Portal hypertension triggers local activation of inducible nitric oxide synthase gene in colonic mucosa

An Update: Portal Hypertensive Gastropathy and Colopathy

Complications of portal hypertension include portal hypertensive gastropathy and colopathy. These disorders may cause chronic or acute gastrointestinal bleeding. The diagnosis is made endoscopically; therefore, there is great variability in their assessment. Portal hypertensive gastropathy can range from a mosaic-like pattern resembling snakeskin mucosa to frankly bleeding petechial lesions. Portal hypertensive colopathy has been less well-described and is variably characterized (erythema, vascular lesions, petechiae). Treatment is challenging and results are inconsistent. Currently, available evidence does not support the use of beta-blockers for primary prevention. Further investigation of the pathogenesis, natural history, and treatment of these disorders is needed.

Portal hypertensive gastropathy and colopathy

Portal hypertensive gastropathy (PHG) and colopathy (PHC) are considered complications of portal hypertension. Both entities are clinically relevant because they may cause insidious blood loss or even acute massive gastrointestinal hemorrhage. Endoscopic evaluation is necessary for the diagnosis of PHG and PHC. The existence of different endoscopic criteria for PHG and PHC makes consensus difficult and results in a broad range of reported prevalence. Therapy targeted at reduction of portal pressure and mucosal blood flow has been used to treat acute bleeding; nonselective β-blockers are the most frequently used agents. Further studies are needed to clarify the natural history, pathogenesis, and treatment of PHG and PHC.

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Endothelial, but not the inducible, nitric oxide synthase is detectable in normal and portal hypertensive rats

BACKGROUND

Chronic portal hypertension is accompanied by a nitric oxide (NO) dependent vasodilation. Three isoforms of NO producing synthases (NOS) are characterized: neuronal NOS (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS). Sources of increased NO levels in chronic hypertension is disputed.

METHODS

To determine eNOS and iNOS expression in different organs of portal hypertensive and control rats, we divided Sprague-Dawley rats in 6 groups: (1). Partial portal vein ligated rats, (2). Bile duct ligated rats, (3). Carbon tetrachloride treated rats, (4). Sham operated rats, (5). Untreated control rats, and (6). LPS treated rats. Immunohistochemistry (IHC) and immunoblotting (IB) using antibodies against eNOS or iNOS were carried out on samples from thymus, aorta, heart, lung, oesophagus, liver, spleen, kidney, pancreas, small and large intestine.

RESULTS

IHC revealed an even eNOS expression in all groups. Expression of iNOS was restricted to macrophages in organs of LPS treated and the thymus of rats. IB mirrored these results.

CONCLUSION

In chronic portal hypertension, the main source for NO production depends on eNOS activity.

Endothelial dysfunction in cirrhosis and portal hypertension

Portal hypertension (PHT) is a common clinical syndrome associated with chronic liver diseases; it is characterized by a pathological increase in portal pressure. Pharmacotherapy for PHT is aimed at reducing both intrahepatic vascular tone and elevated splanchnic blood flow. Due to the altered hemodynamic profile in PHT, dramatic changes in mechanical forces, both pressure and flow, may play a pivotal role in controlling endothelial and vascular smooth muscle cell signaling, structure, and function in cirrhotics. Nitric oxide, prostacyclin, endothelial-derived contracting factors, and endothelial-derived hyperpolarizing factor are powerful vasoactive substances released from the endothelium in response to both humoral and mechanical stimuli that can profoundly affect both the function and structure of the underlying vascular smooth muscle. This review will examine the contributory role of hormonal- and mechanical force-induced changes in endothelial function and signaling and the consequence of these changes on the structural and functional response of the underlying vascular smooth muscle. It will focus on the pivotal role of hormonal and mechanical force-induced endothelial release of vasoactive substances in dictating the reactivity of the underlying vascular smooth muscle, i.e., whether hyporeactive or hyperreactive, and will examine the extent to which these substances may exert a protective and/or detrimental influence on the structure of the underlying vascular smooth muscle in both a normal hemodynamic environment and following hemodynamic perturbations typical of PHT and cirrhosis. Finally, it will discuss the intracellular processes that regulate the release/expression of these vasoactive substances and that control the transformation of this normally protective cell to one that may promote the development of vasculopathy in PHT.