the diagnosis of adrenal cortex dysfunction in the dog, cat and horse. Analytical problems concerning the determination of corticosteroid levels are discussed and the pathology of adrenal dysfunction is briefly presented. The paper focuses on the problems in establishing physiological norms for adrenal function based on the established assays. Own experiences and other reported data are referred to.
Comparison of the adrenocortical response to both pharmacological and physiological stresses in sport horses. Seven sport horses were investigated to compare physiological and pharmacological stresses on the plasma glucocorticosteroid levels. Venous blood was sampled and analysed for cortisol concentrations before and after each type of stress. The physiological stress was induced by the completion of a cross-country and the pharmacological one, by an intravenous ACTH administration (200 micrograms) in the same horses, one week after the course. Both exercise and ACTH injection induced a highly significant cortisol increase of 79 +/- 0.10% and 160 +/- 0.18%, respectively. The relative plasma cortisol ...
Effect of age on isoproterenol-induced maximal heart rate in horses. The effect of age on maximal heart rate induced by IV infusion of isoproterenol was studied in 19 healthy, sedentary, normothermic horses ranging in age from 0.25 to 9.90 years. Isoproterenol was administered IV (1.0 micrograms/kg of body weight/min) for 3 minutes, and the heart rate attained during the last 30 seconds of the infusion was determined. Linear regression of the maximal heart rate on age suggested that the rate decreased with age in a trend described by the equation: maximal heart rate (beats/min) = 209.63 - 3.28 x age (years). The regression coefficient (r) for this relation was ...
Isoproterenol-induced maximal heart rate in normothermic and hyperthermic horses. The heart rate (HR) induced by maximal beta-adrenergic activation, which was elicited by infusion of isoproterenol, was studied in 8 healthy horses before (control) and after hyperthermia was induced by IV administration of 2,4-dinitrophenol (DNP). Isoproterenol was administered IV at 1.0 micrograms.kg-1.min-1 for 3 minutes, and the HR was determined during the final 30 seconds of the infusion. As the rectal temperature increased (P less than 0.001) from 38.2 +/- 0.1 C (mean +/- SEM; normothermic control) to 40.1 +/- 0.1 C at 60 minutes after DNP administration, the isoproterenol-induced HR al...
Effects of intravenous xylazine hydrochloride on blood glucose, plasma insulin and rectal temperature in neonatal foals. The effects of intravenous xylazine hydrochloride on blood glucose, plasma insulin and rectal temperature were investigated in six foals at 10 and 28 days of age. These variables were also measured in three foals at 19 days of age when saline alone was injected. Rectal temperature fell significantly after 30 mins in both groups of xylazine treated foals and was still depressed after 120 mins. Hypothermia did not occur in the saline control group. There was no significant change in blood glucose or plasma insulin concentrations during the 120 mins following either xylazine or saline administrat...