In situ measurement of nitric oxide production in cardiac isografts and rejecting allografts by an electrochemical method.

A number of previous studies have indirectly (electron paramagnetic resonance, nitrite/nitrate, ribonuclease protection assay for inducible nitric oxide synthase (iNOS) mRNA, l-citrulline assay) demonstrated the production of nitrogen monoxide (NO) during early cardiac allograft rejection. This study reports the first direct, quantitative measurement using an electrochemical method of NO produced from rejecting allograft tissue studied in vitro. A rat heterotopic abdominal transplant preparation was utilized. Day 7 isograft (ACI to ACI) or allograft (Lewis to ACI) transplanted hearts were atraumatically harvested and suspended at 4 degrees C in Ringers-Hepes solution. An electrochemical system highly sensitive and specific for NO consisting of a Nafion-coated platinum disk electrode (lower limit, 50 nM NO) coupled to an analysis system measured ongoing oxidation of NO. Measurements were carried out after inserting the electrode in the tissue block and warming the block to 25 degrees C. Additional measurements were also made after incubation of tissue with aminoguanidine (AG), a relatively selective iNOS inhibitor. Direct measurements (mean +/- SEM) from allograft tissue indicated a fourfold increase in NO as compared with isografts (13.41 +/- 4.40 microM NO vs. 3.43 +/- 2.04 microM NO). Incubation of allograft tissue with AG reduced NO levels to isograft levels (13.41 +/- 4.40 microM NO vs. 5.94 +/- 3.14 microM NO); AG had no effect on measured isograft NO levels. Direct, quantitative measurement of NO from tissue is feasible and reproducible, and discrimination between different levels of NO production can be made. These results confirm the imputed results from the previous studies using this experimental model. This technology promises to be a valuable tool for evaluating specific modulators of NO production studied under a variety of physiologic and pathophysiologic conditions.