Nitric oxide synthase isoform expression in a porcine model of granulationtissue formation

Background. This study was designed to determine whether the nitric oxide ( NO) pathway is involved in. wound granulation tissue formation. Methods. A section of the pig abdominal wall (excluding the shin) was excis ed, cheating an incisional hernia. The resulting defect was repaired with s ilicone sheeting in a manner that mimics a temporary abdominal wall closure . During the 14-day experimental period, porcine omentum adhered to the per itoneal edges of the defect and a highly vascularized granulation tissue fo rmed on both sides of the sheeting. Granulation tissue thickness and wound fluid volume were monitored by ultmasonography and epigastric artery flow v elocity was monitored by color Doppler flow analysis at days 2, 4, 7 9 11, and 14. Fluid was serially harvested from the wound compartment at days 2, 4, 7, 9, 11, and 14 for nitrite/nitrate (NOx) analysis. Finally, granulatio n tissue was harvested at day 14 for immunohistochemical and molecular anal yses. Results, There was a significant increase in granulation tissue thickness a nd wound fluid volume during the 14-day study period. Blood flow to the wou nd increased significantly by day 4 and returned toward baseline by day 14. Wound fluid NOx levels significantly increased from days 7 to 11 and then decreased to near baseline values by day 14. Wound fluid arginine levels si gnificantly decreased when compared with peritoneal fluid and plasma levels at day 14, while wound fluid ornithine levels significantly increased. Imm unohistochemical analysis of granulation tissue at day 14 revealed nitric o xide synthase (NOS) 2 was present in the majority of the cells in the granu lation tissue. NOS 3 was expressed in endothelial cells only and NOS 1 expr ession was not observed in the granulation tissue. Conclusions. This study suggests that NO, NOS 2, and arginine may play crit ical roles in granulation tissue formation and wound healing Arginase and N OS 2 mar compete for available arginine as a substrate, thereby limiting la ter NO production in favor of sustained ornithine synthesis.