Dynamics of sodium retention in preascitic cirrhotic rats assessed through parathyroid hormone injection.

Extracellular Ca(++) stimulates membrane-bound calcium-sensing receptors (CaRs). CaRs stimulation leads to PGE2-mediated decrease in protein content of Na(+)-K(+)-2Cl(-) co-transporters (BSC-1) in the thick ascending limb (TAL) of Henle's loop and of aquaporin 2 (AQP2) water channels in collecting ducts. Parathyroid hormone (PTH) increases CaRs and decreases BSC-1 and AQP2 tubular content. To assess the Ca(++)-dependent diuretic system in preascitic cirrhosis, we evaluated renal function, hormonal status, PGE2 urinary excretion, and renal content of BSC-1 and CaRs in three groups of rats: control rats received s.c. 5% glucose solution; two groups of rats with CCl4-induced preascitic cirrhosis received either s.c. glucose solution or five s.c. doses of 10 mcg/Kg PTH (one dose every 12 hours) prior to study. Cirrhotic rats, when compared to controls, showed reduced urine volume and sodium excretion; moreover, western blot analysis revealed reduced CaRs and increased BSC-1 protein content in cirrhotic rat kidneys. S.c. administration of PTH normalized urine and sodium excretion in cirrhotic rats and also increased renal plasma flow, PGE2 urinary excretion, and free-water clearance. Finally, PTH reduced BSC-1 and augmented CaRs content in cirrhotic rat kidneys. In conclusion, in preascitic cirrhosis sodium retention is associated with down-regulation of renal CaRs and up-regulation of tubular Na(+)-K(+)-2Cl(-) co-transporters. PTH returns these biomolecular changes, along with sodium and urine excretions, to normality, suggesting that exaggerated sodium reabsorption occurs primarily in the Henle's loop in preascitic cirrhosis.

Calcium-dependent diuretic system in preascitic liver cirrhosis.

BACKGROUND & AIMS: Extracellular Ca(++) activates cell membrane calcium-sensing receptors (CaRs), leading to renal tubule production of prostaglandins E(2) (PGE(2)), which decrease both sodium reabsorption in the thick ascending limb of Henle's loop and free-water reabsorption in collecting ducts. AIMS & METHODS: To assess the activity of this diuretic system in experimental cirrhosis, we evaluated renal function, hormonal status, PGE(2) urinary excretion, and renal tissue concentrations of Na(+)-K(+)-2Cl(-) co-transporters (BSC-1) and CaRs in three groups of rats: one group of controls receiving 5% glucose solution (vehicle) intravenously and two groups of rats with CCl(4)-induced preascitic cirrhosis receiving either vehicle or 0.5mg i.v. Poly-l-Arginine (PolyAg), a CaR-selective agonist. RESULTS: Compared to controls, cirrhotic rats showed reduced urine volume and sodium excretion (p<0.05). Western blot analysis revealed reduced CaRs and increased BSC-1 protein content in kidneys of cirrhotic rats compared with controls (all p<0.01). PolyAg-treated cirrhotic rats had their urine and sodium excretion returned to normal; PolyAg also increased renal plasma flow, PGE(2) urinary excretion, and free-water clearance in cirrhotic rats (all p<0.01 v. untreated cirrhotic animals). CONCLUSIONS: In preascitic cirrhosis, sodium retention may be linked to down-regulation of renal CaRs and up-regulation of tubular sodium-retaining channels. Calcimimetic drugs normalize preascitic sodium retention.

Solute-free water retention in preascitic cirrhotic rats following intravenous water loading.

Increased extracellular fluid volume (ECF) characterizes compensated cirrhosis. To identify the mechanisms of fluid retention in cirrhosis through clearance methods, 10 control and 10 preascitic rats with CCl(4)-induced cirrhosis were studied following i.v. loading with 1 ml 5% glucose solution. Glomerular filtration rate and renal plasma flow were evaluated through inulin and para-aminohippurate clearances; water and electrolyte handling was assessed measuring urine and plasma osmolarity, electrolyte excretions, and tubular solute-free water reabsorption (TFWR = osmolar clearance minus urinary output); ECF was assessed through hormonal status determination. After water loading, cirrhotic rats had increased ECF (lower plasma renin activity and aldosterone and higher atrial natriuretic peptide levels, all P<0.03), solute-free water retention (increased TFWR and decreased plasma osmolarity, all P<0.05), reduced absolute and fractional sodium excretions (P<0.05). Cirrhotic rats showed sodium retention in the medullary thick ascending limb of Henle's loop (i.e. increased values of TFWR for any given value of osmolar clearance). Trans-tubular potassium gradient in medullary collecting duct was similar in the two groups (P=0.55), ruling out aldosterone-dependent sodium retention and potassium hyper-secretion. In experimental preascitic cirrhosis NaCl retention in the ascending limb of Henle's loop increases medullary interstitial tonicity leading to vasopressin-independent water back-diffusion in thin descending limb of Henle's loop and collecting duct.

Natriuretic and aquaretic effects of intravenously infused calcium in preascitic human cirrhosis: physiopathological and clinical implications.

BACKGROUND: Preascitic cirrhosis is characterised by subtle renal sodium retention. Calcium inhibits Na(+)-K(+)-2Cl(-) cotransport in the Henle's loop and could potentially correct sodium-handling abnormalities at that site. AIM: To investigate the effects of calcium infusion on sodium handling in 10 patients with preascitic cirrhosis and nine healthy controls after 1 week of sodium loading of 200 mmol sodium/day. METHODS: All patients underwent a 3 h supine determination of inulin, para-aminohippurate, lithium and free-water clearances, absolute and fractional excretions of sodium, potassium and calcium and plasma concentrations of renin, aldosterone, norepinephrine and vasopressin. The same were repeated over a further 3 h supine period including 60 min intravenous infusion of 33 mg/min calcium gluconate. RESULTS: After sodium loading, the 24 h urinary sodium excretion in patients with cirrhosis was lower than that in controls (p<0.03). Calcium infusion significantly decreased plasma norepinephrine levels (p<0.03), and induced greater increases in fractional delivery of sodium to the Henle's loop (p<0.5) in those with cirrhosis than in controls. This was associated with a decreased fractional reabsorption of sodium beyond the proximal tubule (p<0.03), resulting in greater urinary volume, sodium excretion and free-water clearance in those with cirrhosis than in controls (all with p<0.05). Because the aldosterone-driven potassium secretion, as assessed by the computation of tubular-capillary gradient of [K(+)] in the collecting duct, was similar in the two groups and unaffected by calcium, sodium retention must have occurred in the Henle's loop in those with cirrhosis. CONCLUSION: Calcium is natriuretic in patients with preascitic cirrhosis; it also decreases norepinephrine release, which could be responsible for decreased reabsorption of sodium in the Henle's loop.

Overexpression of kidney neutral endopeptidase (EC 3.4.24.11) and renal function in experimental cirrhosis.

Neutral endopeptidase degrades atrial natriuretic peptide (ANP) and bradykinin and may generate endothelin-1 from big-endothelin. In advanced cirrhosis, sodium retention is accompanied by elevated plasma ANP levels, and infusion of ANP causes hypotension, but in normal humans increasing the concentration of ANP through the inhibition of neutral endopeptidase, localized in renal proximal tubule cells, causes natriuresis without any arterial pressure drop. The purpose of this study was the assessment of kidney neutral endopeptidase expression and responses to candoxatrilat (a specific inhibitor of this enzyme) in rats with CCl4-induced cirrhosis. Two groups of control rats (n = 5) were injected with vehicle or 3 mg/kg candoxatrilat. Three groups of cirrhotic rats with ascites (n = 10) received vehicle alone or 3 or 10 mg/kg candoxatrilat. In cirrhotic rats, Western blot analysis revealed a 170% increase in renal neutral endopeptidase protein content (P < 0.03), mainly in the proximal nephron and macula densa, and both candoxatrilat dosages increased plasma ANP levels, urinary volume, and urinary excretion of sodium, ANP, and cGMP compared with vehicle alone (all P < 0.03). Candoxatrilat (10 mg/kg) also reduced tubular solute-free water reabsorption (P < 0.03) in cirrhotic rats, but renal blood flow, arterial pressure, and plasma renin activity were unaffected. Neutral endopeptidase inhibition has natriuretic and aquaretic actions in cirrhosis without any effect on blood pressure and kidney perfusion due to a significant overexpression of this enzyme in renal cortex.

CTLA4 gene polymorphism in Italian patients with colorectal adenoma and cancer.

BACKGROUND AND AIMS: Colorectal cancer is a major health problem. Colonoscopic colorectal cancer screening is cumbersome and expensive. Identification of genetic risk of colorectal cancer may help to select the subjects who could benefit from colonoscopy. The immune system plays a fundamental role in the human-environment interaction, and the carcinogenic effects of many environmental factors are mediated by the chronic activation of the immune system in a genetic-controlled fashion. Cytotoxic T lymphocyte associated antigen 4 (CTLA4) plays an inhibitory role in regulating lymphocyte functions. The loss of CTLA4 function is responsible for loss of mucosal lymphocyte tolerance. The G allele at position +49 of exon 1 of the CTLA4 gene affects the CTLA4 function. We evaluated in an association study the role of CTLA4 A+49G polymorphism as a risk factor for colorectal neoplasm. PATIENTS AND METHODS: Five hundred and fifty-six patients (male 295; female 261) who underwent colonoscopy at our Centre were enrolled in the study and divided into three groups: Colorectal cancer (132 patients, M/F 68/64, mean age 66+/-11 years); Colorectal adenoma (186 patients, M/F 110/76, mean age 65+/-11 years); Healthy controls (238 patients, M/F 117/121, mean age 63+/-10 years). DNA was extracted from peripheral blood, CTLA4 gene was amplified by using specific primers, and A+49G polymorphism was analysed by restriction enzyme digestion. RESULTS: No statistically significant differences in the genotype distribution among Control and Adenoma groups (p=0.93), Control and Carcinoma groups (p=0.52), and Adenoma and Carcinoma groups (p=0.53) were observed. CONCLUSION: There is no significant correlation between CTLA4 A+49G polymorphism and the risk of colorectal neoplasm among Italian Caucasians.

Evidence of a dynamic aldosterone-independent distal tubular control of renal sodium excretion in compensated liver cirrhosis.

BACKGROUND AND AIM: In preascitic cirrhosis increased sodium retention occurs in kidney distal tubule in spite of normal aldosterone plasma levels. No clearance technique can dissect the respective contribution to sodium retention exerted by Henle's loop, distal convoluted tubule and collecting duct, so we evaluated proximal and distal tubular sodium handling in preascites during two manoeuvres that temporarily increase aldosterone secretion. METHODS: Ten patients with compensated cirrhosis and nine controls were studied in recumbency, during standing and after dopamine receptor blockade with metoclopramide through: 4 h renal clearances of sodium, potassium, lithium and creatinine; plasma levels of active renin and aldosterone. RESULTS: Whilst comparable in recumbency, aldosterone levels significantly rose during standing and after metoclopramide in both groups. In patients, dopaminergic blockade caused a fall of distal sodium delivery (P < 0.01) but urinary sodium excretion was unchanged because the reabsorbed fraction of distal sodium delivery also fell (P < 0.03). Cirrhotic patients showed the same findings in the passage from recumbency to standing. CONCLUSIONS: In preascitic cirrhosis, the distal tubular segments of the nephron are able to cope with decreases in tubular flow by reducing reabsorption at an aldosterone-independent site (possibly the loop of Henle).

Renal tubular events following passage from the supine to the standing position in patients with compensated liver cirrhosis: loss of tubuloglomerular feedback.

BACKGROUND AND AIMS: Patients with preascitic liver cirrhosis display significant renal sodium retention in the upright posture and an exaggerated natriuresis during recumbency. To date, intrarenal sodium handling in these patients has not been studied using lithium clearance and fractional excretion techniques during recumbency and orthostatism. METHODS: Ten patients with preascitic (Child-Pugh A) liver cirrhosis and 10 healthy subjects underwent the following measurements during recumbency and then after four hours of standing: (a) active renin and aldosterone plasma levels; and (b) renal clearance of creatinine, sodium, potassium, and lithium (an index of fluid delivery to the loop of Henle). RESULTS: Unlike the control group, in the upright posture patients had significantly lower values of lithium clearance and fractional excretion compared with recumbency (21.6 (8.6) v 30.5 (10.2) ml/min (p<0.03) and 12.8 (4.4)% v 20.8 (4.9)% (p<0.01), respectively). Our patients showed maintenance of the glomerular-tubular balance-that is, the correlation between creatinine clearance and proximal tubular reabsorption of fluid-during both recumbency and in the upright posture (r=0.96, p<0.001; r=0.97, p<0.001, respectively). In contrast, patients displayed tubuloglomerular feedback only in the supine position. This was demonstrated by the observation of a negative correlation between lithium fractional excretion (a measure of the fractional delivery of sodium to the distal nephron) and filtered sodium load only in recumbency (r=-0.73; p< 0.03) and not during standing (r=0.22; p> 0.05). CONCLUSIONS: This study suggests that both the reduction in fluid and sodium delivery to the distal nephron and loss of tubuloglomerular feedback (the mechanism increasing glomerular filtration rate when the distal tubule is reached by a reduced sodium load) contribute towards the tendency to sodium retention in compensated cirrhosis during prolonged upright posture.

Systemic nitric oxide production and renal function in nonazotemic human cirrhosis: a reappraisal.

OBJECTIVES: Several studies in human cirrhosis have demonstrated increased nitric oxide (NO) production. In experimental animals, intracerebroventricular administration of NO donors causes a marked depression of the endogenous dopaminergic activity, a function known to be physiologically recruited and exerting a natriuretic function in patients with compensated cirrhosis. The aim of this study is to evaluate the interaction between the systemic plasma levels of NO, the endogenous dopaminergic activity and the main parameters of renal function in patients with liver cirrhosis of differing degrees of severity. METHODS: A total of 21 patients (11 with preascitic and 10 with nonazotemic diuretic-free ascitic cirrhosis) and 10 healthy control subjects underwent the following tests: a) basal plasma renin activity (PRA) and aldosterone levels; b) renal clearances of sodium, potassium, inulin, para-minohippurate and lithium (the latter being a measure of the fluid delivery to the distal nephron); c) NO systemic plasma levels measured through paramagnetic resonance spectroscopy as nitrosylhemoglobin complexes; d) endogenous dopaminergic activity, evaluated by means of the incremental prolactin and aldosterone plasma levels after dopaminergic blockade with i.v. metoclopramide. RESULTS: NO plasma values and endogenous dopaminergic activity, although significantly increased with respect to healthy controls, were not different in the two groups of patients. The plasma NO/PRA ratio was significantly higher in the group of compensated patients with respect to ascitic cirrhotics (respectively, 18.3 +/- 11.8 vs 3.5 +/- 2.6 A.U./ng/ml/h, p < 0.001). Compared with compensated cirrhotics, patients with ascites showed significantly lower values of glomerular filtration rate (GFR) and renal plasma flow (RPF). Interestingly, GFR values were substantially the same in the ascitic patients and the control subjects. Compensated patients displayed a significant positive correlation between metoclopramide-induced incremental aldosterone plasma levels (i.e., endogenous dopaminergic tone) and fractional excretion of sodium (r = 0.58; p < 0.05). In the group of compensated patients, NO levels correlated inversely with creatinine plasma concentrations (r = -0.85; p < 0.001) and directly with inulin clearance (r = 0.65; p < 0.05). CONCLUSIONS: These data show that, at least in compensated cirrhotic patients, the stimulation of systemic NO production and the increased dopaminergic function may be mechanisms preventing renal perfusion, GFR, and fractional excretion of sodium from precocious reductions.

Time-dependent modifications of splanchnic circulation in female pigs submitted to end-to-side portacaval anastomosis.

Fractional systemic bioavailability of orally administered drugs was found to be unexpectedly low in liver cirrhosis, even after surgical portal-systemic shunting. Fecal loss or intestinal first-pass elimination were assumed to explain the finding. In this paper we evaluated alternative pathophysiological interpretations relating low bioavailability to adaptive circulatory modifications. D-Sorbitol was used because its hepatic extraction is very high and hepatic removal follows a flow-dependent clearance regimen. D-Sorbitol bioavailability was measured at steady state in pigs submitted to end-to-side portacaval anastomosis, immediately after surgery and four weeks later. Intestinal first-pass elimination dependent on fecal loss and intraluminal degradation was excluded by administering D-sorbitol into the superior mesenteric artery. Almost complete bioavailability was observed immediately after surgery (N = 6, 0.96+/-0.08); four weeks later the bioavailability dropped (-36.8+/-18.7%; P < 0.001) while hepatic clearance significantly increased (+83.6+/-47.9%; P < 0.01). Experimental data support the hypothesis that adaptive circulatory changes spontaneously occur after some time, leading to a lower than expected portal bioavailability.

Renal distal tubular handling of sodium in central fluid volume homoeostasis in preascitic cirrhosis.

BACKGROUND/AIMS: Patients with preascitic liver cirrhosis have an increased central plasma volume, and, for any given plasma aldosterone concentration, they excrete less sodium than healthy controls. A detailed study of the distribution of sodium reabsorption along the segments of the renal tubule, especially the distal one, is still lacking in preascitic cirrhosis. METHODS: Twelve patients with Child-Pugh class A cirrhosis and nine control subjects (both groups on a normosodic diet) were submitted to the following investigations: (a) plasma levels of active renin and aldosterone; (b) four hour renal clearance of lithium (an index of fluid delivery to the loop of Henle), creatinine, sodium, and potassium; (c) dopaminergic activity, as measured by incremental aldosterone response to intravenous metoclopramide. RESULTS: Metoclopramide induced higher incremental aldosterone responses, indicating increased dopaminergic activity in patients than controls, which is evidence of an increased central plasma volume (+30 min: 160.2 (68.8) v 83.6 (35.2) pg/ml, p<0.01; +60 min: 140.5 (80.3) v 36. 8 (36.1) pg/ml, p<0.01). Patients had increased distal fractional sodium reabsorption compared with controls (26.9 (6.7)% v 12.5 (3. 4)% of the filtered sodium load, p<0.05). In the patient group there was an inverse correlation between: (a) absolute distal sodium reabsorption and active renin (r -0.59, p<0.05); (b) fractional distal sodium reabsorption and sodium excretion (r -0.66, p<0.03). CONCLUSIONS: These data suggest that in preascitic cirrhosis the distal fractional tubular reabsorption of sodium is increased and critical in regulating both central fluid volume and sodium excretion.

Endogenous dopaminergic activity in Child-Pugh A cirrhosis: potential role in renal sodium handling and in the maintenance of clinical compensation.

BACKGROUND: We studied the main determinants of aldosterone secretion in a group of 20 patients with biopsy-proven Child-Pugh A cirrhosis without previous ascites or diuretic consumption. METHODS: We evaluated the plasma levels of adrenocorticotrophic hormone (ACTH), active renin and aldosterone (both supine at 07.00 h and after 30 min of upright posture),and active renin and aldosterone responses 30 min and 60 min after the administration of metoclopramide, a dopamine DA2 antagonist (10 mg e.v.). Nine normal subjects were also submitted to the metoclopramide stimulation test. RESULTS: Compared with control subjects, the patients showed significantly greater incremental aldosterone responses both 30 min and 60 min after metoclopramide (+30 min: 157.5+/-73.3 vs. 83.5+/-32.2 pg mL(-1), P< 0003; +60 min: 142.1+/-87.2 vs. 36.8+/-39.0 pg mL(-1), P < 0-001). We found significant positive correlations between amplitude of aldosterone response 30 min after metoclopramide and 24-h urinary fractional excretion of sodium (r=0.61, P < 0.01) and basal morning aldosterone levels (r=0.69, P < 0.001). CONCLUSIONS: The higher incremental aldosterone responses observed after metoclopramide in cirrhotic patients are expressions of increased dopaminergic activity in these patients compared with control subjects. Moreover, the correlation we found between the degree of dopaminergic activity and 24-h urinary fractional excretion of sodium suggests a role for endogenous dopamine as a relevant mediator of natriuresis in cirrhosis, at least in patients with compensated disease.

Beneficial hemodynamic effects of dipyridamole on portal circulation in cirrhosis.

OBJECTIVE: Dipyridamole is a vasodilator that inhibits the cellular uptake of adenosine, which physiologically reduces the resistance to hepatic arterial flow inside the liver. This study aims at assessing the acute effect of dipyridamole on functional liver plasma flow (measured as the extrarenal sorbitol clearance) and on the Doppler US Congestion Index of the portal vein (the ratio between the cross-sectional area of this vein and the mean velocity of portal flow), which correlates with the severity of portal hypertension. METHODS: We have determined the extrarenal sorbitol clearance (14 cases) and the Congestion Index (seven cases) before and at 30, 60, and 90 min after the oral administration of 25 mg dipyridamole in patients with liver cirrhosis. We also measured the effect of dipyridamole on functional liver plasma flow in six healthy subjects. RESULTS: Dipyridamole increased the extrarenal sorbitol clearance in controls (+17%, p < 0.01) and in cirrhotic patients (+15%, p < 0.01). The drug decreased the portal Congestion Index in all patients, averaging -24% (p < 0.05) 90 min after its oral administration. CONCLUSIONS: This result was due both to a mean decrease of the portal sectional area and to a mean increase in portal flow velocity. In conclusion, these data suggest that dipyridamole should decrease the vascular resistance to portal flow in cirrhosis; this effect may be mediated by an adenosine-dependent vasodilation in the intrahepatic site or along the portosystemic collaterals.

Assessment of functional liver mass and plasma flow in acromegaly before and after long-term treatment with octreotide.

Functional liver mass and functional liver plasma flow (FLPF) were assessed in 11 patients with clinical features of acromegaly by determining galactose elimination capacity (GEC) and extrarenal clearance of sorbitol, before and 5 to 7 months after treatment with the long-acting somatostatin analog, octreotide (150 to 600 micrograms/d in three subcutaneous injections). Growth hormone (GH) and insulin-like growth factor-I (IGF-I) levels, as well as liver size by ultrasound, were also recorded. Baseline GEC was increased in every patient but one, for a mean of 0.78 +/- 0.10 g/min (normal, 0.53 +/- 0.07; P < .01). At reevaluation after 5 to 7 months of octreotide treatment, a significant reduction of GEC was observed (0.62 +/- 0.08 g/min, P < .001). Changes of GEC paralleled those of GH (38.6 +/- 34.4 v 11.7 +/- 15.2 micrograms/L, P < .01) and IGF-I (5.0 +/- 1.7 v 2.7 +/- 2.2 U/ml, P < .001). Significant correlations were found between GEC and GH (r = .50, P < .05) and between GEC and IGF-I (r = .55, P < .01). FLPF, assessed by extrarenal clearance of sorbitol, was within the normal limit in all cases (0.98 +/- 0.19 v 0.97 +/- 0.12 L/min, NS) and remained normal after 5 to 7 months of octreotide treatment (0.99 +/- 0.11 L/min). Hepatic structure determined with ultrasonic scanning and conventional liver-function tests were basally normal in all patients, with a slight increase of liver volume in three cases. No change of biochemical and/or morphological features occurred during follow-up evaluation. The results support the hypothesis that GH and especially IGF-I enhance liver metabolic capacity; conversely, functional liver perfusion is largely independent of their actions. Our data also suggest that octreotide is unable to produce well-structured changes of liver circulation when administered long-term.

Effects of nifedipine on functional liver plasma flow in normal subjects and in patients with cirrhosis.

The short-term effects of nifedipine (10 mg administered sublingually) on functional liver plasma flow, measured by calculating the extrarenal clearance of sorbitol, were investigated in 12 normal volunteers and 40 patients with cirrhosis scored according to Child-Pugh classification. Nifedipine significantly increased functional liver plasma flow in healthy subjects (23%, p < 0.0001) and in patients with cirrhosis in the Child-Pugh class A group (19%, p < 0.001); in patients in the Child-Pugh class B group functional liver plasma flow was not modified, whereas in the patients in the Child-Pugh class C group it was significantly reduced (-7%, p < 0.02). The mean arterial pressure showed a significant reduction in all groups studied. According to the pathophysiologic meaning of functional liver plasma flow, it is suggested that nifedipine meets criteria for an ideal test substance to evaluate the functional reserve of the liver. Furthermore, when used with the Child-Pugh classification, its effect on functional liver plasma flow may be useful to improve the efficiency of the Child-Pugh classification, in establishing the prognosis of patients with cirrhosis.