Renal effects of nitric oxide synthesis inhibition in cirrhotic rats

Can Chronic Nitric Oxide Inhibition Improve Liver and Renal Dysfunction in Bile Duct Ligated Rats?

The aims of the present work were to study the effects of chronic NO inhibition on liver cirrhosis and to analyze its relationship with liver and kidney damage markers. Two inhibitors of NO synthesis (inducible NO synthase (iNOS) inhibitor, aminoguanidine (AG), and nonselective NOS inhibitor, L-nitroarginine methyl ester (L-NAME)) were administered for 6 weeks to bile duct ligated (BDL) rats 3 days after surgery. The present study showed that BDL was associated with liver injury and renal impairment. BDL increased liver NO content and myeloperoxidase (MPO) activity. This was corroborated by increased oxidative stress, TNF-α, TGF-1β, and MMP-13 genes overexpression. Although both drugs reduced NO synthesis and TNF-α gene overexpression, only AG improved renal dysfunction and liver damage and reduced liver oxidative stress. However, L-NAME exacerbated liver and renal dysfunction. Both drugs failed to modulate TGF-1β and MMP-13 genes overexpression. In conclusion, inhibition of NO production by constitutive nitric oxide synthase (cNOS) plays a crucial role in liver injury and renal dysfunction while inhibition of iNOS by AG has beneficial effect. TNF-α is not the main cytokine responsible for liver injury in BDL model. Nitric oxide inhibition did not stop the progression of cholestatic liver damage.

Chronic nitric oxide synthase inhibition exacerbates renal dysfunction in cirrhotic rats

The present study investigated sodium balance and renal tubular function in cirrhotic rats with chronic blockade of the nitric oxide (NO) system. Rats were treated with the nonselective NO synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME) starting on the day of common bile duct ligation (CBL). Three weeks of daily sodium balance studies showed that CBL rats developed sodium retention compared with sham-operated rats and that l-NAME treatment dose dependently deteriorated cumulative sodium balance by reducing urinary sodium excretion. Five weeks after CBL, renal clearance studies were performed, followed by Western blotting of the electroneutral type 3 sodium/proton exchanger (NHE3) and the Na-K-ATPase present in proximal tubules. Untreated CBL rats showed a decreased proximal reabsorption with a concomitant reduction of NHE3 and Na-K-ATPase levels, indicating that tubular segments distal to the proximal tubules were responsible for the increased sodium reabsorption. l-NAME-treated CBL rats showed an increased proximal reabsorption measured by the lithium clearance method and showed a marked increase in NHE3 and Na-K-ATPase protein levels. Our results show that chronic l-NAME treatment exacerbates the sodium retention found in CBL rats by a significant increase in proximal tubular reabsorption.

Inducible nitric oxide synthase and glomerular hemodynamics in rats with liver cirrhosis

This study was designed to test the hypothesis that glomerular de novo expression of inducible nitric oxide synthase (iNOS) contributes to renal hemodynamic abnormalities in liver cirrhosis developed 3 wk after common bile duct ligature (CBDL). De novo expression of iNOS mRNA was detected by RT-PCR in RNA extracts from isolated CBDL rat glomeruli whereas no iNOS mRNA was found in control rat glomerular RNA. Immunohistochemical staining for iNOS was negative in control animals whereas, in CBDL rats, positive iNOS staining was detected in an apparently mesangial pattern in all glomeruli. Western blots of protein extracts from isolated glomeruli of CBDL rats, but not control animals, showed a prominent iNOS band of 130 kDa. Mean arterial pressure (MAP), renal plasma flow (RPF; p-aminohippurate clearance), and glomerular filtration rate (GFR; inulin clearance) were unaltered in CBDL rats, but the application of 4 mg/kg L-N(6)-(1-iminoethyl)lysine, a specific inhibitor of iNOS, reduced GFR and RPF significantly in CBDL rats, whereas control animals were not affected. Similar results were obtained with lipopolysaccharide (LPS)-pretreated animals, which were studied as a positive control for iNOS expression and as a model for recent iNOS induction. We conclude that de novo expression of iNOS occurs in glomeruli of rats with liver cirrhosis and that nitric oxide, generated by iNOS, contributes to the maintenance of glomerular filtration in the early state of this disease.

Renal interstitial hydrostatic pressure and sodium excretion during acute volume expansion in diabetic rats

Experiments were performed to test the hypothesis that the renal interstitial hydrostatic pressure (RIHP) response to acute volume expansion is suppressed in diabetes mellitus. Sprague-Dawley rats received streptozotocin (STZ rats; 65 mg/kg ip) or vehicle (Sham rats). Two weeks later, RIHP and Na(+) excretion responses to acute graded volume expansion with isotonic saline were quantified under Inactin anesthesia (0.1 mg/kg ip). In Sham rats, acute graded volume expansion to 10% body wt produced increases in RIHP (Delta = 12.2 +/- 2.4 mmHg), urine flow (Delta = 54 +/- 8 microliter. min(-1). g(-1)), and Na(+) excretion (Delta = 11.5 +/- 1.9 mueq. min(-1). g(-1)). In STZ rats, these volume expansion-induced responses were significantly blunted (RIHP by 50%, urine flow by 81%, and Na(+) excretion by 76%). Renal decapsulation eliminated the differences between STZ and Sham rats with regard to volume expansion-induced increases in RIHP, urine flow, and Na(+) excretion. Renal denervation normalized the RIHP response to volume expansion and improved the diuretic and natriuretic responses in STZ rats. Moreover, diuretic and natriuretic responses to direct changes in RIHP (induced by renal interstitial volume expansion) were blunted in STZ rats. We conclude that diminished alterations in RIHP, as well as a reduced impact of RIHP on Na(+) excretion, contribute to the impaired diuretic and natriuretic responses to acute volume expansion during the early stage of diabetes.

Role of protein kinase C in mesenteric pressor responses of rats with portal hypertension

1. Hyporesponsiveness to vasoconstrictors is a characteristic abnormality of liver diseases of uncertain origin. In the present study, we have evaluated the involvement of protein kinase C (PKC) in the reduced pressor response to methoxamine (MTX) of a rat model of portal hypertension induced by partial portal vein ligation (PVL). Experiments were performed in the isolated and perfused mesentery. 2. The pressor response to MTX was reduced in PVL compared to that of control animals (Sham) and pretreatment with NG-nitro-L-arginine (L-NOARG, 10(-4) M) or removal of the endothelium potentiated the response of both groups. However, only removal of the endothelium completely eliminated the reduced pressor response to MTX of the PVL vessels. 3. Pretreatment of the mesentric vessels with calphostin C (10(-6) M), a PKC inhibitor, reduced the response to MTX of Sham to a level similar to that of untreated PVL vessels, but did not change that of PVL animals. 4. Mesenteric pressor responses to a PKC activator, phorbol 12,13-dibutyrate (PDBu), were similar in vessels from both PVL and Sham rats and pretreatment with L-NOARG or removal of the endothelium enhanced those responses while indomethacin (10(-5) M) decreased them. In all cases, the responses to PDBU were similar in PVL vessels compared to Sham. 5. These results indicate that the reduced pressor response to MTX of the mesenteric vascular bed of PVL rats is due to an endothelial alteration, compatible with an enhanced production of nitric oxide. The lack of response to calphostin C in PVL vessels suggests an impairment in agonist-induced PKC activation. Since direct activation of PKC induces a normal pressor response, it is concluded that the endothelial alteration interacts with the mechanism producing PKC activation, which results in a lower pressor response of the PVL mesenteric vaculature.