Selective Beta 2-adrenoceptor Agonist Research Articles

Role of endothelin in the pathophysiology of migraine: A new view on an old player

There is cumulating evidence that endothelin-1 (ET-1) may play a role in migraine, however controversial findings still impede a conclusion to be drawn. Herein we tested the hypothesis that endothelin ETB receptors are major contributors to migraine-like responses. ET-1, IRL-1620 (selective ETB receptor agonist) or CGRP were injected into the trigeminal ganglion (TG) of female Wistar rats, and the development of periorbital mechanical allodynia was assessed hourly with von Frey hairs. Twenty-four hours later, rats were exposed to an aversive light for 1 h, after which the reactivation of periorbital mechanical allodynia (indicating photic sensitivity) was assessed up to 4 h. Moreover, the effect of systemic Bosentan (ETA/ETB receptors antagonist) or the selective antagonists of ETA (BQ-123) and ETB (BQ-788) receptors injected into the TG were evaluated against CGRP-induced responses. ET-1 and IRL-1620 injection into the TG induced periorbital mechanical allodynia and photic sensitivity. Bosentan attenuated periorbital mechanical allodynia but failed to affect photic sensitivity induced by CGRP. Selective blockade of ETB receptors in the TG fully prevented the development of periorbital mechanical allodynia and photic sensitivity induced by CGRP, but ETA receptor blockade caused only a slight reduction of periorbital mechanical allodynia without affecting photic sensitivity. ETB receptor-operated mechanisms in the TG may contribute to migraine-like responses in female rats.

Endothelin-1 decreases the expression of Ephrin-A and B subtypes in cultured rat astrocytes through ETB receptors

Ephrin family proteins are cell surface molecules that regulate several cellular functions through cell-cell interactions. During nervous tissue repair after injury, the expression of ephrin subtypes in astrocytes is altered, affecting the axonal elongation and migration of neuronal precursors. However, the mechanism regulating the expression of ephrin subtypes in astrocytes has not been investigated. Herein, we studied the effects of endothelin-1 (ET-1) on the expression of ephrin subtypes in cultured rat astrocytes. Our results showed that ET-1 (100 nM) treatment for 1−24 h reduced the expression of ephrin-A2, -A4, -B2, and -B3 mRNA and protein in astrocytes, whereas the expression of ephrin-A1, -A3, -A5, and -B1 mRNA were not affected. Sarafotoxin S6c, a selective ETB receptor agonist, decreased the expression of ephrin-A2, -A4, -B2, and -B3 in cultured astrocytes. The decrease in ephrin-A2, -A4, -B2, and -B3 expression by ET-1 treatment was reduced in the presence of BQ788, an ETB receptor antagonist, while FR139317, an ETA receptor antagonist, had no effects. These results suggest that ET-1 is a signaling molecule that downregulates ephrin-A2, -A4, -B2, and -B3 expression in astrocytes.

Central endothelin ETB receptor activation reduces blood pressure and catecholaminergic activity in the olfactory bulb of deoxycorticosterone acetate-salt hypertensive rats

Endothelins regulate catecholaminergic activity in the olfactory bulb (OB) in normotensive and hypertensive animals. Administration of an endothelin ETA receptor antagonist decreases blood pressure in deoxycorticosterone acetate-salt (DOCA-salt) rats along with a reduction in tyrosine hydroxylase (TH) activity and expression. In the present work, we sought to establish the role of brain endothelin ETB receptor on blood pressure regulation and its relationship with the catecholaminergic system within the OB of DOCA-Salt rats. Sprague-Dawley male rats were divided into control and DOCA-Salt groups. Blood pressure, heart rate and TH activity as well as neuronal nitric oxide synthase (nNOS) expression were assessed following IRL-1620 (selective endothelin ETB receptor agonist) applied to be brain. IRL-1620 significantly reduced systolic, diastolic, and mean arterial pressure in DOCA-Salt hypertensive rats. It also decreased TH activity, TH total and phosphorylated forms expression as well as its mRNA in the OB of hypertensive animals. The expression of phospho-Ser1417-nNOS, which reflects nNOS activation, was significantly decreased in the of OB of DOCA-salt rats, but it was enhanced by IRL-1620. These findings suggest that DOCA-Salt hypertension depends on endogenous central endothelin ETA receptor activity, rather than on ETB, and that low endothelin ETB stimulation is essential for blood pressure elevation in this animal model. The effect of endothelin ETA receptor antagonism may also result from endothelin ETB receptor overstimulation. The present study shows that endothelin receptors are involved in the regulation of TH in the OB and that such changes are likely implicated in the hemodynamic control and sympathetic outflow.

Effect of mirabegron on tight junction molecules in primary cultured rat Sertoli cells.

Mirabegron is a selective beta3-adrenoceptor (β3 -AR) agonist, which is commonly used for the treatment of overactive bladder. This medicine is associated with atrophy of reproductive organs in rats. However, no study has examined the detailed action and mechanism of its toxicity in reproductive cells. In this study, we examined the effect of mirabegron on primary cultured rat Sertoli cells. Firstly, RT-PCR and immunocytochemistry revealed that β3 -AR was present in rat Sertoli cells. Then, primary cultured rat Sertoli cells were treated with mirabegron. Quantitative real-time PCR revealed that mirabegron treatment induced a significant increase in claudin-11 mRNA, which is crucial for spermatogenesis. Western blot analysis also showed that mirabegron treatment significantly activated p44/42 mitogen-activated protein kinase (MAPK). After additional treatment with U0126, a specific noncompetitive inhibitor of mitogen-activated protein kinase kinase (MAPKK), the upregulation of claudin-11 mRNA induced by mirabegron was reduced. At the same time, immunocytochemistry showed mirabegron treatment disturbed claudin-11 localisation to tight junction, which was recovered when treated with mirabegron in the presence of U0126. These results suggest that mirabegron treatment is associated with assembly of the blood-testis barrier through p44/42 MAPK pathway. These findings could explain one of the underlying mechanisms of reproductive toxicity induced by mirabegron.

MP60-02 MOLECULAR CHANGES INDUCED BY MIRABEGRON IN RAT SERTOLI CELL PRIMARY CULTURE

You have accessJournal of UrologyInfertility: Basic Research & Pathophysiology1 Apr 2018MP60-02 MOLECULAR CHANGES INDUCED BY MIRABEGRON IN RAT SERTOLI CELL PRIMARY CULTURE Mikito Tanaka, Koji Chiba, Takaki Ishida, Kenta Sumii, Teruo Fukuda, Keisuke Okada, Kei Matsushita, and Masato Fujisawa Mikito TanakaMikito Tanaka More articles by this author , Koji ChibaKoji Chiba More articles by this author , Takaki IshidaTakaki Ishida More articles by this author , Kenta SumiiKenta Sumii More articles by this author , Teruo FukudaTeruo Fukuda More articles by this author , Keisuke OkadaKeisuke Okada More articles by this author , Kei MatsushitaKei Matsushita More articles by this author , and Masato FujisawaMasato Fujisawa More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.1894AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Beta-adrenoceptors mediate the catecholamine-induced activation of adenylate cyclase through the action of G proteins. Mirabegron is a selective beta3-adrenoceptor (ADRB3) agonist that has been approved for the treatment of overactive bladder. Studies in rats showed that mirabegron was associated with atrophy and/or reduced weights of the accessory reproductive organs, and in females, prolonged diestrus and decreased numbers of live fetuses. In this study, we evaluated the potential effects of mirabegron on the molecular expressions in rat Sertoli cell (SC) primary culture. METHODS SCs were purified from testes of 18-day-old Sprague-Dawley rats. Primary cultures were treated with 1μM mirabegron in the absence or presence of 10μM U0126, a selective non-competitive inhibitor of Mitogen-Activated Protein (MAP) kinase kinase. Immunofluorescent (IF) study was performed using the primary SC culture to determine the expression of ADRB3 in rat SCs. Protein samples were extracted from whole cell homogenates. Western blot (WB) analysis was performed to explore phosphorylation of MAP kinases. Total RNA was also extracted from SCs. Quantitative real-time RT-PCR (q-PCR) analysis was conducted to determine the expression levels of tight junction related mRNAs. RESULTS IF study showed that ADRB3 was present in rat SCs. WB analyses showed that mirabegron treatment induced the significant activation of p44/42 MAPK. Q-PCR showed that mirabegron treatment led to significant increase in claudin-11 mRNA levels. After additional treatment with U0126, mirabegron-induced up-regulation of Claudin-11 had reduced. CONCLUSIONS These data suggest that ADRB3 is present in rat SCs. ADRB3 may be associated with spermatogenesis through p44/42 MAPK induced tight junction molecules alteration in rat SCs. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e790 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Mikito Tanaka More articles by this author Koji Chiba More articles by this author Takaki Ishida More articles by this author Kenta Sumii More articles by this author Teruo Fukuda More articles by this author Keisuke Okada More articles by this author Kei Matsushita More articles by this author Masato Fujisawa More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Nuclear Factor‐kappaB‐Mediated Endothelin Receptor Up‐Regulation Increases Renal Artery Contractility in Rats

Increased renal artery contractility leads to renal vasospasm and ischaemia as well as kidney damage. This study was designed to examine the hypothesis that organ culture of renal arteries induces transcriptional up-regulation of endothelin type A (ETA ) and type B2 (ETB2 ) receptors in the smooth muscle cells via activation of nuclear factor-kappaB (NF-κB) and subsequently increases renal artery contractility. Rat renal artery segments were organ-cultured for 6 or 24hr to increase endothelin receptor-mediated contraction. To dissect molecular mechanisms involved in this process, inhibitors for NF-κB signalling pathway (MG-132 and BMS345541), transcription (actinomycin D) and translation (cycloheximide) were used during organ culture. Endothelin receptors were studied using a sensitive myograph (functional contractility), real-time PCR (mRNA analysis) and immunohistochemistry (protein localization). Compared with fresh segments, contractile responses to endothelin-1 (non-selective endothelin receptor agonist) and sarafotoxin 6c (selective ETB receptor agonist) were significantly increased in the segments after 24hr of organ culture; ETB2 receptor-mediated maximal contraction increased from 2.7±0.5 to 135.3±5.1 (p<0.001), and potency (pEC50 ) of ETA receptor agonist increased from 8.20±0.04 to 8.72±0.07 (p<0.001). This was in parallel with increased corresponding mRNA and protein expression for ETA and ETB2 receptors. BMS345541, MG-132, actinomycin D or cyclohexamide, respectively, suppressed the up-regulation of ETA and ETB2 receptors. Immunostaining performed with specific antibody showed that IκB was phosphorylated during organ culture. In conclusion, activation of NF-κB mediates up-regulation of ETA and ETB2 receptors and subsequently increases renal artery contractility, which may contribute to renal vasospasm and ischaemia as well as kidney damage.

Ethanol Consumption Increases Endothelin-1 Expression and Reactivity in the Rat Cavernosal Smooth Muscle

We investigated the effects of chronic ethanol consumption on the cavernosal smooth muscle (CSM) reactivity to endothelin-1 (ET-1) and the expression of ET system components in this tissue. Male Wistar rats were treated with heavy dose of ethanol (20% v/v) for 6 weeks. Reactivity experiments were performed in the isolated rat CSM. Plasma and CSM nitrate generation and also superoxide anion generation in rat CSM were measured by chemiluminescence. Protein and mRNA levels of pre-pro-ET-1, endothelin-converting enzyme-1 (ECE-1), ETA and ETB receptors, eNOS, nNOS and iNOS were assessed by western immunoblotting and quantitative real-time polymerase chain reaction, respectively. Chronic ethanol consumption increased plasma ET-1 levels and the contractile response induced by this peptide in the isolated CSM. The relaxation induced by acetylcholine, but not IRL1620, a selective ETB receptor agonist, was reduced in CSM from ethanol-treated rats. BQ123, a selective ETA receptor antagonist, produced a rightward displacement of the ET-1 concentration-response curves in CSM from control, but not ethanol-treated rats. Reduced levels of nitrate were found in the plasma and CSM from ethanol-treated rats. Ethanol consumption increased superoxide anion generation in the rat CSM. The mRNA levels of pre-pro-ET-1, ECE-1, ETA and ETB receptors, eNOS, nNOS and iNOS were not altered by ethanol consumption. Protein levels of ET-1, ETA receptor and iNOS were higher in the CSM from rats chronically treated with ethanol. The major findings of the present study are that heavy ethanol consumption increases plasma ET-1 levels and the contraction induced by the peptide in the CSM. Increased CSM reactivity to ET-1 and altered protein levels of ET-1 and ETA receptors could play a role in the pathogenesis of erectile dysfunction associated with chronic ethanol consumption.

Results of a Randomized Phase III Trial of Mirabegron in Patients with Overactive Bladder

Many patients with overactive bladder discontinue pharmacotherapy due to suboptimal efficacy or side effects. Mirabegron, a β3-adrenoceptor agonist, may offer an effective and well tolerated alternative treatment for overactive bladder. A randomized, double-blind, placebo controlled trial was conducted in the United States and Canada. After a 2-week placebo run-in period, adults with overactive bladder symptoms for 3 or more months were randomized 1:1:1 to receive placebo, 50 or 100 mg mirabegron once daily for 12 weeks. Efficacy data were collected via patient completed diaries and quality of life assessments. Co-primary efficacy end points were changes from baseline to final visit in mean number of incontinence episodes per 24 hours and micturitions per 24 hours. Key secondary micturition and incontinence end points were also evaluated. Safety assessments included treatment emergent adverse events, laboratory assessments, vital signs, electrocardiograms and post-void residual volume. Compared to placebo, 50 and 100 mg mirabegron groups demonstrated statistically significantly greater mean decreases (95% CI) from baseline for incontinence episodes (-1.13 [-1.35, -0.91], -1.47 [-1.69, -1.25] and -1.63 [-1.86, -1.40]) and micturitions (-1.05 [-1.31, -0.79], -1.66 [-1.92, -1.40] and -1.75 [-2.01, -1.48]) per 24 hours (p <0.05). Significant improvements in all key secondary end points were observed for both mirabegron doses vs placebo. The incidence of frequently reported treatment emergent adverse events (hypertension, urinary tract infection, headache, nasopharyngitis) was similar in the mirabegron and placebo groups. Dry mouth was reported for 1.5%, 0.5% and 2.1% of patients in the placebo, 50 and 100 mg mirabegron groups, respectively. Once daily mirabegron in a 50 or 100 mg dose is an effective treatment for overactive bladder symptoms with a low occurrence of side effects.

Human Choroidal Melanocyte Signal Transduction Responses to Various Pharmacological Agents: Focus on Endothelin Receptors

Purpose: The receptor-coupled signal transduction systems present in isolated human choroidal melanocytes (HCOMs) were investigated.Methods: [3H]-inositol phosphates ([3H]-IPs) generated in the cells were measured by ion-exchange chromatography. cAMP generated in the cells was quantified using an enzyme immunoassay.Results: Initially, HCOM cells were challenged with a relatively high concentration (e.g., 1 µM–1 mM) of a variety of pharmacological agents in order to determine which functional receptors were present in these cells. Full concentration-response pharmacological studies were subsequently conducted on endothelin receptors. While a number of prostaglandins (PGs) (e.g., PGD2, PGE2, PGF2α, cloprostenol, latanoprost acid, U-46619), histamine, carbachol, bombesin, and arginine-vasopressin were essentially inactive at stimulating the phosphoinositide (PI) hydrolysis response, endothelin-1 (ET-1) potently and efficaciously generated [3H]-IPs. Concentration-response studies yielded the following potency (EC50) and efficacy (Emax relative to ET-1) data: ET-1 EC50 = 3.4 ± 1.4 nM, Emax = 100%, n = 3; BQ-3020 (ETB receptor-selective agonist) EC50 = 13 ± 4 nM, Emax = 73 ± 2%, n = 3). The effects of ET-1 on [3H]-IPs production were blocked by the ETB receptor-selective antagonist, BQ-788 (IC50 = 10 ± 5 nM, n = 3), while the ETA receptor-selective antagonist (BQ-610) was essentially inactive. In the adenylyl cyclase (AC) assay, while isoproterenol (10 µM), ET-1 (1 µM) and PGE2 (10 µM) stimulated cAMP production, numerous other PGs (e.g., PGD2, PGF2α, PGI2, latanoprost, latanoprost acid, U-46619 and BW245C [all at > 10 µM]) were inactive.Conclusions: It is concluded that HCOMs express functionally active ETB receptors that mediate the production of [3H]-IPs. Additionally, HCOMs generate cAMP in response to ET-1, PGE2, and isoproterenol. These data may have relevance to the melanogenic activity of HCOM cells.

Beta 2-adrenoceptor influences on the alpha 1- and alpha 2-mediated vasoconstriction induced by phenylpropanolamine and its two component enantiomers in the pithed rat.

Phenylpropanolamine (PPA, (+/-)-norephedrine) is commonly found in appetite suppressants and nasal decongestants. Within the cardiovascular system of the pithed rat, the drug and its two component enantiomers ((-)- and (+)-norephedrine) are largely direct-acting agonists. The interaction between simultaneous alpha 1-, alpha 2- and beta 2-adrenoceptor mediated effects of the drug and its two enantiomers have been examined using the cardiovascular system of the pithed rat. On all adrenoceptors tested the potency was (-)- greater than (+/-)-, greater than (+)-norphedrine. The alpha 1- and alpha 2-mediated pressor responses of each were enhanced in the presence of the beta 2-adrenoceptor antagonist, ICI 118,551, and diminished in the presence of the selective beta 2-adrenoceptor agonist salbutamol. It is concluded that each form of the drug possesses the intrinsic ability to interact with the alpha 1-, alpha 2- and beta 2-adrenoceptors in the system used and that the interaction with those adrenoceptors determines the net increase in diastolic blood pressure that follows the intravenous administration of the compounds. These findings have a bearing on the recent controversy regarding the use of beta-blocking agents in the treatment of overdosage of the drug.

Cardiovascular Effects of MN-221 (Bedoradrine) Administered With Albuterol in Dogs

PURPOSE: Beta-agonists are accepted as first-line treatment for patients with asthma or COPD, but are known to have cardiovascular side-effects. MN-221 is a highly selective beta2 adrenoceptor agonist which may limit beta 1-mediated side effects. This study was conducted to assess the cardiovascular impact of MN-221 intravenously administered in addition to albuterol.

LPS from Porphyromonas gingivalis increases the sensitivity of contractile response mediated by endothelin-B (ET B) receptors in cultured endothelium-intact rat coronary arteries

The purpose of our study was to examine if lipopolysaccharide (LPS) from Porphyromonas gingivalis ( P.g.) modifies the vasomotor responses to Endothelin-1 (ET-1) and Sarafotoxin 6c (S6c) in rat coronary arteries. The arteries were studied directly or following organ culture for 24 h in absence and presence of 2.5 EU/ml LPS. The contractile responses of coronary arteries were investigated by using the selective ETB receptor agonist S6c (1 pM–0.3 μM) and ET-1 (1 pM–0.3 μM). The functional studies demonstrated an augmented contractile response only to S6c in isolated rat coronary arteries after organ culture (with or without LPS). These contractile responses by S6c were blocked by the selective ETB receptor antagonist BQ788 in both vessel groups. The augmented contractile response to S6c was supported by immunohistochemistry, where a significant increase in fluorescence intensity for ETB receptors in smooth muscle cells was observed after organ culture. The presence of LPS in the culture medium significantly increased the sensitivity of endothelium-intact coronary artery to S6c as compared to endothelium-denuded segments. Our results showed a significant increase in both ETB receptor protein levels and S6c-induced maximal contraction in coronary arteries upon 24 h of organ culture, which was further sensitized by LPS.

Catecholamine-induced myocardial fibrosis and oxidative stress is attenuated by &lt;I&gt;Terminalia arjuna&lt;/I&gt; (Roxb.)

Myocardial fibrosis and oxidative stress accompany a number of cardiac disorders such as hypertrophic cardiomyopathy, hypertensive heart disease and cardiac failure. Stem bark of Terminalia arjuna has been advocated for cardiac ailments. The present study evaluated the effects of T. arjuna bark extract on myocardial fibrosis and oxidative stress induced by chronic beta-adrenoceptor stimulation. Aqueous extract of T. arjuna bark was evaluated at 63, 125 and 250 mg/kg given orally for antifibrotic and antioxidant effects in rats given the selective beta-adrenoceptor agonist isoprenaline (5 mg/kg s.c.) for 28 days. Captopril (50 mg/kg per day, given orally), an inhibitor of angiotensin-converting enzyme used as a standard cardioprotective drug, was used as a positive control. Isoprenaline caused fibrosis, increased oxidative stress and cardiac hypertrophy (increased heart weight : body weight ratio and cardiomyocyte diameter). The T. arjuna bark extract and captopril significantly prevented the isoprenaline-induced increase in oxidative stress and decline in endogenous antioxidant level. Both also prevented fibrosis but not the increase in heart weight : body weight ratio. T. arjuna protects against myocardial changes induced by chronic beta-adrenoceptor stimulation.

Involvement of NO and MEK/ERK pathway in enhancement of endothelin-1-induced mesenteric artery contraction in later-stage type 2 diabetic Goto-Kakizaki rat

Endothelin (ET)-1 is a likely candidate for a key role in diabetic vascular complications. However, no abnormalities in the vascular responsiveness to ET-1 have been identified in the chronic stage of type 2 diabetes. Our goal was to look for abnormalities in the roles played by ET receptors (ET(A) and ET(B)) in the mesenteric artery of the type 2 diabetic Goto-Kakizaki (GK) rat and to identify the molecular mechanisms involved. Using mesenteric arteries from later-stage (32-38 wk old) individuals, we compared the ET-1-induced contraction and the relaxation induced by the selective ET(B) receptor agonist IRL1620 between GK rats and control Wistar rats. Mesenteric artery ERK activity and the protein expressions for ET receptors and MEK were also measured. In GK rats (vs. age-matched Wistar rats), we found as follows. 1) The ET-1-induced contraction was greater and was attenuated by BQ-123 (ET(A) antagonist) but not by BQ-788 (ET(B) antagonist). In the controls, BQ-788 augmented this contraction. 2) Both the relaxation and nitric oxide (NO) production induced by IRL1620 were reduced. 3) ET-1-induced contraction was enhanced by N(G)-nitro-l-arginine (l-NNA; NO synthase inhibitor) but suppressed by sodium nitroprusside (NO donor). 4) The enhanced ET-1-induced contraction was reduced by MEK/ERK pathway inhibitors (PD-98059 or U0126). 5) ET-1-stimulated ERK activation was increased, as were the ET(A) and MEK1/2 protein expressions. 6) Mesenteric ET-1 content was increased. These results suggest that upregulation of ET(A), a defect in ET(B)-mediated NO signaling, and activation of the MEK/ERK pathway together represent a likely mechanism mediating the hyperreactivity to ET-1 examined in this study.

Endothelin mediated contraction of equine laminar veins

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. To characterise the response of equine laminar veins to ET-1 and evaluate the ET-1 receptor subtypes that mediate this response. 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 (BQ123) and ETB (BQ788) receptor antagonists, and L-NAME, a nitric oxide synthase blocker. The selective ETB receptor agonist BQ3020 was investigated alone and following incubation with L-NAME, with or without BQ788. Endothelin-1 contraction of laminar veins was significantly inhibited by BQ123 but not by BQ788. In the presence of L-NAME, sensitivity of laminar veins to ET-1 was enhanced 4-fold, and further addition of BQ788 did not alter this increased sensitivity. BQ3020 induced no venoconstriction; however, in the presence of L-NAME, it caused contraction of veins with approximately 30% of the efficacy of ET-1. The action of BQ3020 in the presence of L-NAME was abolished by BQ788. Both ETA and ETB receptors are involved in the net tonic response to ET-1 in normal laminar veins. A population of ETB receptors may be present on the vascular endothelium and on smooth muscle of laminar veins, and the action of ET-1 at these 2 sites is likely to be approximately equal and opposite. Our results clarify the function of the ET-1 receptor subtypes in laminar veins from healthy horses. Further study of ET-1 receptors in laminitic horses is therefore warranted.

Effects of the β3-Adrenergic Receptor Agonist Disodium 5-[(2R)-2-[[(2R)-2-(3-Chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL-316243) on Bladder Micturition Reflex in Spontaneously Hypertensive Rats

The present study investigated whether beta3-adrenoceptor activation acts on the bladder afferent pathway by examination of the visceromotor reflex (VMR) and pressor responses to urinary bladder distension (UBD) and whether beta3-adrenoceptor activation produces urinary bladder relaxation in hyperactive spontaneously hypertensive rats (SHRs) in comparison with their normotensive control rats [Wistar-Kyoto (WKY)]. Using the VMR responses to noxious UBD as a measure of bladder afferent signal transmission, SHRs did not present a sensitized bladder phenotype. However, reduced bladder compliance accompanied by a reduced void threshold was detected in the SHR detrusor. Furthermore, the selective beta3-adrenoceptor agonist disodium 5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL-316243) (i.v.) failed to attenuate VMR or pressor responses to UBD in either SHRs or WKY rats, but it dose-dependently inhibited rhythmic contraction (RC) in SHRs. The minimal effective dose was 0.001 mg/kg. Using the same model in WKY rats, CL-316243 did not elicit significant inhibition of contractions in the bladder RC assay. These results suggest that SHRs represent abnormal efferent/detrusor function (detrusor overactivity) without mechanosensory afferent hypersensitivity. The beta3-adrenoceptor agonist CL-316243 acts on the detrusor muscle to increase urine storage in SHRs.

Memory Processing in the Avian Hippocampus Involves Interactions between β-Adrenoceptors, Glutamate Receptors, and Metabolism

Noradrenaline is known to modulate memory formation in the mammalian hippocampus. We have examined how noradrenaline and selective beta-adrenoceptor (AR) agonists affect memory consolidation and how antagonists inhibit memory consolidation in the avian hippocampus. Injection of selective beta-AR agonists and antagonists at specific times within 30 min of a weakly or strongly reinforced, single-trial, bead discrimination learning test in 1-day-old chicks allowed us to determine the pattern of beta-AR involvement in hippocampal memory processing. Different beta-AR subtypes were recruited in temporal sequence after learning in the order beta(1), beta(3), and beta(2.) We provide evidence that the effect of manipulation of beta(1)-ARs by selective agonists and antagonists within 2.5 min of training parallels the action of NMDA receptor agonists and antagonists. Activation of beta(3)- and beta(2)-ARs facilitated memory but utilized different mechanisms: beta(3)-ARs by stimulating glucose uptake and metabolism, and beta(2)-ARs by increasing the breakdown of glycogen--with both metabolic events occurring in astrocytes and affecting intermediate memory. The different receptors are activated at different times within the lifetime of labile memory and within 30 min of learning. We have defined separate roles for the three beta-ARs in memory and demonstrated that the avian hippocampus is involved in learning and memory in much the same way as the hippocampus in the mammalian brain.

The complex venous response to the ETB receptor (ETBR) agonist sarafotoxin S6C

Arteries and veins are both actively engaged in the control of cardiovascular function. However, they display many functional differences, such as the involvement in the endothelin system. In the endothelium, ETBR mediates nitric oxide (NO) release and relaxation, while on smooth muscle cells (SMCs) it mediates contraction. Although the ETBR is present on SMCs of both rat aorta (RA) and vena cava (RVC), stimulation with S6C, a selective ETBR agonist, leads to contraction of the RVC, but not RA. We hypothesized that the venous endothelial ETBR is less functionally active than the arterial one. Therefore we studied the ability of S6C to act as a relaxing agent when used on contracted, endothelium-intact RA and RVC. In PGF2α (20 μM)-contracted RA, S6C (100 nM) induced a relaxation (21.5±4.8% PGF2α-induced contraction). By contrast, in the RVC, S6C induced a four-phase response (short relaxation-short contraction-long relaxation-long contraction). BQ788, the ETBR antagonist (1 μM), blocked the S6C-induced relaxation in the aorta, while it only altered the short contractile phase of the VC response. The RVC response to S6C cannot be explained by a different ability of venous and arterial endothelium to produce NO, since ACh (10 μM) induced a similar relaxation of RA and RVC, which was completely blocked by LNNA (100 μM). These data highlight increasingly complex functions of the ETBR in the cardiovascular system.

Adrenergic dependence of the endothelin‐mediated pressor response in Dahl salt‐resistant and salt‐sensitive rats

We have previously shown that selective endothelin A (ETA) receptor antagonism augments the stress-mediated rises in arterial pressure and norepinephrine in Dahl salt-resistant (DR), but not salt-sensitive (DS) rats. Since these effects were absent during mixed ETA/B receptor blockade, we tested the hypothesis that there is greater adrenergic dependence of the ETB-mediated pressor response in DR vs. DS rats. Pressor responses to the selective ETB receptor agonist sarafotoxin (S6c) were examined in anesthetized male DR and DS rats during ganglion blockade. S6c produced comparable dose-dependent increases in arterial pressure in both DR and DS rats. In DR rats, pretreatment with the selective α1 adrenergic antagonist prazosin (PZ; 1 mg/kg) blunted the peak pressor response to 0.1 (17±2 vs. 24±2 mmHg, PZ vs. untreated, p<0.05) and 1 nmol/kg S6c (23±2 vs. 35±4 mmHg, PZ vs. untreated, p<0.01). Peak pressor response to 1 nmol/kg S6c was also lower in DS rats treated with PZ (20±4 vs. 47±12 mmHg, PZ vs. untreated, p<0.01). There was a greater reduction in the steady-state response to 1 nmol/kg S6c in treated DS (-3+4 vs. 35±16 mmHg, PZ vs. untreated) than in DR rats (14±2 vs. 24±6 mmHg, PZ vs. untreated). Together, these data suggest that the pressor response to ETB receptor activation is partially dependent on α1 adrenergic stimulation; however, the adrenergic component is not enhanced in DR vs. DS rats.

IRL-1620 Increases the Efficacy of Radiation Treatment in Mice Bearing Lymphoma Cell Induced Tumors.

PURPOSE. IRL-1620, a selective ETB receptor agonist, has been reported to selectively enhance tumor blood flow and potentiate the efficacy of chemotherapeutics in various tumor models. Improved tumor perfusion is associated with a net increase in tumor oxygenation, which may be exploited to increase the effectiveness of radiotherapy. Since tumor oxygenation increases the radiation-induced cellular damage, IRL-1620 may be helpful to increase radiation sensitivity of tumor. The present study was conducted to determine whether administration of IRL-1620 prior to radiation enhances the efficacy of radiotherapy.STUDY DESIGN. Male Swiss albino mice (6–8 weeks old; 25–30 g) were used for the study. Tumor was induced by the subcutaneous inoculation of Dalton's Lymphoma cells (1 million) on the right hind limb. Tumor volume was measured using a digital caliper. Animals with a tumor volume of about 1cc were selected for the study and were divided into six groups (10 mice per group). Group I: No treatment; Group II: IRL-1620 (9 nmol/kg, 5 doses on alternate days); Group III: Radiation (5 × 4 Gy using Cobalt-60 Teletherapy unit (Theratron 780, Canada) on alternate days administered at 1 Gy/min); Group VI: IRL-1620 (1 nmol/kg) + radiation, 5 doses on alternate days; Group V: IRL-1620 (3 nmol/kg) + radiation, 5 doses on alternate days; Group VI: IRL-1620 (9 nmol/kg) + radiation, 5 doses on alternate days. Mice were shielded with lead except for a 3-cm-diameter circular field where the tumor was centered. IRL-1620 was administered via tail vein 15 minutes prior to radiation administration. Tumor diameter was measured twice a week for a total of 70 days.RESULTS. Tumor bearing mice without any treatment showed a progressive increase in tumor volume and all the animals died by 53 days after tumor induction. Radiation alone did not significantly reduce tumor volume when compared to controls (possible due to hypoxic condition). There was no significant increase in the survival. All the animals (10 out of 10) died by 56 days after tumor induction. Animals treated with radiation 15 min after administration of 9 nmol/kg IRL-1620 reduced the tumor volume significantly and there was significant increase in life span. It was found that only 4 out 10 animals died by 70 days after tumor induction. Animals treated with radiation 15 min after administration of 3 nmol/kg IRL-1620 delayed the development of tumors. It was found that 7 out 10 animals died by 70 days after tumor induction. Animals treated with radiation 15 min after administration of 1 nmol/kg IRL-1620 along with radiation delayed tumor development. It was found that 9 out 10 animals died by 70 days after tumor induction.CONCLUSION. It is concluded that IRL-1620 significantly enhanced the efficacy of radiation treatment in Dalton's Lymphoma cells induced tumor model by reducing tumor volumes and increasing the survival.