Effects of acute rejection on L-arginine/iNOS pathway in canine heart transplantation.
BACKGROUND
The inflammatory process resulting from ischemia-reperfusion and acute rejection is a strong modulator of the endothelial nitric oxide synthase expression of both constitutive and inducible isoforms.


OBJECTIVE
To assess the expression of the endothelial constitutive nitric oxide synthase (ecNOS) and inducible nitric oxide synthase (iNOS) activity in conductance coronary arteries after reperfusion and acute rejection in the canine heart transplantation setting.


METHODS
Expression of ecNOS and iNOS was evaluated in two groups of mongrel dogs (n=7) that underwent heterotopic heart transplantation without immunosuppression. The first group was studied after 24 h of reperfusion and the second after five days of acute untreated rejection. A third group (n=7) consisting of normal unoperated dogs was used as control. Functional vascular status of iNOS isoforms was studied in organ chambers, and tissue enzyme expression by histological and immunohistochemical studies.


RESULTS
At harvest, vonWillebrand factor was present on the coronary endothelium of all groups. Both transplanted groups displayed iNOS and ecNOS expression by immunohistochemical study. The control group only displayed ecNOS expression. L-arginine induced endothelium-dependent relaxations in group 1 and group 2 but not in the control group. This was inhibited by the iNOS inhibitor aminoguanidine. Endothelium-independent contractility and relaxation were unaffected.


CONCLUSIONS
In this experimental setting, a specific endothelial expression of iNOS was observed early on after acute rejection. The functional aspect of this endothelial iNOS expression was reversible with aminoguanidine.
Demers
Philippe
P
Department of Surgery, Montreal Heart Institute, Québec, Canada.
Elkouri
Stéphane
S
Sirois
Martin G
MG
Cartier
Raymond
R
D000818:Animals; D001120:Arginine; D003331:Coronary Vessels / Q000201:enzymology; D015237:Dinoprost; D004195:Disease Models, Animal; D004285:Dogs; D004730:Endothelium, Vascular / Q000201:enzymology; D005260:Female; D006084:Graft Rejection / Q000097:blood / Q000276:immunology*; D016027:Heart Transplantation / Q000276:immunology*; D007150:Immunohistochemistry; D008297:Male; D019001:Nitric Oxide Synthase / Q000097:blood*; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D009599:Nitroprusside; D011189:Potassium Chloride; D015427:Reperfusion Injury / Q000097:blood*
D009599:Nitroprusside; D011189:Potassium Chloride; D001120:Arginine; D015237:Dinoprost; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III