Receptors in horses are specialized protein molecules located on the surface of or within cells. They are responsible for receiving and transmitting signals from various stimuli, such as hormones, neurotransmitters, and environmental changes. These receptors play a significant role in numerous physiological processes, including immune response, sensory perception, and cellular communication. Types of receptors found in horses include adrenergic receptors, which mediate responses to adrenaline and noradrenaline, and muscarinic receptors, involved in the parasympathetic nervous system. Variations in receptor function and expression can influence equine health and behavior. This page compiles peer-reviewed research studies and scholarly articles that explore the types, functions, and implications of receptors in equine biology and health management.
Minelli A, Allegrucci C, Mezzasoma I, Ronquist G, Lluis C, Franco R.Membrane vesicles of horse seminal plasma present at their surface a highly specific serine-type protease, dipeptidyl peptidase IV/CD26, a surface antigen known to characterize human prostasomes. Horse sperm cells expressed at their surface A(1) adenosine receptors (A(1)AR) and ecto-adenosine deaminase (ecto-ADA), both detected by immunoblot analysis, whereas CD26 was visualized at the equatorial segment by immunofluorescence microscopy. In addition to CD26, horse membrane vesicles showed ecto-ADA. The fusion process between horse sperm cells and vesicles was evidenced by confocal microscopy, ...
Cheng FP, Gadella BM, Voorhout WF, Fazeli A, Bevers MM, Colenbrander B.The aim of the present study was to investigate whether the induction of stallion sperm acrosome reaction (AR) by progesterone is mediated by binding of progesterone to a receptor on the sperm plasma membrane or to an intracellular progesterone receptor. Progesterone-BSA conjugate labeled with fluorescein isothiocyanate (P-BSA-FITC) in combination with a vital stain, ethidium homodimer, was applied to visualize the presence of the progesterone receptor on living spermatozoa. Alternatively, an indirect immunofluorescence technique employing a monoclonal antibody (C-262) against human intracellu...
Lennard SN, Gerstenberg C, Allen WR, Stewart F.Northern blot and in situ hybridization techniques have demonstrated a marked increase in mRNA encoding epidermal growth factor (EGF) in the endometrium of mares, coincident with the start of interdigitation between the allantochorion and endometrium during placentation. In the present study, the unusually high EGF expression in the epithelium of the endometrial glands was shown to be maintained until at least day 250 of gestation (term = 320-340 days) in mares carrying normal horse conceptuses. However, in mares carrying failing donkey-in-horse pregnancies created by embryo transfer, EGF expr...
Prieto D, Hernández M, Rivera L, García-Sacristán A, Simonsen U.The distribution of neuropeptide Y (NPY)-immunoreactive (IR) nerves, as well as the functional effects of NPY and the Y1- and Y2-receptor agonists, [Leu31,Pro34]NPY and NPY(13-36), respectively, have been investigated in vitro in both visceral and arterial smooth muscle of the horse intravesical ureter. NPY-IR nerve fibres were widely distributed along the entire length of the ureter, although the intravesical part was the most richly innervated region, and the only one where NPY-IR ganglion cells were found. NPY (10(-7) M) did not affect either basal tone or spontaneous rhythmic contractions ...
Bousfield GR, Butnev VY, Gotschall RR, Baker VL, Moore WT.There are two species for which both pituitary and placental gonadotropins are readily available, humans and horses. The human gonadotropins are better characterized than equine gonadotropins. Nevertheless, the latter are very interesting because they provide exceptions to some of the general structure-function principles derived from studies on human and other mammalian gonadotropins. For example, separate genes encode the hLH beta and hCG beta subunits while a single gene encodes eLH beta and eCG beta. Thus, eCG and eLH differ only in their oligosaccharide moieties and eLH is the only LH tha...
Wilson SM, Rakhit S, Murdoch R, Pediani JD, Elder HY, Baines DL, Ko WH, Wong PY.Experiments were undertaken using cultured equine sweat gland epithelial cells that express purine receptors belonging to the P2U subclass which allow the selective agonist uridine triphosphate (UTP) to increase the concentration of intracellular free Ca2+ ([Ca2+]i). Experiments using pertussis toxin (Ptx), which inactivates certain guanine-nucleotide-binding proteins (G-proteins), showed that this response consisted of Ptx-sensitive and Ptx-resistant components, and immunochemical analyses of the G-protein alpha subunits present in the cells showed that both Ptx-sensitive (alpha i1-3) and Ptx...
Bryant CE, Clarke KW.Spirals of endothelially denuded equine saphenous vein were used to study the pre- and post-junctional effects of medetomidine in vitro. The pD2 values were calculated for noradrenaline (6.7 +/- 0.1), phenylephrine (5.6 +/- 0.1), BHT 920 (6.2 +/- 0.2) and UK 14304 (5.7 +/- 0.2). Medetomidine produced a biphasic response, with a pD(2)1 of 8.2 +/- 0.1 and a pD(2)2 of 5.7 +/- 0.1 in the equine saphenous vein (n = 6). Prazosin (10(-7) M) significantly shifted the second phase of the medetomidine concentration-response curve to the right (pD(2)1 was 8.1 +/- 0.2 and pD(2)2 was 5.0 +/- 0.2, P < 0....
Miyamoto A, Obi T, Nishio A.The vasomotor effects of 5-hydroxytryptamine (5-HT) on isolated equine basilar arteries were studied. 5-HT induced contractions of equine basilar arteries in a concentration-dependent manner, with a pEC50 value (with 95% confidence limits) of 7.35 (7.08-7.62). Similar results were obtained with endothelium-denuded basilar arteries. Contractions were not competitively inhibited by the 5-HT2 receptor antagonist ketanserin at low concentrations of 5-HT. Conversely, at high concentrations of 5-HT, contractions were inhibited by ketanserin in a concentration-dependent manner, with a pA2 value of 8....
Poole AW, Heath MF, Evans RJ.Pre-incubation of equine platelets in platelet-rich plasma with adenosine 5'-diphosphate (ADP) induced a reduction in aggregation responsiveness to subsequent additions of ADP. The desensitisation was shown to be homologous since the responsiveness to platelet-activating factor, thrombin, collagen, 5-hydroxytryptamine or ionomycin remained unchanged. Adenosine 5'-(beta-thio)-diphosphate (ADP beta S), a non-hydrolysable analogue of ADP, was shown to act as an agonist inducing aggregation by interaction with the ADP receptor. ADP beta S was then used in the desensitisation studies in which resid...
Simmons TR, Cook JA, Moore JN, Halushka PV.Thromboxane (TX) A2 has been implicated as an important pathophysiologic mediator of a variety of cardiovascular diseases. Monocytes synthesize TXA2 and it modulates their function. This study sought to characterize monocyte TXA2 receptors. Radioligand binding studies were performed on membranes prepared from equine peripheral blood monocytes using [125I]BOP, a TXA2 receptor agonist. [125I]BOP bound to a single class of binding sites (Kd = 1.0 +/- 0.3 nM and Bmax = 389 +/- 191 fmol/mg protein; n = 5). Several TXA2 receptor agonists and antagonists competed for binding with [125I]BOP. I-BOP pro...
Deumer J, de Haan F, Tulp MT, van den Hoven R.The effects of an oral isoxsuprine-resin preparation on the blood flow in the thoracic limb of seven horses was determined by thermography. Treatment with the oral resin preparation resulted in increased skin temperatures compared with the non-medicated controls. The maximal temperature differences, 2.2 degrees C for the horses treated with 0.9 mg/kg and 1.8 degrees C for the horses treated with 1.2 mg/kg, occurred four hours after dosing. Plasma total isoxsuprine, determined in three horses, was detectable two hours after oral dosing and maximal eight hours after dosing, but free isoxsuprine ...
Stankov B, Cozzi B, Lucini V, Fumagalli P, Scaglione F, Fraschini F.Melatonin receptors were characterized in the brains of three mammals (rabbit, horse and sheep) by an in vitro binding technique, using 2-[125I]iodomelatonin as labelled ligand. Although binding sites for melatonin have been described recently in several vertebrate species (including the sheep), the rabbit and the horse have not been the subject of investigation so far. Apart from characterization, the present report describes receptor distribution in a number of brain regions, thus allowing for direct interspecies comparison under the same methodological conditions. 2-[125I]iodomelatonin labe...
Tajima M, Fujinaga T, Okamoto Y, Otomo K, Koike T.The relationship between the optimum concentration of mitogen which induces lymphocyte blastogenic response and the receptor occupancy by mitogen was investigated. The receptor occupancies which induced maximal blastogenic activity in equine, bovine and canine peripheral blood lymphocytes (PBL) were 31.1 per cent, 26.5 per cent and 38.4 per cent with phytohaemagglutinin-P, and 48.2 per cent, 17.9 per cent and 24.5 per cent with concanavalin A, respectively. The data clearly show that each animal species had its own optimum concentration of mitogen for stimulation of PBL. Optimum concentration ...
Mattioli M, Galeati G, Seren E.Prostaglandin F-2 alpha (PGF-2 alpha) receptors of bovine and equine corpora lutea (C.L.) were studied. From both the equilibrium binding data and the dissociation kinetics behaviour, two affinity classes of receptors are evident in the mare, with apparent dissociation constants (Kd) of 1,5 x 10(-9) M and 3.5 x 10(-8) M. Bovine PGF-2 alpha receptors present a homogeneous population of binding sites with Kd = 1 x 10(-8) M. Both bovine and equine C.L. receptors bind PGF-2 alpha in a specific manner; only 13, 14-dihydro-PGF-2 alpha considerably cross-reacts with these receptors. Since in the mare...
Nádasdi L, Yamashiro D, Li CH, Izdebski J.Five analogs of equine β-melanotropin have been synthesized by the solid phase method. The NH2-terminal aspartic acid was substituted with amino acids (Gly, Trp, Ile, Lys and Nα-acetyl-Asp) differing widely in physicochemical properties. On the basis of their lipolytic potencies it was concluded that this position plays a negligible role in this activity.
Li CH, Ng TB, Yamashiro D, Chung D, Hammonds RG, Tseng LF.Beta-endorphin has been isolated from equine pituitaries. Its amino acid sequence is identical to that of ovine, bovine and camel beta-endorphins except for substitution of the threonine residue at position 6 by serine. The equine beta-endorphin has also been synthesized by the solid-phase method. In comparison with the human hormone, equine beta-endorphin was shown to possess 3 times the receptor-binding activity in rat membrane preparations and 1.6 times the analgesic potency in the mouse tail-flick assay.
Stewart F, Allen WR.The role of equine chorionic gonadotrophin (CG, formerly termed Pregnant Mare serum Gonadotrophin, PMSG) in maintaining equine pregnancy was investigated by examining the effects of this hormone on the maternal ovaries during early gestation and relating these findings to the receptor binding activities of CG in vitro. Measurement of plasma progestagen profiles in mares and donkeys carrying horse, donkey, mule ( female horse X male donkey) and hinny (female donkey X male horse) conceptuses confirmed that CG induced several secondary ovulations and thus maintained maternal progestagen concentra...
Chidambaram RM, Eades SC, Moore RM, Hosgood G, Venugopal CS.To characterize the in vitro response of equine cecal longitudinal smooth muscle (CLSM) to endothelin (ET)-1 and assess the role of ETA and ETB receptors in those ET-1-induced responses. Methods: 36 horses without gastrointestinal tract disease. Methods: To determine cumulative concentration-response relationships, CLSM strips were suspended in tissue baths containing graded concentrations of ET-1 (10(-9) to 10(-6)M) with or without BQ-123 (ETA receptor antagonist); with or without IRL-1038 (ETB receptor antagonist); or with both antagonists at concentrations of 10(-9), 10(-7), and 10(-5)M. To...
Zizzadoro C, Caruso M, Punzi S, Crescenzo G, Zongoli F, Belloli C.Hemodynamic perturbations, partly resulting from abnormal vasoconstriction of digital vessels, have been implicated in the pathogenesis of bovine and equine laminitis. This study compared the responsiveness of isolated bovine (BDA) and equine (EDA) digital arteries to pharmacological agents that stimulate receptor systems involved in the regulation of normal vessel tone. The role of the endothelium and the short- and longer-term effects of an experimentally induced endothelial damage were also evaluated. Species-related differences were found in the vessel reactivity to all of the receptor ago...
Martínez AC, Rivera L, Raposo R, García-Sacristán A, Benedito S.The effect of histamine (10(-9)-10(-3) M) on horse penile dorsal artery was evaluated. Precontracted vessels showed a biphasic response (relaxation-contraction) to histamine, while at basal tone, histamine only induced a contractile effect. The H1 receptor agonist, 2-pyridylethylamine (PEA) (10(-9)-10(-3) M), induced concentration-dependent relaxation in precontracted rings and provoked vasoconstriction at basal tone. Mepyramine (10(-9)-10(8) M), an H1 receptor antagonist, competitively antagonized the relaxant response to histamine (pA2 = 9.7) and PEA (pA2 = 9.2). At basal tone, mepyramine (1...
Mattioli M, Galeati G, Seren E.Prostaglandin F-2 alpha (PGF-2 alpha) receptors of bovine and equine corpora lutea (C.L.) were studied. From both the equilibrium binding data and the dissociation kinetics behaviour, two affinity classes of receptors are evident in the mare, with apparent dissociation constants (Kd) of 1,5 x 10(-9) M and 3.5 x 10(-8) M. Bovine PGF-2 alpha receptors present a homogeneous population of binding sites with Kd = 1 x 10(-8) M. Both bovine and equine C.L. receptors bind PGF-2 alpha in a specific manner; only 13, 14-dihydro-PGF-2 alpha considerably cross-reacts with these receptors. Since in the mare...
Lennard SN, Gerstenberg C, Allen WR, Stewart F.Northern blot and in situ hybridization techniques have demonstrated a marked increase in mRNA encoding epidermal growth factor (EGF) in the endometrium of mares, coincident with the start of interdigitation between the allantochorion and endometrium during placentation. In the present study, the unusually high EGF expression in the epithelium of the endometrial glands was shown to be maintained until at least day 250 of gestation (term = 320-340 days) in mares carrying normal horse conceptuses. However, in mares carrying failing donkey-in-horse pregnancies created by embryo transfer, EGF expr...
Tajima M, Fujinaga T, Okamoto Y, Otomo K, Koike T.The relationship between the optimum concentration of mitogen which induces lymphocyte blastogenic response and the receptor occupancy by mitogen was investigated. The receptor occupancies which induced maximal blastogenic activity in equine, bovine and canine peripheral blood lymphocytes (PBL) were 31.1 per cent, 26.5 per cent and 38.4 per cent with phytohaemagglutinin-P, and 48.2 per cent, 17.9 per cent and 24.5 per cent with concanavalin A, respectively. The data clearly show that each animal species had its own optimum concentration of mitogen for stimulation of PBL. Optimum concentration ...
Talboom JS, Engler-Chiurazzi EB, Whiteaker P, Simard AR, Lukas R, Acosta JI, Prokai L, Bimonte-Nelson HA.In women, ovarian hormone loss at menopause has been related to cognitive decline, and some studies suggest that estrogen-containing hormone therapy (HT) can mitigate these effects. Recently, the Women's Health Initiative study found that conjugated equine estrogens, the most commonly prescribed HT, do not benefit cognition. Isolated components of conjugated equine estrogens (tradename Premarin(®)) have been evaluated in vitro, with delta(8,9)-dehydroestrone (∆(8)E1) and equilin showing the strongest neuroprotective profiles. It has not been evaluated whether ∆(8)E1 or equilin impact cogn...
Poole AW, Heath MF, Evans RJ.Pre-incubation of equine platelets in platelet-rich plasma with adenosine 5'-diphosphate (ADP) induced a reduction in aggregation responsiveness to subsequent additions of ADP. The desensitisation was shown to be homologous since the responsiveness to platelet-activating factor, thrombin, collagen, 5-hydroxytryptamine or ionomycin remained unchanged. Adenosine 5'-(beta-thio)-diphosphate (ADP beta S), a non-hydrolysable analogue of ADP, was shown to act as an agonist inducing aggregation by interaction with the ADP receptor. ADP beta S was then used in the desensitisation studies in which resid...
Thomasy SM, Moeller BC, Stanley SD.To compare the density and binding characteristics of opioid receptor subtypes in horse, rat, and guinea pig cerebral cortex and cerebellum. Methods: Prospective receptor binding study. Methods: Whole brains were obtained from four neurologically normal adult horses during necropsy. Rat and guinea pig brains were obtained commercially. Methods: The cerebellum and cerebral cortex were dissected from each brain, and tissue homogenates prepared. A radioligand binding technique with the highly selective ligands [(3)H]-DAMGO, [(3)H]-U69593, and [(3)H]-DPDPE was used to identify the mu- (mu), kappa-...
Retamal CA, Dias AJ, Brasil FC, Lanzana FR, López ML.The expression of α-D-mannosidase activity was fluorometrically and electrophoretically assessed in spermatozoa, epididymal fluid and homogenates of stallion epididymal tissue. Enzyme activity had regional differences; it was higher (P<0.05) in samples from the cauda epididymal region than in samples from the proximal caput region (largely composed of efferent ducts). Based on enzyme activity, as a function of pH of the assay substrate, electrophoretic analysis in native and native/SDS-PAGE conditions, and the effect of inhibitors or activators, we inferred the presence of at least two cat...
Hajek P, Ungemach FR, Abraham G.Muscarinic acetylcholine receptor (mAChR)-mediated guanine nucleotide-binding regulatory protein (G protein) activation and the functional interaction between receptors and the respective G proteins were investigated using an agonist-induced [(35)S]guanosine-5'-O-(gamma-thiotriphosphate) ([(35)S]GTPgammaS)-binding approach in membranes of 3 native equine airway segments (trachea, bronchus and lung), which differ tremendously in mAChR density and subtype distribution; especially subtypes that couple negatively to adenylyl cyclase through G(i/0) proteins, i.e. M(2) receptors. The assay was initi...
Keen JA, Hillier C, McGorum BC, Nally JE.Endothelin-1 (ET-1) may be a key mediator in the pathogenesis of laminitis, but endothelin-mediated responses in the venous microcirculation of the equine foot have yet to be fully characterised. Objective: To characterise the response of equine laminar veins to ET-1 and evaluate the ET-1 receptor subtypes that mediate this response. Methods: Small veins (150-500 microns) draining the equine digital laminae from healthy horses and ponies subjected to euthanasia at an abattoir were investigated using wire myography. Concentration response curves were constructed for ET-1 in the presence of ETA ...
Barnabé MA, Elliott J, Harris PA, Menzies-Gow NJ.Hypoadiponectinaemia is a risk factor for endocrinopathic laminitis, but the directionality and nature of its association with insulin dysregulation is unclear. Objective: To investigate the effects of short-term induced hyperinsulinaemia and dexamethasone challenge on circulating [total adiponectin] and whole blood expression of adiponectin (AdipoR1 and AdipoR2), insulin, and insulin-like growth factor 1 (IGF-1) receptors in insulin-sensitive ponies. Methods: In vivo experiment. Methods: Six never-laminitic, insulin-sensitive, native-breed UK ponies first underwent a dexamethasone challenge (...
Stejskalova K, Janova E, Splichalova P, Futas J, Oppelt J, Vodicka R, Horin P.Toll-like receptors (TLRs) represent an important part of the innate immune system. While human and murine TLRs have been intensively studied, little is known about TLRs in non-model species. The order Perissodactyla comprises a variety of free-living and domesticated species exposed to different pathogens in different habitats and is therefore suitable for analyzing the diversity and evolution of immunity-related genes. We analyzed TLR genes in the order Perissodactyla with a focus on the family Equidae. Twelve TLRs were identified by bioinformatic analyses of online genomic resources; their ...
Zamith Cunha R, Semprini A, Salamanca G, Gobbo F, Morini M, Pickles KJ, Roberts V, Chiocchetti R.Cannabinoid receptors are expressed in human and animal trigeminal sensory neurons; however, the expression in the equine trigeminal ganglion is unknown. Ten trigeminal ganglia from five horses were collected post-mortem from an abattoir. The expression of cannabinoid receptors type 1 (CB1R) and type 2 (CB2R), and the cannabinoid-related receptors like transient receptor potential vanilloid type 1 (TRPV1), peroxisome proliferator-activated receptor gamma (PPARɣ), and G protein-related receptor 55 (GPR55) in the trigeminal ganglia (TG) of the horse were studied, using immunofluorescence on cry...
Nissen SD, Saljic A, Carstensen H, Braunstein TH, Hesselkilde EM, Kjeldsen ST, Hopster-Iversen C, D'Souza A, Jespersen T, Buhl R.Second-degree atrioventricular (AV) block at rest is very common in horses. The underlying molecular mechanisms are unexplored, but commonly attributed to high vagal tone. Unassigned: To assess whether AV block in horses is due to altered expression of the effectors of vagal signalling in the AV node, with specific emphasis on the muscarinic acetylcholine receptor (M) and the G protein-gated inwardly rectifying K (GIRK4) channel that mediates the cardiac current. Unassigned: Eighteen horses with a low burden of second-degree AV block (median 8 block per 20 h, IQR: 32 per 20 h) were assign...
Galinelli NC, Bamford NJ, de Laat MA, Sillence MN, Harris PA, Bailey SR.Insulin dysregulation in horses is characterised by hyperinsulinaemia and/or tissue insulin resistance and is associated with increased risk of laminitis. There is growing evidence in other species that dopamine attenuates insulin release from the pancreas; however, this has yet to be examined in horses. The present study aimed to identify whether there are cells capable of producing or responding to dopamine within the equine gastrointestinal mucosa and pancreas. Tissue samples were collected from the stomach, small and large intestines, and pancreas of six mature horses following euthanasia....
Bruschetta G, Zanghì G, Giunta RP, Ferlazzo AM, Satué K, D'Ascola A, Fazio E.Horse transport is considered a cause of stress in animals and is known to affect the 5-HT concentrations in both the brain and other tissues. The aim of this research was to investigate the effect of horse transportation and slaughter stress on plasma serotonin's concentration and the expression levels of the related 5-HT1B and 5-HT2A receptors in PBMCs. Furthermore, the IL-12 levels and a variety of blood parameters, including triglycerides, total cholesterol, glucose, aspartate aminotransferase, creatine phosphokinase, lactate dehydrogenase, were also considered. This research was carried o...
