Role of endothelial nitric oxide synthase in the development of portal hypertension in the carbon tetrachloride-induced liver fibrosis model.

Portal hypertension (PHT) is a complication of liver cirrhosis and directly increases mortality and morbidity by increasing the propensity of venous hemorrhage. There are two main underlying causations for PHT, increased hepatic resistance and systemic hyperdynamic circulation. Both are related to localized aberrations in endothelial nitric oxide synthase (eNOS) function and NO biosynthesis. This study investigates the importance of eNOS and systemic hyperdynamic-associated hyperemia to better understand the pathophysiology of PHT. Wild-type and eNOS(-/-) mice were given the hepatotoxin CCl(4) for 4-12 wk. Hepatic fibrosis was determined histologically following collagen staining. Portal venous pressure, hepatic resistance, and hyperemia were determined by measuring splenic pulp pressure (SPP), hepatic portal-venous perfusion pressure (HPVPP), abdominal aortic flow (Qao), and portal venous flow (Qpv). Hepatic fibrosis developed equally in wild-type and eNOS(-/-) CCl(4)-exposed mice. SPP, Qao, and Qpv increased rapidly in wild-type CCl(4)-exposed mice, but HPVPP did not. In eNOS(-/-) CCl(4) mice, Qao was not increased, SPP was partially increased, and HPVPP and Qpv were increased nonsignificantly. We concluded that the systemic hyperemia component of hyperdynamic circulation is eNOS dependent and precedes increased changes in hepatic resistance. Alternative mechanisms, possibly involving cyclooxygenase, may contribute. eNOS maintains normal hepatic resistance following CCl(4)-induced fibrosis. Consequently, increased portal pressure following chronic CCl(4) exposure is linked to hyperdynamic circulation in wild-type mice and increased hepatic resistance in eNOS(-/-) mice.

Thalidomide ameliorates portal hypertension via nitric oxide synthase independent reduced systolic blood pressure.

AIM: Portal hypertension is a common complication of liver cirrhosis and significantly increases mortality and morbidity. Previous reports have suggested that the compound thalidomide attenuates portal hypertension (PHT). However, the mechanism for this action is not fully elucidated. One hypothesis is that thalidomide destabilizes tumor necrosis factor α (TNFα) mRNA and therefore diminishes TNFα induction of nitric oxide synthase (NOS) and the production of nitric oxide (NO). To examine this hypothesis, we utilized the murine partial portal vein ligation (PVL) PHT model in combination with endothelial or inducible NOS isoform gene knockout mice. METHODS: Wild type, inducible nitric oxide synthase (iNOS)(-/-) and endothelial nitric oxide synthase (eNOS)(-/-) mice received either PVL or sham surgery and were given either thalidomide or vehicle. Serum nitrate (total nitrate, NOx) was measured daily for 7 d as a surrogate of NO synthesis. Serum TNFα level was quantified by enzyme-linked immunosorbent assay. TNFα mRNA was quantified in liver and aorta tissue by reverse transcription-polymerase chain reaction. PHT was determined by recording splenic pulp pressure (SPP) and abdominal aortic flow after 0-7 d. Response to thalidomide was determined by measurement of SPP and mean arterial pressure (MAP). RESULTS: SPP, abdominal aortic flow (Qao) and plasma NOx were increased in wild type and iNOS(-/-) PVL mice when compared to sham operated control mice. In contrast, SPP, Qao and plasma NOx were not increased in eNOS(-/-) PVL mice when compared to sham controls. Serum TNFα level in both sham and PVL mice was below the detection limit of the commercial ELISA used. Therefore, the effect of thalidomide on serum TNFα levels was undetermined in wild type, eNOS(-/-) or iNOS(-/-) mice. Thalidomide acutely increased plasma NOx in wild type and eNOS(-/-) mice but not iNOS(-/-) mice. Moreover, thalidomide temporarily (0-90 min) decreased mean arterial pressure, SPP and Qao in wild type, eNOS(-/-) and iNOS(-/-) PVL mice, after which time levels returned to the respective baseline. CONCLUSION: Thalidomide does not reduce portal pressure in the murine PVL model by modulation of NO biosynthesis. Rather, thalidomide reduces PHT by decreasing MAP by an undetermined mechanism.

Tumor necrosis factor alpha signaling in the development of experimental murine pre-hepatic portal hypertension.

The cytokine tumor necrosis factor alpha (TNFa) has previously been identified in the development of portal hypertension (PHT) by facilitating portal venous and systemic hyperemia. TNFa is reported to contribute to hyperemia via endothelial nitric oxide synthase (eNOS) induction and nitric oxide (NO) production. This study examines this hypothesis by utilizing TNFa receptor knockout mice and a murine model of pre-hepatic PHT. Plasma TNFa and NOx and tissue TNFa mRNA levels were determined in wild-type mice 0-7d post induction of pre-hepatic PHT by partial portal vein ligation (PVL). TNFa receptor knockout mice also received PVL or sham surgery and splenic pulp pressure, abdominal aortic flow and portal-systemic shunting were recorded 7d following. Portal pressure and systemic hyperemia developed rapidly following PVL. Plasma NOx was increased temporarily 2-3 days following PVL and returned to baseline by day 7. Circulating TNFa was below detectable limits of the ELISA used, as such no increase was observed. Hepatic and vascular TNFa mRNA levels were transiently changed after PVL otherwise there was no significant change. TNFa receptor targeted gene deletion did not ameliorate plasma NOx following PVL and had no effect on the development of PHT. TNFa receptor signaling plays no detectable role in the development of systemic hyperemia in the murine model of pre-hepatic PHT. Consequently, increased TNFa observed in intra-hepatic inflammatory models (CCl(4)) and in patients is probably related to inflammation associated with intra-hepatic pathology. Alternatively, TNFa may be signaling via a TNFa receptor independent mechanism.