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.
Beta-adrenoceptors in equine trachea and heart. The density and subtype pattern of beta-adrenoceptors in equine tracheal epithelium, tracheal smooth muscle and heart from 6-9 horses were investigated by radioligand binding studies using the nonselective beta-adrenoceptor antagonist 125I-cyanopindolol (ICYP). The specific binding of ICYP was 341 +/- 162 fmol/mg protein (mean +/- SD) for epithelium, 42 +/- 13 fmol/mg for smooth muscle and 124 +/- 39 and 101+/- 19 fmol/mg for the cardiac atrium and ventricle, respectively. The Kd value of ICYP was 6.7 10.2 pmol/L. In competition studies, different concentrations of either the beta2-selective d...
Effects of intravenously administered yohimbine on antinociceptive, cardiorespiratory, and postural changes induced by epidural administration of detomidine hydrochloride solution to healthy mares. To determine effects of i.v. administered yohimbine on perineal analgesia, cardiovascular and respiratory activity, and head and pelvic limb position in healthy mares following epidural administration of detomidine hydrochloride solution. Methods: 8 healthy mares. Methods: Each mare received detomidine hydrochloride (0.06 mg/kg of body weight), administered in the caudal epidural space, followed 61 minutes later by yohimbine (0.05 mg/kg; test) or sterile saline (0.9% NaCl) solution (control), administered i.v., in a randomized, crossover study design with > or = 2 weeks between treatments. ...
Affinity of isoxsuprine for adrenoreceptors in equine digital artery and implications for vasodilatory action. We used isolated equine digital arteries to study the vasodilatory mechanism of isoxsuprine, and fowl caecum preparations to investigate the affinity of the drug for beta-adrenoceptors. Isoxsuprine is a potent vasodilator of arterial smooth muscle that has been precontracted by an alpha-adrenoceptor agonist such as noradrenaline (log EC50 = -6.33 [-5.98; -6.68]). The present study indicates that its effect is due to alpha-adrenoceptor blockade since: (1) after a long lasting exposure to cumulative doses of isoxsuprine the vasoconstricting action of noradrenaline cannot be restored; (2) isoxsup...
Sweating and skin temperature responses of normal and anhidrotic horses to intravenous adrenaline. Anhidrosis has been recognised for over half a century, but despite some excellent epidemiological studies, there has been little progress in understanding the aetiology of the condition. Using a modified ventilated capsule, we obtained dynamic, quantitative data on sweating responses in anhidrotic horses and normal sweating controls from the same environment. Ten horses with current seasonal anhidrosis and 10 matched normal sweating controls were selected. Each horse was given two 10 min infusions of 1 and 2 micrograms/kg/min adrenaline, separated by at least 6 h. Sweating responses and skin ...
Effects of caffeine and promazine hydrochloride on plasma catecholamines in thoroughbreds at rest and during treadmill exercise. Our aim was to investigate plasma catecholamine responses to so-called 'doping' drugs and exercise in Thoroughbreds. Plasma adrenaline (Ad) and noradrenaline (NA) were determined after the administration of caffeine and promazine hydrochloride (PRZ) using a high performance liquid chromatographic method. Caffeine or PRZ was administered i.m. to Thoroughbreds and its effects on plasma catecholamines at rest and during exercise were compared with the saline control. The treadmill exercise was performed 1 h after administration. A dose of 5.0 mg/kg bwt caffeine was found to significantly increase...
Effect of transport on the intensity of stress reactions in mares and foals. The aim of this study was to determine the effect of transportation on the behaviour and stress responses of the sympatho-adrenal and hypothalamo-pituitary-adrenal systems in mares and their foals by measuring the peripheral plasma concentrations of adrenaline, noradrenaline and cortisol. Control blood samples were taken from mares and their foals (n=5 pairs) on day 8 after parturition to establish whether blood sampling caused any changes in adrenaline, noradrenaline or cortisol concentrations in blood plasma. The experiment was conducted during foal oestrus (on day 9 after parturition). Adre...
Response of newborn foals with thyroid musculoskeletal disease to adrenocorticotrophic hormone (ACTH). Fetal maturation and equine parturition are not understood fully, although the adrenal and thyroid glands are thought to have regulatory roles. Thyroidectomized equine fetuses undergo prolonged gestation, and spontaneous diseases such as thyroid musculoskeletal disease and gestational fescue endophyte exposure are also associated with delayed parturition. Thyroid musculoskeletal disease is characterized by: histologically hyperplastic thyroid glands, chondro-osseous dysplasia and dysgenesis, angular limb deformity, low resting thyroxine and triiodothyronine concentrations, and lack of response...
Simultaneous occurrence of multiple neoplasms and hyperplasias in the adrenal and thyroid gland of the horse resembling multiple endocrine neoplasia syndrome: case report and retrospective identification of additional cases. Neoplastic and hyperplastic disorders that affect multiple endocrine tissues in a single individual are well described in humans but less so in domestic animals. Multiple endocrine neoplasia (MEN) in humans is a genetically determined syndrome characterized by the appearance of benign or malignant proliferations within two or more endocrine glands. The primary endocrine tumors that are characteristic of MEN arise from cells that share the capacity for amine precursor uptake and decarboxylation. Here we describe the case of a 22-year-old Thoroughbred mare that died during an unattended parturit...
The effect of administration of a beta blocker in periparturient mares. This study investigated the effect of a beta blocker on parturition, fetal membrane retention and subsequent fertility in mares. The animals were divided into an experimental group (150 mares treated during second stage labour with propranolol [50 mg i.v.]) and a control group (180 mares with no treatment). Administration of propranolol was associated with a significant decrease in time of expulsion of fetal membranes, and an increase in both exhibition of foal heat and pregnancy rates at this heat.
Investigations on the stereoselective action of isoxsuprine on alpha- and beta-adrenoceptors in equine common digital artery. The affinity and functional effects of isoxsuprine enantiomers were investigated to determine the enantiospecificity of the beta-agonistic and alpha-blocking effects. Functional assays on isolated smooth muscle preparations from equine common digital artery were performed to determine the apparent affinity (pD(2)) and intrinsic activity (alpha(E)) of (-)erythro-isoxsuprine (alphaS, betaR, gammaR) and (+)erythro-isoxsuprine (alphaR, betaS, gammaS). The affinity of two enantiomers for the different adrenoceptor types was studied by radioligand binding assays on membrane preparations from the sam...
The effects of intrafetal ACTH administration on the outcome of pregnancy in the mare. Enhanced adrenocortical activity in the fetus is related to the onset of parturition in many species. The aim of this study was to determine the effect of injection of fetal ACTH on gestational length and fetal viability in the horse. Pony mares (n=23) were studied from 300 days gestation. Seven control mares (Group 1) received three consecutive intrafetal injections of sterile water, while fetuses of a further 16 mares received Depot ACTH1-24. These mares were either allowed to foal spontaneously (Group 2, n=4) or delivery was induced within 3 days of the last fetal injection (Group 3, n=7); ...
Modulation of ACh release from airway cholinergic nerves in horses with recurrent airway obstruction. To evaluate the functional status of neuronal alpha2-adrenoceptors (ARs) and beta2-ARs on ACh release in horses with recurrent airway obstruction (RAO), we examined the effects of the physiological agonists epinephrine (Epi) and norepinephrine (NE) and the beta2-agonists RR- and RR/SS-formoterol on ACh release from airway cholinergic nerves of horses with RAO. Because SS-formoterol, a distomer of the beta2-agonist, increases ACh release from airways of control horses only after the autoinhibitory muscarinic receptors are blocked by atropine, we also tested the hypothesis that if there is an M2...
Hemodynamic effects of thyroidectomy in sedentary horses. To investigate hemodynamic effects of thyroidectomy in horses at rest. Methods: 6 healthy aged Quarter Horse mares. Methods: Horses were monitored for 5 months before and 4 weeks after thyroidectomy and for an additional 4 weeks after administration of thyroid hormone supplement (2.5 microg of thyroxine/kg of body weight, PO, q 12 h, and 0.6 microg of triiodothyronine/kg, PO, q 12 h). Responses to thyroid-stimulating hormone (TSH) were measured before and 4 weeks after thyroidectomy. Other variables monitored daily were resting rectal temperature (T), heart rate (HR), respiratory rate (RR), an...
Pituitary-adrenocortical effects of methoxamine infusion on halothane anaesthetised ponies. This study investigated whether maintenance of normotension using a methoxamine infusion would prevent activation of the stress response during halothane anaesthesia in ponies. After acepromazine premedication, anaesthesia was induced with thiopentone in six ponies, and maintained for 120 minutes with halothane in oxygen and ventilation to normocapnia. Methoxamine (M, 0.013+/-0.005 mg kg(-1) min(-1)) or saline (C) was infused throughout anaesthesia. Sequential blood samples were taken for cortisol and ACTH assay. During anaesthesia normotension (mean arterial blood pressure 101-124 mm Hg) was ...
A comparison between clenbuterol, salbutamol and terbutaline in relation to receptor binding and in vitro relaxation of equine tracheal muscle. Beta2-adrenoceptor agonists are used as bronchodilators in both humans and horses. Of these drugs, clenbuterol is the one most frequently used when treating chronic obstructive pulmonary disease in the horse, while salbutamol and terbutaline are used in the treatment of human asthma. Little is known of the properties of the latter two drugs in equine medicine. We have compared salbutamol and terbutaline with clenbuterol in relation to their ability to relax muscle strips from equine tracheal muscle, precontracted with 40 nM carbachol, in tissue chambers. The affinities of these drugs to the be...
Adrenocortical and metabolic responses to dobutamine infusion during halothane anaesthesia in ponies. The study investigated whether hypotension in halothane-anaesthetised ponies is the stimulus inducing an endocrine stress response by assessing the effect of maintenance of normotension with a dobutamine infusion. Groups of six ponies were studied. After premedication with acepromazine (0.04 mg/kg) anaesthesia was induced with thiopentone (10 mg/kg) and maintained for 120 min with halothane (group AN). Dobutamine was infused to effect (1.1-4.4 microg/kg/min) to maintain arterial pressure at pre anaesthetic levels. The conscious group (CON) were prepared as for AN and then received only dobutam...
Alteration in adrenocortical function in horses with recurrent airway obstruction after aerosol and parenteral administration of beclomethasone dipropionate and dexamethasone, respectively. To determine alteration in adrenocortical function in horses with recurrent airway obstruction (heaves) after aerosol and parenteral administration of beclomethasone dipropionate and dexamethasone, respectively. Methods: 6 horses with inducible and reversible heaves. Methods: Episodes of heaves were induced by exposure to moldy hay and straw for 7 days (natural challenge). Horses then underwent treatment (aerosolized beclomethasone, parenterally administered dexamethasone, and aerosolized propellant) for 7 days. Horses remained in the mold-contaminated environment for 7 days after discontinuat...
The effect of social stress on adrenal axis activity in horses: the importance of monitoring corticosteroid-binding globulin capacity. Plasma cortisol is largely bound to corticosteroid-binding globulin (CBG), which regulates its bioavailability by restricting exit from capillaries. Levels of CBG may be altered by several factors including stress and this can influence the amount of cortisol reaching cells. This study investigated the effect of social instability on plasma concentrations of CBG, total and free (not protein bound) cortisol in horses. Horses new to our research herd ('newcomers') were confined in a small yard with four dominant resident horses for 3-4 h daily for 3-4 (n = 5) or 9-14 (n = 3) days. Jugular blood ...
Role of cAMP and neuronal K+ channels on alpha 2-AR-induced inhibition of ACh release in equine trachea. To investigate the effects of changes in intracellular cAMP on alpha 2-adrenoceptor (AR)-induced inhibition of airway acetylcholine (ACh) release, we examined the effects of the alpha 2-AR agonist clonidine on electrical field stimulation-evoked ACh release from equine tracheal parasympathetic nerves before and after treatment with 8-bromo-cAMP or forskolin. We also tested whether charybdotoxin (ChTX)- or iberiotoxin (IBTX)-sensitive Ca(2+)-activated K+ channels mediate alpha 2-AR-induced inhibition by examining the effect of clonidine in the absence and presence of ChTX or IBTX on ACh release...
Adrenal insufficiency in a neonatal foal. A 3-day-old female Pinto was admitted with profuse watery diarrhea and severe hypovolemic shock. After 1 week of intensive care, the foal developed seizures associated with profound serum electrolyte abnormalities suggestive of hypoadrenocorticism. Treatment with prednisone and isotonic saline (0.9% NaCl) solution led to prompt clinical response. Premature withdrawal of prednisone resulted in relapse of clinical signs. A diagnosis of adrenal insufficiency was made on the basis of clinical signs, electrolyte abnormalities, low baseline cortisol concentration, and lack of response to administrat...
Catecholamine and cortisol responses of horses to incremental exertion. The responses of the plasma concentrations of catecholamines and cortisol in horses to varied relative intensities of exertion were examined. The plasma concentrations of cortisol, epinephrine and norepinephrine increased significantly (p < 0.05) with exertion. The plasma cortisol concentrations at relative work intensities of 48.3% +/- 1.4%, 82.3% +/- 2.0% and 99.6% +/- 0.4% of VO2max were 114%, 124%, and 126%, respectively, of those at rest, whereas the plasma epinephrine concentrations were 239%, 772% and 3483%, and the norepinephrine concentrations were 138%, 255%, and 1121% of the valu...
Cortisol, peptides and catecholamines in cerebrospinal fluid, pituitary effluent and peripheral blood of ponies. Cannulation of the pituitary effluent in horses is a useful method for investigating the release of pituitary hormones in loco (Irvine and Alexander 1987). Adrenocorticotropic hormone (ACTH) and arginine vasopression (AVP) concentrations in plasma collected from the intercavemous sinus, which receives all the pituitary outflow, were several times greater than those measured in peripheral plasma (Redekopp et at 1986). However, no studies evaluating the pituitary contribution to endogenous opioid secretion have been reported in the equine species. Cerebrospinal fluid (CSF) directly reflects CNS ...
Persistent desensitisation of the beta 2 adrenoceptors expressed by cultured equine sweat gland epithelial cells. Adrenaline, forskolin and ATP all evoked accumulation of cyclic AMP in equine sweat gland epithelial cells, although the response to adrenaline was more transient than that to forskolin and ATP. Cells preincubated in adrenaline (10 micromol l-1, 32 min) showed essentially complete, homologous desensitisation, and this phenomenon reversed slowly (half-time 6.3+/-0.9 h). After 10 min of recovery from preincubation in adrenaline, isobutylmethylxanthine (IBMX, 5 mmol l-1) had no effect upon the desensitisation and the cells showed no loss of sensitivity to ATP and forskolin. After 10 h, however, t...
Effect of exercise on erythrocyte beta-adrenergic receptors and plasma concentrations of catecholamines and thyroid hormones in Thoroughbred horses. The effects of exercise stress on erythrocyte beta-adrenergic receptor characteristics and plasma concentrations of adrenaline, noradrenaline and thyroid hormones were studied in Thoroughbred racehorses during rest and after exercise. Five minutes after a maximal speed race of 1200 +/- 200 m (mean +/- s.d.), both plasma adrenaline and noradrenaline concentrations increased with respect to basal values (from 2.48 +/- 0.15 to 3.83 +/- 0.27 and from 2.13 +/- 0.11 to 3.53 +/- 0.27 nmol/l respectively). The increment of adrenaline was greater in high performance (HP) as compared to low performance ...
In vitro responses to noradrenaline of small intestine taken from normal and grass sickness-affected horses. Small intestine was taken from the caudal flexure of the duodenum and the terminal ileum proximal to the ileocaecal fold of 25 horses, 9 with acute grass sickness (AGS), 12 with subacute grass sickness (SAGS) and 12 with chronic grass sickness (CGS). The motility in the samples was measured isometrically either within 1 h of death or after storage for 24 h at 4 degree C. In control tissue, noradrenaline produced contractions of muscle strips which did not involve a muscarinic cholinergic mechanism and which were unaffected by the alpha 1 antagonist prazosin but were blocked by the alpha 2 anta...
Differences between longitudinal and circular smooth muscle in beta-adrenergic control of motility of isolated equine ileum. To identify beta-adrenoceptor subtypes involved in motility inhibition of circular and longitudinal smooth muscle layers of equine ileum. Methods: Isolated strips of equine ileum circular smooth muscle and membrane preparations from circular and longitudinal muscle layers. Methods: Functional assays of circular muscle preparations and radioligand binding assays and measurements of cAMP production in smooth muscle membranes from circular and longitudinal layers. Results: Selective beta-adrenergic agonists exerted inhibitory effects on circular muscle preparations. Binding studies of cell membra...
Immunocytochemical localization of adrenocorticotropic hormone-immunoreactive cells of the pars intermedia in thoroughbreds. To analyze and characterize adenoma and hyperplasia of the pars intermedia (PI) of Thoroughbred mares. Methods: 165 Thoroughbred mares, without clinical signs of hyperadrenocorticism that had been euthanatized or had died, of causes such as sudden death, colic, pneumonia, or trauma, and were necropsied. Five of those horses, 17 to 25 years old, had a large pituitary gland at necropsy. Eight mares, 5 to 15 years old with normal-size pituitary gland, were selected at random for comparison. Methods: A morphologic comparison of the pituitary gland between horses with and without tumors of the PI w...
Alpha-adrenoceptors in equine digital veins: evidence for the presence of both alpha1 and alpha2-receptors mediating vasoconstriction. Rings of equine digital vein examined under conditions of isometric tension recording constricted to alpha-adrenoceptor agonists with an order of potency of 5-bromo-6-[2-imidazolin-2-yl-amino]-quinoxaline bitartrate (UK 14304) = noradrenaline > 6-Allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo-(4,5-d) azepine (BHT-920) > phenylephrine > dopamine > methoxamine. The maximum force generated was greatest for the non-selective agonist noradrenaline and lowest for the alpha2-selective agonist BHT-920 with the other agonists between these two extremes. Selective inactivation of alpha1-adreno...