nitroarginine and Hypertension--Portal

In liver cirrhosis/portal hypertension, collaterals as varices may bleed and are influenced by vasoresponsiveness. An angiotensin blockade ameliorates portal hypertension but the influence on collaterals is unknown.. Portal hypertension and cirrhosis were induced by portal vein (PVL) and common bile duct ligation (BDL). Hemodynamics, real-time PCR of angiotensin II receptors (AT(1)R, AT(2)R) in the left adrenal vein (LAV, sham) and splenorenal shunt derived from LAV (PVL, BDL) were performed. With an in situcollateral perfusion model, angiotensin II vasoresponsiveness with different preincubations was evaluated: (1) vehicle; (2) AT(1)R blocker losartan; (3) losartan plus nonselective nitric oxide synthase (NOS) inhibitor (N(ω)-nitro-L-arginine); (4) AT(2)R blocker PD123319; (5) PD123319 plus N(ω)-nitro-L-arginine; (6) N(ω)-nitro-L-arginine, and (7) losartan plus inducible NOS inhibitor aminoguanidine.. LAV AT(1)R and AT(2)R expression decreased in PVL and BDL rats. Losartan attenuated angiotensin II-elicited vasoconstriction but PD123319 had no effect. N(ω)-nitro-L-arginine but not aminoguanidine reversed the losartan effect.. Angiotensin receptors are downregulated in the collateral vessel of portal hypertensive and cirrhotic rats. The AT(1)R blockade attenuates the angiotensin II vasoconstrictive effect, suggesting AT(1)R mediates collateral vasoconstriction and the influence of AT(2)R is negligible. The lack of aminoguanidine influence indicates that endothelial NOS participates in the losartan effect.

Topics: Animals; Collateral Circulation; Down-Regulation; Guanidines; Hypertension, Portal; Imidazoles; Ligation; Liver Cirrhosis; Losartan; Male; Nitric Oxide Synthase; Nitroarginine; Portal Vein; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Vasoconstriction

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor can enhance endothelial nitric oxide synthase expression and induce vasodilatation. The vasodilatory effect may be detrimental to portal-systemic collaterals due to aggravating the shunting degrees. The present study investigated the effects of pravastatin, a HMG-CoA reductase inhibitor, on the collateral vascular responsiveness to endothelin-1 (ET-1) and portal-systemic shunting in portal hypertensive rats.. The partial portal vein-ligated (PVL) rats received either pravastatin (25 mg/kg per day) or distilled water since 2 days prior to until 7 days after ligation. On the 8(th) day following hemodynamic measurements, the collateral vascular responsiveness to ET-1 was evaluated by an in situ collateral perfusion model. The shunting degrees of collaterals were evaluated by constructing vascular flow-pressure curves and color microsphere study, respectively. PVL rats underwent pre-incubation with: (i) Krebs solution (control); or Krebs solution plus (ii) 2 x 10(-5) M pravastatin; (iii) pravastatin + N(omega)-nitro-L-arginine (10(-4) M); and (iv) pravastatin + indomethacin (10(-5) M), followed by ET-1 (10(-10)-10(-7) M) administration to evaluate the collateral vascular responsiveness.. In chronic study, pravastatin did not modify systemic and portal hemodynamics and collateral vascular responsiveness to ET-1. The resistances of flow-pressure curves and the microsphere study demonstrated similar shunting degrees between both groups. Furthermore, pravastatin pre-incubation didn't reduce collateral perfusion pressure to ET-1.. Chronic pravastatin administration does not induce detrimental effects on hemodynamics and collaterals in PVL rats, nor does it influence the shunting degree. In addition, it does not modify the vasoconstrictive effect of ET-1 on the collaterals of PVL rats.

Topics: Animals; Collateral Circulation; Cyclooxygenase Inhibitors; Disease Models, Animal; Dose-Response Relationship, Drug; Endothelin-1; Enzyme Inhibitors; Hemodynamics; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Hypertension, Portal; Indomethacin; Male; Nitric Oxide Synthase; Nitroarginine; Portal System; Pravastatin; Rats; Rats, Sprague-Dawley; Regional Blood Flow; Time Factors; Vascular Resistance; Vasoconstriction; Vasoconstrictor Agents

To investigate the effects of verapamil on nitric oxide (NO) synthesis in a portal vein-ligated rat model.. Systemic and splanchnic hemodynamics were measured by radiolabeled microspheres in portal hypertensive rats after acute administration of verapamil (2 mg/kg) on chronic treatment with N(w)-nitro-L-arginine (NNA)(80 mg/kg) and/or indomethacin (2 mg/kg).. Verapamil (2 mg/kg) caused a marked fall in both arterial pressure and cardiac output accompanied by an insignificant change in the portal pressure and no change in portal venous inflow. This result suggested that verapamil did not cause a reduction in portal vascular resistance of portal hypertensive rats, which was similar between N(w)- nitro-L-arginine-treated and indomethacin-treated groups.. In portal hypertensive rats pretreated with NNA and/or indomethacin, acute verapamil administration can not reduce the portal pressure, suggesting that NO and prostaglandin play an important role in the pathogenesis of splanchnic arterial vasodilation in portal hypertension.

Topics: Animals; Epoprostenol; Hemodynamics; Hypertension, Portal; Indomethacin; Male; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Splanchnic Circulation; Verapamil

Clonidine, an alpha2-agonist, has been shown to be useful in the treatment of hepatic portal hypertension in cirrhosis. The mechanism has been attributed to a clonidine-induced decrease in sympathetic activity. While clonidine has been shown to stimulate the alpha2-adrenoceptors of blood vessels, there is limited knowledge of the effects of clonidine on the circular muscle of the hepatic portal vein which regulates its blood flow. To investigate clonidine-induced contraction of the circular muscle of the hepatic portal vein and to clarify the possible role of the endothelium in the contraction, we examined the effects of clonidine on the isometric contraction of endothelium-intact and -removed ring preparations of the rat hepatic portal vein. In endothelium-intact preparations, clonidine caused a concentration-dependent increase in the amplitude of contractions. Inhibition of NO synthesis with Nomega-nitro-L-arginine (L-NNA) elevated the resting tone, and increased the amplitude of the clonidine-induced contractions. Inhibition of cyclooxygenase by diclofenac did not change the amplitude of the clonidine-induced contractions observed both in the presence and absence of L-NNA. Application of a single concentration of clonidine induced a clear increase in amplitude of both twitch and tonic contractions. Twitch and tonic contractions induced by clonidine were inhibited by yohimbine. When the endothelium was damaged by sodium deoxycholate, tonic contractions induced by clonidine were completely suppressed, whereas the increase in twitch contractions was not influenced by chemical damage of the endothelium. Neither SKF-96365, a nonselective cation channel blocker, nor superoxide dismutase, a free radical scavenger, in the presence of catalase, changed the tonic contraction induced by clonidine. These results indicate that stimulation of alpha2-adrenoceptors enhanced twitch contractions and induced tonic contractions in the circular muscle of the rat hepatic portal vein, especially in the absence of NO. The latter, but not the former, occurs through an endothelium-dependent pathway.

Topics: Adrenergic alpha-Agonists; Animals; Clonidine; Diclofenac; Endothelium, Vascular; Humans; Hypertension, Portal; In Vitro Techniques; Isometric Contraction; Liver Cirrhosis; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Portal Vein; Rats; Rats, Wistar

The importance of nitric oxide (NO) in the pathogenesis of portal hypertension (PHT) has been extensively studied, but whether or not prostacyclin (PGI(2)) plays a role in formation and development of hyperdynamic circutatory state in PHT has not been verified. The present study was undertaken to investigate the possible interaction between prostacyclin (PGI(2)) and nitric oxide (NO) in the hyperdynamic circulatory state of rats with chronic portal hypertension (PHT), by measuring the hemodynamic changes and expression of cyclooxygenase (COX) mRNA in vessels and small intestine after administration of N(omega)-nitro-L-arginine (L-NNA) or indomethacin (INDO) either in the short-term (7 days) or long-term (15 days).. Ninety-seven male Sprague-Dawley rats were divided into three groups: intrahepatic portal hypertension (IHPH) induced by injection of CCl(4), prehepatic portal hypertension (PHPH) induced by partial stenosis of the portal vein, and sham-operated controls (SO). Animals of each group received L-NNA or INDO either for 7 or 15 days, with saline as control. Splanchnic hemodynamics was measured by the radioactive microsphere technique. The concentration of NO in serum was determined as the nitrate; nitrite ratio (NO(2)(-)/NO(3)(-), micromol/L) by a colorometric method, and that of PGI(2) was measured by specific radioimmunoassay for its stable hydrolysis product 6-keto-PGF(1alpha) (pg/ml). The reverse transcription-polymerase chain reaction measured the levels of COX-1 mRNA in the superior mesenteric artery, thoracic aorta, and small intestine of these rats.. Compared with SO rats, COX-1 mRNA expression and the concentrations of plasma 6-keto-PGF(1alpha) and serum NO(2)(-)/NO(3)(-) were enhanced in both IHPH and PHPH rats; splanchnic vascular resistance (SVR) decreased, but portal venous inflow (PVI) markedly increased (P<0.05). Seven or 15 days of L-NNA treatment reduced COX-1 mRNA expression in these vessels and the small intestine, concomitant with a significant decrease in the concentration of plasma PGI(2) and serum NO in IHPH and PHPH rats (P<0.05). At the same time, PVI decreased but SVR increased significantly (P<0.05). In both IHPH and PHPH rats, the COX-1 mRNA expression and the concentration of plasma PGI(2) after No synthase (NOS) blockade for 15 days were higher than those for 7 days, whereas the hyperdynamic circulatory state was improved after NOS blockade for 15 days compared with 7 days. The concentration of PGI(2) treated by INDO for 15 days was not significantly different from that after 7-day COX blockade, and hemodynamics restored hyperdynamic circulatory state.. The hyperdynamic circulatory state in rats with PHT is correlated with the concentration of serum NO. There is a possible interaction between PGI(2) and NO in the hyperhemodynamics of PHT. PGI(2) is probably not the mediator in the formation and development of the hyperdynamic circulatory state in rats with chronic PHT.

Topics: Animals; Cyclooxygenase 1; Epoprostenol; Gene Expression; Hypertension, Portal; Indomethacin; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Prostaglandin-Endoperoxide Synthases; Rats; Rats, Sprague-Dawley; RNA, Messenger; Splanchnic Circulation; Time Factors

To investigate the role of prostacyclin (PGI(2)) and nitric oxide (NO) in the development and maintenance of hyperdynamic circulatory state of chronic portal hypertensive rats.. Ninety male Sprague-Dawley rats were divided into three groups: intrahepatic portal hypertension (IHPH) group by injection of CCl(4), prehepatic portal hypertension (PHPH) group by partial stenosis of the portal vein and sham-operation control (SO) group. One week after the models were made, animals in each group were subdivided into 4 groups: saline controlled group (n = 23), Nomega-nitro-L-arginine (L-NNA) group (n = 21) group, indomethacin (INDO) group (n = 22) and high-dose heparin group (n = 24). The rats were administrated 1 mL of saline, L-NNA (3.3 mg/kg.d) and INDO (5 mg/kg.d) respectively through gastric tubes for one week, then heparin (200 IU/Kg/min) was given to rats by intravenous injection for an hour. Splanchnic and systemic hemodynamics were measured using radioactive microsphere techniques. The serum nitrate/nitrite (NO(2)(-)/NO(3)(-)) levels as a marker of production of NO were assessed by a colorimetric method, and concentration of 6-keto-PGF1alpha, a stable hydrolytic product of PGI(2), was determined by radioimmunoassay.. The concentrations of plasma 6-keto-PGF1alpha (pg/mL) and serum NO(2)(-)/NO(3)(-) (micromol/L) in IHPH rats (1123.85+/-153.64, 73.34+/-4.31) and PHPH rats (891.88+/-83.11, 75.21+/-6.89) were significantly higher than those in SO rats (725.53+/-105.54, 58.79+/-8.47) (P<0.05). Compared with SO rats, total peripheral vascular resistance (TPR) and spanchnic vascular resistance (SVR) decreased but cardiac index (CI) and portal venous inflow (PVI) increased obviously in IHPH and PHPH rats (P<0.05). L-NNA and indomethacin could decrease the concentrations of plasma 6-keto-PGF1alpha and serum NO(2)(-)/NO(3)(-) in IHPH and PHPH rats (P<0.05). Meanwhile, CI, FPP and PVI lowered but MAP, TPR and SVR increased (P<0.05). After deduction of the action of NO, there was no significant correlation between plasma PGI(2) level and hemodynamic parameters such as CI, TPR, PVI and SVR. However, after deduction of the action of PGI(2), NO still correlated highly with the hemodynamic parameters, indicating that there was a close correlation between NO and the hemodynamic parameters. After administration of high-dose heparin, plasma 6-keto-PGF(1alpha) concentrations in IHPH, PHPH and SO rats were significantly higher than those in rats administrated vehicle (P<0.05). On the contrary, levels of serum NO(2)(-)/NO(3)(-) in IHPH, PHPH and SO rats were significantly lower than those in rats administrated Vehicle (P<0.05). Compared with those rats administrated vehicle, the hemodynamic parameters of portal hypertensive rats, such as CI and PVI, declined significantly after administration of high-dose heparin (P<0.05), while TPR and SVR increased significantly (P<0.05).. It is NO rather than PGI(2) that is a mediator in the formation and maintenance of hyperdynamic circulatory state of chronic portal hypertensive rats.

Topics: Animals; Anticoagulants; Cyclooxygenase Inhibitors; Enzyme Inhibitors; Epoprostenol; Heparin; Hypertension, Portal; Indomethacin; Male; Nitric Oxide; Nitroarginine; Portal System; Rats; Rats, Sprague-Dawley; Splanchnic Circulation

Recent studies have shown that endothelial nitric oxide (NO) is involved in modulating the vascular response to vasoconstrictors in portal-systemic collaterals of portal hypertensive rats. This study investigated which isoform of NO synthase is involved in the collateral circulation of portal hypertensive rats.. The relaxation response to acetylcholine (10(-8) M, 10(-7) M and 10(-6) M) in norepinephrine (NE)-preconstricted portal-systemic collaterals was investigated after incubation with vehicle (Krebs solution), a preferential inducible NO synthase inhibitor (aminoguanidine [AG]), or a non-selective NO synthase inhibitor (Nomega-nitro-L-arginine [NNA]), in rats with partial portal vein ligation. Mean arterial pressure was measured before the perfusion experiments.. Bodyweight and mean arterial pressure before the perfusion studies were similar in the vehicle, AG and NNA groups. Preincubation with NNA, but not AG, produced a significant increase in baseline perfusion pressure compared with the vehicle group (p < 0.05). The increase in perfusion pressure in response to NE was enhanced in the presence of NNA (p < 0.05), but not AG. In addition, preincubation with NNA, but not AG, significantly suppressed acetylcholine-induced relaxation in the portal-systemic collaterals (p < 0.05).. These results suggest that constitutive, rather than inducible, NO synthase is involved in the vascular response to vasoconstrictors in the portal-systemic collaterals of portal hypertensive rats.

Topics: Acetylcholine; Animals; Collateral Circulation; Hypertension, Portal; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Portal System; Rats; Rats, Sprague-Dawley; Vasodilation

Endothelin-1 (ET-1) may induce intrahepatic vasoconstriction and consequently increase portal pressure. Endothelin-1 has been shown to exert a direct vasoconstrictive effect on the collateral vessels in partially portal vein-ligated rats with a high degree of portal-systemic shunting. This study investigated the collateral vascular responses to ET-1, the receptors in mediation and the regulation of ET-1 action by nitric oxide and prostaglandin in cirrhotic rats with a relatively low degree of portal-systemic shunting.. The portal-systemic collaterals of common bile duct-ligated (BDL) cirrhotic rats were tested by in situ perfusion. The concentration-response curves of collaterals to graded concentrations of ET-1 (10(-10)-10(-7) m) with or without BQ-123 (ET(A) receptor antagonist, 2 x 10(-6) m), BQ-788 (ET(B) receptor antagonist, 10(-7) m) or both were recorded. In addition, the collateral responses to ET-1 with preincubation of N(omega)-nitro-L-arginine (NNA, 10(-4) M), indomethacin (INDO, 10(-5) M) or in combination were assessed.. Endothelin-1 significantly increased the perfusion pressures of portal-systemic collaterals. The ET-1-induced constrictive effects were inhibited by BQ-123 or BQ-123 plus BQ-788 but not by BQ-788 alone. The inhibitory effect was greater in the combination group. Pretreatment of NNA or NNA plus INDO equivalently enhanced the response of ET-1 while pretreatment of INDO alone exerted no effect.. Endothelin-1 has a direct vasoconstrictive effect on the collaterals of BDL cirrhotic rats, mainly mediated by ET(A) receptor. Endogenous nitric oxide may play an important role in modulating the effects of ET-1 in the portal-systemic collaterals of BDL cirrhotic rats.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Antihypertensive Agents; Collateral Circulation; Common Bile Duct; Endothelin Receptor Antagonists; Endothelin-1; Enzyme Inhibitors; Hypertension, Portal; Indomethacin; Ligation; Liver Cirrhosis, Experimental; Male; Nitric Oxide; Nitroarginine; Oligopeptides; Peptides, Cyclic; Piperidines; Portal System; Prostaglandin Antagonists; Rats; Rats, Sprague-Dawley; Vasoconstriction; Vasoconstrictor Agents

To investigate the effects of prostacyclin (PGI(2)) and nitric oxide (NO) in the development of hyperdynamic circulatory state on chronic portal hypertensive rats.. Sixty-six male SD rats were divided into three groups, namely intrahepatic portal hypertension (IHPH) by injection of CCl(4), prehepatic portal hypertension (PHPH) by partial stenosis of the portal vein for 2 weeks and sham-operated controls (SO). Animals in each group were divided further into 3 subgroups and received N(omega)-nitro-L-arginine (L-NNA), indomethacin and saline (as control), respectively. Splanchnic and systemic hemodynamics was measured using radioactive microsphere techniques. The NO concentration in serum was determined by nitrates-nitrites which were measured using a colorimetric method, and concentration of PGI(2) was determined using specific radioimmunoassay for its stable hydrolytic product, 6-keto-PGF(1 alpha).. The concentrations of plasma 6-keto-PGF(1 alpha) and serum nitrates + nitrites in IHPH rats (1 123.85 +/- 153.64; 73.34 +/- 4.31) and in PHPH rats (891.88 +/- 83.11; 75.21 +/- 6.89) were significantly higher than those of SO rats (725.53 +/- 105.54;58.79 +/- 8.47). L-NNA and indomethacin could decrease the concentrations of plasma 6-keto-PGF(1 alpha) and serum nitrates + nitrites in IHPH and PHPH rats (P < 0.05). At the same time, CI, FPP and PVI were lowered while MAP, TPR and SVR were increased (P < 0.05). After deduction of NO action, there were no significant correlation between plasma PGI(2) level and hemodynamic parameters such as CI, TPR, PVI and SVR. However, after deduction of PGI(2) action, NO was still correlated highly with those hemodynamic parameters.. It is NO rather then PGI(2) that is a mediator in the formation and development of hyperdynamic circulatory state in chronic portal hypertensive rats.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Cyclooxygenase Inhibitors; Disease Models, Animal; Enzyme Inhibitors; Epoprostenol; Hemodynamics; Hypertension, Portal; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; omega-N-Methylarginine; Random Allocation; Rats; Rats, Sprague-Dawley

Portal hypertension induces neuroendocrine activation and a hyperkinetic circulation state. This study investigated the consequences of portal hypertension on heart structure and function. Intrahepatic portal hypertension was induced in male Sprague-Dawley rats by chronic bile duct ligation (CBDL). Six weeks later, CBDL rats showed higher plasma angiotensin-II and endothelin-1 (P <.01), 56% reduction in peripheral resistance and 73% reduction in pulmonary resistance (P <.01), 87% increase in cardiac index and 30% increase in heart weight (P <.01), and increased myocardial nitric oxide (NO) synthesis. In CBDL rats, macroscopic analysis demonstrated a 30% (P <.01) increase in cross-sectional area of the left ventricular (LV) wall without changes in the LV cavity or in the right ventricle (RV). Histomorphometric analysis revealed increased cell width (12%, P <.01) of cardiomyocytes from the LV of CBDL rats, but no differences in myocardial collagen content. Myocytes isolated from the LV were wider (12%) and longer (8%) than right ventricular myocytes (P <.01) in CBDL rats but not in controls. CBDL rats showed an increased expression of ANF and CK-B genes (P <.01). Isolated perfused CBDL hearts showed pressure/end-diastolic pressure curves and response to isoproterenol identical to sham hearts, although generated wall tension was reduced because of the increased wall thickness. Coronary resistance was markedly reduced. This reduction was abolished by inhibition of NO synthesis with N-nitro-L-arginine. Expression of eNOS was increased in CBDL hearts. In conclusion, portal hypertension associated to biliary cirrhosis induces marked LV hypertrophy and increased myocardial NO synthesis without detectable fibrosis or functional impairment. This observation could be relevant to patients with cirrhosis.

Topics: Animals; Bile Ducts; Cyclic GMP; Enzyme Inhibitors; Heart; Hypertension, Portal; Hypertrophy, Left Ventricular; In Vitro Techniques; Isoenzymes; Ligation; Liver Cirrhosis, Biliary; Male; Myocardium; Nitric Oxide Synthase; Nitroarginine; Organ Size; Rats; Rats, Sprague-Dawley

Systemic vasodilation is the initiating event of the hyperdynamic circulatory state, being most likely triggered by increased levels of vasodilators, primarily nitric oxide (NO). Endothelial NO synthase (eNOS) is responsible for this event. We tested the hypothesis that gene deletion of eNOS and inducible NOS (iNOS) may inhibit the development of the hyperdynamic circulatory state in portal hypertensive animals. To test this hypothesis, we used mice lacking eNOS (eNOS-/-) or eNOS/iNOS (eNOS/iNOS-/-) genes. A partial portal vein ligation (PVL) was used to induce portal hypertension. Sham-operated animals were used as a control. Hemodynamic characteristics were tested 2 wk after surgery. As opposed to our hypothesis, PVL also caused significant reduction in peripheral resistance in eNOS-/- compared with sham animals (0.33 +/- 0.02 vs. 0.41 +/- 0.03 mmHg. min x kg body wt x ml(-1); P = 0.04) and in eNOS/iNOS-/- animals with PVL compared with that of the sham-operated group (0.44 +/- 0.02 vs. 0.54 +/- 0.04; P = 0.03). This demonstrates that, despite gene deletion of eNOS, the knockout mice developed hyperdynamic circulation. Compensatory vasodilator molecule(s) are upregulated in place of NO in the systemic and splanchnic circulation in portal hypertensive animals.

Topics: Animals; Blood Circulation; Enzyme Inhibitors; Hemodynamics; Hypertension, Portal; Mice; Mice, Knockout; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroarginine

Portal hypertension is associated with increased hepatic and collateral resistance to an increased portal blood flow. Endothelin-1 (ET-1) can induce intrahepatic vasoconstriction and consequently increase portal pressure. It is unknown if ET-1 also modulates portal pressure by a direct vasoconstrictive effect on collaterals. This study investigated the collateral vascular responses to ET-1, the receptors in mediation, and the regulation of ET-1 action by nitric oxide and prostaglandin. The portal-systemic collaterals of partially portal vein-ligated rats were tested by in situ perfusion. The concentration-response curves of collaterals to graded concentrations of ET-1 (10(-10)-10(-7) mol/L) with or without BQ-123 (ET(A) receptor antagonist, 2 x 10(-6) mol/L), BQ-788 (ET(B) receptor antagonist, 10(-7) mol/L) or both were recorded. In addition, the collateral responses to ET-1 with preincubation of n(omega)-nitro-L-arginine (NNA; 100 mol/L), indomethacin (INDO; 10 mol/L), or in combination were performed. ET-1 increased the perfusion pressure of collaterals and its effect was significantly suppressed by BQ-123 alone and BQ-123 plus BQ-788, but not BQ-788 alone (P <.05). Incubation with NNA, INDO, or both significantly enhanced the response of collaterals to ET-1 (P < .05). These results show that ET-1 produces a direct vasoconstrictive effect on the collateral vessels of portal hypertensive rats. This effect is mediated by ET(A,) but not ET(B), receptors. Both nitric oxide and prostaglandin modulate the collateral vascular response to ET-1 and may therefore participate in the development and maintenance of portal hypertension.

Topics: Animals; Collateral Circulation; Cyclooxygenase Inhibitors; Drug Combinations; Endothelin Receptor Antagonists; Endothelin-1; Hypertension, Portal; Indomethacin; Male; Nitric Oxide; Nitroarginine; Oligopeptides; Peptides, Cyclic; Piperidines; Portal System; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptor, Endothelin B; Vasoconstriction

Angiogenesis plays a pivotal role in many processes. Here, we studied whether angiogenesis to basic fibroblast growth factor (bFGF) in normal and portal hypertensive rats requires nitric oxide (NO).. To measure angiogenesis in vivo, two Teflon rings filled with collagen I (Vitrogen 100) were fixed in the mesenteric cavity at day 0, with one supplemented with bFGF (100 ng). Portal hypertension was induced by partial portal vein ligation (PVL). Sham-operated rats served as controls (CON). The role of NO was tested by adding the NO formation antagonist N(omega)-nitro-L-arginine (NNA; 3.3 mg/kg per day) to the drinking water. After 16 days, rings were explanted and embedded, and vessels were morphometrically counted.. bFGF significantly stimulated vessel formation per implant in CON rats (from 624 +/- 97 without stimulation to 1123 +/- 171, n = 11, P < 0.01), but not in PVL rats (from 1106 +/- 174 without stimulation to 1046 +/- 202, n = 9). Without stimulation, numbers of ingrown vessels were significantly (P < 0.05) higher in PVL compared to CON rats. NNA substantially inhibited angiogenesis in both groups (P < 0.01). Vessel numbers were 202 +/- 124 for PVL (n = 5) and 197 +/- 14 for CON (n = 5) animals. bFGF did not reverse angiogenesis prevented by NNA (373 +/- 98 for PVL, 265 +/- 26 for CON, n = 5 per group, NS).. NO formation inhibition diminishes both unstimulated and bFGF-stimulated angiogenesis in CON rats. Moreover, bFGF cannot rescue NNA-inhibited angiogenesis in PVL rats.

Topics: Animals; Enzyme Inhibitors; Fibroblast Growth Factor 2; Hypertension, Portal; Male; Neovascularization, Physiologic; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley; Reference Values

Systemic and especially splanchnic arterial vasodilation accompany chronic portal hypertension. Different soluble mediators causing this vasodilation have been proposed, the strongest evidence being for nitric oxide (NO). No data exist if structural vascular changes may partly account for this vasodilatory state. Here, we developed a new in vivo quantitative angiogenesis assay in the abdominal cavity and determined if: 1) portal hypertensive rats show increased angiogenesis; and 2) angiogenesis is altered by inhibiting NO formation. Portal hypertension was induced by partial portal vein ligation (PVL). Sham-operated rats served as controls (CON). During the index operation (day 0), a teflon ring filled with collagen I (Vitrogen 100) was sutured in the mesenteric cavity. After 16 days, rings were explanted, embedded in paraffin, and ingrown vessels counted using a morphometry system. The role of NO was tested by adding an antagonist of NO formation (Nomega-nitro-L-arginine [NNA], 3.3 mg/kg/d) into the drinking water. The mean number of ingrown vessels per implant was significantly higher in PVL rats compared with CON rats, i.e., 1,453 +/- 187 versus 888 +/- 116, respectively (P <.05; N = 5 per group). NNA significantly (P <.01) inhibited angiogenesis in PVL (202 +/- 124; N = 5) and in CON (174 +/- 25; N = 6) rats, respectively. In contrast, the beta-adrenergic blocker, propranolol, did not prevent angiogenesis either in PVL or CON rats in a separate set of experiments (data not shown). The conclusions drawn from this study are that: 1) rats with portal hypertension show increased angiogenesis; and 2) inhibition of NO formation significantly prevents angiogenesis in both PVL and CON rats. Therefore, splanchnic vasodilation in chronic portal hypertension may also be a result of structural changes.

Topics: Adrenergic beta-Antagonists; Animals; Body Weight; Disease Models, Animal; Hypertension, Portal; Image Processing, Computer-Assisted; Implants, Experimental; Male; Neovascularization, Pathologic; Nitric Oxide; Nitroarginine; Propranolol; Rats; Rats, Sprague-Dawley

Chronic high blood flow and the hyperdynamic circulatory syndrome in portal hypertension are associated with endothelial constitutive nitric oxide (NO) synthase (eNOS) upregulation and increased NO release. In portal vein-ligated (PVL) rats the splanchnic circulation is not yet hyperdynamic on day 3 postoperatively. In vitro perfused superior mesenteric arteries (SMAs) of day 3 PVL and sham rats were challenged with increasing flow rates or the alpha-adrenoreceptor agonist methoxamine (30 and 100 microM) before and after incubation with the NO inhibitor, Nomega-nitro-L-arginine (L-NNA, 10(-4) M). Perfusate NO metabolite (NOx) concentrations were measured by chemiluminescence. PVL rats expressed a significant hyporesponsiveness to increases in flow rate or methoxamine that was overcome by incubation with L-NNA. The PVL vasculature showed significantly higher slopes of NOx production vs. flow-induced shear stress, higher increases in perfusate NOx concentration in response to methoxamine, and higher eNOS protein levels (Western blot) compared with sham rats. In conclusion, eNOS-upregulation and increased NO release by the SMA endothelium occur before the development of the hyperdynamic splanchnic circulation, suggesting a primary role of NO in the pathogenesis of arterial vasodilatation.

Topics: Animals; Blood Flow Velocity; Blood Pressure; Endothelium, Vascular; Hypertension, Portal; Kinetics; Luminescent Measurements; Male; Mesenteric Artery, Superior; Methoxamine; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Rats; Rats, Sprague-Dawley; Splanchnic Circulation; Stress, Mechanical

This study investigated the effect of vasopressin on portal-systemic collaterals in portal hypertensive rats and the influence of nitric oxide (NO) and prostaglandin on the responsiveness of collateral vessels to vasopressin. The vascular responsiveness to graded concentrations of vasopressin was tested with or without the incubation of n(omega)-nitro-L-arginine (NNA) (100 micromol/L) and/or indomethacin (10 micromol/L) in perfused collateral vascular beds of rats with portal hypertension induced by partial portal vein ligation. In addition, concentration-response curves to vasopressin with incubation of a vasopressin V(1) receptor antagonist d(CH(2))(5)Tyr(Me) arginine vasopressin and concentration-response curves to a V(2) receptor agonist 1-desamino-8-D-arginine vasopressin were performed. Vasopressin significantly increased the perfusion pressure of collaterals, and this effect was suppressed by the addition of the V(1) receptor antagonist. Perfusion with the V(2) receptor agonist had no effect on the collaterals. Incubation with NNA, indomethacin, or both significantly potentiated the response of collaterals to vasopressin. In addition, the pressor response to vasopressin in the combination group was significantly higher than that in the NNA-alone group. The results show that vasopressin produces a direct vasoconstrictive effect on the portal-systemic collaterals of portal hypertensive rats. This effect is mediated by the vasopressin V(1,) but not V(2), receptors. The attenuation of the response to vasopressin by NO and prostaglandin suggest a function role of both mediators in the regulation of the portal-systemic collateral circulation in portal hypertensive rats.

Topics: Animals; Collateral Circulation; Deamino Arginine Vasopressin; Dose-Response Relationship, Drug; Hypertension, Portal; Indomethacin; Male; Nitric Oxide; Nitroarginine; Portal System; Prostaglandins; Rats; Rats, Sprague-Dawley; Vasopressins

Portal hypertension is associated with systemic vasodilatation and vascular hyporeactivity, and is reversed by inhibiting nitric oxide biosynthesis. Nitric oxide and calcitonin gene-related peptide are neurotransmitters of non-adrenergic non-cholinergic nerves. The role of nitric oxide and calcitonin gene-related peptide in nerve-stimulated vasodilatation in portal hypertension is unknown.. We tested (i) if in vitro perfused superior mesenteric arterial vascular beds of portal hypertensive rats (induced by partial portal vein ligation) showed an increased vasodilatation to periarterial nerve stimulation compared to normal controls, and (ii) if this vasodilatation was modulated by nitric oxide and calcitonin gene-related peptide antagonism.. Vasodilatatory responses to periarterial nerve stimulation (10 V, 1 ms) with increasing frequencies (Hertz, 2-12) in preconstricted vessels (methoxamine and guanethidine) were significantly smaller in vessel preparations of control (n=8) compared to portal hypertensive (n=7) rats, values with 8 Hertz being 32.3+/-3.6% and 44.9+/-3.6%, respectively (p<0.05). This difference was reversed by inhibiting nitric oxide and calcitonin gene-related peptide action with the nitric oxide-biosynthesis inhibitor N(omega)-Nitro-L-arginine, values for 8 Hertz being 28.7+/-4.8% (controls) and 37.8+/-3.3% (portal hypertensive, ns) or with the calcitonin gene-related peptide antagonist CGRP8-37, values being 25.2+/-2.8% (controls) and 27.8+/-4.2% (portal hypertensive, ns), respectively (n=4-6 per group). Vasodilatation to the beta-agonist isoproterenol was not significantly different between groups with and without calcitonin gene-related peptide and nitric oxide antagonism.. Portal hypertensive rats display a significantly enhanced vasodilatation to periarterial nerve stimulation, which is reversed by inhibiting the non-adrenergic non-cholinergic neurotransmitters nitric oxide and especially calcitonin gene-related peptide.

Topics: Animals; Calcitonin Gene-Related Peptide; Electric Stimulation; Hypertension, Portal; Male; Mesenteric Artery, Superior; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Peptide Fragments; Rats; Rats, Sprague-Dawley; Reference Values; Sympathetic Nervous System; Vasodilation

Increased nitric oxide production has been implicated in impaired vascular responsiveness to vasoconstrictors in portal hypertension. However, there is no firm evidence concerning the involved nitric oxide synthase isoform. The present study investigated the possible contribution of one nitric oxide synthase isoform, the endothelial constitutive Ca2+-calmodulin dependent, in the overproduction of nitric oxide in portal hypertension.. Vascular responses to norepinephrine and acetylcholine were evaluated in isolated thoracic aortic rings from normal and portal vein stenosed rats.. An impaired concentration-dependent contraction to norepinephrine was observed in intact rings from portal hypertensive rats compared to controls. The hyporeactivity to norepinephrine was reversed after endothelium denudation, the inhibition of nitric oxide synthase with L-NOARG or the inhibition of calmodulin with W-7, but not after pre-incubation with indomethacin. Stimulation of intact rings with norepinephrine after the inhibition of calmodulin with calmidazolium was followed by a decreased vascular response in vessels from normal rats but not in those from portal hypertensive rats. Stimulation of intact rings with norepinephrine in a Ca2+-free medium was followed by a decreased vascular response in vessels from both portal hypertensive and normal rats. No difference in vasoconstrictive responses was observed between the two groups after calmidazolium or in a Ca2+-free medium. Relaxation induced by acetylcholine in norepinephrine-precontracted rings was more marked in rings from portal hypertensive rats than in controls. No differences in the vasodilator responses were observed after relaxations had been inhibited by the removal of the endothelium, pre-incubation with L-NOARG, indomethacin, W-7 or calmidazolium and in a Ca2+-free medium.. This study demonstrates the involvement of the endothelial constitutive Ca2+-calmodulin dependent nitric oxide synthase isoform in the overproduction of nitric oxide in portal hypertension.

Topics: Animals; Aorta, Thoracic; Calcium-Calmodulin-Dependent Protein Kinases; Cyclooxygenase Inhibitors; Disease Models, Animal; Endothelium, Vascular; Enzyme Inhibitors; Hypertension, Portal; Indomethacin; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Norepinephrine; Rats; Rats, Sprague-Dawley; Sulfonamides; Vasoconstriction; Vasoconstrictor Agents; Vasodilator Agents

Portal hypertension (PH) is associated with a hyperdynamic splanchnic circulation, partially mediated by nitric oxide-dependent mechanisms. The aim of the present study was to evaluate the influence of PH and nitric oxide on pancreatic islet blood flow. PH was induced by a calibrated stenosis of the portal vein in male Sprague-Dawley rats. Control were sham-operated. Ten days later pancreatic, duodenal, colonic, and arterial hepatic blood flows were measured with microspheres. All splanchnic blood flow values were markedly increased in the PH rats. The fraction of whole pancreatic blood flow diverted through the islets increased from approximately 5 to 15%. Intravenous administration of the nitric oxide synthase inhibitor NG-nitro-L-arginine (25 mg/kg body weight) in rats with PH 10 min before blood flow measurements decreased pancreatic, duodenal, colonic, and arterial hepatic blood flow to control values. Pancreatic islet blood flow was also decreased, but more markedly than that of the whole pancreas. Pancreatic islet morphology was normal, and the rate of islet cell replication was not influenced. PH induced a preferential increase in pancreatic islet blood flow, which is likely to be associated with an increased production of nitric oxide.

Topics: Animals; Blood Flow Velocity; Enzyme Inhibitors; Hypertension, Portal; Islets of Langerhans; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Splanchnic Circulation

To evaluate the role of the inducible and endothelial constitutive nitric oxide synthase in vascular hyporeactivity to vasopressors in portal hypertension, in vitro experiments were performed on intact and endothelium-denuded isolated thoracic aortic rings from portal vein-ligated and sham-operated rats in control conditions, in the presence of aminoguanidine alone, considered to be a selective inhibitor of the inducible nitric oxide synthase, and of aminoguanidine and the nonselective nitric oxide synthase inhibitor N(G)-nitro-L-arginine. In control conditions, hyporeactivity to noradrenaline was observed in both rings with and without endothelium from portal hypertensive versus sham-operated rats. In the rings with endothelium, aminoguanidine reverted this hyporeactivity in portal hypertensive rats. N(G)-Nitro-L-arginine caused an additional shift to the left of the concentration-response curves to noradrenaline in portal hypertensive and a similar shift in sham-operated rats. In the endothelium-denuded rings, aminoguanidine caused no significant changes in portal hypertensive rats, whereas a significant shift to the right in the sham-operated rats was noted, however similar as the shift in the time controls not preincubated with aminoguanidine. No significant further changes were observed after preincubation with the two inhibitors. The endothelium-dependent relaxations to acetylcholine were attenuated in portal hypertensive versus sham-operated rats; addition of aminoguanidine shifted the relaxation curves to the left in portal hypertensive but not in sham-operated rats. These results provide indirect evidence for an increased activity of the inducible nitric oxide synthase in the intact aortic rings but not in the endothelium-denuded rings from portal vein-ligated rats, where other factors seem to be responsible for the observed hyporeactivity to noradrenaline. The endothelial constitutive nitric oxide synthase in rings from portal vein-ligated rats shows a reduced activity which is alleviated after inhibition of the inducible enzyme by aminoguanidine.

Topics: Acetylcholine; Animals; Aorta, Thoracic; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Induction; Enzyme Inhibitors; Guanidines; Hypertension, Portal; In Vitro Techniques; Male; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Norepinephrine; Rats; Rats, Wistar

Portal hypertension goes along with vascular hyporeactivity, partly mediated by nitric oxide (NO). Interactions between the adrenergic nervous system and NO in portal hypertension are undetermined. We tested (1) whether superior mesenteric arterial beds of portal hypertensive rats have an altered sensitivity to periarterial nerve stimulation (PNS) and (2) the role of NO in modulating nerve-stimulated responses. Vasopressor responses to PNS (Hz, 2-32) were similar in preparations of partial portal vein-ligated (PVL, n = 12) and control (CON, n = 12) rats (60.0 +/- 6.7 and 47.8 +/- 6.1 CmH2O respectively) for 24 Hz (NS), but sensitivity of vessels of portal hypertensive animals displayed a significant rightward shift [Hz needed for 50% of maximal response (HZ50) being 15.5 +/- 0.4 and 12.9 +/- 0.6 for PVL and CON respectively, P < 0.001]. NO formation inhibition by N omega-nitro-L-arginine (10(-4) mol L-1) significantly increased responses to PNS (P < 0.05), the absolute values for 24 Hz being 101.4 +/- 11.7 cmH2O for PVL (n = 8) and 86.4 +/- 11.4 cmH2O for CON (n = 7) (NS). NO formation inhibition reversed the hyposensitivity in preparations of PVL, Hz50 being 13.9 +/- 0.5 and 13.2 +/- 0.2 for PVL and CON respectively (NS). Adrenergic receptor antagonism with prazosin (10(-7) mol L-1) and yohimbine (10(-6) mol L-1) inhibited PNS-mediated vasopressor reactivity (n = 6 per group, P < 0.001), confirming the nervous origin of vasoconstrictor responses. It is concluded that (1) portal hypertension goes along with a significant hyposensitivity to PNS and (2) this hyposensitivity is reversed by NO-formation inhibition

Topics: Animals; Electric Stimulation; Hypertension, Portal; Male; Nitric Oxide; Nitroarginine; Peripheral Nerves; Prazosin; Rats; Rats, Sprague-Dawley; Vasoconstriction

Chronically portal-hypertensive rats show in vitro vascular hyporeactivity in large part mediated by the endothelium-derived vasodilator nitric oxide. We tested whether long-term octreotide treatment (15 micrograms/kg subcutaneously in 5% D/W, 8-hourly) corrects the in vitro vascular hyporeactivity. Increases in perfusion pressures (delta mm Hg) to potassium chloride (30-300 mmol/L) of in vitro perfused superior mesenteric arterial vascular beds of partial portal vein-ligated (PVL) rats were significantly (P < .05) higher in octreotide (n = 9) compared with placebo (n = 10, 5% D/W) treated animals. Octreotide significantly (P < .05) increased mean arterial pressure compared with placebo, the values being 129 +/- 3 and 117 +/- 4 mm Hg, respectively. Furthermore, a significant (P < .001) correlation was observed between in vitro vascular reactivity and mean arterial pressure. Incubation of separate vascular beds (n = 7 for both PVL and sham-operated rats) with octreotide (10(-6) mol/L) did not enhance pressure responses to 125 mmol/L potassium chloride, and failed to increase perfusion pressures in preconstricted vessel preparations (n = 6), excluding a direct inhibitory effect on NO. In summary, long-term octreotide treatment prevents in vitro vascular hyporeactivity in prehepatic portal-hypertensive rats, and octreotide does not exert its action through direct effects on endothelium-derived NO.

Topics: Animals; Arginine; Blood Pressure; Enzyme Inhibitors; Hypertension, Portal; In Vitro Techniques; Male; Mesenteric Artery, Superior; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Octreotide; Potassium Chloride; Rats; Rats, Sprague-Dawley; Stimulation, Chemical; Vasoconstriction; Vasoconstrictor Agents

The role of nitric oxide (NO) in the hyperkinetic circulation in portal hypertension has not been clearly elucidated. Different doses of NO inhibitors, haemodynamic values and experimental conditions might explain the discrepant results. The aim of the present study was to investigate the acute effects of a specific biosynthesis inhibitor of NO, Nomega-nitro-L-arginine (L-NNA), on the systemic and splanchnic circulation in normal conscious rats and rats with portal hypertension due to either partial portal vein stenosis or secondary biliary cirrhosis. The administration of L-NNA (15 to 960 micrograms.kg-1.min-1) induced a significant dose dependent increase in arterial pressure which was not different among the three groups of rats. Following an acute and maximal vasopressive dose of L-NNA (1 mg.kg-1.min-1) cardiac index decreased more in portal vein stenosed and cirrhotic rats (-45 +/- 3% and -45 +/- 2%, respectively) than in normal rats (-31 +/- 2%), and systemic vascular resistance increased more in the two groups of portal hypertensive rats than in normals (+ 161 +/- 13% and + 154 +/- 10% vs + 85 +/- 6%, respectively). L-NNA caused a greater decrease in portal tributary blood flow in portal vein stenosed and cirrhotic rats (-63 +/- 4% and -55 +/- 4%, respectively) than in normal rats (-45 +/- 6%). Similarly, the increase in portal territory vascular resistance was significantly more marked in portal vein stenosed and cirrhotic rats (+ 337 +/- 62% and + 214 +/- 24%, respectively) than in normal rats (+ 153 +/- 23%). Portal pressure did not change. Following the acute administration of L-NNA, no significant difference in splanchnic and systemic haemodynamics were noted between portal vein stenosed and normal rats, except for portal pressure. In cirrhotic rats, splanchnic and systemic values remained different from normal rats. This study confirms that NO plays a role in the haemodynamic changes in portal hypertension, and shows that NO inhibitors have a dose-dependent effect in conscious portal hypertensive rats.

Topics: Animals; Arginine; Consciousness; Constriction; Dose-Response Relationship, Drug; Enzyme Inhibitors; Hemodynamics; Hypertension, Portal; Liver Cirrhosis, Biliary; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Portal Vein; Rats; Rats, Sprague-Dawley; Splanchnic Circulation; Vasoconstriction

Hyporesponsiveness to vasoconstrictors in portal hypertension has been shown to involve increased production of nitric oxide in large arteries in vitro. Small arteries (diameter 50-500 microns) are partly responsible for peripheral resistance and probably have different regulatory mechanisms from large arteries. The purpose of this study was to investigate the hyporeactivity of small mesenteric resistance arteries in portal hypertensive rats and to determine the role of nitric oxide and prostaglandins in this hyporesponsiveness.. Third branch mesenteric arteries from normal and portal hypertensive rats obtained by portal vein ligation were isolated and suspended in myographs for isometric tension recording. Reactivity to vasoconstrictors was assessed by dose-responses to phenylephrine (Phe 10(-8) to 10(-3) M) and by potassium chloride (KCl 45 mM). Acetylcholine (Ach 10(-5) M) was administered in pre-contracted KCl 45 mM arterial rings to evaluate endothelium-dependent relaxation. Pre-incubations with N-nitro-L-arginine (L-NNA 10(-4) M, a specific inhibitor of nitric oxide synthase, or with indomethacin (10(-5) M), a specific inhibitor of cyclo-oxygenase, were performed to compare the individual roles of nitric oxide and prostaglandins in KCl 45 mM-induced contractions.. Impaired responses to Phe (3731 +/- 851 microN and 5971 +/- 745 microN, respectively; p < 0.05) and to KCl (2197 +/- 251 vs 2804 +/- 222 microN, respectively; p < 0.05) were observed in mesenteric resistance arterial rings from portal hypertensive rats compared to rings from normal rats. Ach-dependent relaxation did not significantly differ between normal (-25.7 +/- 5.1%) and portal hypertensive (-17.3 +/- 3.3%) rats. Indomethacin induced a similar significant increase in KCl-induced contraction in normal (3472 +/- 400 microN) and portal hypertensive (3432 +/- 654 rats. Nitric oxide synthesis inhibition had no effect in normal rats (3032 +/- 368 microN) but significantly increased KCl-induced contraction in portal hypertensive rats (3331 +/- 551 microN).. These results demonstrate the existence of a hyporesponsiveness to vasoconstrictors in small mesenteric resistance arteries of portal hypertensive rats, which seems to be due to increased production of nitric oxide.

Topics: Acetylcholine; Animals; Dose-Response Relationship, Drug; Hypertension, Portal; Indomethacin; Male; Mesenteric Arteries; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Phenylephrine; Potassium Chloride; Prostaglandins; Rats; Rats, Sprague-Dawley; Reference Values; Vascular Resistance; Vasoconstriction

The hyperdynamic circulation of cirrhosis and portal hypertension has been postulated to be due to the vasodilatory effects of nitric oxide. However, studies using pharmacological inhibitors of nitric oxide synthase have yielded conflicting results. We aimed to measure nitric oxide synthase activity in tissues from two different rat models of cirrhosis and portal hypertension.. Cirrhosis was induced by chronic bile duct ligation, and prehepatic portal hypertension by portal vein stenosis. Controls were sham-operated. A fourth group was treated with lipopolysaccharide endotoxin. Ca(2+)-dependent and Ca(2+)-independent nitric oxide synthase activity was assayed by measuring the conversion rate of 14C-arginine to 14C-citrulline in homogenates of stomach, jejunum, liver, kidney and aorta.. Jejunal homogenates from the portal vein-stenosed rats showed a significant 10-fold elevation of Ca(2+)-dependent nitric oxide synthase activity. Cirrhotic rat kidney showed significantly decreased Ca(2+)-dependent and Ca(2+)-independent nitric oxide synthase activity. Endotoxin treatment increased Ca(2+)-independent nitric oxide synthase activity in jejunum and liver. There was no increase in Ca(2+)-independent nitric oxide synthase activity in any tissues from cirrhotic or portal hypertensive rats.. We conclude that the lack of increase in Ca(2+)-independent nitric oxide synthase activity does not support the hypothesis that nitric oxide is the major cause of hyperdynamic circulation in cirrhosis.

Topics: Animals; Calcium; Hypertension, Portal; Liver Cirrhosis, Experimental; Male; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley

In the present study we have evaluated the role of nitric oxide and prostaglandins in the renal vascular response to a vasoconstrictor (methoxamine) and to endothelium-dependent (acetylcholine) and independent (sodium nitroprusside) vasodilators.. The experiments were performed in isolated and perfused kidneys of portal vein ligated and sham rats under various treatments.. Baseline renal perfusion pressure was lower in the portal vein ligated than in the sham group (37.2 +/- 2.6 vs 48.4 +/- 2.5 mmHg). Indomethacin (10(-5)M) did not modify baseline renal perfusion pressure in any group, but the nitric oxide inhibitor N(W)-Nitro-L-Arginine (10(-4) M) increased it in both sham and portal vein ligated kidneys, but without abolishing the differences between them. The vasoconstrictor renal response to methoxamine was blunted in portal vein ligated rats compared to controls. Indomethacin did not modify this renal hyporesponsiveness, but N(W)-Nitro-L-Arginine completely abolished it. In another set of experiments, both acetylcholine and nitroprusside caused dose-dependent vasodilation in kidneys, preconstricted with methoxamine, from sham and portal vein ligated rats, and there were no significant differences between them. N(W)-Nitro-L-Arginine reduced acetylcholine-induced vasodilation and did not modify the vasodilation evoked by nitroprusside.. These results indicate that the renal vasculature of portal vein ligated rats shows a basal reduction in perfusion resistance that is not related to nitric oxide or prostaglandins. However, increased nitric oxide production interferes with the effects of the alfa-agonist methoxamine. This suggests that nitric oxide plays an important role in the modulation of the renal vascular responses to vasoconstrictors in portal hypertension.

Topics: Acetylcholine; Animals; Enzyme Inhibitors; Hypertension, Portal; In Vitro Techniques; Indomethacin; Kidney; Male; Methoxamine; Nitric Oxide; Nitroarginine; Nitroprusside; Perfusion; Prostaglandins; Rats; Rats, Sprague-Dawley; Renal Circulation; Vasoconstriction; Vasodilator Agents

To test the possible role of nitric oxide production in long-term portal vein ligation in the rat, where the hyperdynamic circulation was reported to be absent, in vivo experiments on isolated thoracic aortic rings from partial portal vein ligated or sham-operated rats were performed, 6 months postoperatively. The concentration-response curves to noradrenaline of both intact and endothelium-denuded rings from portal hypertensive rats were significantly shifted to the right as compared to those from sham-operated animals. In intact rings, addition of NG-nitro-L-arginine, a specific inhibitor of nitric oxide synthase, resulted in a significant shift of the curves to the left in sham-operated and portal vein ligated rats. In endothelium-denuded rings, addition of NG-nitro-L-arginine resulted in a significant shift of the curves to the left in portal vein ligated but not in sham-operated animals. After blockade of the nitric oxide biosynthesis with NG-nitro-L-arginine, the negative logarithm of the concentration of nonadrenaline causing half-maximal response did not significantly differ any more between portal vein ligated and sham-operated rats; in endothelium-denuded rings hyporeactivity to noradrenaline persisted in portal vein ligated rats. Only in the intact rings did NG-nitro-L-arginine significantly increase the maximal contractions. No differences were demonstrated in endothelium-dependent relaxations to acetylcholine between sham-operated and portal hypertensive animals. From these results, it can be concluded that in vitro aortic hyporeactivity to noradrenaline is still present in long-term portal vein ligated rats, and that it results at least partially from activation of the L-arginine: nitric oxide pathway in the aortic vascular wall.

Topics: Animals; Aorta, Thoracic; Arginine; Enzyme Inhibitors; Hypertension, Portal; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Norepinephrine; Rats; Rats, Wistar; Vasoconstriction; Vasoconstrictor Agents

Nitric oxide, a vasodilator synthesized from L-arginine by vascular endothelial cells, may play a role in the development of portal-systemic collaterals. This study investigated the effect of long-term inhibition of NO secretion on portal systemic shunting.. Systemic and splanchnic hemodynamics and the degree of portal-systemic shunting were evaluated in partial portal vein-ligated rats after administration of placebo (0.9% saline) or N omega-nitro-L-arginine (NNA) (approximately 2 micrograms.kg-1 x min-1) intravenously for 6 days.. NNA treatment induced increases in splanchnic arterial resistance (P < 0.001) and portal-collateral resistance (P < 0.05) and a decrease in portal venous inflow (P < 0.05). Portal pressure was not changed (NS). The splenic-systemic shunting was significantly decreased from 81% +/- 5% in the placebo-treated group to 69% +/- 4% in the NNA-treated group (P < 0.05), paralleled by an insignificant reduction in the mesenteric-systemic shunting (64% +/- 7% vs. 50% +/- 6%, NS). The attenuation of portal-systemic shunting by NNA was further shown by an increase in the vascular resistance of portal-systemic collateral venous bed using an in situ portal-systemic collateral perfusion model (1.27 +/- 0.05 vs. 1.07 +/- 0.03 cm H2O.mL-1 x min-1; P < 0.001).. The results show that in portal hypertensive rats, NNA reduces portal-systemic shunting without reducing portal pressure, suggesting that NO plays a role in the collateralization of the portal system. In addition, high flow through the portal-collateral bed is probably an important driving force that is independent of portal hypertension for the development of portal-systemic shunting in portal-hypertensive rats.

Topics: Animals; Arginine; Hemodynamics; Hypertension, Portal; Male; Mesentery; Nitric Oxide; Nitroarginine; Perfusion; Portal System; Rats; Rats, Sprague-Dawley

In portal hypertensive states, peripheral vasodilation leads to sodium retention and plasma volume expansion. N omega-nitro-L-arginine, a specific biosynthesis inhibitor of the vasodilator nitric oxide, has been shown to acutely reverse peripheral vasodilation and the vascular hyporesponsiveness to endogenous and exogenous vasoconstrictors observed in portal hypertensive rats. This study investigated whether N omega-nitro-L-arginine treatment in portal hypertensive rats prevents peripheral vasodilation and therefore ameliorates plasma volume expansion and sodium retention. For 2 days before partial portal vein ligation or sham operation and then continuously for 4 days after the operation, animals received either placebo (0.9% saline) or N omega-nitro-L-arginine (approximately 2 micrograms/kg/min) intravenously through a subcutaneously implanted Alzet osmotic pump (model 2ML1; Alza, Palo Alto, CA). In portal hypertensive rats, N omega-nitro-L-arginine treatment significantly increased mean arterial pressure (placebo vs. N omega-nitro-L-arginine, 123 +/- 4 vs. 150 +/- 2 mm Hg, respectively; p < 0.001) and systemic vascular resistance (3.8 +/- 0.2 vs. 5.6 +/- 0.3 mm Hg/ml/min/100 gm body weight; p < 0.001), associated with a decrease in the cardiac index (33.5 +/- 1.0 vs. 27.0 +/- 1.1 ml/min/100 gm body weight; p < 0.001). N omega-nitro-L-arginine treatment also induced a decrease in plasma volume (4.6 +/- 0.1 vs. 4.1 +/- 0.1 ml/100 gm body weight; p < 0.001) and extracellular sodium space (39.4 +/- 0.7 vs. 37.4 +/- 0.4 ml/100 gm body weight; p < 0.05) without changes in serum sodium.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Arginine; Blood Pressure; Blood Volume; Capillaries; Extracellular Space; Hemodynamics; Hypertension, Portal; Male; Nitroarginine; Rats; Rats, Sprague-Dawley; Sodium; Vasodilation

This study examined whether an increased activity of the endothelium-derived relaxing factor, nitric oxide, may account for the hyporesponsiveness to vasoconstrictors in portal hypertension. We performed dose-response curves to methoxamine, an alpha-adrenoceptor agonist, with and without N omega-nitro-L-arginine, a specific inhibitor of nitric oxide synthesis, in experimental portal hypertension. Partial portal vein-ligated or sham-operated rats were pretreated with a continuous intravenous infusion of either N omega-nitro-L-arginine (50 micrograms.kg-1.min-1) or saline. Thirty minutes after starting the infusion of N omega-nitro-L-arginine or saline an infusion of methoxamine (10, 30 and 100 micrograms.kg-1.min-1) was added. Total peripheral resistance was calculated from mean arterial pressure and cardiac index. Repeated measurements of cardiac index were performed by a thermodilution technique. In portal vein-ligated rats pretreated with saline, the increase in total peripheral resistance after methoxamine infusion was significantly less than that of sham-operated rats (0.2 +/- 0.1 vs. 1.0 +/- 0.3, 0.6 +/- 0.1 vs. 1.6 +/- 0.3 and 3.7 +/- 0.5 vs. 6.1 +/- 0.7 mm Hg.ml-1.min.100 gm, p less than 0.05, methoxamine 10, 30 and 100 micrograms.kg-1.min-1, respectively). In the presence of N omega-nitro-L-arginine, the change in total peripheral resistance after methoxamine infusion was similar in both groups (p greater than 0.05). In conclusion, this study demonstrates that a vascular hyporesponsiveness to methoxamine is present in portal vein-ligated rats and that this hyporesponsiveness is reversed by blockade of nitric oxide.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Arginine; Blood Pressure; Blood Vessels; Dose-Response Relationship, Drug; Hypertension, Portal; Male; Methoxamine; Nitric Oxide; Nitroarginine; Rats; Rats, Sprague-Dawley; Vascular Resistance

The role of endogenous endothelium-derived relaxing factor (EDRF) in splanchnic blood flow was assessed in normal and portal vein-stenosed rats (PSRs). Specific and maximal inhibition of EDRF was achieved by intravenous administration of NG-nitro-L-arginine (L-NOARG) as a 1.75 mumol/kg bolus, followed by constant infusion of 1.75 mumol/kg for 20 min. Pretreatment with L-arginine (175 mumol/kg iv) completely blocked both hypertension and the reduction in blood flow induced by L-NOARG. Pretreatment with D-arginine (175 mumol/kg iv) and prazosin (500 micrograms/kg iv) did not attenuate the pressor effect of L-NOARG. These results indicate that L-NOARG selectively blocks EDRF. The blood flow to the stomach, duodenum, jejunum, ileum, cecum, and colon in control rats was 81.1 +/- 8.7, 199.1 +/- 21.9, 153.3 +/- 20.0, 68.6 +/- 10.6, 79.4 +/- 11.8, and 59.3 +/- 7.8 ml.min-1.100 g-1, respectively, and in PSRs was 141.4 +/- 10.8, 244.0 +/- 10.4, 208.3 +/- 9.8, 126.8 +/- 13.0, 166.9 +/- 16.5, and 94.8 +/- 4.7 ml.min-1.100 g-1, respectively. Blood flow was measured using the radioactive microsphere method. L-NOARG significantly reduced blood flow to the stomach, duodenum, jejunum, ileum, cecum, and colon in control rats by 47, 44, 48, 55, 40, and 41%, respectively, and in PSRs by 30, 27, 36, 33, 28, and 23%, respectively. The magnitude of blood flow reduction in PSRs was lower than in normal rats. These results indicate that EDRF plays an important role in control of the splanchnic circulation, but its effect on the hyperdynamic circulation observed in PSRs is insignificant.

Topics: Animals; Arginine; Chronic Disease; Hypertension, Portal; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Inbred Strains; Reference Values; Regional Blood Flow; Renal Circulation; Splanchnic Circulation; Testis

The endothelial cell plays an important role in the local control of vascular smooth muscle tone. Portal hypertension is accompanied by systemic vasodilatation and a decreased response to vasoconstrictors, changes especially evident in the superior mesenteric arterial bed. To evaluate a possible effect of the locally released endothelium-derived relaxing factor nitric oxide (NO), we tested the effect of NO blockade in in vitro perfused superior mesenteric arterial beds of normal (sham) and portal hypertensive (PVL) rats, induced by partial portal vein ligation. A significant (n = 7/group; P = 0.02) hyporeactivity to the vasoconstrictive properties of the alpha-adrenoceptor agonist methoxamine (3 x 10(-6) to 3 x 10(-4) M) was prevented by blocking NO formation in PVL compared with sham rats, using the stereospecific biosynthesis antagonist N omega-nitro-L-arginine (10(-4) M, n = 7/group; NS for all methoxamine concentrations tested). This effect was reversed by the NO precursor L-arginine (10(-3) M, n = 5/group). In conclusion, these in vitro results in mesenteric vessels demonstrate that 1) portal hypertension is accompanied by a hyporeactivity to the vasopressor methoxamine and 2) locally released NO in this preparation is responsible for the decreased vasoconstrictive response.

Topics: Acetylcholine; Animals; Arginine; Dose-Response Relationship, Drug; Hypertension, Portal; Kinetics; Male; Mesenteric Arteries; Methoxamine; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Nitroprusside; Perfusion; Rats; Rats, Inbred Strains