Evidence for the role of angiotensin II biosynthesis in the rat internal anal sphincter tone

A systematic review of translation and experimental studies on internal anal sphincter for fecal incontinence

The complexity in the molecular mechanism of the internal anal sphincter (IAS) limits preclinical or clinical outcomes of fecal incontinence (FI) treatment. So far, there are no systematic reviews of IAS translation and experimental studies that have been reported. This systematic review aims to provide a comprehensive understanding of IAS critical role in FI. Previous studies revealed the key pathway for basal tone and relaxation of IAS in different properties as follows; calcium, Rho-associated, coiled-coil containing serine/threonine kinase, aging-associated IAS dysfunction, oxidative stress, renin-angiotensin-aldosterone, cyclooxygenase, and inhibitory neurotransmitters. Previous studies have reported improved functional outcomes of cellular treatment for regeneration of dysfunctional IAS, using various stem cells, but did not demonstrate the interrelationship between those results and basal tone or relaxation-related molecular pathway of IAS. Furthermore, these results have lower specificity for IAS-incontinence due to the included external anal sphincter or nerve injury regardless of the cell type. An acellular approach using bioengineered IAS showed a physiologic response of basal tone and relaxation response similar to human IAS. However, in both cellular and acellular approaches, the lack of human IAS data still hampers clinical application. Therefore, the IAS regeneration presents more challenges and warrants more advances.

BDNF rescues aging-associated internal anal sphincter dysfunction

Aging can lead to rectoanal incontinence due to internal anal sphincter (IAS) dysfunction, which is characterized by a decrease in IAS tone and contractility and an increase in nonadrenergic noncholinergic (NANC) relaxation. We aimed to determine whether brain-derived neurotropic factor (BDNF) rescues this aging-associated IAS dysfunction (AAID). To do so, we studied the effects of BDNF on the basal and G protein-coupled receptors (GPCR)-stimulated IAS smooth muscle tone and on NANC relaxation in Fischer 344 rats representing different age groups [26-mo-old (aging) vs. 6-mo-old (young)], before and after tyrosine kinase receptor B (TrkB) antagonist K252a. We also used isolated smooth muscle cells (SMCs) to determine the effects of BDNF before and after different agonists. For some studies, we monitored NO release using smooth muscle perfusates. BDNF reversed AAID by rescuing the basal IAS tone and agonists [thromboxane A₂ analog (U46619) and angiotensin II (ANG II)]-induced contractility, and NANC relaxation. These rescue effects of BDNF were selective as K252a attenuated the changes in the IAS without modifying the effects of K⁺depolarization. Because of the direct association between the basal and GPCR-stimulated IAS tone and RhoA/ROCK activation, we speculate that this pathway in the rescue effects of BDNF. Conversely, our data suggest that aging-associated increased NANC relaxation is reversed by decreased release of NO and decrease in the sensitivity of the released inhibitory neurotransmitter. In summary, BDNF rescue of AAID involves RhoA/ROCK and inhibitory neurotransmission. These data have direct implications for the role of BDNF in the pathophysiology and therapeutic targeting of aging-associated rectoanal motility disorders.NEW & NOTEWORTHY These studies demonstrate that brain-derived neurotropic factor (BDNF) rescues the aging-associated internal anal sphincter (IAS) dysfunction, characterized by a decrease in IAS tone, and increase in non-adrenergic noncholinergic relaxation. We determined the effects of BDNF on the basal and GPCR (TXA₂ and ANG II)-stimulated IAS tone, and on NANC relaxation, before and after TrkB inhibitor K252a. BDNF may have an important role in the pathophysiology and therapeutic targeting of certain rectoanal motility disorders.

BDNF augments rat internal anal sphincter smooth muscle tone via RhoA/ROCK signaling and nonadrenergic noncholinergic relaxation via increased NO release

Presently, there are no studies examining the neuromodulatory effects of brain-derived neurotropic factor (BDNF) on the basal internal anal sphincter (IAS) tone and nonadrenergic noncholinergic (NANC) relaxation. To examine this, we determined the neuromuscular effects of BDNF on basal IAS smooth muscle tone and the smooth muscle cells (SMCs) and the effects of NANC nerve stimulation before and after high-affinity receptor tyrosine kinase receptor B (TrkB) antagonist K252a. We also investigated the mechanisms underlying BDNF-augmented increase in the IAS tone and NANC relaxation. We found that BDNF-increased IAS tone and SMC contractility were TTX resistant and attenuated by K252a. TrkB-specific agonist 7,8-dihydroxyflavone, similar to BDNF, also produced a concentration-dependent increase in the basal tone, whereas TrkB inhibitors K252a and ANA-12 produced a decrease in the tone. In addition, BDNF produced leftward shifts in the concentration-response curves with U46619 and ANG II (but not with bethanechol and K⁺ depolarization), and these shifts were reversed by K252a. Effects of Y27632 and Western blot data indicated that the BDNF-induced increase in IAS tone was mediated via RhoA/ROCK. BDNF-augmented NANC relaxation by electrical field stimulation was found to be mediated via the nitric oxide (NO)/soluble guanylate cyclase (sGC) pathway rather than via increased sensitivity to NO. In conclusion, the net effect of BDNF was that it caused an increase in the basal IAS tone via RhoA/ROCK signaling. BDNF also augmented NANC relaxation via NO/sGC. These findings may have relevance to the role of BDNF in the pathophysiology and therapeutic targeting of the IAS-associated rectoanal motility disorders.NEW & NOTEWORTHY These studies for the first time to our knowledge demonstrate that increased levels of brain-derived neurotrophic factor (BDNF; conceivably released from smooth muscle cells and/or the enteric neurons) has two major effects. First, BDNF augments the internal anal sphincter (IAS) tone via tyrosine kinase receptor B/thromboxane A2-receptor, angiotensin II receptor type 1/RhoA/ROCK signaling; and second, it increases nonadrenergic noncholinergic relaxation via nitric oxide/soluble guanylate cyclase. These studies may have relevance in therapeutic targeting in the anorectal motility disorders associated with the IAS.

Downregulation of thromboxane A2 and angiotensin II type 1 receptors associated with aging-related decrease in internal anal sphincter tone

Aging-associated decrease in internal anal sphincter (IAS) tone (AADI) is a major contributor in the rectoanal incontinence (RI). To determine the pathogenesis of AADI, we investigated the effect of aging on GPCR activation and related downstream signaling. We particularly investigated two GPCRs that characterize IAS smooth muscle cells (SMCs): thromboxane A2 and angiotensin II type 1. Two groups of Fischer 344 rats (6-month-old [young group] and 26-month-old [old group]) were employed to determine the GPCR function by isometric contraction, the expressions of GPCRs, and their downstream regulatory signaling proteins (regulator of G-protein signaling 2, RGS2; GPCR Kinase 5, GRK5; and β-arrestin, Arrb2) using RT-PCR, qPCR, and western blot analyses. We used reversible biotinylation to monitor the GPCR trafficking using SMCs. Aging selectively attenuated thromboxane A2 and Ang II-induced IAS contraction. RT-PCR, qPCR, and WB data revealed a significant decrease in the expressions of the GPCRs and increase in the expression of RGS2, GRK5, and Arrb2. The increased GPCR internalization and decreased recycling under aging were validated by reversible biotinylation. We conclude that downregulation of GPCR, accompanied by upregulation of regulatory proteins, plays an important role in receptor desensitization and may be important underlying mechanisms of RI in certain aging patients.

Comparison of captopril (0.5%) cream with diltiazem (2%) cream for chronic anal fissure: a prospective randomized double-blind two-centre clinical trial

AIM

This study compared the efficacy of topical captopril with topical diltiazem in the treatment of chronic anal fissure (CAF).

METHOD

Fifty patients aged between 15 and 75 years with CAF were included in a prospective randomized, double-blind clinical trial. They were randomly allocated to either captopril (0.5%) cream or diltiazem (2%) cream in a dose of 2 cm of cream on the perianal skin every 12 h for 8 weeks. The intensity of pain upon defaecation was evaluated every 10 days using a visual analogue scale. Bleeding on defaecation, pruritus and the presence of perianal irritation were also recorded before and during the trial.

RESULTS

The average pain scores were lower in the diltiazem group on the 20th and 30th days. From day 40 to the end of the trial the average pain scores of the two groups did not differ significantly. There were no significant differences in bleeding or perianal irritation between the groups, but the incidence of pruritus was considerably higher in the captopril group, and at the end of the trial 45.8% of the patients in this group still suffered from pruritus.

CONCLUSION

Topical captopril and diltiazem were found to be equally effective in the management of pain, bleeding and perianal irritation due to CAF, but due to the high incidence of pruritus observed with topical captopril this medication is not recommended for the treatment of CAF.

Activation of angiotensin II type 1 receptors and contractile activity in human sigmoid colon in vitro

AIM

To analyse the effects of angiotensin II (Ang II) on the contractility of human sigmoid colon, and to characterize the subtype(s) of receptor(s) involved and the related action mechanism.

METHODS

The contractility of sigmoid colon circular muscle strips was recorded isometrically. RT-PCR and immunohistochemistry were used to reveal the eventual existence of a local renin-angiotensin system (RAS) and the distribution of Ang II receptors.

RESULTS

Transcripts encoding for the Ang II type 1 (AT1 ) and the Ang II type 2 (AT2 ) receptor subtypes and for the angiotensin-converting enzyme in the whole-thickness muscular wall were observed. Ang II caused a concentration-dependent contractile response, which is antagonized by losartan, AT1 receptor antagonist, but not by PD123319, AT2 receptor antagonist. The joint application of losartan and PD123319 did not produce any additive effect. The contractile response to Ang II was partially reduced by tetrodotoxin, Na(+) voltage-gated neural channel blocker, and to some extent by SR48968, tachykinin NK2 receptor antagonist. However, hexamethonium, nicotinic receptor antagonist, atropine, cholinergic muscarinic receptor antagonist and SR140333, tachykinin NK1 receptor antagonist, were ineffective. Immunohistochemical analysis showed that AT1 receptors were expressed on the smooth muscle layers and myenteric plexus.

CONCLUSION

Ang II positively modulates the spontaneous contractile activity of human sigmoid colon via activation of post-junctional and pre-junctional AT1 receptors, the latter located on the enteric nerves that modulate the release of tachykinins. The presence of the components of RAS in the human colon suggests that Ang II can be also locally generated to control colonic motility.

Nature of extracellular signal that triggers RhoA/ROCK activation for the basal internal anal sphincter tone in humans

The extracellular signal that triggers activation of rho-associated kinase (RhoA/ROCK), the major molecular determinant of basal internal anal sphincter (IAS) smooth muscle tone, is not known. Using human IAS tissues, we identified the presence of the biosynthetic machineries for angiotensin II (ANG II), thromboxane A2 (TXA2), and prostaglandin F2α (PGF2α). These end products of the renin-angiotensin system (RAS) (ANG II) and arachidonic acid (TXA2 and PGF2α) pathways and their effects in human IAS vs. rectal smooth muscle (RSM) were studied. A multipronged approach utilizing immunocytochemistry, Western blot analyses, and force measurements was implemented. Additionally, in a systematic analysis of the effects of respective inhibitors along different steps of biosynthesis and those of antagonists, their end products were evaluated either individually or in combination. To further describe the molecular mechanism for the IAS tone via these pathways, we monitored RhoA/ROCK activation and its signal transduction cascade. Data showed characteristically higher expression of biosynthetic machineries of RAS and AA pathways in the IAS compared with the RSM. Additionally, specific inhibition of the arachidonic acid (AA) pathway caused ~80% decrease in the IAS tone, whereas that of RAS lead to ~20% decrease. Signal transduction studies revealed that the end products of both AA and RAS pathways cause increase in the IAS tone via activation of RhoA/ROCK. Both AA and RAS (via the release of their end products TXA2, PGF2α, and ANG II, respectively), provide extracellular signals which activate RhoA/ROCK for the maintenance of the basal tone in human IAS.

Heme oxygenase-1 upregulation modulates tone and fibroelastic properties of internal anal sphincter

A compromise in the internal anal sphincter (IAS) tone and fibroelastic properties (FEP) plays an important role in rectoanal incontinence. Herein, we examined the effects of heme oxygenase (HO)-1 upregulation on these IAS characteristics in young rats. We determined the effect of HO-1 upregulator hemin on HO-1 mRNA and protein expressions and on basal IAS tone and its FEP before and after HO-1 inhibitor tin protoporphyrin IX. For FEP, we determined the kinetics of the IAS smooth muscle responses, by the velocities of relaxation, and recovery of the IAS tone following 0 Ca(2+) and electrical field stimulation. To characterize the underlying signal transduction for these changes, we determined the effects of hemin on RhoA-associated kinase (RhoA)/Rho kinase (ROCK) II, myosin-binding subunit of myosin light chain phosphatase 1, fibronectin, and elastin expression levels. Hemin increased HO-1 mRNA and protein similar to the increases in the basal tone, and in the FEP of the IAS. Underlying mechanisms in the IAS characteristics are associated with increases in the genetic and translational expressions of RhoA/ROCKII, and elastin. Fibronectin expression levels on the other hand were found to be decreased following HO-1 upregulation. The results of our study show that the hemin/HO-1 system regulates the tone and FEP of IAS. The hemin/HO-1 system thus provides a potential target for the development of new interventions aimed at treatment of gastrointestinal motility disorders, specifically the age-related IAS dysfunction.

Angiotensin IV induced contractions in human jejunal wall musculature in vitro

Angiotensin II (AngII) has been reported to mediate contractile actions in rats and human jejunal wall musculature. However, except for one report showing the angiotensin IV (AngIV) contractile effects on the internal anal sphincter of rats, no data is available describing the action of AngIV on smooth muscle in human small intestine. The aim of this study was to investigate the expression and localization of the enzymes responsible to AngIV formation, as well as the receptor, and to elucidate the contractile function of AngIV in the muscular layer of human jejunum in vitro. Jejunal smooth muscle was taken from 23 patients undergoing Roux-en-Y gastric bypass surgery and was used to record isometric tension in vitro in response to AngIV alone and in the presence of losartan or PD123319. ELISA, western blot and immunohistochemistry were used to investigate the expression and localization of key components for AngIV formation: the enzymes aminopeptidases-A, B, M, and the AngIV receptor insulin-regulated aminopeptidase (IRAP). AngIV elicited concentration-dependent contraction in both longitudinal and circular smooth-muscle preparation. Presence of losartan abolished AngIV-induced contraction, but not PD123319. The main peptide AngII, as well as the enzymes aminopeptidases-A, B and M was detected in all muscle samples. Immunohistochemistry localized the enzymes and IRAP in the myenteric plexus between longitudinal and circular muscle layers. The present study indicates that all enzymes necessary for AngIV formation exist in human jejunal smooth muscle and that the contractile action elicited by AngIV is primarily mediated through the AngII type 1 receptor.

The muscular expression of RAS in patients with achalasia

INTRODUCTION

Angiotensin II (AngII) elicits smooth muscle contractions via activation of AngII type 1 receptor (AT1R) in the intestinal wall and in sphincter regions in several species. Achalasia is a rare swallowing disorder and is characterized by a loss of the wave-like contraction that forces food through the oesophagus and a failure of the lower oesophageal sphincter to relax during swallowing.

AIMS AND METHODS

The present study was undertaken to elucidate expression and distribution of a local renin-angiotensin system (RAS) in the muscular layer of distal normal human oesophagus as well as in patients with achalasia using western blot analysis, immunohistochemistry and polymerase chain reaction (PCR).

RESULTS

AT1R, together with enzyme renin and cathepsin D expression were decreased in patients with achalasia. In contrast, the mast cells chymase, cathepsin G, neprilysin and the receptor for angiotensin 1-7 peptides, the MAS receptor, were increased in patients with achalasia.

CONCLUSION

The results showed the existence of a local RAS in human oesophageal muscular layer. The enzymes responsible for AngII production are different and there has been a shift in receptor physiology from AT1R to MAS receptor in patients with achalasia. These changes in the RAS might play a significant role in the physiological motor control for patients with achalasia.

The effect of topical anal captopril on resting anal pressure in healthy volunteers: the first human pilot study

BACKGROUND

Previous laboratory studies have shown that angiotensin II is produced locally in the rat internal anal sphincter causing potent contraction. The aim of this first human study was to evaluate the safety and manometric effects of topical application of captopril (an ACE inhibitor) on the resting anal pressure in healthy adult volunteers.

METHODS

Ten volunteers, mean age 32.5 years (range, 19-48 years), underwent anorectal manometric evaluation of the mean anal resting pressure (MRAP) and the length of the high-pressure zone (HPZ) before 20 and 60 min after topical application of captopril (0.28 %) cream. Cardiovascular variables (systolic blood pressure, diastolic blood pressure and pulse) were measured before and for up to 1 h after cream application. Side effects were recorded. Adverse events and patient comfort after the cream application were evaluated within a 24-h period by completing a questionnaire.

RESULTS

There was no significant change overall in MRAP following captopril administration, although in half the patients, there were reductions in MRAP after treatment. Half the patients had a reduction in the mean resting HPZ length; however, there was no overall difference between pre- and post-treatment values. There was no effect on basic cardiovascular parameters and no correlation between manometric and cardiovascular variables.

CONCLUSIONS

Topical application of captopril cream may result in a reduction in MRAP in volunteers without anorectal disease. Its use is associated with minimal side effects. It may be a new potential therapeutic option in the treatment of anal fissure. Further studies are required to determine the optimal concentration, dose and frequency of application.

Angiotensins inhibit cell growth in GH3 lactosomatotroph pituitary tumor cell culture: a possible involvement of the p44/42 and p38 MAPK pathways

The local renin-angiotensin system is present in the pituitary. We investigated the effects of angiotensins on GH3 lactosomatotroph cells proliferation in vitro and the involvement of p44/42 and p38 MAPK inhibitors in the growth-regulatory effects of angiotensins. Materials and Methods. Cell viability using the Mosmann method and proliferation by the measurement of BrdU incorporation during DNA synthesis were estimated. Results. Ang II and ang IV decreased the viability and proliferation of GH3 cells. Inhibitor of p44/42 MAPK attenuated the effects of ang II on cell viability and proliferation but did not affect the ang 5-8-dependent actions. Inhibitor of p38 MAPK prevented the decrease in the number of GH3 cells in ang-II- and ang-IV-treated groups. Conclusions. The growth-inhibitory effect of ang II is possibly mediated by the p44/42 MAPK. The p38 MAPK appears to mediate the inhibitory effects of both ang II and ang 5-8 upon cell survival.

RhoA/ROCK pathway is the major molecular determinant of basal tone in intact human internal anal sphincter

The knowledge of molecular control mechanisms underlying the basal tone in the intact human internal anal sphincter (IAS) is critical for the pathophysiology and rational therapy for a number of debilitating rectoanal motility disorders. We determined the role of RhoA/ROCK and PKC pathways by comparing the effects of ROCK- and PKC-selective inhibitors Y 27632 and Gö 6850 (10(-8) to 10(-4) M), respectively, on the basal tone in the IAS vs. the rectal smooth muscle (RSM). Western blot studies were performed to determine the levels of RhoA/ROCK II, PKC-α, MYPT1, CPI-17, and MLC(20) in the unphosphorylated and phosphorylated forms, in the IAS vs. RSM. Confocal microscopic studies validated the membrane distribution of ROCK II. Finally, to confirm a direct relationship, we examined the enzymatic activities and changes in the basal IAS tone and p-MYPT1, p-CPI-17, and p-MLC(20), before and after Y 27632 and Gö 6850. Data show higher levels of RhoA/ROCK II and related downstream signal transduction proteins in the IAS vs. RSM. In addition, data show a significant correlation between the active RhoA/ROCK levels, ROCK enzymatic activity, downstream proteins, and basal IAS tone, before and after ROCK inhibitor. From these data we conclude 1) RhoA/ROCK and downstream signaling are constitutively active in the IAS, and this pathway (in contrast with PKC) is the critical determinant of the basal tone in intact human IAS; and 2) RhoA and ROCK are potential therapeutic targets for a number of rectoanal motility disorders for which currently there is no satisfactory treatment.

Biosynthetic pathways and the role of the MAS receptor in the effects of Angiotensin-(1-7) in smooth muscles

Ang-(1–7) is produced via degradation of Ang II by the human angiotensin converting enzyme, also known as ACE2. In the cardiovascular system, Ang-(1–7) has been shown to produce effects that are opposite to those of Ang II. These include smooth muscle relaxation and cardioprotection. While the roles of Ang-(1–7) in other systems are currently topic of intense research, functional data suggest a relaxation action in gastrointestinal smooth muscles in a way that corroborates the results obtained from vascular tissues. However, more studies are necessary to determine a relevant role for Ang-(1–7) in the gastrointestinal system. The Ang-(1–7) actions are mediated by a distinct, functional, Ang-(1–7) receptor: the Mas receptor as shown by diverse studies involving site-specific binding techniques, selective antagonists, and targeted gene deletion. This paper provides an overview of the functional role and the molecular pathways involved in the biosynthesis and activity of Ang-(1–7) in diverse systems.

Role of rho kinase in the functional and dysfunctional tonic smooth muscles

Tonic smooth muscles play pivotal roles in the pathophysiology of debilitating diseases of the gastrointestinal and cardiovascular systems. Tonic smooth muscles differ from phasic smooth muscles in the ability to spontaneously develop myogenic tone. This ability has been primarily attributed to the local production of specific neurohumoral substances that can work in conjunction with calcium sensitization via signal transduction events associated with the Ras homolog gene family, member A (RhoA)/Rho-associated, coiled-coil containing protein kinase 2 (ROCK II) pathways. In this article, we discuss the molecular pathways involved in the myogenic properties of tonic smooth muscles, particularly the contribution of protein kinase C vs the RhoA/ROCK II pathway in the genesis of basal tone, pathophysiology and novel therapeutic approaches for certain gastrointestinal and cardiovascular diseases. Emerging evidence suggests that manipulation of RhoA/ROCK II activity through inhibitors or silencing of RNA interface techniques could represent a new therapeutic approach for various gastrointestinal and cardiovascular diseases.

Specific and complementary roles for nitric oxide and ATP in the inhibitory motor pathways to rat internal anal sphincter

BACKGROUND

The neurotransmitters mediating inhibitory pathways to internal anal sphincter (IAS) have not been fully characterized. Our aim was to assess the putative release of nitric oxide, purines and vasoactive intestinal peptide (VIP) from inhibitory motor neurons (MNs) and their role in the myogenic tone, resting membrane potential (RMP) of smooth muscle cells (SMC), spontaneous inhibitory junction potentials (sIJP), mechanical relaxation, and IJP induced by electrical field stimulation (EFS) or nicotine.

METHODS

Rat IAS strips were studied using organ baths, microelectrodes, and immunohistochemistry.

KEY RESULTS

Internal anal sphincter strips developed active myogenic tone (0.31 g), enhanced and stabilized by prostaglandin F(2α) (PGF2α). L-NNA (1 mmol L(-1)) depolarized SMC and increased tone but did not modify sIJP. In contrast, the specific P2Y(1) receptor antagonist MRS2500 (1 μmol L(-1)) did not modify the RMP or the basal tone but abolished sIJP. Electrical field stimulation and nicotine (10 μmol L(-1)) caused IAS relaxation (-45.9%VS-52.2%), partially antagonized by L-NNA (35%-45%, P ≤ 0.05) and fully abolished by MRS2500 (P ≤ 0.001). Electrical field stimulation induced a biphasic inhibitory junction potential (IJP), the initial fast component was selectively blocked by MRS2500 and the sustained slow component was blocked by L-NNA. Vasoactive intestinal peptide 6-28 (0.1 μmol L(-1)) or α-chymotrypsin (10 U mL(-1)) did not modify the RMP, sIJP, EFS-induced IJP, or relaxation. P2Y(1) receptors were immunolocalized in the circular SMC of IAS.

CONCLUSIONS & INFERENCES

The effects of inhibitory MNs on rat IAS are mediated by a functional co-transmission process involving nitrergic and purinergic pathways through P2Y(1) receptors with specific and complementary roles on the control of tone, sIJP, and hyperpolarization and relaxation of IAS following stimulation of inhibitory MNs.

The angiotensin II type 2 receptor and the gastrointestinal tract

The renin-angiotensin system (RAS) is well known for its vital involvement in body fluid homeostasis and circulation. However, very little research has been devoted to the impact of this regulatory system on the gastrointestinal (GI) system. This is surprising because the GI tract is fundamental for the intake and excretion of fluid and electrolytes (and nutrients), and it accommodates a large proportion of bodily haemodynamics and host defence systems. The RAS is well expressed and active in the GI tract, although the exact roles for the key mediator angiotensin II (Ang II) and its receptors in general, and the type 2 (AT 2) receptor in particular, are not completely settled. There are several reports showing Ang II regulation of intestinal fluid and electrolyte transport. For example, mucosaprotective duodenal bicarbonate-rich secretion is inhibited by Ang II via type 1 (AT1) receptor-mediated facilitation of sympathoadrenergic activity, but this secretory process can also be stimulated by Ang II via AT2 receptors. Novel data from human oesophagus and jejunum suggest that the AT1 receptor mediates muscular contractions and that the AT2 receptor regulates epithelial functions. Data are accumulating suggesting involvement of AT1 and AT2 receptors in GI inflammation and carcinogenesis. The picture of the RAS and AT 2 receptor in the GI tract is, however, far from complete. Much more basic research is needed with regard to GI pathophysiology before concluding clinical significance and potential applicability of pharmacological interferences with the RAS.

Arachidonic acid metabolites follow the preferential course of cyclooxygenase pathway for the basal tone in the internal anal sphincter

Present studies determined the roles of the cyclooxygenase (COX) versus the lipoxygenase (LO) pathways in the metabolic pathway of arachidonic acid (AA) in the internal anal sphincter (IAS) tone. Studies were performed in the rat IAS versus the nontonic rectal smooth muscle (RSM). Indomethacin, the dual COX inhibitor, but not nordihydroguaiaretic acid (NDGA), the LO inhibitor, produced a precipitous decrease in the IAS tone. However, when added in the background of indomethacin, NDGA caused significant reversal of the IAS tone. These inhibitors had no significant effect on the RSM. To follow the significance of COX versus LO pathways, we examined the effects of AA and its metabolites. In the IAS, AA caused an increase in the IAS tone (Emax=38.8+/-3.0% and pEC50=3.4+/-0.1). In the RSM, AA was significantly less efficacious and potent (Emax=11.3+/-3.5% and pEC50=2.2+/-0.3). The AA metabolites (via COXs) PGF2alpha and U-46619 (a stable analog of thromboxane A2) produced increases in the IAS tone and force in the RSM. Conversely, AA metabolites (via 5-LO) lipoxin A4, 5-HETE, and leukotriene C4 decreased the IAS tone. Finally, the contractile effects of AA in the IAS were selectively attenuated by the COX-1 but not the COX-2 inhibitor. Collectively, the specific effects of AA and the COX inhibitor, the Western blot and RT-PCR analyses showing specifically higher levels of COX-1, suggest a preferential role of the COX (specifically COX-1) pathway versus the LO in the regulation of the IAS tone.

COX-1 vs. COX-2 as a determinant of basal tone in the internal anal sphincter

Prostanoids, produced endogenously via cyclooxygenases (COXs), have been implicated in the sustained contraction of different smooth muscles. The two major types of COXs are COX-1 and COX-2. The COX subtype involved in the basal state of the internal anal sphincter (IAS) smooth muscle tone is not known. To identify the COX subtype, we examined the effect of COX-1- and COX-2-selective inhibitors, SC-560 and rofecoxib, respectively, on basal tone in the rat IAS. We also determined the effect of selective deletion of COX-1 and COX-2 genes (COX-1(-/-) and COX-2(-/-) mice) on basal tone in murine IAS. Our data show that SC-560 causes significantly more efficacious and potent concentration-dependent decreases in IAS tone than rofecoxib. In support of these data, significantly higher levels of COX-1 than COX-2 mRNA were found in the IAS. In addition, higher levels of COX-1 mRNA and protein were expressed in rat IAS than rectal smooth muscle. In wild-type mice, IAS tone was decreased 41.4 +/- 3.4% (mean +/- SE) by SC-560 (1 x 10(-5) M) and 5.4 +/- 2.2% by rofecoxib (P < 0.05, n = 5). Basal tone was 0.172 +/- 0.021 mN//mg in the IAS from wild-type mice and significantly less (0.080 +/- 0.015 mN/mg) in the IAS from COX-1(-/-) mice (P < 0.05, n = 5). However, basal tone in COX-2(-/-) mice was not significantly different from that in wild-type mice. We conclude that COX-1-related products contribute significantly to IAS tone.

Neuroimmune interaction and anorectal motility in children with food allergy-related chronic constipation

OBJECTIVES

Food allergy is thought to trigger functional constipation in children but the underlying mechanisms are still unknown. Mast cells (MCs) and their relationship with nerve fibers (NFs) in the rectal mucosa, as well as anorectal motility, were studied in children with refractory chronic constipation before and after an elimination diet for cow's milk, egg, and soy proteins.

METHODS

Thirty-three children (range: 1-10.8 years) underwent anorectal manometry and suction rectal biopsy before and after 8 weeks of oligoantigenic diet. MCs and NFs were identified immunohistochemically. Quantification of MCs (%MC/area) and MCs within 10 microm of NFs (%MC-NF/area) was performed by computer-assisted analysis.

RESULTS

Eighteen children responded to the diet (R-group) and fifteen did not (the NR-group). At baseline there was a significant difference in anal resting pressure (ARP; mm Hg), percentage of relaxation (%R), and residual pressure (RP; mm Hg) of anal canal during rectal distension between the R-group (66+/-4.1, 84.3+/-2.8, 10.4+/-2.3, respectively) and the NR-group (49+/-5, 92.2+/-1.7, 4.8+/-1.7, respectively; P<0.05). After the diet, significant changes in ARP, RP, and %R were observed only in the R-group (44+/-3.7, 93.7+/-1.5, 3.8+/-1.2, respectively; P<0.05). At baseline, the R-group showed an increase in %MC/area (8.3+/-0.7) and %MC-NF/area (5.2+/-2.6) with respect to the NR-group (5.1+/-0.5 and 2.3+/-0.4, respectively; P<0.05). After the diet, only the R-group showed a significant reduction of %MC/area and %MC-NF/area (4.4+/-0.5 and 2.2+/-0.4, respectively; P<0.001). Both ARP and RP significantly correlated with %MC/area and %MC-NF/area; %R showed a significant inverse correlation with both %MC/area and %MC-NF/area.

CONCLUSIONS

In children with food allergy-related chronic constipation, an increase in both rectal MC density and spatial interactions between MCs and NFs correlates with anal motor abnormalities. These variables are significantly affected by the diet.

Role of phospholipase A2 (group I secreted) in the genesis of basal tone in the internal anal sphincter smooth muscle

The role of phospholipase A(2) (PLA(2)) in the genesis of basal tone in the internal anal sphincter (IAS) is not known. We determined the effects of PLA(2) and inhibitors on the basal tone and intraluminal pressures (IASP) in the rat IAS vs. rectal smooth muscles (RSM). In addition, we determined the correlations between the IAS tone, PLA(2) levels, and the actual enzymatic activity. Inhibition of PLA(2) by 4-bromophenacyl bromide (universal inhibitor of PLA(2)) and MJ33 [selective inhibitor of secreted isoform of PLA(2) (sPLA(2))] caused concentration-dependent decrease in the IAS tone and in the IASP. Maximal decreases in the IAS tone and IASP by 4-bromophenacyl bromide and MJ33 were 58.8 +/- 6.9 and 51.5 +/- 6.3%, and 66.7 +/- 5.1 and 79.8 +/- 8.2%, respectively. The sPLA(2) inhibitors were approximately 100 times more potent in decreasing the IASP than the mean blood pressure. Conversely, the selective inhibitors of the cytosolic and calcium-independent PLA(2) arachidonyl trifluoromethyl ketone and bromoenol lactone, respectively, produced no significant effect. The IAS had characteristically higher levels of sPLA(2) activity (26.5 +/- 4.9 micromol.min(-1).ml(-1)) vs. the RSM (3.2 +/- 0.4 micromol.min(-1).ml(-1)), and higher levels of sPLA(2) as shown by Western blot and RT-PCR. Interestingly, administration of sPLA(2) transformed RSM into the tonic smooth muscle like that of the IAS: it developed basal tone and relaxed in response to the electrical field stimulation. From the present data, we conclude that sPLA(2) plays a critical role in the genesis of tone in the IAS. PLA(2) inhibitors may provide potential therapeutic target for treating anorectal motility disorders.

A review of chronic anal fissure management

Anal fissure management has rapidly progressed in the last 15 years as our understanding of fissure pathophysiology has developed. All methods of treatment aim to reduce the anal sphincter spasm associated with chronic anal fissures. Surgical techniques have been used for over 100 years with success. Lateral internal sphincterotomy remains the surgical treatment of choice for many practitioners. Postoperative impairment of continence remains controversial. Recently, less invasive methods of treatment have been explored. Topical nitrates, calcium channel blockers and botulinum toxin are established treatments. These and other non-surgical treatments are described in this review. Various guidelines and treatment algorithms for anal fissure are also discussed.

Actions by angiotensin II on esophageal contractility in humans

BACKGROUND & AIMS

Angiotensin II is a potent activator of smooth muscles but has not been much investigated with regard to gastrointestinal motor activity. This study explores expression of the renin-angiotensin system (RAS) in human esophageal musculature and actions by Angiotensin II both in vitro and in vivo.

METHODS

Muscular specimens of esophageal body and lower esophageal sphincter were obtained from patients undergoing resection as a result of mucosal neoplasm. Healthy volunteers participated in functional examinations of esophageal motility assessed by high-resolution manometry and multiple transmucosal potential-difference measurements.

RESULTS

Gene transcripts of key components of RAS were found in the esophageal musculature. Immunohistochemistry revealed a distinct staining for Angiotensin II type 1 (AT(1)) receptors in the muscular bundles and blood-vessel walls, whereas Angiotensin II type 2 receptors were confined to blood vessels only. Angiotensin II caused concentration-dependent contractions in vitro, which were inhibited by the AT(1) receptor antagonist losartan but not by the Angiotensin II type 2 receptor antagonist PD123319. Administration of the AT(1) receptor antagonist candesartan reduced the amplitude of swallow-induced peristaltic contractions and both the length and pressure amplitude of baseline high-pressure zone at the esophagogastric junction. Neither swallow-induced axial movements, nor the contraction after transient lower esophageal sphincter relaxations, were influenced by candesartan pretreatment.

CONCLUSIONS

The study demonstrates a local RAS in the musculature of the distal esophagus and that Angiotensin II is a potent stimulator of esophageal contractions via the AT(1) receptor. The results suggest that Angiotensin II participates in the physiological control of the human esophageal motor activity.

Translocation of AT1- and AT2-Receptors by Higher Concentrations of Angiotensin II in the Smooth Muscle Cells of Rat Internal Anal Sphincter

Previous studies have reported bimodal effects by angiotensin II (Ang II) in the rat internal anal sphincter (IAS), a concentration-dependent contraction (at lower concentrations) and relaxation (at higher concentrations). The experiments suggest the above-mentioned responses are the result of Ang II subtype I receptor(s) (AT(1)-R) and subtype II receptor(s) (AT(2)-R) activation, respectively. These studies determined the role and mechanism of AT(2)-R-induced relaxation of the smooth muscle cells (SMCs) from the IAS in response to Ang II. Laser confocal microscopy showed that in the basal state, the AT(1)-Rs reside in the plasma membrane, whereas AT(2)-Rs are present in the cytosol. Higher concentrations of Ang II caused movement of AT(1)-R and AT(2)-R in opposite directions to the cytosol and the membrane, respectively. Losartan (AT(1)-R antagonist) but not S-(+)-1-([4-(dimethylamino)-3-methylphenyl]methyl)-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo(4,5-c)pyridine-6-carboxylic acid (PD123319; AT(2)-R antagonist) selectively inhibited these movements. These results are based on biotinylation assays, confocal images, and Western blot analyses of the densities of AT(1)-Rs and AT(2)-Rs in the plasma membrane versus cytosolic fractions of the IAS SMCs. Ang II in higher concentrations did not change the total contents of Ang II receptors. These data combined with the functional data using measurements of IAS SMC lengths suggest that internalization of AT(1)-R and externalization of AT(2)-R may be responsible for the activation of the AT(2)-R, which leads to the relaxation of the IAS with higher concentrations of Ang II.

Angiotensin II induced contraction of rat and human small intestinal wall musculature in vitro

BACKGROUND

Angiotensin II (Ang II) is a well-known activator of smooth muscle in the vasculature but has been little explored with regard to intestinal wall muscular activity. This study investigates pharmacological properties of Ang II and expression of its receptors in small-intestinal smooth muscle from rats and humans.

METHODS

Isometric recordings were performed in vitro on small intestinal longitudinal muscle strips. Protein expressions of Ang II typ 1 (AT1R) and typ 2 (AT2R) receptors were assessed by Western blot.

RESULTS

Ang II elicited concentration-dependent contractions of rat jejunal and ileal muscle preparations. The concentration-response curve (rat ileum, EC(50): 1.5 +/- 0.9 x 10(-8) M) was shifted to the right by the AT1R receptor antagonist losartan (10(-7) M) but was unaffected by the AT2R antagonist PD123319 (10(-7) M) as well as by the adrenolytic guanethidine (3 x 10(-6) M) and the anticholinergic atropine (10(-6) M). Human duodenal, jejunal and ileal longitudinal muscle preparations all contracted concentration-dependently in response to Ang II. The concentration-response curve (human jejunum, EC(50): 1.5 +/- 0.8 x 10(-8) M) was shifted to the right by losartan (10(-7) M) but was unaffected by PD123319 (10(-7) M). Both AT1R and AT2R were detected in all segments of the rat small intestinal wall musculature, whereas only AT1R was readily detectable in the human samples.

CONCLUSION

Ang II elicits contractions of small-intestinal longitudinal muscle preparations from the small intestine of rats and man. The pharmacological pattern and protein expression analyses indicate mediation via the AT1R.

Angiotensin-converting enzyme and angiotensin II receptor subtype 1 inhibitors restitute hypertensive internal anal sphincter in the spontaneously hypertensive rats

The present study determined the effects of the angiotensin-converting enzyme (ACE) inhibitor captopril and angiotensin II receptor subtype 1 (AT1-R) antagonist losartan on the internal anal sphincter pressures (IASP) in spontaneously hypertensive rats (SHR) versus normotensive Wistar-Kyoto rats (WKY). The SHR had significantly higher IASP (21.7 +/- 0.8 mm Hg) than the WKY (14.7 +/- 0.9 mm Hg), which was associated with the higher levels of angiotensin II (Ang II) in plasma (50.3 +/- 0.9 pg/ml) and in muscle bath perfusates (72.7 +/- 11.8 pg/ml) compared with the WKY (p < 0.05). Captopril and losartan decreased the IASP in SHR and WKY, but they were more potent in SHR. Captopril and losartan normalized the IASP in the SHR, whereas these agents may compromise rectoanal continence in the WKY. Reverse transcriptase-polymerase chain reaction and Western blots showed higher levels of angiotensinogen, renin, ACE, and AT1-R in the internal anal sphincter (IAS) of SHR. Ang II caused concentration-dependent contraction of IAS smooth muscle strips from WKY (pEC50 = 8.5 +/- 0.1) and SHR (pEC50 = 8.6 +/- 0.2). Losartan (100 nM) significantly (p < 0.05) inhibited this effect. From these data, we conclude that 1) hypertensive IAS in SHR is primarily the result of renin-angiotensin system up-regulation, 2) ACE inhibitors and AT(1)-R antagonists simply relieve the hypertensive IAS, and 3) the differential effect of these inhibitors in the hypertensive versus the normotensive IAS may explain the lack of incontinence as a side effect in hypertensive patients receiving ACE inhibitors and AT1-R antagonists.

Dynamic expression of the angiotensin II type 2 receptor and duodenal mucosal alkaline secretion in the Sprague-Dawley rat

Activation of angiotensin II type 2 receptors (AT2R) has been shown to stimulate duodenal mucosal alkaline secretion (DMAS) in Sprague-Dawley rats (S-D). This finding could not be confirmed in another line of S-D, and the present study investigates whether the level of AT2R expression determines the response to the AT2R agonist CGP42112A. DMAS was measured in anaesthetized rats using in situ pH-stat titration. Real-time PCR and Western blot were used to assess AT1R and AT2R RNA and protein expression, respectively. CGP42112A (0.1 microg kg(-1)min(-1) I.V.) elicited a 45% net increase in DMAS in the previous S-D line studied, whereas no change occurred in the new S-D line. Luminal administration of prostaglandin E2 (10(-5) M) increased DMAS similarly in both S-D lines. AT2R protein expression was significantly higher in tissue from the previous line compared to the new line. Individual AT1R to AT2R ratios (RNA and protein) were significantly higher in the new line compared to the previous S-D line. In the new S-D line intravenous infusion of angiotensin II (Ang II; 10 microg kg(-1) h(-1)) over 120 min significantly lowered the duodenal AT1aR to AT2R RNA ratio. Prolonged Ang II infusion over 240 min increased AT2R protein expression and evoked a 42% stimulatory response in DMAS to CGP42112A. The level of local AT2R expression determines the effect of the AT2R agonist CGP42112A on rat duodenal mucosal alkaline secretion. AT2R expression should be confirmed before interpreting the experimental effects of pharmacological interferences with this receptor.

Autocrine regulation of internal anal sphincter tone by renin-angiotensin system: comparison with phasic smooth muscle

The myogenic control mechanisms that govern the basal tone in the internal anal sphincter (IAS) are not known. The present studies determined the autocrine regulation of ANG II in the IAS. The studies were performed in the freshly isolated smooth muscle cells (SMC) of the IAS. We determined the presence of ANG II precursor angiotensinogen (Angen), and the enzymes that convert it into ANG II, using functional, molecular biology, and immunocytochemical studies in rats. ANG II levels in the SMC were determined using ELISA. The IAS SMC generate ANG II at a rate severalfold higher than those from the adjoining smooth muscle of rectum (RSM). RT-PCR data show that IAS exclusively expresses significant higher levels of renin, Angen, and angiotensin-converting enzyme (ACE). These data were confirmed using Western blot analyses and immunocytochemistry. In the IAS SMC, H-77 (10 microM; renin inhibitor) and captopril (1 microM; ACE inhibitor) decreased the basal as well as Angen-increased levels of ANG II. The following functional data corroborate the role of renin-angiotensin system (RAS) in the IAS tone. Angen produced concentration-dependent shortening of the IAS SMC that was inhibited by H-77 and captopril. In addition, H-77 or captopril caused a concentration-dependent fall in the IAS tone vs. nontonic tissues. Basal tone in IAS is partially under the autocrine control of cellular RAS evident by the expression of mRNA coding Angen, renin, and ACE and translation to the respective proteins in the SMC.

The internal anal sphincter: regulation of smooth muscle tone and relaxation

Basal tone in the internal anal sphincter (IAS) is primarily myogenic. Neurohumoral substances like angiotensin II may partially provide external signal for the basal tone in the IAS. The sphincteric relaxation on the contrary is neurogenic by activation of non-adrenergic non-cholinergic (NANC) nerves that release nitric oxide (NO), vasoactive intestinal polypeptide (VIP) and perhaps carbon monoxide. Because of the presence of spontaneous tone, the IAS offers an excellent model to investigate the nature of the inhibitory neurotransmission for NANC relaxation. Work from different laboratories in different species concludes that NO is the major contributor in the NANC relaxation. This may invoke the role of other inhibitory neurotransmitters such as VIP, working partly via NO. An understanding of the basic regulation of basal tone in the IAS and nature of inhibitory neurotransmission are critical in the pathophysiology and therapeutic potentials in the anorectal motility disorders.

Identification of Human Aminopeptidase O, a Novel Metalloprotease with Structural Similarity to Aminopeptidase B and Leukotriene A4 Hydrolase

We have cloned and characterized a human brain cDNA encoding a new metalloprotease that has been called aminopeptidase O (AP-O). AP-O exhibits a series of structural features characteristic of aminopeptidases, including a conserved catalytic domain with a zinc-binding site (HEXXHX18E) that allows its classification in the M1 family of metallopeptidases or gluzincins. The structural complexity of AP-O is further increased by the presence of an additional C-terminal domain 170 residues long, which is predicted to have an ARM repeat fold originally identified in the Drosophila segment polarity gene product Armadillo. This ARM repeat domain is also present in aminopeptidase B, aminopeptidase B-like, and leukotriene A4 hydrolase and defines a novel subfamily of aminopeptidases that we have called ARM aminopeptidases. Northern blot analysis revealed that AP-O is mainly expressed in the pancreas, placenta, liver, testis, and heart. Human AP-O was produced in Escherichia coli, and the purified recombinant protein hydrolyzed synthetic substrates used for assaying aminopeptidase activity. This activity was abolished by general inhibitors of metalloproteases and specific inhibitors of aminopeptidases. Recombinant AP-O also cleaved angiotensin III to generate angiotensin IV, a bioactive peptide of the renin-angiotensin pathway with multiple actions on diverse tissues, including brain, testis, and heart. On the basis of these results we suggest that AP-O could play a role in the proteolytic processing of bioactive peptides in those tissues where it is expressed.