Modulation of growth factor and cytokine expression by nitric oxide during rat colon anastomotic healing

We have previously shown that inhibition of nitric oxide generated by inducible nitric oxide synthase (iNOS) results in impaired colon anastomotic healing. Therefore, we proceeded to assess whether disruption of iNOS activity alters the normal pattern of growth factor expression during anastomotic healing. Two groups of male Sprague-Dawley rats underwent distal colonic division and anastomosis, jugular venous catheterization and subcutaneous placement of polyvinyl alcohol sponges. The first group (n = 10) received q8 hour intravenous injections of 10 mg/kg L-N-iminoethyl-lysine (L-NIL, a selective inhibitor of iNOS), while the second group (n = 12) received equal volumes of saline. On postoperative day 5, animals were sacrificed and anastomotic bursting pressure was determined. Histologic sections of the anastomosis were subjected to in situ hybridization versus mRNA of the proteins listed below. Positive controls were reacted with a poly-thymidine (poly-T) probe versus ubiquitous mRNA poly-adenine tails. Positively stained cells were quantified using a calibrated optical grid encompassing 0.5 mm(2) area centered over the anastomosis. Results are reported as the number of positive cells per 1000 cells positive for poly-T. L-NIL treated animals demonstrated an 18% decrease in wound fluid NO(X) compared to controls (29.2 +/- 1.2 vs. 34.6 +/- 2.0 microM, mean +/- SEM; P = 0.035). This corresponded to a 17% decrease in anastomotic bursting pressure (153 +/- 4 vs. 182 +/- 8 mm Hg, mean +/- SEM; P < 0.05). L-NIL also markedly increased the number of cells expressing transforming growth factor-beta, tumor necrosis factor-alpha, vascular endothelial growth factor, and both inducible and endothelial forms of nitric oxide synthase. L-NIL had no effect on the expression of basic fibroblast growth factor. The data demonstrate that iNOS inhibition markedly disrupts the profile of cytokine and growth factor mRNA normally expressed during anastomotic healing. This provides in vivo evidence that NO modulates gene expression during anastomotic healing.