Nitric oxide synthase (NOS) inhibition for one week improves renal sodium and water excretion in cirrhotic rats with ascites

Nitric oxide synthase inhibition does not improve renal function in cirrhotic patients with ascites

OBJECTIVES

Based mainly on animal experiments, nitric oxide (NO) has been proposed to account for the peripheral arterial vasodilation and hyperdynamic circulation in liver cirrhosis. The aim of this study was to clarify whether a reduction of NO synthesis would ameliorate the circulatory and renal dysfunction in decompensated cirrhotic patients.

METHODS

The effects of N(G)-monomethyl-L-arginine-acetate (L-NMMA), an NO synthesis inhibitor, were studied. After a 60-min basal period, a total of 10 patients received increasing doses of L-NMMA, five patients (Low) received 12.5, 25, and 50 microg/kg/min, and five patients (High) received 25, 50, and 100 microg/kg/min as a constant infusion during 3 h, followed by a postinfusion period. Five patients (Placebo) received saline infusions only. Glomerular filtration rate and renal plasma flow were measured by clearance techniques with (99m)Tc-diethylenetriamine-pentaacetate and (131)I-Hippuran.

RESULTS

L-NMMA infusion resulted in an increased blood pressure, decreased heart rate, and dose-dependent suppression of renin of up to 42.1 +/- 7.1% (p < 0.01) and angiotensin II of up to 39.9 +/- 9.6%, (p < 0.01) levels. Sodium and water excretion were not improved, most likely because of a reduction in renal blood flow of up to 29.1 +/- 8.1% (p < 0.01).

CONCLUSION

Despite a partial correction of the hyperdynamic circulation, inhibition of NO synthesis does not improve sodium and water excretion in decompensated cirrhosis, probably because of an accompanying decrease in renal plasma flow. Intrarenal NO synthesis may be important for maintaining intrarenal hemodynamics in decompensated cirrhotic patients.

Increase in renal glutathione in cholestatic liver disease is due to a direct effect of bile acids

Hepatic synthesis and plasma levels of glutathione are markedly decreased in chronic liver disease. Because glutathione turnover is highest in kidneys, we examined whether changes in kidney glutathione occur in chronic cholestasis and whether they are related to kidney dysfunction in liver disease. Kidney and plasma GSH and GSSG were measured 1) in bile duct-ligated (BDL) rats; 2) in healthy rats after bile acid loading to mimic cholestasis; and 3) after irreversible inhibition of glutathione synthetase with buthionine-sulfoximine (BSO), where glutathione consumption, urinary volume, and sodium excretion were also estimated. In addition, gamma-glutamylcysteine synthetase (gamma-GCS) mRNA, protein, and enzymatic specific activity were measured in kidney tissue after BDL. After BDL, kidney GSH and GSSG increased within hours by 67 and 66%, respectively. The increases were not related to plasma glutathione, which decreased below control values. Intravenous bile acid loading caused identical increases in GSH and GSSG as occurred after BDL, when glycine- or taurine-conjugated dihydroxy bile acids were administered. Glutathione consumption, as estimated after blocking of de novo synthesis with BSO, was significantly increased after BDL (127 vs. 44 nmol x g-1 x min-1). gamma-GCS mRNA and enzymatic specific activity were significantly reduced 5 days after BDL, whereas protein concentrations did not change. The urinary sodium concentration was 70% lower in BDL than in control rats. Depletion of renal glutathione normalized sodium excretion by increasing urinary sodium concentration and urinary volume. The increase in kidney glutathione after BDL seems to be mediated by an increase in plasma bile acids and is critically related to sodium retention. The increase in GSH consumption despite reduced gamma-GCS activity indicates a decreased GSH turnover tentatively due to reduced renal GSH efflux by competition with organic anions at membrane transport proteins.

Regulation of heme oxygenase-1 by nitric oxide during hepatopulmonary syndrome

During hepatopulmonary syndrome caused by liver cirrhosis, pulmonary endothelial nitric oxide (NO) synthase (NOS) expression and NO production are increased. Increased NO contributes to the blunted hypoxic pressor response (HPR) during cirrhosis and may induce heme oxygenase-1 (HO-1) expression and carbon monoxide (CO) production, exacerbating the blunted HPR. We hypothesized that NO regulates the expression of HO-1 during cirrhosis, contributing to hepatopulmonary syndrome. Cirrhosis was induced in rats by common bile duct ligation (CBDL). Rats were studied 2 and 5 wk after CBDL or sham surgery. Lung HO-1 expression was elevated 5 wk after CBDL. Liver HO-1 was increased at 2 wk and remained elevated at 5 wk. In catheterized rats, the blunted HPR was partially restored by HO inhibition. Rats treated with the NOS inhibitor N(G)-nitro-L-arginine methyl ester for the entire 2- or 5-wk duration had normalized HO-1 expression and HPR. These data provide in vivo evidence for the NO-mediated upregulation of HO-1 expression and support the concept that hepatopulmonary syndrome is multifactorial, involving not only NO, but also HO-1 and CO.

Effect of L-NAME on nitric oxide and gastrointestinal motility alterations in cirrhotic rats

AIM: To investigate the effect of L-NAME on nitric oxide and gastrointestinal motility alterations in cirrhotic rats.

METHODS: Rats with cirrhosis induced by carbon tetrachloride were randomly divided into two groups, one (n = 13) receiving

0.5 mg·kg^-1 per day of N G-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, for 10 d, whereas the other group (n = 13) and control (n = 10) rats were administrated the same volume of 9 g•L⁻¹ saline. Half gastric emptying time and 2 h residual rate were measured by SPECT, using ^99mTc-DTPA-labeled barium sulfate as test meal. Gastrointestinal transition time was recorded simultaneously. Serum concentration of nitric oxide (NO) was determined by the kinetic cadmium reduction and colorimetric methods. Immunohistochemical SABC method was used to observe the expression and distribution of three types of nitric oxide synthase (NOS) isoforms in the rat gastrointestinal tract. Western blot was used to detect expression of gastrointestinal NOS isoforms.

RESULTS: Half gastric emptying time and trans-gastrointestinal time were significantly prolonged (124.0 ± 26.4 min; 33.7 ± 8.9 min; 72.1 ± 15.3 min; P < 0.01), (12.4 ± 0.5 h; 9.5 ± 0.3 h; 8.2 ± 0.8 h; P < 0.01), 2 h residual rate was raised in cirrhotic rats than in controls and cirrhotic rats treated with L-NAME (54.9% ± 7.6%, 13.7% ± 3.2%, 34.9% ± 10.3%, P < 0.01). Serum concentration of NO was significantly increased in cirrhotic rats than in the other groups (8.20 ± 2.48) μmol•L⁻¹, (5.94 ± 1.07) μmol•L⁻¹, and control (5.66 ± 1.60) μmol•L⁻¹, P < 0.01. NOS staining intensities which were mainly located in the gastrointestinal tissues were markedly lower in cirrhotic rats than in the controls and cirrhotic rats after treated with L-NAME.

CONCLUSION: Gastrointestinal motility was remarkably inhibited in cirrhotic rats, which could be alleviated by L-NAME.Nitric oxide may play an important role in the inhibition of gastrointestinal motility in cirrhotic rats.

Relationship between protein kinase C alterations and nitric oxide overproduction in cirrhotic rat aortas

BACKGROUND

Although nitric oxide (NO) overproduction and protein kinase C (PKC) alterations may play a role in systemic haemodynamic changes in cirrhotic rat aortas, the relationship between NO synthase (NOS) hyperactivation and PKC hypoactivation is unknown. Therefore, the relationships between NOS and PKC activities were studied in cirrhotic rat aortas.

METHODS

The effects of NOS inhibition by Nw-nitro-L-arginine (LNNA) on the contractile response to phorbol myristate acetate (PMA), a PKC activator, were studied. The effects of NOS inhibition and those of S-nitroso-N acetyl-DL-penicillamine (SNAP), an NO donor, on PKC activity were also evaluated. The effects of PKC activation and inhibition on total NOS and inducible NOS (iNOS) activities were measured. Nitric oxide synthase inhibition caused an increase in PMA-induced contraction and an increase in PKC activity in cirrhotic rat aortas. S-nitroso-N acetyl-DL-penicillamine induced downregulation of PKC activity. Total basal aortic NOS activity was significantly higher in cirrhotic rats than in control rats and activation of PKC by PMA induced a decrease in total aortic NOS activity. Protein kinase C downregulation caused an increase in both total aortic NOS and iNOS activities only in control rats, whereas only iNOS activity increased in cirrhotic rats.

CONCLUSION

In cirrhotic rat aortas, NO overproduction plays a role in the decreased PKC activation that leads to reduced aortic contraction. Overactivation of aortic NOS in cirrhotic rats may be because of, in part, the reduced PKC activity.

Acute effects of nitric oxide synthase inhibition on systemic, hepatic, and renal hemodynamics in patients with cirrhosis and ascites

BACKGROUND

Nitric oxide synthase (NOS) inhibition has been demonstrated to correct systemic vasodilation and renal hypoperfusion in studies of patients with cirrhosis. In patients with decompensated cirrhosis, NOS blockade increases arterial pressure, but the acute effects on hepatic and renal hemodynamics are not known.

METHODS

We examined the acute systemic, hepatic, and renal hemodynamic effects of N(G)-monomethyl-L-arginine (L-NMMA) in 10 patients with decompensated cirrhosis. After baseline measurements, 3 mg/kg L-NMMA was administered as an IV bolus. At 20 minutes, if mean arterial pressure did not increase by at least 10 mm Hg above the baseline value, a second injection of 6 mg/kg was administered.

RESULTS

In 5 of 10 patients, the second injection of L-NMMA 6mg/kg was necessary to achieve at least a 10 mm Hg increase in mean arterial pressure. Acute NOS inhibition increased systemic vascular resistance and decreased cardiac output, without causing changes in the hepatic venous pressure gradient. Hepatic blood flow decreased, but the indocyanine green intrinsic clearance and extraction remained unchanged. Plasma renin activity (from 9.5 +/- 2.9 to 6.7 +/- 1.6 ng/ml/h) and urinary prostaglandin E2 (from 299 +/- 40 to 112 +/- 36 pg/ml) significantly decreased. No significant changes in glomerular filtration rate, renal plasma flow, and natriuresis occurred, however.

CONCLUSIONS

Acute L-NMMA infusion in patients with decompensated cirrhosis reduced hepatic blood flow and decreased plasma renin activity and urinary prostaglandin E2, without causing significant changes in renal hemodynamics.

Inducible nitric oxide synthase in renal transplantation

The importance of the endothelial isoform of nitric oxide synthase (eNOS) has been well established. Endothelium-derived nitric oxide has been shown to be essential for vascular homeostasis and modulation of eNOS has thus become a target in prevention of cardiovascular disease. The role of the inducible form of nitric oxide synthase (iNOS) in vascular biology, however, is less clear. Classically, iNOS has been regarded as an enzyme that produces nmolar amounts of the nitric oxide radical, thereby leading to cellular damage. More recent data, however, have shown that the iNOS can be a superoxide, peroxynitrite as well as a nitric oxide-producing enzyme, while the biological effects of iNOS probably depend upon the sort of radical species released by the enzyme as well as the anti-oxidant capacity of the cellular microenvironment of the enzyme. This brief review discusses these aspects in relation to renal transplantation.

Endothelin is an important determinant of renal function in a rat model of acute liver and renal failure

BACKGROUND AND AIMS

Renal failure occurs in approximately 55% of patients with acute liver failure. We have previously shown that plasma endothelin 1 concentrations are elevated in patients with acute liver failure and the hepatorenal syndrome. There are few reported satisfactory animal models of liver failure together with functional renal failure. In this study, a rat model of acute liver failure induced by galactosamine that also develops renal failure was first characterised. This model was used to investigate the hypothesis that endothelin 1 is an important mediator involved in the pathogenesis of renal impairment that occurs in acute liver failure.

METHODS

Acute liver failure was induced in male Sprague-Dawley rats by intraperitoneal injection of galactosamine together with treatment with the endothelin receptor antagonist Bosentan. Twenty four hour urine collections were made using a metabolic cage. Renal blood flow was measured in anaesthetised animals.

RESULTS

This model developed renal failure and liver failure in the absence of any significant renal pathology, and with an accompanying fall in renal blood flow. Plasma concentrations of endothelin 1 were increased twofold following the onset of liver and renal failure (p<0.05), and there was significant upregulation of the endothelin receptor A (ET(A)) in the renal cortex (p<0.05). Administration of Bosentan prevented the development of renal failure when given before or 24 hours after the onset of liver injury (p<0.05) but had no effect on liver injury itself, or on renal blood flow.

CONCLUSIONS

This study demonstrates that this animal model has many of the features needed to be regarded as a model of renal failure that occurs in acute liver failure. The observation that plasma levels of endothelin 1 and ET(A) receptors are increased and upregulated, and that renal failure is prevented by an endothelin antagonist supports the hypothesis originally put forward that ET(A) is important in the pathogenesis of renal failure that occurs in patients with acute liver failure.

Clinical management of ascites and its complications

Development of ascites is a poor prognostic sign with a 1 year mortality rate of up to 50%. Cirrhotic patients who develop ascites should therefore be evaluated for liver transplantation. Even though current therapies of ascites are not associated with a survival benefit, the elimination of ascites will improve quality of life and prevent the development of lethal complications such as SBP and HRS. Therapy of ascites should be directed at correcting the pathophysiologic abnormalities that lead to ascites formation, namely sodium retention, reduced effective arterial blood volume, and sinusoidal hypertension.

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.

Nitric oxide and the liver

In recent years, the role of nitric oxide (NO) in the pathogenesis of liver disease and its complications has been extensively studied. There remain, however, many areas of controversy. In particular, the effect of NO on vascular function in the systemic circulation and the hepatic microcirculation has received the greatest attention. It has been proposed on the one hand that increased NO synthesis is responsible for the development of the hyperdynamic circulation in cirrhosis, while decreased production of NO within the hepatic microcirculation may be important in the development of parenchymal tissue damage and the onset of portal hypertension. The purpose of this review is to examine the available data concerning the role of NO in liver disease and to discuss some of the controversies and contradictions that surround it.

Water-losing and water-retaining states: role of water channels and vasopressin receptor antagonists

Alterations in water metabolism are present in conditions such as diabetes insipidus, syndrome of inappropriate antidiuretic hormone secretion, cardiac failure, cirrhosis, and pregnancy. Recent advances in molecular biology have enhanced our understanding of disordered water metabolism in these conditions. This review examines the roles of central vasopressin synthesis and release and collecting duct vasopressin V2 receptor and aquaporin-2 water channel regulation in water-losing and water-retaining states.

Neuronal nitric oxide synthase and systemic vasodilation in rats with cirrhosis

Cirrhosis is typically associated with a hyperdynamic circulation consisting of low blood pressure, low systemic vascular resistance (SVR), and high cardiac output. We have recently reported that nonspecific inhibition of nitric oxide synthase (NOS) with nitro-L-arginine methyl ester reverses the hyperdynamic circulation in rats with advanced liver cirrhosis induced by carbon tetrachloride (CCl(4)). Although an important role for endothelial NOS (eNOS) is documented in cirrhosis, the role of neuronal NOS (nNOS) has not been investigated. The present study was carried out to specifically investigate the role of nNOS during liver cirrhosis. Specifically, physiological, biochemical, and molecular approaches were employed to evaluate the contribution of nNOS to the cirrhosis-related hyperdynamic circulation in CCl(4)-induced cirrhotic rats with ascites. Cirrhotic animals had a significant increase in water and sodium retention. In the aorta from cirrhotic animals, both nNOS protein expression and cGMP concentration were significantly elevated compared with control. Treatment of cirrhotic rats for 7 days with the specific nNOS inhibitor 7-nitroindazole (7-NI) normalized the low SVR and mean arterial pressure, elevated cardiac index, and reversed the positive sodium balance. Increased plasma arginine vasopressin concentrations in the cirrhotic animals were also repressed with 7-NI in association with diminished water retention. The circulatory changes were associated with a reduction in aortic nNOS expression and cGMP. However, 7-NI treatment did not restore renal function in cirrhotic rats (creatinine clearance: 0.76 +/- 0.03 ml. min(-1). 100 g body wt(-1) in cirrhotic rats vs. 0.79 +/- 0.05 ml. min(-1). 100 g body wt(-1) in cirrhotic rats+7-NI; P NS. ). Taken together, these results indicate that nNOS-derived NO contributes to the development of the hyperdynamic circulation and fluid retention in cirrhosis.

Pressor and renal effects of cross-linked hemoglobin in anesthetized cirrhotic rats

BACKGROUND/AIMS

Cross-linked hemoglobin (XL-Hb), a hemoglobin-based oxygen carrier, is currently under investigation as a blood substitute. In the present study we have evaluated its pressor and renal effects in a rat model of liver cirrhosis by bile duct ligation.

METHODS

Experiments were performed 3 weeks after surgery in anesthetized rats In the first protocol, the ability of XL-Hb to recover blood pressure after a hypotensive hemorrhage (0.5 ml/min, 10 min) was analyzed. In the second protocol, the pressor and renal effects produced by the administration of XL-Hb were evaluated during a period of 3 h.

RESULTS

After a hypotensive hemorrhage (0.5 ml/min, 10 min), resuscitation with XL-Hb resulted in greater and faster recovery of blood pressure than with the administration of blood. In non-hemorrhaged rats, administration of XL-Hb (5% of blood volume) reversibly increased blood pressure in bile duct ligation and in control rats, but this effect was of longer duration in the control animals. XL-Hb also induced brisk increases in water and sodium excretion in both groups of animals, but the response of the control animals was more intense and sustained than that of the bile duct ligation rats. Glomerular filtration rate and renal blood flow showed slight decreases, but they were well maintained around the baseline levels. All the parameters studied were normalized 3 h later. In additional experiments, the effect of a bolus of L-NAME (10 mg/kg), an inhibitor of nitric oxide synthase, 1 h after the administration of XL-Hb was partially reduced, suggesting that the effect of XL-Hb may be secondary to the disappearance of circulating nitric oxide.

CONCLUSIONS

XL-Hb seems to be effective as a resuscitative solution in case of hemorrhage in cirrhotic rats Moreover, this blood substitute only moderately and reversibly elevates blood pressure and does not adversely affects renal function.

Vascular nitric oxide production during the development of two experimental models of portal hypertension

BACKGROUND/AIMS

The aim of this study was to determine the relative roles of constitutive NOS (NOS3) and inducible NOS (NOS2) isoforms during the development of two models of portal hypertension in rats.

METHODS

Vascular reactivity of aortic rings for norepinephrine was performed in control, sham-operated, portal-vein-stenosed and secondary biliary cirrhotic rats 1, 4, 7, 14 and 28 days after surgery. NOS activity and nitrate plasma levels were also measured.

RESULTS

An impaired response to norepinephrine observed in sham-operated, portal-vein-stenosed and cirrhotic rats at days 1 and 4 compared with controls was reversed after L-NNA and aminoguanidine. Portal hypertensive rats remained hyporeactive at days 7, 14 and 28 compared with sham-operated rats. At days 7 and 14 in portal-vein-stenosed rats, vascular hyporeactivity was reversed by L-NNA and W7. At days 14 and 28 in cirrhotic rats, vascular hyporeactivity was reversed by L-NNA and W7. Nitrate levels increased at day 1 in the 3 groups, and increased at days 14 and 28 in portal hypertensive rats. Total NOS-activity increased in cirrhotic rats at day 28, in portal-vein-stenosed rats at day 14, and in sham-operated rats at day 1 compared to controls. NOS2 activity increased only in sham-operated rats at day 1.

CONCLUSIONS

This study shows that for two models of portal hypertension, increased NO production in the first days is related to NOS2 induction secondary to surgery. On the other hand, when portal hypertension has fully developed, the NOS3 isoform appears to play the major role.

Effects of chronic octreotide treatment on renal changes during cirrhosis in rats

We examined the effect of a new long-acting release formula (LAR) of the somatostatin analogue, octreotide, on development of sodium retention and functional and structural changes in the thick ascending limb of Henle's loop (TAL) in rats with cirrhosis induced by common bile duct ligation (CBL). CBL and sham-operated control rats were treated with octreotide-LAR (10 mg/kg body weight subcutaneously, as a single dose) or vehicle at the time of CBL or sham-CBL. The rats were instrumented with chronic catheters, and sodium balance and renal function were examined 4 weeks after CBL or sham operation. Octreotide-LAR treatment significantly inhibited sodium retention in CBL rats and prevented renal vasodilatation without changes in glomerular filtration rate (GFR). The natriuretic response to a test dose of furosemide (7.5 mg/kg body weight intravenously) was significantly increased in CBL rats, and when expressed in terms of natriuretic efficiency (mmol Na/mg furosemide in urine), the natriuretic response was increased by 57% relative to sham-operated controls. Stereological examination of kidneys demonstrated a 53% increase in the volume of the inner stripe of the outer medulla and a 108% increase in the volume of TAL epithelium in cirrhotic rats relative to controls. The increased natriuretic efficiency of furosemide as well as the hypertrophy of the inner stripe and the TAL in this renal zone were absent in CBL rats treated with octreotide-LAR. These results suggest that octreotide-LAR treatment inhibits sodium retention in cirrhotic rats, partly by inhibition of increased furosemide-sensitive sodium reabsorption in the TAL.

Portal hypertension

Cirrhosis represents the end stage of any chronic liver disease. Two major syndromes result from cirrhosis: portal hypertension and hepatic insufficiency. Additionally, vasodilatation and the hyperdynamic circulation are hemodynamic abnormalities typical of cirrhosis and portal hypertension. Complications of cirrhosis occur as a consequence of a combination of these factors. Gastroesophageal varices result almost solely from portal hypertension, although the hyperdynamic circulation contributes to variceal growth and hemorrhage. Ascites results from sinusoidal hypertension and sodium retention, which is, in turn, secondary to vasodilatation and activation of neurohumoral systems. Hyponatremia and the hepatorenal syndrome result from water retention and renal vasoconstriction, respectively, both of which are also consequences of peripheral vasodilatation. Vasodilatation that occurs in the pulmonary circulation leads to the hepatopulmonary syndrome. Another complication of cirrhosis, portosystemic encephalopathy, is a consequence of both portal hypertension (shunting of blood through portosystemic collaterals) and hepatic insufficiency. This paper reviews the recent advances in the pathophysiology and management of the complications of cirrhosis and portal hypertension.

Evidence for a vasopressin system in the rat heart

Traditionally, a hypothalamo-neurohypophysial system is thought to be the exclusive source of arginine vasopressin (AVP), a potent antidiuretic, vasoconstricting, and growth-stimulating neuropeptide. We have identified de novo synthesis of AVP in the heart as well as release of the hormone into the cardiac effluents. Specifically, molecular cloning of sequence tags amplified from isolated, buffer-perfused, and pressure-overloaded rat hearts allowed the detection of cardiac AVP mRNA. Subsequent experiments revealed a prominent induction of AVP mRNA (peak at 120 minutes, 59-fold, P<0. 01 versus baseline) and peptide (peak at 120 minutes, 11-fold, P<0. 01 versus baseline) in these isolated hearts. Newly induced vasopressin peptide was localized most prominently to endothelial cells and vascular smooth muscle cells of arterioles and perivascular tissue using immunohistochemistry. In addition to pressure overload, nitric oxide (NO) participated in these alterations, because inhibition of NO synthase by Nomega-nitro-L-arginine methyl ester markedly depressed cardiac AVP mRNA and peptide induction. Immediate cardiac effects related to cardiac AVP induction in isolated, perfused, pressure-overloaded hearts appeared to be coronary vasoconstriction and impaired relaxation. These functional changes were observed in parallel with AVP induction and largely prevented by addition of a V1 receptor blocker (10(-8) mol/L [deamino-Pen1, O-Me-Tyr2, Arg8]-vasopressin) to the perfusion buffer. Even more interesting, pressure-overloaded, isolated hearts released the peptide into the coronary effluents, offering the potential for systemic actions of AVP from cardiac origin. We conclude that the heart, stressed by acute pressure overload or NO, expresses vasopressin in concentrations sufficient to cause local and potentially systemic effects.

Acute effects of the oral administration of midodrine, an alpha-adrenergic agonist, on renal hemodynamics and renal function in cirrhotic patients with ascites

The effects of the acute administration of arterial vasoconstrictors on renal plasma flow (RPF) and urinary sodium excretion (UNaV) in cirrhotic patients with ascites with or without hepatorenal syndrome (HRS) are still controversial. As a consequence, vasoconstrictors are not actually used in the treatment of renal sodium retention or HRS in these patients, regardless of the several lines of evidence suggesting that these renal functional abnormalities are related to a marked arterial vasodilation. The lack of an orally available effective arterial vasoconstrictor probably represents a further reason for this omission. Consequently, the present study was made to evaluate the acute effects of the oral administration of midodrine, an orally available -mimetic drug, on systemic and renal hemodynamics and on UNaV in cirrhotic patients with ascites. Mean arterial pressure (MAP), heart rate (HR), cardiac index (CI), systemic vascular resistance (SVR), left forearm blood flow (LFBF), left leg blood flow (LLBF), RPF, glomerular filtration rate (GFR), UNaV, plasma renin activity (PRA), plasma concentration of antidiuretic hormone (ADH), and the serum levels of nitrite and nitrate (NOx) were evaluated in 25 cirrhotic patients with ascites (17 without HRS and 8 with type 2 HRS) before and during the 6 hours following the oral administration of 15 mg of midodrine. During the first 3 hours after the drug administration, a significant increase in MAP (89.6 +/- 1.7 vs. 81.80 +/- 1.3 mm Hg; P < .0001) and SVR (1, 313.9 +/- 44.4 vs. 1,121.2 +/- 60.1 dyn . sec . cm-5; P < .0001) accompanied by a decrease in HR (69 +/- 2 vs. 77 +/- 3 bpm; P < .005) and CI (2,932.7 +/- 131.4 vs. 3,152.5 +/- 131.4 mL . min-1 . m2 BSA; P < .0025) was observed in patients without HRS. No change was observed in LFBF and LLBF. The improvement in systemic hemodynamics, which was also maintained during the the 3- to 6-hour period after midodrine administration, was accompanied by a significant increase in RPF (541.5 +/- 43.1 vs. 385.7 +/- 39.9 mL . min-1; P < .005), GFR (93.1 +/- 6.5 vs. 77.0 +/- 6.7 mL . min-1; P < .025), and UNaV (92.7 +/- 16.4 vs. 72.2 +/- 10.7 microEq . min-1; P < .025). In addition, a decrease in PRA (5.33 +/- 1.47 vs. 7.74 +/- 2.17 ng . mL-1 . h; P < .05), ADH (1.4 +/- 0.2 vs. 1.7 +/- 0.2 pg . mL-1; P < .05), and NOx (33.4 +/- 5.0 vs. 49.3 +/- 7.3 micromol-1; P < .05) was found. In patients with HRS, the effects of the drug on the systemic hemodynamics was smaller and shorter. Accordingly, regardless of a significant decrease in PRA (15.87 +/- 3.70 vs. 20.70 +/- 4.82 ng . mL-1 . h; P < .0025) in patients with HRS, no significant improvement was observed in RPF, GFR, or UNaV. In conclusion, the acute oral administration of midodrine is associated with a significant improvement in systemic hemodynamics in nonazotemic cirrhotic patients with ascites. As a result, renal perfusion and UNaV also improve in these patients. By contrast, midodrine only slightly improves systemic hemodynamics in patients with type 2 HRS, with no effect on renal hemodynamics and renal function.

Pathophysiology of renal fluid retention

Central to a unifying hypothesis of body fluid regulation is maintenance of arterial circulatory integrity. This may be disturbed by arterial underfilling, either from reduction in cardiac output or by peripheral arterial vasodilation. In cardiac failure (CF), cardiac output falls and the nonosmotic release of arginine vasopressin (AVP) and expression of AVP mRNA in the hypothalamus are stimulated. V2 AVP receptor antagonists correct the impaired water excretion in rats with low-output CF, increase solute free water clearance, correct the hyponatremia in congestive CF patients, and normalize urinary concentrations of the aquaporin-2 (AQP-2) water channels. In conditions associated with peripheral vasodilation, such as cirrhosis, nonosmotic release of AVP also occurs, and AQP-2 gene expression in the rat kidney is up-regulated. In cirrhosis, nitric oxide-mediated vasodilation occurs early prior to water retention. V2 antagonists reverse the latter. In normal pregnancy, plasma AVP is relatively high for the degree of hypoosmolality. Pregnant rats up-regulate AQP-2 in the renal papilla, an effect reversed by V2 receptor antagonists. This supports the hypothesis that AVP is an important mediator of renal water retention in pregnancy. In summary, AVP-mediated water retention through collecting duct AQP-2 water channels is important in both low-output CF and high-output states such as cirrhosis and pregnancy. V2 receptor antagonists reverse the water retention and down-regulate AQP-2 water channels.

Sodium

Disorders of serum sodium are both the most common and probably most the poorly understood electrolyte disorders in clinical medicine. In the past few years increased knowledge about the non-osmotic release of vasopressin and the cloning of vasopressin receptors and of vasopressin-regulated water channels (AQP2) has enhanced our understanding of these disorders. Also controversies surrounding the treatment of hyponatraemic patients have led to well-accepted therapeutic guidelines.