Back to Annual Meeting Program

Introduction:
Post-operative intraabdominal adhesions are a major source of morbidity and our understanding of their formation remains incomplete. Our laboratory has previously shown that reduced peritoneal fibrinolysis and increased oxidative stress are implicated in adhesiogenesis. Peritoneal fibrinolytic activity, determined by tissue plasminogen activator (tPA) activity, is modulated by the mesothelial RAS. We hypothesized that losartan, by blocking the angiotensin II receptor (AIIR) and modulating the peritoneal RAS, could reduce adhesions.
Methods:
Wistar rats (n=50) were randomized to non-operative controls (NonOp), operative controls (Op+Saline) or intraperitoneal (IP) administration of losartan (Op+Losartan). Operated rats were administered either 1-ml normal saline or losartan (100mg/kg) via IP injection 6-hrs pre-operatively, intra-operatively, 6- and 12-hrs post-operatively. Adhesions were induced using our ischemic button model and scored on POD7. Additional rats were sacrificed on POD1 for peritoneal tissue analysis of 8-isoprostane (a marker of oxidative stress) by ELISA and AIIR mRNA by PCR. AIIR protein expression was studied by immunohistochemical staining. Peritoneal fluid was also collected on POD1 to measure tPA activity by kinetic assay. Additionally, an in vitro study of AIIR MAP-Kinase signaling was performed using primary rat peritoneal mesothelial cells treated with angiotensin II (AII), losartan (Los), or angiotensin II + losartan (AII+Los) and downstream phospho-ERK levels were measured via Western blot.
Results:
Losartan significantly decreased adhesion formation by 73.3% compared to Op+Saline (16.7±4.6 vs. 62.5±4.2%, p<0.001). While surgery increased tPA activity levels by 1.7-fold compared with NonOp, Op+Losartan further increased tPA 1.4-fold compared to Op+Saline (0.56±0.01 vs. 0.95±0.18 vs. 2.24±0.5 U/ml, p<0.05). AIIR mRNA levels were upregulated 5.1-fold in Op+Losartan compared to Op+Saline (31.9±2.0 vs. 6.3±0.5 fold change of NonOp, p<0.01). Immunohistochemical analysis also showed increased AIIR staining of peritoneal mesothelial cells in Op+Losartan compared to Op+Saline. While in vitro rat peritoneal mesothelial cells administered AII showed a 95-fold increase in phospho-ERK protein levels compared to controls, the addition of losartan (AII+Los) attenuated this response by 70% (1 vs. 95.0±19.2 vs. 28.5±8.2 fold change of NonOp, p<0.05). The oxidative stress biomarker 8-isoprostane was reduced by 45% in Op+Losartan versus Op+Saline (8.4±0.7 vs. 4.6±0.6 ng/mg protein, p<0.05).
Conclusions:
Losartan significantly reduces intraabdominal adhesions, suggesting a novel mode-of action for this ARB. Both regulation of peritoneal fibrinolytic activity by RAS and attenuation of postoperative peritoneal oxidative stress are implicated.