Internal Anal Sphincter Tone Research Articles

Sa2030 Role of MicroRNA-139-5p (Mir-139-5p) in the Myogenic Basal Tone of Internal Anal Sphincter (IAS) vs. the Phasic Rectal Smooth Muscle (RSM): Studies in Purified Smooth Muscle Cells (SMCS)

Sa2030 Role of MicroRNA-139-5p (Mir-139-5p) in the Myogenic Basal Tone of Internal Anal Sphincter (IAS) vs. the Phasic Rectal Smooth Muscle (RSM): Studies in Purified Smooth Muscle Cells (SMCS)

Comparative study of local calcium channel blocker application and lateral internal sphincterotomy in the treatment of chronic anal fissure: study of 50 cases.

Background: The treatment of chronic anal fissure has changed greatly during the past two decades with ongoing research directed at lowering the internal anal sphincter tone and avoiding the risk of fecal continence disturbance. Glycerin trinitrate, topical calcium channel blockers and anal dilators and botulinum toxin injection alone are all known to be able to lower the internal anal sphincter tone but results have been disappointing in curing chronic anal fissure, often marginally better than to placebo. The surgical treatment in the form of lateral internal sphincterotomy is the gold standard for chronic anal fissure. Aims & Objective: The aim of this prospective study was to assess the efficacy of medical treatment in form of topical calcium channel blocker and surgery in the management of chronic anal fissure. The objective is to compare the efficacy with regard to complete healing, recurrence, incontinence and other complications after treatment with topical calcium channel blocker and lateral anal sphincterotomy. Material and Methods: From October 2010 to October 2012, 50 patients with typical chronic anal fissure completed the study. 25 patients were initially treated with topical calcium channel blocker for 8 weeks and rests 25 were treated with lateral anal sphincterotomy. During the follow-up healing rates, symptoms, incontinence scores, and therapy adverse effects were recorded. Results: Overall healing rates were 60% after 8 weeks therapy with topical calcium channel blocker. Whereas overall healing after lateral internal sphincterotomy group was 88% with no recurrence. Conclusion: Lateral internal sphincterotomy is far more effective than medical treatment, with significantly increased healing rates while avoiding risk of incontinence.

Tu2003 Rho Kinase is the Major Molecular Pathway for the Basal Tone in Intact Human Internal Anal Sphincter (IAS) Smooth Muscle

Tu2003 Rho Kinase is the Major Molecular Pathway for the Basal Tone in Intact Human Internal Anal Sphincter (IAS) Smooth Muscle

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.

Basal internal anal sphincter tone, inhibitory neurotransmission, and other factors contributing to the maintenance of high pressures in the anal canal

Maintenance of the basal tone in the internal anal sphincter (IAS) is critical for rectoanal continence. Effective evacuation requires a fully functional rectoanal inhibitory reflex (RAIR)-mediated relaxation of the IAS via inhibitory neurotransmission (INT). Systematic studies examining the nature of the INT in different species have identified nitric oxide (NO) as the major inhibitory neurotransmitter. However, other mediators such as vasoactive intestinal polypeptide (VIP), ATP, and carbon monoxide (CO) may also play species-specific role under certain experimental conditions. Measurements of the intraluminal pressures in the IAS along with the force of the isolated IAS tissues are the mainstay in the basic studies for the molecular mechanisms underlying the basal tone and in the nature of the INT. The identification of NO as the inhibitory neurotransmitter has led to major advances in the diagnosis and treatment of a number of rectoanal motility disorders associated with the IAS dysfunction. Besides the IAS, the high pressures in the anal canal are affected by the external anal sphincter (EAS) function, and its malfunction may also lead to rectoanal incontinence. Different approaches including biofeedback have been attempted to improve the EAS function, with variable outcomes. There is a dire need for the innovative ways to improve the week high pressures zone in the anal canal. This viewpoint focuses on two studies that extend the above concept of multiplicity of inhibitory neurotransmitters (Neurogastroenterol Motil 2011 23 e11–25), and that high pressures in the anal canal can be improved by the EAS plication (Neurogastroenterol Motil 2011 23 70–5).

3-Hydroxymethyl coenzyme A reductase inhibition attenuates spontaneous smooth muscle tone via RhoA/ROCK pathway regulated by RhoA prenylation

RhoA prenylation may play an important step in the translocation of RhoA in the basal internal anal sphincter (IAS) smooth muscle tone. Statins inhibit downstream posttranslational RhoA prenylation by 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibition (HMGCRI). The role of statins in relation to RhoA prenylation in the pathophysiology of the spontaneously tonic smooth muscle has not been investigated. In the present studies, we determined the effect of classical HMGCRI simvastatin on the basal IAS tone and RhoA prenylation and in the levels of RhoA/Rho kinase (ROCK) in the cytosolic vs. membrane fractions of the smooth muscle. Simvastatin produced concentration-dependent decrease in the IAS tone (via direct actions at the smooth muscle cells). The decrease in the IAS tone by simvastatin was associated with the decrease in the prenylation of RhoA, as well as RhoA/ROCK in the membrane fractions of the IAS, in the basal state. The inhibitory effects of the HMGCRI were completely reversible by geranylgeranyltransferase substrate geranylgeranyl pyrophosphate. Relaxation of the IAS smooth muscle via HMGCRI simvastatin is mediated via the downstream decrease in the levels of RhoA prenylation and ROCK activity. Studies support the concept that RhoA prenylation leading to RhoA/ROCK translocation followed by activation is important for the basal tone in the IAS. Data suggest that the role of HMG-CoA reductase may go beyond cholesterol biosynthesis, such as the regulation of the smooth muscle tone. The studies have important implications in the pathophysiological mechanisms and in the novel therapeutic approaches for anorectal motility disorders.

The relationship between internal rectal prolapse and internal anal sphincter function

Faecal incontinence is commonly seen in patients with internal rectal prolapse (IRP), although the mechanism is not clear. This study assessed the relationship between IRP and anal sphincter function. Patients both with IRP diagnosed on proctography and those with external rectal prolapse (ERP) were identified from a prospective database generated from a tertiary referral pelvic floor clinic. The results of anorectal manometry were analysed, and the relationship between sphincter pressure and grade of prolapse was assessed. A total of 515 patients were identified with clinical evidence of ERP or proctographic evidence of internal and external prolapse. There were 88 with grade 5 or external prolapse [mean maximal resting pressure (MRP) 28.5 (standard error 2.1) mmHg], 156 with grade 4 prolapse [44.0 (1.8) mmHg], 153 with grade 3 prolapse [49.2 (1.6) mmHg], 88 with grade 2 prolapse [56.2 (2.1) mmHg] and 29 patients with grade 1 rectal prolapse [56.8 (4.5) mmHg]. There was a significant reduction in the mean MRP with increasing grade of prolapse from grade 2 to 5. By contrast, there was no relationship between prolapse grade and mean maximal squeeze pressure, except in patients with ERP, in whom the squeeze pressure was significantly lower compared with patients with IRP. This is the first large-scale study to show the relationship between internal prolapse and MRP. The observation that squeeze pressure is unchanged suggests that the effect of internal prolapse on continence occurs mainly through a reduction in internal anal sphincter tone.

Pharmacology of the internal anal sphincter and its relevance to faecal incontinence

1 The internal anal sphincter (IAS) has a spontaneous tone and is the main contributor to the maintenance of faecal continence. The spontaneous resting tone exhibited by the sphincter can be modified by neurotransmitters from the autonomic and enteric nervous systems. 2 In this review, the influence of the sympathetic and parasympathetic nervous systems on IAS tone are discussed and the putative roles of nitric oxide, carbon monoxide, vasoactive intestinal peptide and adenosine triphosphate in non-adrenergic non-cholinergic transmission are considered. 3 Faecal incontinence is a common condition that places a heavy financial burden on the health service and severely affects patients' quality of life. Resting anal pressure is reduced in patients with faecal incontinence and agents that increase sphincter tone tend to relieve symptoms. The results of clinical studies of the use of phenylephrine to treat faecal incontinence are reviewed. 4 It is concluded that the IAS is a potential target for drug development for the treatment of faecal incontinence.

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.

Selectivity of ROCK inhibitors in the spontaneously tonic smooth muscle

The selectivity of different Rho kinase (ROCK) inhibitors in the spontaneously tonic smooth muscle has not been investigated. We examined this issue using Y-27632 [(R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarbox anecarboxamide, 2HCl], H-1152 [(S)-(+)-(2-methyl-5-isoquinolinyl) sulfonylhomopiperazine, 2HCl], HA-1077 [(5 isoquinolinesulfonyl) homopiperazine, 2HCl], and ROCK inhibitor II [N-(4-pyridyl)-N'-(2,4,6-trichlorophenyl)urea]. We compared these inhibitors in the spontaneously tonic smooth muscle of the internal anal sphincter (IAS). ROCK, protein kinase C (PKC), and myosin light chain kinase (MLCK) activities were determined in the IAS, before and after different ROCK inhibitors. Y-27632 and H-1152 were approximately 30-fold more potent in the IAS (IC(50): 4.4 x 10(-7) and 7.9 x 10(-8) M, respectively) vs. the phasic rectal smooth muscle (RSM) (IC(50): 1.3 x 10(-5) and 2.5 x 10(-6) M, respectively). HA-1077 and ROCK inhibitor II were equipotent in the IAS vs. RSM. In the IAS, H-1152 was the most potent whereas ROCK inhibitor II is the least. Y-27632 and H-1152 caused concentration-dependent decrease in the IAS tone that correlates directly with the decreases in ROCK activity, without significant effect in the PKC and MLCK activities. This specifically selective correlation between ROCK activity and decrease in the IAS tone was absent in the case of HA-1077 and ROCK inhibitor II, which also inhibited PKC and MLCK. We conclude that the IAS tone is critically dependent on ROCK activity, and H-1152 and Y-27632 are the most selective and potent ROCK inhibitors in the IAS.

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.

RhoA Prenylation Inhibitor Produces Relaxation of Tonic Smooth Muscle of Internal Anal Sphincter

RhoA prenylation is a critical step for the translocation of RhoA to the membrane and its activation in response to agonist-induced sustained contraction of the smooth muscle. However, the effect and role of RhoA prenylation in the spontaneously tonic smooth muscle, such as internal anal sphincter (IAS), is not known. Present studies determined RhoA prenylation and its association with the basal tone in the IAS before and after the RhoA prenylation inhibitor, geranylgeranyl transferase inhibitor GGTI-297 [N-4-[2(R)-amino-3-mercaptopropyl]amino-2-naphthylbenzoyl-(L)-leucine,TFA]. Western blot analyses of cytosolic and membrane fractions determined the effects of RhoA prenylation inhibition on the cellular distribution of the RhoA. Additional studies were performed to determine the relationship between RhoA prenylation and Rho kinase (ROCK) activity. GGTI-297 decreased prenylation of RhoA, decreased ROCK activity, and caused a corresponding fall in the IAS tone. These inhibitory effects following RhoA prenylation blockade were demonstrated to be directly on the spontaneously contracted IAS smooth muscle cells. Western blot analysis revealed high levels of RhoA in the IAS smooth muscle cellular membrane in the basal state, and GGTI-297 shifted the RhoA localization to the cytosol. RhoA prenylation may play an important role in the translocation of RhoA to the smooth muscle cell membrane leading to its activation and for the maintenance of basal tone in the IAS.

Spontaneously tonic smooth muscle has characteristically higher levels of RhoA/ROK compared with the phasic smooth muscle

The internal anal sphincter (IAS) tone is important for the rectoanal continence. The RhoA/Rho kinase (ROK) pathway has been associated with the agonist-induced sustained contraction of the smooth muscle, but its role in the spontaneously tonic smooth muscle is not known. Present studies compared expression of different components of the RhoA/ROK pathway between the IAS (a truly tonic SM), the rectal smooth muscle (RSM) (a mixture of phasic and tonic), and anococcygeus smooth muscle (ASM) (a purely phasic SM) of rat. RT-PCR and Western blot analyses were performed to determine RhoA, ROCK-II, CPI-17, MYPT1, and myosin light-chain 20 (MLC20). Phosphorylated CPI-17 at threonine-38 residue (p(Thr38)-CPI-17), MYPT1 at threonine-696 residue (p(Thr696)-MYPT1), and MLC20 at threonine-18/serine-19 residues (p(Thr18/Ser19)-MLC20) were also determined in the basal state and after pretreatment with the ROK inhibitor Y 27632. In addition, we compared the effect of Y 27632 on the basal isometric tension and ROK activity in the IAS vs. the RSM. Our data show the highest levels of RhoA, ROCK-II, CPI-17, MLC20, and of phospho-MYPT1, -CPI-17, and -MLC20 in the IAS followed by in the RSM and ASM. Conversely, MYPT1 levels were lowest in the IAS and highest in the ASM. In the IAS, Y 27632 caused a concentration-dependent decrease in the basal tone, levels of phospho-MYPT1, -CPI-17, and -MLC20, and ROK activity. We conclude that RhoA/ROK plays a critical role in the basal tone in the IAS by the inhibition of MLC phosphatase via the phosphorylation of MYPT1 and CPI-17.

The role of pelvic floor denervation in the aetiology of idiopathic faecal incontinence.

Weakness of the muscles of the pelvic floor and external anal sphincter may in theory be caused by a traction injury to the pelvic nerves incurred as a result of the excessive perineal descent that accompanies straining in the descending perineum syndrome (DPS). To investigate the role of this weakness in the aetiology of idiopathic faecal incontinence (IFI), measurements of perineal position, puborectalis mean fibre density (MFD), anal canal pressures, rectal sensation, capacity, and compliance were made in continent (DPS alone, n = 20) and incontinent (DPS + I, n = 19) patients with DPS, and a group of age and sex matched control subjects (n = 20). Perineal descent on straining was greater in DPS alone than in DPS + I. Puborectalis MFD was raised by similar degree in both DPS groups compared with the control subjects, and external anal sphincter function, assessed as voluntary squeeze pressure, was impaired by similar degree in DPS + I and DPS alone compared with the control subjects. Maximal basal anal canal pressure and rectal compliance were significantly reduced in DPS + I compared with DPS alone and the control subjects. Thus IFI did not result from progression of neurogenic muscle weakness, but occurred when there was also diminished internal anal sphincter tone and reduced rectal compliance.

External and internal anal sphincter responses to rectal distension in normal subjects and in patients with idiopathic faecal incontinence.

The responses of the external anal sphincter and the internal anal sphincter to rectal distension were studied in 18 female patients who had idiopathic faecal incontinence with perineal descent and 11 female control subjects, by measuring pressures at six sites within the anal canal and the electrical activity of the external sphincter. The pressure profile in the normal anal canal, at rest, was asymmetric with the highest pressure recorded in the outermost channels. Rectal distension caused a transient increase in the activity of the external sphincter, which was associated with an increase in anal pressure, particularly in the outermost two channels. This was followed by a symmetrical reduction in anal pressure throughout the anal canal, caused by relaxation of the internal sphincter and shortening of the high-pressure zone. Two patterns of response were observed in the patients with idiopathic incontinence. Twelve patients (group 1) showed normal anal relaxation, but the maximum anal pressures recorded during rectal distension or a conscious squeeze were abnormally low, suggesting weakness of the external anal sphincter. The remaining six subjects (group 2), who were older than the group 1 patients, had much lower resting pressures and showed only external sphincter contraction in response to rectal distension, with no obvious internal sphincter relaxation. However, the maximum pressures recorded during a conscious contraction of the external sphincter were lower in this group than in the normal control subjects. These results suggest that group 2 patients have impaired internal anal sphincter tone, as well as external anal sphincter weakness. This may explain why all except one of the group 2 patients, compared with only 17 per cent of group 1 patients, reported incontinence to both solids and liquids.

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.

Topical Nitric Oxide Treatment after Pull Through Operations for Hirschsprung Disease

The diagnosis and treatment of Hirschsprung disease are well standardized. Symptoms of obstruction after surgery for Hirschsprung disease may result from residual spasticity of the internal anal sphincter. Nitric oxide (NO) is the chemical messenger mediating relaxation of the internal anal sphincter and its exogenous application results in a relaxation response in smooth muscle. The purpose of this study was to investigate topical NO application for obstructive symptoms after surgery for Hirschsprung disease and to correlate the symptoms with manometric findings with a view to directing further management. The authors reviewed application of topical NO on six symptomatic children who were operated for Hirschsprung disease. Eighteen patients older than 3 years of age were evaluated for anorectal manometric, functional and clinical outcome. The symptoms included enterocolitis in three patients and constipation in three patients. NO ointment was applied twice daily for 6 weeks in symptomatic patients and manometry was repeated. Anorectal manometric evaluation of six patients showed high internal anal sphincter tone without reflex relaxation on applying distending pressure to the rectum. Marked improvement of symptoms was noted after 6-week application of topical NO and maximal internal anal resting pressure decreased significantly (35% reduction). After ceasing application of topical ointment, increased maximal anal resting pressure was seen again. Although anal sphincter hypertonicity is not thought to be the only cause of post-operative obstructive symptoms, relaxation of the internal anal sphincter may improve the symptoms. Topical NO can be used for treatment of obstructive symptoms in Hirschsprung disease. We managed our symptomatic patients successfully with local NO application with a reversible chemical sphincterotomy. NO could be used as a therapeutic modality.

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

Background & Aims: The internal anal sphincter tone is important for anorectal continence. This study examined the role of angiotensin II as a neurohumoral signal for the myogenic tone in the internal anal sphincter. Methods: We determined the effect of angiotensin I, II, III, and IV and angiotensin-(1–7) on the basal tone of the rat internal anal sphincter smooth muscle before and after selective receptor antagonists and biosynthesis inhibitors. Selective pharmacological tools used were losartan (for the AT 1 receptor), PD123,319 (for AT 2), A-779 [for angiotensin-(1–7)], captopril (for angiotensin-converting enzyme), and amastatin (for aminopeptidases A and N). Angiotensins were measured by using high-performance liquid chromatography/UV. Western blot studies were used to determine AT 1 and AT 2 receptors, ACE, and aminopeptidases A and N. Results: Angiotensin I, II, and III produced concentration-dependent contraction in the internal anal sphincter mediated by AT 1 receptors. However, in the higher concentrations (from 100 nM to 10 μM), angiotensin II showed an inhibitory effect via AT 2 receptors. Captopril (1 μM) inhibited the biosynthesis of angiotensin II in the internal anal sphincter, antagonized the contractile effects of angiotensin I, and, importantly, caused a decrease in the basal tone. Amastatin inhibited the effects of angiotensin II while augmenting those of angiotensin III. In contrast, angiotensin-(1–7) and angiotensin IV had only minor effects in the internal anal sphincter. Angiotensin I, II, and III; angiotensin-converting enzyme; aminopeptidase A and aminopeptidase N; AT 1; and AT 2 receptors were shown to be present in the internal anal sphincter. Conclusions: Locally produced angiotensin II may partially regulate basal tone in the internal anal sphincter.

Botulinum toxin injection inhibits myogenic tone and sympathetic nerve function in the porcine internal anal sphincter.

Botulinum toxin is an effective treatment for anal fissure, though there is a lack of agreement over the optimal site for its injection. This reflects our current ignorance of its mechanism, and whether it has any action on the nerves of the internal anal sphincter (IAS). This study set out to resolve this issue through use of a pig model. Eight pigs were studied in pairs: one of each pair received a botulinum toxin injection into the anal sphincter, whilst the other acted as its control. Manometry was performed every two weeks under anaesthesia. Pigs were slaughtered at between four and six weeks after injection and the properties of the IAS compared in vitro. Whilst maximum anal resting pressure (MARP) increased slowly in control pigs during the experimental period, reflecting weight gain, a fall was observed in treated pigs. In vitro, IAS strips from control pigs generated 400 mg of spontaneous tone per gram of tissue (+/- 45; standard error), compared to 250 (+/- 25) mg/g tissue from treated pigs (P < 0.01). Electric Field Stimulation at 50 Hz produced 150 (+/- 22) mg contraction/gram tissue in IAS strips from control pigs compared to 53 (+/- 13) mg/g tissue in treated pigs (P < 0.0005). This contractile response was blocked by guanethidine. Botulinum toxin has a significant action on the IAS. It reduces myogenic tone and contractile responses of this tissue to sympathetic nerve stimulation. Further studies are required to clarify its mechanism of action more precisely.