We investigated in rats the influence of the lymphatic system and of tumor necrosis factor (TNF) on the lung inflammation resulting from intestinal ischemia/reperfusion (I/R) performed by 45-min occlusion of the superior mesenteric artery followed by 2 h of reperfusion. A group of rats had the thoracic lymph duct ligated before I/R. In lungs, intestinal I/R evoked a significant neutrophil recruitment, and enhanced microvascular permeability, in addition to generation of TNF in serum. In the gut, there was lowered lactate dehydrogenase (LDH) activity and increased microvascular permeability. Upon lymph duct ligation, I/R rats had a significant reduction of pulmonary neutrophil recruitment and plasma extravasation, in addition to high amounts of TNF in the lymph, contrasting with undetectable levels in the serum. In addition, LDH gut levels in these animals were close to basal values; there was also some (yet significant) reduction of microvascular permeability, suggesting that the ligation of the lymphatic duct exerted some degree of protection against the intestinal injury caused by I/R. In I/R rats, the treatment with pentoxifylline (PTX) reduced TNF in serum and blunted other lung alterations. The gut alterations caused by intestinal I/R were largely blocked by PTX. On the other hand, in I/R rats with lymph duct ligation, PTX exacerbated the reduction of pulmonary neutrophil recruitment, but did not affect pulmonary and intestinal microvascular permeabilities. Similarly, intestinal LDH activity and serum TNF levels were unaffected. Overall, our data show that the pulmonary and gut injuries induced by intestinal I/R are partially dependent on TNF, which is conceivably generated in the injured gut tissue due to intestinal I/R and carried by the lymphatic system. Thus, the mesenteric lymphatic drainage seems to play a role as a path modulator of the pulmonary and intestinal dysfunctions that follow a gut trauma.

These findings suggest that variables related to defensive mechanisms, such as lymphocyte recirculation and particles uptake into the lymph nodes can benefit from insulin treatment, whereas glycemic control can benefit transport mechanisms in the lymphatic system, such as lymph flow and lymphatic transport of particles.

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Intestinal ischemia/reperfusion (I/R) causes local and remote injuries that are multifactorial and essentially inflammatory in nature. To study the putative influences of nitric oxide (NO) and tumor necrosis factor alpha (TNF-alpha) on the release of interleukin (IL) 1beta and IL-10 and the involvement of lymphatic system on a systemic inflammation caused by I/R, we have quantified the serum and lymph levels of IL-1beta and IL-10 in rats during I/R after treatment with inhibitors of NO synthase (N-nitro-L-arginine methyl ester hydrochloride [L-NAME]) or TNF-alpha (pentoxifylline [PTX]). Intestinal I/R was performed by means of a 45-min occlusion of the mesenteric artery, followed by 2-h reperfusion; groups of rats subjected to I/R had the thoracic lymph duct ligated immediately before the procedure. The I/R caused a significant increase of the serum levels of IL-1beta and IL-10 in rats with intact thoracic lymph duct, whereas the thoracic duct ligation blunted the serum release of IL-1beta and elevated that of IL-10. The levels of the cytokines collected in the lymph after I/R increased, and even more increase was observed in L-NAME-treated rats. L-NAME significantly increased the lymph levels of IL-1beta and IL-10; in serum, however, only IL-1beta increased in rats with either intact or ligated thoracic lymph duct. The treatment with PTX reduced the serum levels of IL-1beta irrespective of the lymph circulation interruption but was effective to increase the IL-10 levels in intact rats during I/R. The lymphatic levels of IL-1beta of rats subjected to I/R were reduced and those of IL-10 were increased after treatment with PTX. In conclusion, during I/R, the serum levels of IL-1beta seem modulated by stimulant mechanisms that could be associated with TNF-alpha and inhibited by NO and by the integrity of the thoracic lymphatic flow. On the other hand, IL-10 seems controlled by TNF-alpha-related, largely NO-independent mechanisms. Thus, it is reasonable to suppose that an endogenous mechanism that can limit the systemic inflammatory response ensuing an I/R splanchnic trauma exists.

Acute lung injury following intestinal I/R depends on neutrophil-endothelial cell interactions and on cytokines drained from the gut through the lymph. Among the mediators generated during I/R, increased serum levels of IL-6 and NO are also found and might be involved in acute lung injury. Once intestinal ischemia itself may be a factor of tissue injury, in this study, we investigated the presence of IL-6 in lymph after intestinal ischemia and its effects on human umbilical vein endothelial cells (HUVECs) detachment. The involvement of NO on the increase of lung and intestinal microvascular permeability and the lymph effects on HUVEC detachment were also studied. Upon anesthesia, male Wistar rats were subjected to occlusion of the superior mesenteric artery during 45 min, followed by 2-h intestinal reperfusion. Rats were treated with the nonselective NO synthase (NOS) inhibitor L-NAME (N(omega)-nitro-L-arginine methyl ester) or with the selective inhibitor of iNOS aminoguanidine 1 h before superior mesenteric artery occlusion. Whereas treatment with L-NAME during ischemia increased both IL-6 levels in lymph and lung microvascular permeability, aminoguanidine restored the augmented intestinal plasma extravasation due to ischemia and did not induce IL-6 in lymph. On the other hand, IL-6 and lymph of intestinal I/R detached the HUVECs, whereas lymph of ischemic rats upon L-NAME treatment when incubated with anti-IL-6 prevented HUVEC detachment. It is shown that the intestinal ischemia itself is sufficient to increase intestinal microvascular permeability with involvement of iNOS activation. Intestinal ischemia and absence of constitutive NOS activity leading to additional intestinal stress both cause release of IL-6 and increase of lung microvascular permeability. Because anti-IL-6 prevented the endothelial cell injury caused by lymph at the ischemia period, the lymph-borne IL-6 might be involved with endothelial cell activation. At the reperfusion period, this cytokine does not seem to be modulated by NO.

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Intestinal I/R (i-I/R) is an insult associated to further adult respiratory distress syndrome and multiple organ failure. This study was designed to evaluate the repercussions of i-I/R on bronchial reactivity to the cholinergic agent methacholine. Anesthetized rats were subjected to superior mesenteric artery occlusion (45 min) and killed after clamp release and defined intestinal reperfusion periods (30 min, 2, 4, or 24 h). Intestinal I/R caused a progressive bronchial hyporesponsiveness (BHR) that was maximal upon 2 h but reverted within 24 h of intestinal reperfusion. The BHR observed at 2-h i-I/R was prevented by NOS inhibitors (N-L-nitroarginine methyl ester and aminoguanidine) or the KATP channel blocker glibenclamide. Moreover, 2-h i-I/R increased the pulmonary iNOS mRNA expression, a fact prevented by lymphatic thoracic duct ligation. The methacholine reactivity of 2-h i-I/R bronchial segments incubated with NOS inhibitors or glibenclamide was similar to that of naive tissues. In vivo blockade of IL-1beta receptors or lymphatic duct ligation before 2-h i-I/R both abolished BHR. Incubation of naive bronchial segments with lymph collected from 2-h i-I/R rats determined BHR, an effect fully preventable by ex vivo blockade of IL-1beta receptors. Incubation of naive bronchial segments with IL-1beta, but not with IL-10 or TNF-alpha, significantly induced BHR that was prevented by N-L-nitroarginine methyl ester. Our data suggest that a gut ischemic insult generates IL-1beta that, upon reperfusion, travels through the lymph into the lungs. In this tissue, IL-1beta would stimulate the generation of NO that orchestrates the ensuing BHR for which the opening of KATP channels seems to play a pivotal role.

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