Pharmacological characteristics of endothelin receptors on sheep rectal blood vessels

Endothelin-1 and its receptors on haemorrhoidal tissue: a potential site for therapeutic intervention

BACKGROUND AND PURPOSE

Haemorrhoids is a common anorectal condition affecting millions worldwide. We have studied the effect of endothelin-1 (ET-1) and the role of endothelin ET_A and ET_B receptors in haemorrhoid tissue.

EXPERIMENTAL APPROACH

Protein expression of ET-1, ET_A and ET_B receptors were compared between haemorrhoids and normal rectal submucosa using Western blot analysis, with the localization of proteins determined by autoradiography and immunohistochemistry. Effects of ET-1 and sarafotoxin 6a on human colonic and rectal arteries and veins was assessed by wire myography and the involvement of receptor subtypes established by selective antagonists.

KEY RESULTS

Dense binding of [¹²⁵ I]-ET-1 to haemorrhoidal sections was reduced by selective receptor antagonists. A higher density of ET_B than ET_A receptors was found in haemorrhoidal, than in control rectal tissue and confirmed by Western blot analysis. ET_A and ET_B receptors were localized to smooth muscle of haemorrhoidal arteries and veins, with ET_B receptors on the endothelium. Human colonic and rectal arteries and veins were similarly sensitive to ET-1 and affected by the ET_A selective antagonist, but sarafotoxin S6a-induced contractions were more pronounced in veins and antagonized by a selective ET_B receptor antagonist.

CONCLUSIONS AND IMPLICATIONS

ET_A and ET_B receptors are present in human haemorrhoids with ET_B receptors predominating. ET_A receptors are activated by ET-1 to mediate a contraction in arteries and veins, but the latter are selectively activated by sarafotoxin S6a - a response that involves ET_B receptors at low concentrations. Selective ET_B agonists may have therapeutic potential to reduce congestion of the haemorrhoidal venous sinusoids.

Approach to hemorrhoids

Hemorrhoids are a very common anorectal disorder defined as the symptomatic enlargement and abnormally downward displacement of anal cushions. The current pathophysiologies of hemorrhoids include the degenerative change of supportive tissue within the anal cushions, vascular hyperplasia, and hyperperfusion of hemorrhoidal plexus. Low-grade hemorrhoids are easily and effectively treated with dietary and lifestyle modification, medical intervention, and some office-based procedures. An operation is usually indicated in symptomatic high-grade and/or complicated hemorrhoids. Whilst hemorrhoidectomy has been the mainstay of surgical treatment, more recently other approaches have been employed including Ligasure hemorrhoidectomy, stapled hemorrhoidopexy, and doppler-guided hemorrhoidal artery ligation. Post-procedural pain and disease recurrence remain the most challenging problems in the treatment of hemorrhoids. This article deals with modern approaches to hemorrhoids based on the latest evidence and reviews of the literature. The management of hemorrhoids in complicated situations is also discussed.