INDUCTION OF NITRIC-OXIDE SYNTHASE IN THE HUMAN CARDIAC ALLOGRAFT IS ASSOCIATED WITH CONTRACTILE DYSFUNCTION OF THE LEFT-VENTRICLE

Background The mechanisms underlying cardiac contractile dysfunction a fter transplantation remain poorly defined. Previous work has revealed that inducible nitric oxide synthase (iNOS) is expressed in the rat h eterotopic cardiac allograft during rejection; resultant overproductio n of nitric oxide (NO) might cause cardiac contractile dysfunction via the negative inotropic and cytotoxic actions of NO. In this investiga tion, we tested the hypothesis that induction of iNOS may occur and be associated with cardiac allograft contractile dysfunction in humans. Methods and Results We prospectively studied 16 patients in the first year after cardiac transplantation at the time of serial surveillance endomyocardial biopsy. Clinical data, the results of biopsy histology, and echocardiographic and Doppler evaluation of left ventricular syst olic and diastolic function were recorded. Total RNA was extracted fro m biopsy specimens, and mRNA for beta-actin, detected by reverse trans cription-polymerase chain reaction (RT-PCR) using human specific prime rs, was used as a constitutive gene control; iNOS mRNA was similarly d etected by RT-PCR using human specific primers. iNOS protein was detec ted in biopsy frozen sections by immunofluorescence. Myocardial cGMP w as measured by radioimmunoassay, and serum nitrogen oxide levels (NOx= NO2+NO3) were measured by chemiluminescence. iNOS mRNA was detected in allograft myocardium at some point in each patient and in 59 of 123 b iopsies (48%) overall. In individual patients, iNOS mRNA expression wa s episodic and time dependent; the frequency of expression was highest during the first 180 days after transplant (P=.0006). iNOS protein as sociated with iNOS mRNA was detected by immunofluorescence in cardiac myocytes. iNOS mRNA expression was not related to the ISHLT histologic al grade of rejection or to serum levels of NOx but was associated wit h increased levels of myocardial cGMP (P=.01) and with both systolic ( P=.024) and diastolic (P=.006) left ventricular contractile dysfunctio n measured by echocardiography and Doppler. Conclusions These data sup port a relation between iNOS mRNA expression and contractile dysfuncti on in the human cardiac allograft.