Functional and molecular evidence for beta 1-, beta 2- and beta 3- adrenoceptors in human colon

The role of l-cysteine/Hydrogen sulfide pathway on β3-Adrenoceptor- induced relaxation in mouse gastric fundus

In this study, we investigated the possible role of the l-cysteine/hydrogen sulfide pathway in β₃-adrenoceptors-mediated relaxation in isolated mouse gastric fundus tissue. l-cysteine (endogenous H₂S; 10^-6-10^-2 M), sodium hydrogen sulfide (NaHS; exogenous H₂S; 10^-6-10^-3 M), selective β₃-adrenoceptors agonist BRL 37344 (10^-9-10^-4 M) and non-selective β-adrenoceptor agonist isoprenaline (10^-9-10^-4 M) produced concentration-dependent relaxation in mouse gastric fundus. The non-selective β-adrenoceptors antagonist propranolol (10^-6 M) inhibited the relaxant response to isoprenaline but not to BRL 37344. On the other hand, the selective β₃-adrenoceptors antagonist SR 59230A (10^-5 M) inhibited the relaxant responses to BRL 37344. In addition, cystathionine-gamma-lyase (CSE) inhibitor D,L-propargylglycine (PAG, 10^-2 M), cystathionine-beta-synthase inhibitor (CBS) aminooxyacetic acid (AOAA, 10^-2 M), and the combination of these inhibitors significantly reduced the relaxant responses induced by l-cysteine and BRL 37344. Pre-incubation of gastric fundal strips with propranolol (10^-6 M) and SR 59230A (10^-5 M) did not affect relaxations to l-cysteine and NaHS. Also, the existence of CSE, CBS, 3-mercaptopurivate sulfur transferase (3-MST) enzymes and β₃-adrenoceptors were detected in gastric fundal tissue. Furthermore, basal H₂S release was detected in the measurements. H₂S level increased in the presence of l-cysteine, NaHS, and BRL 37344. The increase in H₂S level by l-cysteine and BRL 37344 decreased significantly with PAG and AOAA enzyme inhibitors. These results suggest that endogenous H₂S is synthesized from l-cysteine at least by CBS and CSE enzymes. Also, β₃-adrenoceptors are found in the mouse stomach fundus and mediate BRL 37344-induced relaxations, and l-cysteine/hydrogen sulfide pathway plays a partial role in β₃-adrenoceptors-mediated relaxation in mouse gastric fundus tissue.

Biogenic Amines: Signals Between Commensal Microbiota and Gut Physiology

There is increasing interest in the interactions among the gut microbiota, gut, and brain, which is often referred to as the "microbiota-gut-brain" axis. Biogenic amines including dopamine, norepinephrine, serotonin, and histamines are all generated by commensal gut microorganisms and are suggested to play roles as signaling molecules mediating the function of the "microbiota-gut-brain" axis. In addition, such amines generated in the gut have attracted attention in terms of possible clues into the etiologies of depression, anxiety, and even psychosis. This review covers the latest research related to the potential role of microbe-derived amines such as catecholamine, serotonin, histamine, as well as other trace amines, in modulating not only gut physiology but also brain function of the host. Further attention in this field can offer not only insight into expanding the fundamental roles and impacts of the human microbiome, but also further offer new therapeutic strategies for psychological disorders based on regulating the balance of resident bacteria.

ATP-sensitive and maxi potassium channels regulate BRL 37344-induced tocolysis in buffaloes-an in vitro study

Cellular coupling of beta₃-adrenoceptors (β₃-ADR) to potassium channels in myometrium is largely unknown. In vitro study was undertaken to unravel the presence of β₃-adrenergic receptors (ADR) and the role of K⁺-channels in mediating β₃-ADR-induced relaxation in isolated myometrial strips from cyclic non-pregnant water buffaloes. Isometric tension was recorded in isolated myometrial strips using data acquisition system based physiograph. Compared to SR 59230A, BRL 37344 was found to be more potent in inducing β₃-dependent myometrial relaxation which was significantly (p < 0.05) inhibited in the presence of β₃ antagonist, SAR 150640. The immunoreactive protein to β₃-ADR was also detected in membrane fraction of myometrial protein. Further, incubation with BRL 37344 (10 μM) significantly (p < 0.05) increased c-AMP accumulation (37.58 ± 9.52 pmol/mg protein; n = 4) in the myometrial strips compared to basal c-AMP level (16.85 ± 3.87 pmol/mg protein; n = 4). The concentration response curves (CRC) of BRL 37344 were significantly (p < 0.05) shifted towards right in the presence of K_ATP channels specific blocker, glibenclamide (10 μM) and maxi K⁺-channels (BK_Ca) specific blocker, iberiotoxin (100 nM), with decrease in both efficacy and potency as compared to control. However, 4-aminopyridine (4-AP), a specific blocker of the voltage gated K⁺-channels (Kv), failed to alter the CRC of BRL 37344. Existence of immunoreactive protein to Kir6.1, α-subunit of BK_Ca and Kv1.1 channels were also detected in the membrane fraction of myometrial protein. Based on the above findings, it can be concluded that BRL 37344 is a potent stimulator of β₃-adrenoceptors in buffalo myometrium and besides mediating their effect through rise in c-AMP, they are coupled to K_ATP and BK_Ca channels in inducing tocolytic effects.

Safety and tolerability of β3-adrenoceptor agonists in the treatment of overactive bladder syndrome - insight from transcriptosome and experimental studies

INTRODUCTION

We have reviewed the safety and tolerability of β3-adrenoceptor agonists, specifically mirabegron and solabegron, a newly emerging drug class for the treatment of the overactive bladder syndrome. We discuss them mechanistically in the context of expression and other preclinical data.

AREAS COVERED

Based on a systematic PubMed search, incidence of overall adverse events, hypertension, dry mouth, and constipation are comparable between mirabegron or solabegron and placebo. Hypertension is the most frequently observed adverse event, but has a similar incidence with mirabegron and placebo. Nevertheless, severe uncontrolled hypertension has become a contraindication for use of mirabegron based on observation of severe hypertension in association with mirabegron exposure. The overall incidence of adverse events is also similar between mirabegron and the muscarinic receptor antagonist tolterodine, but the incidence of dry mouth is much lower with mirabegron.

EXPERT OPINION

The high β3-adrenoceptor mRNA expression in the human ovaries is not associated with reproductive side effects. Generally, β3-adrenoceptors exhibit a rather restricted expression in human tissues, which may explain the overall good tolerability of agonists acting on this receptor. We propose that expression profiles and functional preclinical studies can be important tools in the prediction of adverse event profiles in first-in-class drugs.

β3-Adrenoceptor agonists for overactive bladder syndrome: Role of translational pharmacology in a repositioning clinical drug development project

β3-Adrenoceptor agonists were originally considered as a promising drug class for the treatment of obesity and/or type 2 diabetes. When these development efforts failed, they were repositioned for the treatment of the overactive bladder syndrome. Based on the example of the β3-adrenoceptor agonist mirabegron, but also taking into consideration evidence obtained with ritobegron and solabegron, we discuss challenges facing a translational pharmacology program accompanying clinical drug development for a first-in-class molecule. Challenges included generic ones such as ligand selectivity, species differences and drug target gene polymorphisms. Challenges that are more specific included changing concepts of the underlying pathophysiology of the target condition while clinical development was under way; moreover, a paucity of public domain tools for the study of the drug target and aspects of receptor agonists as drugs had to be addressed. Nonetheless, a successful first-in-class launch was accomplished. Looking back at this translational pharmacology program, we conclude that a specifically tailored and highly flexible approach is required. However, several of the lessons learned may also be applicable to translational pharmacology programs in other indications.

Selective β2-AR Blockage Suppresses Colorectal Cancer Growth Through Regulation of EGFR-Akt/ERK1/2 Signaling, G1-Phase Arrest, and Apoptosis

The stress-upregulated catecholamines-activated β1- and β2-adrenergic receptors (β1/2-ARs) have been shown to accelerate the progression of cancers such as colorectal cancer (CRC). We investigated the underlying mechanism of the inhibition of β1/2-ARs signaling for the treatment of CRC and elucidated the significance of β2-AR expression in CRC in vitro and in clinical samples. The impacts of β1/2-AR antagonists in CRC in vitro and CRC-xenograft in vivo were examined. We found that repression of β2-AR but not β1-AR signaling selectively suppressed cell viability, induced G1-phase cell cycle arrest, caused both intrinsic and extrinsic pathways-mediated apoptosis of specific CRC cells and inhibited CRC-xenograft growth in vivo. Moreover, the expression of β2-AR was not consistent with the progression of CRC in vitro or in clinical samples. Our data evidence that the expression profiles, signaling, and blockage of β2-AR have a unique pattern in CRC comparing to other cancers. β2-AR antagonism selectively suppresses the growth of CRC accompanying active β2-AR signaling, which potentially carries wild-type KRAS, in vitro and in vivo via the inhibition of β2-AR transactivated EFGR-Akt/ERK1/2 signaling pathway. Thus, β2-AR blockage might be a potential therapeutic strategy for combating the progressions of β2-AR-dependent CRC.

Myogenic effect of SP-1f and SP-1h two novel β3-adrenoceptor (β3-AR) agonists in human colonic circular smooth muscle

The effect of two novel β3-adrenoceptor (β3-AR) agonists SP-1f and SP-1h on human colon circular smooth muscle contractility and β3-AR mRNA expression have been determined. β3-AR is ascertained co-participates to the control of the gut motility. Isometric tension on human colon muscle strips was measured in response to increasing concentrations of SP-1f, SP-1h and (-)-isoprenaline, alone and in the presence of Betaxolol, ICI 11,855 and SR 59230A (β1-, β2- and β3-AR antagonists, respectively). (-)-Isoprenaline concentration-dependently relaxed circular muscle strips with an EC50=0.32±0.06μM. Such an effect was antagonized either by the contemporaneously presence of Betaxolol and ICI 11,855 [(-)-isoprenaline EC50=1.75±0.35μM, pKB=7.88±0.10] or by Betaxolol, ICI 11,855 and SR 59230A [(-)-isoprenaline EC50=3.49±0.38μM, pKB=8.51±0.14]. Besides, SP-1f and SP-1h concentration-dependently relaxed circular muscle strips with an EC50=0.35±0.07μM and 0.45±0.12μM, respectively. These values remained unchanged by blocking the β1- and β2-AR. The presence of SR 59230A antagonized the relaxing effect of SP-1f (EC50=3.51±0.94μM, pKB=8.93±0.16) and did not modify the SP-1h relaxing potency. In colon circular smooth muscle and in mucosa, β3-AR mRNA expression levels were found to be 0.39±0.70 and 0.26±0.12 (P<0.05), respectively. Such results provide further evidence of the β3-adrenoceptor functional role in the human colon and the crucial contribution of SP-1f to the control of the gut dysmotility.

Inhibitory effect of Suaeda asparagoides (Miq.) extract on the motility of rat gastric antrum is mediated by β-adrenoceptor

Suaeda asparagoides (Miq.) has long been used as a Korean folk herbal medicine for the treatment of functional gastrointestinal disorders. However, reports on its pharmacological activity on gastrointestinal motility are scarce. The present study investigated the effects of Suaeda asparagoides water fraction of the extract (SAWF) on antral motility in vitro. Muscle strips from rat gastric antrum were set up in an organ bath in a circular orientation. SAWF (100 µg/mL) inhibited the spontaneous contraction of antral circular muscle strips. These inhibitory effects were not significantly affected by tetrodotoxin (1 µM), N^ω-Nitro-L-arginine methyl ester hydrochloride (100 µM), 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (10 µM), ryanodine (10 µM) and phentolamine (10 µM). SAWF-induced inhibition was mostly restored by cyclopiazonic acid (10 µM). Furthermore, the β-adrenergic receptor antagonist, propranolol (10 µM), abolished SAWF-induced inhibition. These results suggest that SAWF may exert its activity on gastrointestinal smooth muscle via â-adrenergic receptors and sarcoplasmic reticulum Ca²⁺ ATPase.

Expression and activation of β-adrenoceptors in the colorectal mucosa of rat and human

BACKGROUND

The functions of the distal colon are regulated by local and extrinsic neural pathways. In previous studies, we have found that dopamine (DA) and norepinephrine (NE) could evoke colonic ion transport by activating β-adrenoceptors. The present study aims to investigate the segmental differences in expression and activation of β-adrenoceptors in the distal colon in physiological and pathophysiological conditions.

METHODS

Real-time PCR, immunofluorescence, and Western blotting were used to detect the expression of β-adrenoceptors in the rat and human distal colon. Short-circuit current measurements (Isc) were used to assess the role of β-adrenoceptors in ion transport.

KEY RESULTS

DA and NE caused greater suppression of baseline Isc in distal colon adjacent to the rectum than in segments further away from the anus. These responses were inhibited by selective antagonists of β₁- and β₂-adrenoceptors, but not β₃-adrenoceptor. The expression levels of β₁- and β₂-adrenoceptors in colonic mucosa were higher in colorectum than the regions away from the anus of rats and humans. In wrap-restraint stress (2 h), DA-, NE-induced ΔIsc and the expression of β-adrenoceptors in the colorectum were significantly reduced. However, when endogenous catecholamines were depleted by 6-hydroxydopamine (75 mg kg(-1), i.p., 3 days), DA-, NE-induced ΔIsc as well as the expression of β-adrenoceptors were significantly enhanced in the rat colorectum but not in more proximal regions of the distal colon.

CONCLUSIONS & INFERENCES

β₁- and β₂-adrenoceptors are predominantly expressed in the colorectal mucosa. Perturbation of endogenous catecholamine levels influences the expression and activation of β-adrenoceptors in the colorectal region.

Tissue functions mediated by beta(3)-adrenoceptors-findings and challenges

As β₃-adrenoceptor agonists metamorphose from experimental tools into therapeutic drugs, it is vital to obtain a comprehensive picture of the cell and tissue functions mediated by this receptor subtype in humans. Human tissues with proven functions and/or a high expression of β₃-adrenoceptors include the urinary bladder, the gall bladder, and other parts of the gastrointestinal tract. While several other β₃-adrenoceptor functions have been proposed based on results obtained in animals, their relevance to humans remains uncertain. For instance, β₃-adrenoceptors perform an important role in thermogenesis and lipolysis in rodent brown and white adipose tissue, respectively, but their role in humans appears less significant. Moreover, the use of tools such as the agonist BRL 37344 and the antagonist SR59230A to demonstrate functional involvement of β₃-adrenoceptors may lead in many cases to misleading conclusions as they can also interact with other β-adrenoceptor subtypes or even non-adrenoceptor targets. In conclusion, we propose that many responses attributed to β₃-adrenoceptor stimulation may need re-evaluation in the light of the development of more selective tools. Moreover, findings in experimental animals need to be extended to humans in order to better understand the potential additional indications and side effects of the β₃-adrenoceptor agonists that are beginning to enter clinical medicine.

Changes in the mRNA expression of osteoblast-related genes in response to beta(3)-adrenergic agonist in UMR106 cells

Activation of adrenergic receptors (AR) was demonstrated to result in either bone gain or bone loss depending on the activated AR subtypes and concentrations of agonists used. While beta(2)-AR agonist was extensively investigated as an osteopenic agent, effects of beta(3)-AR activation on osteoblasts were still elusive. Rat osteoblast-like UMR106 cells were herein found to express several AR subtypes, including beta(3)-AR. After exposure to a low-dose beta(3)-AR agonist BRL37344 (10 nmol L(-1)), UMR106 cells downregulated the mRNA expression of transcription factors Runx2 and Dlx5, which are important for initiation of osteoblast differentiation. Low-dose BRL37344 also decreased the expression ratio of receptor activator of nuclear factor kappaB ligand (RANKL) over osteoprotegerin (OPG), suggesting the protective effect of beta(3)-AR agonist against bone resorption. Alkaline phosphatase expression was markedly decreased, whereas expressions of osteocalcin and osteopontin were increased by 100 nmol L(-1) BRL37344, indicating that beta(3)-AR activation could accelerate the transition of matrix maturation stage to mineralization stage. In conclusion, beta(3)-AR activation in rat osteoblasts induced alteration in the expression of osteoblast-related transcription factor genes as well as genes required for bone formation and resorption. The present results also suggest that, besides beta(2)-AR, beta(3)-AR is another AR subtype responsible for the sympathetic nervous system-induced bone remodeling.

Adrenergic activation of electrogenic K+ secretion in guinea pig distal colonic epithelium: involvement of beta1- and beta2-adrenergic receptors

Adrenergic stimulation of electrogenic K+ secretion in isolated mucosa from guinea pig distal colon required activation of two beta-adrenergic receptor subtypes (beta-AdrR). Addition of epinephrine (epi) or norepinephrine (norepi) to the bathing solution of mucosae in Ussing chambers increased short-circuit current (Isc) and transepithelial conductance (Gt), consistent with this cation secretion. A beta-adrenergic classification was supported by propranolol antagonism of this secretory response and the lack of effect by the alpha-AdrR antagonists BE2254 (alpha1-AdrR) and yohimbine (alpha2-AdrR). Subtype-selective antagonists CGP20712A (beta1-AdrR), ICI-118551 (beta2-AdrR), and SR59320A (beta3-AdrR) were relatively ineffective at inhibiting the epi-stimulated Isc response. In combination, CGP20712A and ICI-118551 inhibited the response, which supported a synergistic action by beta1-AdrR and beta2-AdrR. Expression of mRNA for both beta1-AdrR and beta2-AdrR was indicated by RT-PCR of RNA from colonic epithelial cells. Protein expression was indicated by immunoblot showing bands at molecular weights consistent with monomers and oligomers. Immunoreactivity (ir) for beta1-AdrR and beta2-AdrR was prominent in basolateral membranes of columnar epithelial cells in the crypts of Lieberkühn as well as intercrypt surface epithelium. Cells in the pericryptal sheath also had beta1-AdrR(ir) but did not have discernable beta2-AdrR(ir). The adrenergic sensitivity of K+ secretion measured by Isc and Gt was relatively low as indicated by EC(50)s of 41 +/- 7 nM for epi and 50 +/- 14 nM for norepi. Adrenergic activation of electrogenic K+ secretion required the involvement of both beta1-AdrR and beta2-AdrR, occurring with an agonist sensitivity reduced compared with reported values for either receptor subtype.

Expression and functional role of beta-adrenoceptors in the human urinary bladder urothelium

We investigated the presence of beta-adrenoceptor subtypes in human urinary bladder urothelium and examined whether beta-adrenoceptors in the urothelium modulate the relaxation responses of isolated human detrusor strips to a beta-adrenoceptor agonist. Expression of beta1-, beta2-, and beta3-adrenoceptor mRNA in urothelium and detrusor smooth muscle was determined by reverse transcription-polymerase chain reaction, and the distribution of beta1-, beta2-, and beta3-adrenoceptors in human urinary bladder urothelium were examined by immunohistochemistry. Paired human longitudinal detrusor strips with and without an intact urothelium were suspended in organ baths to construct concentration-response curves to isoproterenol. The possible involvement of urothelium-derived nitric oxide (NO) in this response was examined in additional experiments with urothelium-intact strips in the presence of NG-nitro-L-arginine methylester (L-NAME). Results confirmed the expression of beta1-, beta2-, and beta3-adrenoceptors in the human urinary bladder urothelium. Further, the presence of the urothelium caused a parallel rightward shift of the concentration-response curve to isoproterenol with a significant reduction in potency (pEC50). L-NAME failed to exert any significant effect on the relaxation response to isoproterenol in the urothelium-intact strips. These results confirm the presence of beta1-, beta2-, and beta3-adrenoceptors in human urinary bladder urothelium. Further, they suggest that urothelial beta-adrenoceptors induce the release of a urothelium-derived factor which inhibits the beta-adrenoceptor agonist-induced relaxation of the human detrusor smooth muscle and that this inhibitory mechanism might not involve NO.

Demonstration of functional neuronal beta3-adrenoceptors within the enteric nervous system

BACKGROUND & AIMS

Although the beta(3)-adrenoceptor (AR) has been suggested to be involved in regulation of gut motility and visceral algesia, the precise mechanisms have been unknown. beta(3)-AR has been postulated to have a nonneuronal expression, being initially characterized in adipocytes and subsequently in the smooth muscle. We aimed to investigate the expression of beta(3)-AR in human enteric nervous system and its role in motility and visceral algesia.

METHODS

The expression of beta(3)-AR in human colon myenteric and submucosal plexus was investigated using immunohistochemistry. The effects of a beta(3)-AR agonist on nerve-evoked and carbachol-induced contractions as well as somatostatin release were investigated in strips of human colon. The effect of an agonist on diarrhea and visceral pain was investigated in vivo in rat models.

RESULTS

beta(3)-AR is expressed in cholinergic neurons in the myenteric plexus and submucosal plexus of human colon. Activation of beta(3)-AR causes the release of somatostatin from human isolated colon. In a rat model of visceral pain, beta(3)-AR agonist elicits somatostatin-dependent visceral analgesia. beta(3)-AR agonists inhibit cholinergically mediated muscle contraction of the human colon, as well as chemically induced diarrhea in vivo in a rat model.

CONCLUSIONS

This is the first demonstration of expression of beta(3)-AR in the enteric nervous system. Activation of these receptors results in inhibition of cholinergic contractions and enhanced release of somatostatin, which may lead to visceral analgesia and inhibition of diarrhea. Therefore, beta(3)-AR could be a novel therapeutic target for functional gastrointestinal disorders.

Tools to study beta3-adrenoceptors

Beta(3)-adrenoceptors mediate some of the effects of catecholamines on tissues such as blood vessels or the urinary bladder and are putative targets for the treatment of diseases such as the overactive bladder syndrome. Progress in the understanding of the presence, function, and regulation of beta(3)-adrenoceptors has been hampered by a lack of highly specific tools. "Classical" beta(3)-adrenoceptor agonists such as BRL 37,344 [(R*, R*)-(+/-)-4[2-[(3-chlorophenyl)-2-hydroxyethyl) amino] propyl] phenoxyacetic acid] and CGP 12,177 [(+/-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one] are only partial agonists in many settings, have limited selectivity over other beta-adrenoceptor subtypes, and may additionally act on receptors other than beta-adrenoceptors. More efficacious and more selective agonists have been reported and, in some cases, are in clinical development but are not widely available for experimental studies. The widely used antagonist SR 59,230 [3-(2-ethylphenoxy)-1-[(1,S)-1,2,3,4-tetrahydronapth-1-ylamino]-2S-2-propanoloxalate] is not selective for beta(3)-adrenoceptors, at least in humans, and may actually be a partial agonist. Radioligands, which are suitable either for the selective labeling of beta(3)-adrenoceptors or for the nonselective labeling of all beta-adrenoceptor subtypes, are also missing. beta(3)- and beta(1)/beta(2) double knockout mice have been reported, but their usefulness for extrapolations in humans is questionable based upon major differences between humans and rodents with regard to the ligand recognition and expression profiles of beta(3)-adrenoceptors. While the common availability of more selective agonists and antagonists at the beta(3)-adrenoceptor is urgently awaited, the limitations of the currently available tools need to be considered in studies of beta(3)-adrenoceptor for the time being.

Zur Funktion des β3-Adrenozeptors am Herzen: Signaltransduktion, inotroper Effekt und therapeutischer Ausblick

Beta-adrenergic stimulation is an important regulatory mechanism of cardiac function. Next to beta1- and beta2-adrenoceptors, the expression of a third beta-adrenoceptor population, the beta3-adrenoceptor, has recently been evidenced in the human heart. Stimulation of cardiac beta3-adrenoceptors leads to a decrease in contractility via a release of nitric oxide (NO). In this context, different molecular mechanisms of endothelial nitric oxide synthase (eNOS) activation have been uncovered to occur as a consequence of beta3-adrenergic stimulation. In both nonfailing and failing myocardium, beta3-adrenergic stimulation may have a protective effect against excessive chatecolaminergic stimulation as it occurs during somatic and mental stress and during heart failure. For this reason, the beta3-adrenoceptor is discussed as a possible target for the pharmacological therapy of heart failure.

Neural contractions in colonic strips from patients with diverticular disease: role of endocannabinoids and substance P

BACKGROUND AND AIMS

Diverticulosis is a common disease of not completely defined pathogenesis. Motor abnormalities of the intestinal wall have been frequently described but very little is known about their mechanisms. We investigated in vitro the neural response of colonic longitudinal muscle strips from patients undergoing surgery for complicated diverticular disease (diverticulitis).

METHODS

The neural contractile response to electrical field stimulation of longitudinal muscle strips from the colon of patients undergoing surgery for colonic cancer or diverticulitis was challenged by different receptor agonists and antagonists.

RESULTS

Contractions of colonic strips from healthy controls and diverticulitis specimens were abolished by atropine. The beta adrenergic agonist (-) isoprenaline and the tachykinin NK1 receptor antagonist SR140333 had similar potency in reducing the electrical twitch response in controls and diseased tissues, while the cannabinoid receptor agonist (+)WIN 55,212-2 was 100 times more potent in inhibiting contractions in controls (IC50 42 nmol/l) than in diverticulitis strips. SR141716, a selective antagonist of the cannabinoid CB1 receptor, had no intrinsic activity in control preparations but potentiated the neural twitch in diseased tissues by up to 196% in a concentration dependent manner. SR141716 inhibited (+)WIN 55,212-2 induced relaxation in control strips but had no efficacy on (+)WIN 55,212-2 responses in strips from diverticular disease patients. Colonic levels of the endogenous ligand of cannabinoid and vanilloid TRPV1 receptors anandamide were more than twice those of control tissues (54 v 27 pmol/g tissue). The axonal conduction blocker tetrodotoxin had opposite effects in the two preparations, completely inhibiting the contractions of control strips but potentiating those in diverticular preparations, an effect selectively inhibited by SR140333.

CONCLUSIONS

Neural control of colon motility is profoundly altered in patients with diverticulitis. Their raised levels of anandamide, apparent desensitisation of the presynaptic neural cannabinoid CB1 receptor, and the SR141716 induced intrinsic response, suggest that endocannabinoids may be involved in the pathophysiology of complications of colonic diverticular disease.

Analysis of DNA double-strand break repair pathways in mice

During the last years significant new insights have been gained into the mechanism and biological relevance of DNA double-strand break (DSB) repair in relation to genome stability. DSBs are a highly toxic DNA lesion, because they can lead to chromosome fragmentation, loss and translocations, eventually resulting in cancer. DSBs can be induced by cellular processes such as V(D)J recombination or DNA replication. They can also be introduced by exogenous agents DNA damaging agents such as ionizing radiation or mitomycin C. During evolution several pathways have evolved for the repair of these DSBs. The most important DSB repair mechanisms in mammalian cells are nonhomologous end-joining and homologous recombination. By using an undamaged repair template, homologous recombination ensures accurate DSB repair, whereas the untemplated nonhomologous end-joining pathway does not. Although both pathways are active in mammals, the relative contribution of the two repair pathways to genome stability differs in the different cell types. Given the potential differences in repair fidelity, it is of interest to determine the relative contribution of homologous recombination and nonhomologous end-joining to DSB repair. In this review, we focus on the biological relevance of DSB repair in mammalian cells and the potential overlap between nonhomologous end-joining and homologous recombination in different tissues.

Epithelial distribution of neural receptors in the guinea pig small intestine

Neural and paracrine agents, such as dopamine, epinephrine, and histamine, affect intestinal epithelial function, but it is unclear if these agents act on receptors directly at the enterocyte level. The cellular localization and villus-crypt distribution of adrenergic, dopamine, and histamine receptors within the intestinal epithelium is obscure and needs to be identified. Single cell populations of villus or crypt epithelial cells were isolated from the jejunum of adult guinea pigs. Enterocytes were separated from intraepithelial lymphocytes by flow cytometry and specific binding was determined using fluorescent probes. α1-adrenergic receptors were located on villus and crypt intraepithelial lymphocytes and enterocytes. β-adrenergic receptors were found on villus and crypt enterocytes. Dopamine receptors were found on all cell types examined, whereas histamine receptors were not detected (<10% for each cell population). These studies demonstrated that (1) receptors for epinephrine and dopamine exist on epithelial cells of the guinea pig jejunum, (2) β-adrenergic receptors are found primarily on villus and crypt enterocytes and (3) intraepithelial lymphocytes contain α1-adrenergic, but have few β-adrenergic, receptors. The presence of neural receptors suggests that these agents are acting, at least in part, at the enterocyte or intraepithelial lymphocyte levels to modulate intestinal and immune function.Key words: enterocyte, receptor, intestine, epithelium.

β3-Adrenoceptors: relaxant function and mRNA detection in smooth muscle cells isolated from the human colon

Functional involvement of β3-adrenoceptors in controlling human gastrointestinal motility has not been unequivocally assessed yet. The direct myogenic contribution of these receptors was examined, by in vitro functional studies and analysis of mRNA expression, on smooth muscle cells separately isolated from taenia coli and circular muscle layers of the human colon. Isoproterenol, a nonselective β-adrenoceptor agonist, relaxed, in a concentration-dependent manner, both human taenia coli and circular colonic smooth muscle cells, although displaying a higher intrinsic activity (65.3 ± 2.3 vs. 55.2 ± 1.4% maximal relaxation) and potency (pEC50: 7.41 ± 0.07 vs. 6.32 ± 0.08) were greater on taenia coli than circular cells. In the presence of the β1-antagonist CGP20712A and of the β2-antagonist ICI 118,551, a 25–30% decrease in isoproterenol intrinsic activity was observed on both cell types and on taenia coli, the nonselective β1/β2-antagonist propranolol produced a rightward shift of the isoproterenol concentration-response curve with mean estimated pKB values (8.12 ± 0.27 at 0.1 µM and 6.45 ± 0.13 at 1 µM) lower than that expected for both β1- and β2-adrenoceptors. CGP12177A and SR 58611A, two β3-adrenoceptor agonists, presented an intrinsic activity comparable to that of isoproterenol in the presence of β1- and β2-antagonists, the former being more potent on taenia coli than on circular smooth muscle cells. β3-Adrenoceptor mRNA was detected by reverse transcription PCR on both cell types. These results strongly suggest a direct functional role of β3-adrenoceptors in the human colon.Key words: adrenoceptors, β3-adrenoceptors, smooth muscle cells, taenia coli, human colon.

The human near-term myometrial beta 3-adrenoceptor but not the beta 2-adrenoceptor is resistant to desensitisation after sustained agonist stimulation

1. In order to compare the beta(2)- and beta(3)-adrenoceptor (beta-AR) desensitisation process in human near-term myometrium, we examined the influence of a pretreatment of myometrial strips with either a beta(2)- or a beta(3)-AR agonist (salbutamol or SR 59119A, respectively, both at 10 microm, for 5 and 15 h) on the relaxation and the cyclic adenosine monophosphate (cAMP) production induced by these agonists. 2. To assess some of the mechanisms potentially implicated in the beta-AR desensitisation process, we studied the influence of such treatment on the number of beta(2)- and beta(3)-AR binding sites, the beta(2)- and beta(3)-AR transcripts expression and the phosphodiesterase 4 (PDE4) activity. 3. Salbutamol, but not SR 59119A, concentration-response curve (CRC) was shifted by a 15 h salbutamol preincubation, with a significant difference in -log EC(20) values (6.31+/-0.13 vs 5.58+/-0.24, for control and 15 h salbutamol pretreatment, respectively, P<0.05). Neither salbutamol nor SR 59119A CRCs were modified after a 15 h preincubation with SR 59119A. 4. A 15 h exposure of myometrial strips to salbutamol significantly reduced the salbutamol-induced (0.60+/-0.26 vs 1.54+/-0.24 pmol mg(-1) protein, P<0.05), but not the SR 59119A-induced, cAMP production. No decrease in cAMP production was observed after a 15 h SR 59119A exposure. 5. A 15 h salbutamol exposure of myometrial strips significantly reduced the beta(2)- but not the beta(3)-AR binding site density, whereas no decrease in the number of beta(2)- and beta(3)-AR binding sites was observed after a 15 h SR 59119A treatment. 6. Neither PDE4 activity nor the beta(2)- and beta(3)-AR mRNA expression levels were affected by salbutamol or SR 59119A treatments. 7. Our results indicate that beta(3)-AR, but not beta(2)-AR, are resistant to the agonist-induced desensitisation. In our model, beta(2)-AR desensitisation is mediated by a decreased number of beta(2)-AR that was not explained by transcriptional regulation of the receptor.

Role of adenylate and guanylate cyclases in beta1-, beta2-, and beta3-adrenoceptor-mediated relaxation of internal anal sphincter smooth muscle

The purpose of the present study was to ascertain the role of adenylate (AC) versus guanylate cyclase (GC) signaling pathways in the internal anal sphincter (IAS) smooth muscle relaxation by beta(1)-, beta(2)-, and beta(3)-adrenoceptor (AR) activation by xamoterol, procaterol, and disodium 5-[(2R)-2-(3-chlorophenyl)-2-hydroxy-ethyl]amino)propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL 316243), respectively. The above-mentioned agonists produced concentration-dependent relaxation of the smooth muscle strips. Both the selective G(i/o)alpha and G(s)alpha antagonists 8,8'-(carbonylbis(imino-3,1-phenylene))bis-(1,3,5-naphthalene trisulfonic acid) (NF 023) and 4,4',4",4"'-(carbonylbis(imino-5,1,3-benzenetriylbis(carbonylimino)))tetrakis-benzene-1,3-disulfonic acid (NF 449), respectively, inhibited the relaxation induced by procaterol. However, only NF 023 inhibited the relaxation induced by xamoterol and CL 316243. 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one, a soluble GC inhibitor, significantly inhibited the relaxation induced by different agonists. In contrast, the selective AC inhibitor [9-(tetrahydro-2'-furyl)adenine] (SQ 22536) inhibited only the relaxation induced by procaterol. (9R,10S,12S)-2,3,9,10,11,12-Hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg: 3',2',1'-kl]pyrrolo[3,4-l][1,6]benzodiazocine-10-carboxylic acid, hexyl ester (KT 5720), a cAMP-dependent protein kinase inhibitor, attenuated the relaxation by procaterol, whereas (9S,10R,12R)-2,3,9,10,11,12, hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9.12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-I][1,6]benzodiazocine-10-carboxylic acid methyl ester (KT 5823), a selective cGMP-dependent protein kinase (PKG) inhibitor, attenuated the relaxation induced by xamoterol and CL 316243. Xamoterol produced significant increase in cGMP levels, whereas only procaterol enhanced the cAMP levels. Western blot analysis confirmed the presence of beta(1), beta(2), and beta(3)-AR subtypes in the IAS. In summary, beta(2)-AR activates both G(s)alpha and G(i/o)alpha-protein subunits and induces relaxation in the rat IAS via both cAMP/cGMP pathways. In contrast, the beta(1)/beta(3)-ARs activation causes the smooth muscle relaxation via G(i/o)alpha-protein subunit/GC/GMP/PKG pathway. These studies are important for the understanding of intracellular mechanisms underlying IAS smooth muscle relaxation and in turn the pathophysiology of certain anorectal motility disorders.

Functional and molecular characterization of beta-adrenoceptors in the internal anal sphincter

The purpose of the present study was to characterize different beta-adrenoceptors (beta-ARs) and determine their role in the spontaneously tonic smooth muscle of the internal anal sphincter (IAS). The beta-AR subtypes in the opossum IAS were investigated by functional in vitro, radioligand binding, Western blot, and reverse transcription-polymerase chain reaction (RT-PCR) studies. ZD 7114 [(S)-4-[2-hydroxy-3-phenoxypropylaminoethoxy]-N-(2-methoxyethyl)phenoxyacetamide], a selective beta(3)-AR agonist, caused a potent and concentration-dependent relaxation of the IAS smooth muscle that was antagonized by the beta(3)-AR antagonist SR 59230A [1-(2-ethylphenoxy)-3-[[(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]-(2S)-2-propanol hydrochloride]. Conversely, the IAS smooth muscle relaxation caused by beta(1)- and beta(2)-AR agonists (xamoterol and procaterol, respectively) was selectively antagonized by their respective antagonists CGP 20712 [(+/-)-2-hydroxy-5-[2-[[2-hydroxy-3-[4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]phenoxy]propyl]amino]ethoxy]-benzamide methanesulfonate salt] and ICI 118551. Saturation binding of [(125)I]iodocyanopindolol to beta-AR subtypes revealed the presence of a high-affinity site (K(d1) = 96.4 +/- 8.7 pM; B(max1) = 12.5 +/- 0.6 fmol/mg protein) and a low-affinity site (K(d2) = 1.96 +/- 1.7 nM; B(max2) = 58.7 +/- 4.3 fmol/mg protein). Competition binding with selective beta-AR antagonists revealed that the high-affinity site correspond to beta(1)/beta(2)-AR and the low affinity site to beta(3)-AR. Receptor binding data suggest the predominant presence of beta(3)-AR over beta(1)/beta(2)-AR. Western blot studies identified beta(1)-, beta(2)-, and beta(3)-AR subtypes. The presence of beta(1)-, beta(2)-, and beta(3)-ARs was further demonstrated by mRNA analysis using RT-PCR. The studies demonstrate a comprehensive functional and molecular characterization of beta(1)-, beta(2)-, and beta(3)-ARs in IAS smooth muscle. These studies may have important implications in anorectal and other gastrointestinal motility disorders.

The preferential beta3-adrenoceptor agonist BRL 37344 increases force via beta1-/beta2-adrenoceptors and induces endothelial nitric oxide synthase via beta3-adrenoceptors in human atrial myocardium

1 The present study investigated the effects of the preferential beta(3)-AR agonist BRL 37344 (BRL) on force of contraction (FOC), Ca(2+)-transient and eNOS-activity in human right atrial myocardium. 2 BRL concentration-dependently caused an increase in FOC that was paralleled by an increase in Ca(2+)-transient and a shortening of time to half peak relaxation (T0.5T). These effects were abolished in the presence of propranolol (0.3 micro M). 3 BRL acted as a competitive antagonist towards isoprenaline and in binding experiments it was shown to have a distinct affinity towards beta(1/2)-AR. 4 In immunohistochemical experiments BRL (10 micro M) increased detection of activated eNOS. This effect remained constant in the presence of propranolol (0.3 micro M). 5 BRL increased directly detected NO in DAF-staining experiments. This increase was significantly smaller in the presence of the NO-inhibitor L-NAME. 6 The inotropic effects of BRL were not changed in the presence of L-NMA. 7 These results suggest that the inotropic effects of BRL in human atrium are mediated via beta(1/2)-AR, whereas the increase of atrial eNOS-activity is due to beta(3)- adrenergic stimulation. This increase in eNOS-activity did not influence atrial myocardial contractility. In conclusion, this study shows that beta(3)-adrenergic stimulation is present in human atrium, but may not be functionally as significant as in the left ventricle.

Abnormal levels of neuropeptide Y and peptide YY in the colon in irritable bowel syndrome

OBJECTIVE

To assess the levels of gut peptides involved in gastrointestinal motor, secretory and sensory function in colonic biopsies in irritable bowel syndrome (IBS) patients and healthy controls.

METHODS

We studied 34 patients with IBS and 15 subjects without gastrointestinal symptoms. The predominant bowel pattern in the IBS patients was constipation in 17 patients (IBS-C) and diarrhoea in 17 patients (IBS-D). With radioimmunoassay, the levels of vasoactive intestinal peptide (VIP), substance P, neuropeptide Y (NPY) and peptide YY (PYY) were analysed in biopsies from the descending colon and ascending colon obtained during colonoscopy.

RESULTS

The IBS patients had lower levels of PYY in the descending colon than the controls, but the levels in the ascending colon did not differ. The NPY levels were lower in IBS-D than in IBS-C, both in the ascending colon and in the descending colon. Low levels of VIP were more common in IBS patients, but mean levels did not differ between groups. No group differences were observed for substance P. The levels of VIP, substance P and NPY were higher in the ascending colon than in the descending colon, whereas the opposite pattern was seen for PYY.

CONCLUSION

IBS patients demonstrate lower levels of PYY in the descending colon than controls. Colonic NPY levels differ between IBS subgroups based on the predominant bowel pattern. These findings may reflect the pathophysiology of IBS and the symptom variation within the IBS population.

Identification and coupling to adenylate cyclase of three different [(3)H]CGP 12177 binding sites in Caco-2 cell membranes

In the present investigation the identification of beta -adrenoceptor (beta -ARs) subtypes in the Caco-2 cell line was performed using radiometric assays. beta -ARs were measured using increasing concentrations of the highly specific beta -AR antagonist (-)[(3)H]CGP 12177 (0.06-4 nM), whereas the beta(1)- and beta(2)-AR subtypes discriminated through selective binding assays using the highly selective unlabelled antagonists CGP 20712A and ICI 118551. Atypical beta -ARs were measured using an incubation system formed by higher concentrations (0.6-20 nM) of (-)[(3)H]CGP 12177. beta - Atypical binding site concentrations (69 +/- 5 fmol mg ml(-1)of membrane protein) were higher than beta(1)-ARs (7 +/- 1) and beta(2)-ARs (24 +/- 2), respectively. The different beta -AR subtype affinities were characterized by binding inhibition experiments and the adrenergic agonists displaced the radioligand from its specific binding sites in the following order of potency: isoproterenol > clenbuterol > dobutamine > SR 58611A; for antagonists the order of potency was: propranolol approximately = ICI118551 approximately = CGP20712A. For atypical beta -ARs the order was: SR 58611A > clenbuterol > dobutamine > isoproterenol for agonists and propranolol > CGP 20712A > ICI 118551 for antagonists. As far as in vitro functional studies are concerned, beta -AR subtypes were shown to be coupled to adenylyl cyclase as their stimulation produced cAMP in an amount significantly higher than basal values. cAMP production after stimulation with dobutamine, clenbuterol, isoproterenol, and SR 58611A was measured using a cAMP radioassay kit. The order of efficacy suggested that the stimulation of beta(2)-ARs was the most effective in inducing the activation of cell signalling mechanisms. The identification of functional beta -ARs in a cancer cell line represents the first step in the study of the possible adrenergic control of cellular activities (e.g. proliferation and/or differentiation), which could suggest the use of this cancer cell line as a model for the study of cell activity or possibly new therapeutic strategies.

beta(1)-Adrenoceptors compensate for beta(3)-adrenoceptors in ileum from beta(3)-adrenoceptor knock-out mice

1. This study examines beta(1)-, beta(2)- and beta(3)-adrenoceptor (AR)-mediated responses, mRNA levels and radioligand binding in ileum from beta(3)-AR knock-out (-/-) (KO) and wild type (+/+) (FVB) mice. 2. In KO and FVB mice, SR59230A (100 nM) (beta(3)-AR antagonist) antagonized responses to (-)-isoprenaline in both KO and FVB mice. (-)-Isoprenaline mediated relaxation of ileum was antagonized weakly by ICI118551 (100 nM) (beta(2)-AR antagonist). Responses to (-)-isoprenaline were more strongly antagonized by CGP20712A (100 nM) (beta(1)-AR antagonist), propranolol (1 microM) (beta(1)-/beta(2)-AR antagonist), carvedilol (100 nM) (non-specific beta-AR antagonist), and CGP12177A (100 nM) (beta(1)-/beta(2)-AR antagonist) in ileum from KO than in FVB mice. 3. Responses to CL316243 (beta(3)-AR agonist) in ileum from FVB mice were antagonized by SR59230A (100 nM) but not by propranolol (1 microM) or carvedilol (100 nM). CL316243 was ineffective in relaxing ileum from KO mice. 4. CGP12177A had no agonist actions in ileum from either KO or FVB mice. 5. beta(1)-AR mRNA levels were increased 3 fold in ileum from KO compared to FVB mice. This was associated with an increased maximum number of beta(1)-/beta(2)-AR binding sites (B(max)). beta(2)-AR mRNA levels were unaffected while no beta(3)-AR mRNA was detected in KO mice. 6. In mouse ileum, beta(3)-ARs and to a lesser extent beta(1)-ARs are the predominant adrenoceptor subtypes mediating relaxation in ileum from FVB mice. In KO mice beta(1)-ARs functionally compensate for the lack of beta(3)-ARs, and this is associated with increased beta(1)-AR mRNA and levels of binding.

Functional assessment of beta adrenoceptor subtypes in human colonic circular and longitudinal (taenia coli) smooth muscle

BACKGROUND AND AIMS

The subtype and species related heterogeneity of beta adrenoceptors prompted a functional reappraisal of these molecular targets of motility inhibition in the human colon.

METHODS

Relaxation of muscle strips was measured in vitro.

RESULTS

The following agonists had decreasing relaxing potency (effective concentration range 10(-8)-10(-4) mol/l): (-)isoprenaline (non-selective), terbutaline (beta(2) selective), CGP 12177 (beta(3) selective, also beta(1), beta(2) antagonist), and SR 58611A (beta(3) selective). Isoprenaline and terbutaline were more potent on circular than taenia strips; CGP 12177 and SR 58611A weakly and partially relaxed taenia but had little effect on circular strips. The potency of isoprenaline on circular strips was greatly reduced by the beta(1) selective antagonist CGP 20712 (10(-7) mol/l), and less so by ICI 118551 (10(-7) mol/l, beta(2) selective). CGP 20712 and ICI 118551 together (both 3 x 10(-6) mol/l) had no effect on taenia relaxation by SR 58611A and rendered isoprenaline and terbutaline virtually inactive on circular strips, although not on taenia, which was relaxed at higher than control concentrations and maximally by isoprenaline. Propranolol, a beta(1), beta(2) non-selective antagonist, at high concentrations (10(-5) mol/l) prevented taenia relaxation by CGP 12177 and SR 58611A; its quantitative antagonism of isoprenaline (in common with that of CGP 12177 used as an antagonist) was competitive in circular strips but not on taenia.

CONCLUSIONS

beta(1), beta(2), and beta(3) adrenoceptors are functionally detectable in the human colon; agonist stimulation of any one type relaxed taenia but only isoprenaline was fully effective at the beta(3) subtype.

beta(3)-adrenoceptor regulation and relaxation responses in mouse ileum

1. This study examines the relationship between beta(3a)- and beta(3b)-adrenoceptor (AR) mRNA levels, beta(3)-AR binding and changes in ileum responses in mice treated with the beta(3)-AR agonist (R, R)-5-[2[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]-propyl]1, 3-benzodioxole-2,2-dicarboxylate (CL316243), or the beta(3)-AR antagonist 3-(2-ethylphenoxy)-1-[(1S)-1,2,3, 4-tetrahydronapth-1-ylamino]-2S-2-propanol oxalate (SR59230A), or dexamethasone or forskolin. 2. Levels of beta(3a)- and beta(3b)-AR mRNA and the maximum number of binding sites (B(max)) in ileum were unaffected following CL316243 treatment, although responses to CL316243 were reduced by 50% following 4 and 24 h treatment, indicating another desensitization mechanism not involving changes in receptor expression or number. beta(3a)-AR mRNA levels were reduced in both brown (BAT) and white adipose tissue (WAT) but beta(3b)-AR mRNA levels were significantly reduced only in WAT. Levels of beta(3a)- and beta(3b)-mRNA returned towards normal with continued treatment. 3. SR59230A treatment markedly increased beta(3)-AR mRN levels in ileum and BAT but not in WAT. The increase in beta(3)-AR mRNA levels in ileum was associated with increased B(max) levels in binding analysis and increased responses to CL316243, suggesting these as the cause of sensitization. 4. Treatment with forskolin (4 h) or dexamethasone (4 h) significantly reduced beta(3a)-AR mRNA levels in BAT and WAT but did not alter levels in ileum. Responses to CL316243 in ileum were unaffected by either treatment. 5. In summary, the beta(3)-AR is differently regulated in adipose tissue and ileum: Treatment with SR59230A increased beta(3)-AR number, mRNA and responsiveness in ileum, whereas treatment with CL316243 reduced responses without affecting beta(3)-AR number or mRNA levels.

Adrenoceptors and colocolonic inhibitory reflex

The colocolonic inhibitory reflex is characterized by inhibition of proximal colonic motility induced by distal colonic distension. The aim of this study was to investigate the underlying neural mechanisms of this reflex, in vivo, using an isolated loop of canine colon. In five beagle dogs, motility was recorded from an exteriorized colonic loop via a serosal strain gauge connected to a digital data logger and chart recorder. Inflation of a balloon in the distal colon resulted in inhibition of motility in the isolated loop. Inhibition of motor activity persisted following injection of propranolol (100 microg/kg intravenously), a beta-adrenoceptor antagonist, but was abolished following administration of the alpha2-adrenoceptor antagonist yohimbine (200 microg/kg intravenously). This study confirms that the colocolonic inhibitory reflex is mediated via the extrinsic nerves to the colon. As the reflex was abolished by alpha2-, but not beta-adrenoceptor blockade, this indicates that the reflex pathway involves alpha2-adrenoceptors.

Alternative splicing generates two isoforms of the beta3-adrenoceptor which are differentially expressed in mouse tissues

The beta3-adrenoceptor (AR) differs from the beta1-AR and beta2-ARs in having introns within and downstream of the coding block. This study demonstrates two splice variants of the mouse beta3-AR which differ within the coding region. Reverse transcription/polymerase chain reaction with intron-spanning primers was used to demonstrate the splice variant of the mouse beta3-adrenoceptor. The novel beta3b-AR has 17 amino acids encoded by exon 2 (SSLLREPRHLYTCLGYP) which differ from the 13 in the known beta3a-AR (RFDGYEGARPFPT). Beta3b-AR mRNA is differentially expressed in mouse tissues, with levels relative to beta3a-AR mRNA highest in hypothalamus, cortex and white adipose tissue, and lower in ileum smooth muscle and brown adipose tissue.

Characterization of beta-adrenoceptor mediated smooth muscle relaxation and the detection of mRNA for beta1-, beta2- and beta3-adrenoceptors in rat ileum

1. Functional and molecular approaches were used to characterize the beta-AR subtypes mediating relaxation of rat ileal smooth muscle. 2. In functional studies, (-)-isoprenaline relaxation was unchanged by CGP20712A (beta1-AR antagonist) or ICI118551 (beta2-AR antagonist) but shifted by propranolol (pKB=6.69). (+/-)-Cyanopindolol, CGP12177 and ICID7114 did not cause relaxation but antagonized (-)-isoprenaline relaxation. 3. BRL37344 (beta3-AR agonist) caused biphasic relaxation. The high affinity component was shifted with low affinity by propranolol, (+/-)-cyanopindolol, tertatolol and alprenolol. CL316243 (beta3-AR agonist) relaxation was unaffected by CGP20712A or ICI118551 but blocked by SR58894A (beta3-AR antagonist; pA2 = 7.80). Enhanced relaxation after exposure to forskolin and pertussis toxin showed that beta3-AR relaxation can be altered by manipulation of components of the adenylate cyclase signalling pathway. 4. The beta-AR agonist RO363 relaxed the ileum (pEC50=6.18) and was blocked by CGP20712A. Relaxation by the beta2-AR agonist zinterol (pEC50=5.71) was blocked by SR58894A but not by ICI118551. 5. In rat ileum, beta1-, beta2- and beta3-AR mRNA was detected. Comparison of tissues showed that beta3-AR mRNA expression was greatest in WAT>colon=ileum >cerebral cortex>soleus; beta1-AR mRNA was most abundant in cerebral cortex > WAT > ileum = colon > soleus; beta2-AR mRNA was expressed in soleus > WAT > ileum = colon > cerebral cortex. 6. These results show that beta3-ARs are the predominant beta-AR subtype mediating rat ileal relaxation while beta1-ARs may produce a small relaxation. The beta2-AR agonist zinterol produces relaxation through beta3-ARs and there was no evidence for the involvement of beta2-ARs in relaxation despite the detection of beta2-AR mRNA.

Functional gut disorders: from motility to sensitivity disorders. A review of current and investigational drugs for their management

Functional gut disorders include several clinical entities defined on the basis of symptom patterns (e.g., functional dyspepsia, irritable bowel syndrome, functional abdominal pain, functional abdominal bloating), for which there is no established pathophysiological mechanism. Because there is no well-defined pathophysiological target, treatment should be aimed at symptom improvement. Prokinetics and antispasmodics have been widely used in the treatment of functional gut disorders on the assumption that disordered motility is the underlying cause of symptoms, and symptom improvement is indeed achievable with these compounds in some, but not all, patients with features of hypo- or hypermotility, respectively. In the first part of this review, we cover the basic pharmacology and discuss the rationale for the clinical use of prokinetics and antispasmodics. On the other hand, in the past few years, the explosive growth in the research focusing on visceral sensitivity and visceral reflexes has suggested that at least some patients with functional gut disorders have altered visceral perception. Thus, the second part of the review covers these developments and focuses on studies addressing the issue of drugs modulating visceral sensitivity.

In vitro inhibition of human colonic motility with SR 59119A and SR 59104A: evidence of a beta3-adrenoceptor-mediated effect

The new beta3-adrenoceptor is present in the gastrointestinal tract of various species. This study aimed to show that this receptor modulates human colonic motility in vitro. We used circular muscle strips from the human colon suspended in single organ baths containing Krebs solution and subjected to an initial 1.5-2 g tension. We measured the effects of different beta3-adrenoceptor agonists, including SR 59104A (N-[(6-hydroxy-1,2,3,4-tetrahydronaphthalen-(2R)-2-yl)methyl]-(2 R)-2-hydroxy-2-(3-chlorophenyl)ethanamine hydrochloride), SR 59119A (N-[(7-methoxy-1,2,3,4-tetrahydronaphthalen-(2R)-2-yl)methyl]-(2R) -2-hydroxy-2-(3-chlorophenyl)ethanamine hydrochloride), BRL 37344 (R,R + S,S) [4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino] propyl] phenoxy] acetic acid), and of isoprenaline and salbutamol in the absence or in the presence of propranolol alone or in combination with the beta3-adrenoceptor antagonist SR 59230A (3-(2-ethylphenoxy)-1-[(1S)-1,2,3,4-tetrahydro-naphthalen-1- ylamino]-(2S)-2-propanol oxalate) on amplitude of spontaneous contractions. To evaluate a possible beta2-adrenoceptor-mediated effect, we studied the action of these compounds on human isolated bronchi. On the human isolated colon, SR 59119A, SR 59104A and isoprenaline reduced the initial amplitude of spontaneous contractions by 60%. The curves obtained in the presence of antagonists suggested an action mediated by beta3-adrenoceptor stimulation, since propranolol did not antagonize the action of SR 59119A and SR 59104A, whereas the combination of propranolol and SR 59230A significantly displaced the concentration-response curve of these agonists to the right. This study provides pharmacological evidence of modulation of human colonic motility, and especially of the amplitude of spontaneous contractions, by the atypical beta-adrenoceptor, the beta3-adrenoceptor.

Differential regulation of beta3-adrenoceptors in gut and adipose tissue of genetically obese (ob/ob) C57BL/6J-mice

1. Levels of beta3-adrenoceptor (AR) mRNA were compared using reverse transcription-polymerase chain reaction (RT PCR) in white adipose tissue (WAT), brown adipose tissue (BAT), ileum and colon from genetically obese (ob/ob) and lean (+/+) C57BL/6J mice. Functional responses to the beta3-AR agonist CL 316243 were also characterized in ileal longitudinal smooth muscle from obese and lean mice. 2. Beta3-AR mRNA levels were significantly higher in WAT (100+/-16%) and BAT (100+/-13%) from lean compared to WAT (21.0+/-0.9%; n=4; P<0.005) and BAT (14.1+/-2.2%; n=5; P<0.01) from obese mice. In contrast, beta3-mRNA levels were not significantly different in ileum (100+/-15%) and colon (100+/-22%) from lean mice, compared to ileum (78+/-13%; n=4; P= 0.31) or colon (82+/-15%; n =4; P=0.52) from obese mice. 3. Concentration-response curves to CL 316243 did not differ significantly in slope or position in ileal longitudinal smooth muscle from obese or lean mice. pEC50 (+/-s.e.mean) values were not significantly different (P= 0.59) between obese (7.90+/-0.13, n = 7) and lean (7.77+/-0.20, n = 7) mice. 4. pKB values for the beta1-AR and beta2-AR selective antagonist propranolol or the beta3-AR selective antagonist SR 58894 against relaxations to CL 316243 were similar in ileum of genetically obese (propranolol 6.31+/-0.22 and 6.13+/-0.12; SR 58894 8.22+/-0.06) and lean mice (propranolol 6.40+/-0.08 and 6.60+/-0.13; SR 58894 8.27+/-0.12) and were consistent with values previously found at beta3-AR. 5. Treatment of lean C57BL/6J mice with dexamethasone (1 mg kg(-1), i.p.) significantly reduced beta3-AR mRNA levels after 4 h in WAT (100+/-6.1 to 41.4+/-4.3; n= 16 18; P<0.0001) and BAT (100+/-8.0 to 35.1+/-5.8; n= 17; P<0.0001), but caused no change in ileum (100+/-6.1 to 101+/-17; n= 10-11; P=0.95) or colon (100+/-11 to 101+/-11; n= 11; P= 0.94). Beta3-mRNA levels in ileum and colon also did not change significantly when examined over 24 h or after the administration of a higher dose of dexamethasone (5 mg kg(-1)). 6. In summary, beta3-AR mRNA levels were considerably lower in WAT and BAT of obese compared to lean mice whereas the levels in ileum and colon were not significantly different. The similar beta3-mRNA levels in ileum of obese and lean mice were associated with indistinguishable responses of carbachol-contracted ileum to a beta3-agonist and similar affinity for beta-antagonists. Administration of glucocorticoids to lean mice reduced beta3-AR mRNA levels in WAT and BAT but not in ileum or colon. These studies show that in mice, beta3-ARs are differentially regulated in ileum and colon compared to adipose tissues.