L-arginine-induced relaxation of the internal anal sphincter is not mediated by nitric oxide

L-Arginine is a feasible supplement to heal chronic anal fissure via reducing internal anal sphincter pressure: a randomized clinical trial study

The hypertonicity of internal anal sphincter resting pressure is one of the main causes of chronic anal fissure. Therefore, the aim of this study was to assess the effect of oral administration of L-arginine on the improvement of the anal fissures by relaxing the internal anal sphincter. Seventy-six chronic anal fissure patients (aged 18-65 years) who were referred to Rasoul-e-Akram Hospital, Tehran, Iran from February 2019 to October 2020 participated in this randomized, double-blind, placebo-controlled trial. Participants were allocated into treatment (L-arginine) and placebo groups. They took a 1000 mg capsule three times a day for 1 month, and then we followed them at the end of the first and third months after the intervention. Clinical symptoms, anal sphincter resting pressure, and quality of life (QoL) were completed at baseline and the end of the study. The analysis of data showed a significant decrease in bleeding, fissure size, and pain for each group; however, in the L-arginine group was more than the control group at the end of the study (P values < 0.001). Following that, a significant increase in QoL was seen just in patients treated with L-arginine (P value = 0.006). In addition, the comparison of anal pressures at baseline and, between groups at the end of the study showed a significant reduction in sphincter pressure in patients treated with L-arginine (P value < 0.001, = 0.049; respectively). The oral administration of 3000 mg L-arginine can heal chronic anal fissures by reducing internal anal sphincter pressure with more negligible side effects. However, we recommend long-term study with more extended follow-up.Clinical trial registry: IRCT20190712044182N1 at Iranian clinical trials, date: 2019-08-27.

Relaxation of the isolated human internal anal sphincter by sildenafil

BACKGROUND

Hypertonicity of the internal anal sphincter (IAS) appears to be involved in the pathogenesis of anal fissure. The relaxant effects of sildenafil, a selective phosphodiesterase 5 (PDE5) inhibitor, on isolated human IAS were investigated.

METHODS

The efficacy (maximal effect, E(max)) and potency (-log IC(50), where IC(50) is half-maximal inhibitory concentration) of the PDE5 inhibitors, sildenafil and zaprinast, and of nitric oxide donors, sodium nitroprusside and glyceryl trinitrate, as relaxants of histamine (0.1 mmol/l)-induced tone were examined in IAS strips under isometric contraction. The presence of PDE5 isoenzymes and changes in intracellular calcium and cyclic nucleotide levels in IAS muscle were tested by real-time reverse transcriptase-polymerase chain reaction, epifluorescence microscopy and enzyme immunoassay respectively.

RESULTS

Sildenafil produced a concentration-related inhibition of the mean(s.e.m.) histamine-induced tone (E(max) 83(2) per cent, - log IC(50) 7.04(0.05); n = 12). Zaprinast produced relaxation to similar degree, but with lower potency. Nitric oxide donors also relaxed IAS. Sildenafil (1 micromol/l) produced a 1.8-fold increase in guanosine 3',5'-cyclic monophosphate content, with no change in adenosine 3',5'-cyclic monophosphate levels. Sildenafil markedly depressed the peak intracellular calcium increase evoked by histamine. PDE5A1, PDE5A2 and PDE5A3 transcripts were expressed in IAS muscle.

CONCLUSION

Sildenafil relaxes the augmented tone of human IAS in vitro. These results support the potential use of this PDE5 inhibitor in the treatment of chronic anal fissure.

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.

Treatment of chronic anal fissure by application of L-arginine gel: a phase II study in 15 patients

PURPOSE

Local application of exogenous nitric oxide donors, such as isosorbide dinitrate and glyceryl trinitrate, promotes fissure healing by reducing anal resting pressure and improving anodermal blood flow. The major drawback of these nitric oxide donors is headache. The overall incidence of this side effect is approximately 40 percent. Recently we have shown in healthy volunteers that L-arginine, being an intrinsic precursor of nitric oxide, reduces anal resting pressure without headache as a side effect. The aim of the present study was to evaluate the effect of L-arginine on anal resting pressure, anodermal blood flow, and fissure healing in patients with chronic anal fissure.

METHODS

Fifteen patients with a chronic anal fissure were included in the present study. Before entering the study 10 patients were unsuccessfully treated by local application of isosorbide dinitrate. Six of these patients experienced severe headache during treatment with isosorbide dinitrate. All patients were treated for at least 12 weeks by local application of a gel containing L-arginine 400 mg/ml five times a day. In patients with a persistent fissure, treatment was continued until 18 weeks. Anal manometry and laser Doppler flowmetry of the anoderm were performed before treatment, 20 minutes after local application of the first dose, and after 12 weeks of treatment. A visual analog scale was used to assess fissure-related pain and headache.

RESULTS

One patient dropped out after one day of treatment, and one was excluded because of violation of the study protocol. After 12 weeks of treatment complete fissure healing was observed in 3 of 13 (23 percent) patients, and after 18 weeks the healing rate was 8 of 13 (62 percent) patients. None of the 13 patients experienced typical nitric oxide-induced headache. The pressure recordings showed a significant reduction of maximum anal resting pressure (mean +/- SD): pretreatment 89 +/- 17 mmHg; 20 minutes after application of the first dose 67 +/- 17 mmHg; 12 weeks after treatment 74 +/- 14 mmHg (P < 0.005). Recordings of anodermal blood flow showed a significant increase in flow: pretreatment 0.36 +/- 0.25 volts; 20 minutes after application of the first dose 0.59 +/- 0.27; 12 weeks after treatment 0.64 +/- 0.33 (P < 0.005).

CONCLUSIONS

Local application of L-arginine promotes fissure healing without headache as a side effect, and L-arginine is effective even in patients not responding to isosorbide dinitrate treatment.