Divergent effects of ischemia/reperfusion and nitric oxide donor on TNFα mRNA accumulation in rat organs

We previously showed that serum TNF alpha bioactivity in rats is proportional to the extent of graded tissue injury caused by laparotomy, intestinal ischemia, and reperfusion and that the spleen is an important source of TNF alpha secretion in this condition. TNF alpha production varies, depending on the type and duration of tissue injury. It is also affected by other mediators, such as nitric oxide (NO). TNF alpha is known to increase NO production, but the effect of NO on the production of TNF alpha has not yet been fully elucidated. In this study we determined the levels of TNF alpha mRNA in rat organs after graded injury caused by anesthesia, laparotomy, intestinal ischemia, and reperfusion and evaluated the effects of the NO donor S-nitroso-N-acetylpenicillamine (SNAP) on it. Samples from different organs were removed, and TNF alpha gene expression was evaluated by semiquantitative RT-PCR. TNF alpha mRNA was not detected in the intestine (the ischemic organ) and in the kidney, brain, heart, or liver after all 4 experimental protocols. In the mesenteric lymph node (draining the ischemic organ) a basal level of expression of TNF alpha mRNA was detected in the control (anesthesia alone) group, which was increased significantly after ischemia. In the spleen (a remote immune organ not directly involved in the ischemia), a significant gradual increase in TNF alpha mRNA, which correlated to the severity of the experimental protocol, was observed. In the lung (a central participant in post-injury multiple organ failure), all interventions increased TNF alpha mRNA. Infusion of SNAP exerted a differential effect on TNF alpha mRNA: diminished its accumulation in the lymph node, enhanced it in the lung, and had no effect in the spleen. The divergent organ pattern of TNF alpha transcription emphasizes the importance of its localized expression, which is critical to the understanding of its autocrine and paracrine actions in ischemia and reperfusion.