International Research Journal of pharmacy and Pharmacology (ISSN 2251-0176) Vol. 1(6) pp. 100-108, September 2011 Available online http://www.interesjournals.org/IRJPP Copyright © 2011 International Research Journals Full Length Research Paper Comparative study between effect of angiotensin converting enzyme inhibitors and angiotensin receptor blockers on acetic acid- induced ulcerative colitis in rats Azza H. El-Medany 1 , Aida A. Guemei 2 , Hanan H. Hagar 3 , Jamila H.El-Medany 4 , Azza M Baraka 5 , 1/3 Department of Pharmacology, College of Medicine at King Khalid University Hospital, King Saudi University, Riyadh, Saudi Arabia 4 Department of Anatomy, College of Medicine at King Khalid University Hospital, King Saudi University, Riyadh, Saudi Arabia 2/5 Department of Clinical Pharmacology, Faculty of Medicine-Alexandria University-Alexandria-Egypt Accepted 29 June, 2011. Accumulating data suggest the involvement of renin angiotensin system (RAS) in the pathogenesis of inflammatory bowel disease. The aim of the present study was to evaluate the potential protective and therapeutic effects of captopril and valsartan on acetic acid induced- ulcerative colitis in rats. The results were assessed by macroscopic and microscopic examinations of colonic tissues as ell as by biochemical measurement of malondialdehyde (MDA), tumor necrosis factor alpha (TNF-α), transforming growth factor- beta1 (TGF-β 1 ), angiotensin converting enzyme (ACE), reduced glutathione (GSH) and platelet activating factor (PAF) levels in colonic tissues. Oral treatment with captopril or valsartan in a dose of 30 mg kg -1 body weight, starting one day before induction of colitis and continuing for 1 week (prophylactic groups) or starting one week after induction of colitis and continuing for another one week (therapeutic groups), significantly reduced MDA, TNF-α, PAF, TGF-β1 and significantly increased colonic GSH in colonic tissues as compared to acetic acid control groups. Captopril and valsartan attenuated the macroscopic and microscopic colonic damage induced by acetic acid. No significant difference between the effect of either drug could be detected other than the significant decrease in ACE activity in colonic tissue exerted by captopril and not by valsartan, These results suggest that either captopril or valsartan may be effective in prophylaxis as well as in treatment of ulcerative colitis through targeting RAS. Keywords: Ulcerative colitis, captopril, valsartan, angiotensin converting enzyme, reduced glutathione, tumor necrosis factor alpha, transforming growth factor beta. INTRODUCTION Inflammatory bowel disease (IBD), comprising both Abbreviations ACE, angiotensin converting enzyme; II, Ang II, angiotensin II; Ang II type 1 , AT1; ARB, angiotensin receptor blocker; IBD, inflammatory bowel disease;GSH, reduced glutathione; MDA, malondialdehyde; PAF, platelet activating factor; RAS, renin angiotensin system; TGF- , transforming growth factor beta; TNF- , tumor necrosis factor alpha. *Corresponding Author Email: mnhbaraka@yahoo.com ulcerative colitis and Crohn’s disease, is a general term for a group of chronic inflammatory disorders of unknown etiology involving the gastrointestinal tract (Israeli et al., 2005). Both conditions result in inflammation, ulceration, edema, bleeding and diarrhea (Sands, 2007). Although many treatments are currently available for IBD, these are only effective for ameliorating the signs and symptoms of the disease. There is, as yet, no cure for this condition. The most commonly used therapies include aminosalicylates, antibiotics, corticosteroids and immunosuppressants, all of which have disadvantages (Sartor, 2004). It is therefore important to find better