Platelet Count Does Not Predict Bleeding in Cirrhotic Patients: Results from the PRO-LIVER Study.

OBJECTIVES: Thrombocytopenia is a hallmark for patients with cirrhosis and it is perceived as a risk factor for bleeding events. However, the relationship between platelet count and bleeding is still unclear. METHODS: We investigated the relationship between platelet count and major or clinical relevant nonmajor bleedings during a follow-up of ∼4 years. RESULTS: A total of 280 cirrhotic patients with different degrees of liver disease (67% males; age 64±37 years; 47% Child-Pugh B and C) were followed up for a median of 1,129 (interquartile range: 800-1,498) days yielding 953.12 patient-year of observation. The annual rate of any significant bleeding was 5.45%/year (3.57%/year and 1.89%/year for major and minor bleeding, respectively). Fifty-two (18.6%) patients experienced a major (n=34) or minor (n=18) bleeding event, predominantly from gastrointestinal origin. Platelet counts progressively decreased with the worsening of liver disease and were similar in patients with or without major or minor bleeding: a platelet count ≤50 × 103/µl was detected in 3 (6%) patients with and in 20 (9%) patients without any bleeding event. Conversely, prothrombin time-international normalized ratio was slightly higher in patients with overall or major bleeding. On Cox proportional hazard analysis, only a previous gastrointestinal bleeding (hazard ratio (HR): 1.96; 95% confidence interval: 1.11-3.47; P=0.020) and encephalopathy (HR: 2.05; 95% confidence interval: 1.16-3.62; P=0.013) independently predicted overall bleeding events. CONCLUSIONS: Platelet count does not predict unprovoked major or minor bleeding in cirrhotic patients.

Treatment with tin prevents the development of hypertension in spontaneously hypertensive rats.

Cytochrome P-450-dependent metabolites of arachidonic acid (AA) increased in the kidneys of young, spontaneously hypertensive rats (SHRs) during the period of rapid elevation of blood pressure (BP) but not in adult SHRs or in Wistar Kyoto rats (WKYs) with normal BP. Treatment of SHRs and WKYs with stannous chloride (SnCl2), which selectively depletes renal cytochrome P-450, restored BP to normal, coincident with a natriuresis, in young but not in adult SHRs and did not affect either BP or sodium excretion in WKYs. Depletion of renal cytochrome P-450 was associated with decreased generation of these AA metabolites only in young SHRs. The antihypertensive effect of SnCl2 in young SHRs was greatly reduced by prevention of its cytochrome P-450-depleting action.

New abdominal collaterals at ultrasound: a clue of progression of portal hypertension.

BACKGROUND: Abdominal ultrasound can detect non-invasively the presence of abdominal portal-systemic collaterals in patients with liver cirrhosis. Abdominal portal-systemic collaterals may be protective from the formation and growth of oesophageal varices, but available data are inconclusive. AIM: We aimed at investigating the relationship between abdominal portal-systemic collaterals and variceal formation and growth. METHODS: We studied 126 cirrhotic patients without (n=43) or with small (n=83) oesophageal varices who entered a protocol of serial ultrasonographic and endoscopic examinations for a median of 55 months. Presence and kind of abdominal portal-systemic collaterals was recorded on first ultrasonography and on each control thereafter. RESULTS: At inclusion, abdominal portal-systemic collaterals were found in 19/43 patients without varices and in 23/83 patients with small varices (NS). There was no difference in variceal formation and growth between patients with and without abdominal portal-systemic collaterals at inclusion. However, patients developing new abdominal portal-systemic collaterals during follow-up had a significantly higher rate of variceal formation (56.2% vs. 22.2%; p=0.024) and growth (52.9% vs. 30.6%; p=0.041) compared with patients with unchanged ultrasonography. CONCLUSIONS: Abdominal collaterals are not protective from the formation or growth of oesophageal varices. Conversely, new abdominal portal-systemic collaterals emergence is a non-invasive clue of formation and progression of varices. Therefore, endoscopy is probably indicated whenever new abdominal portal-systemic collaterals are detected in cirrhotic patients.

Eicosanoid excretion in hepatic cirrhosis. Predominance of 20-HETE.

The cytochrome P450 system transforms AA to hydroxyeicosatetraenoic acid (HETE) metabolites that are vasoactive and affect transport in several nephron segments. A principal product of this system, 20-HETE, participates in key mechanisms that regulate the renal circulation and extracellular fluid volume. We hypothesized that excess production of 20-HETE, which constricts the renal vasculature, contributes to the renal functional disturbances in patients with hepatic cirrhosis, particularly the depression of renal hemodynamics. The development of a precise and sensitive gas chromatographic/mass spectrometric method makes it possible to measure 20-HETE and the subterminal HETEs (16-,17-,18-, and 19-HETEs) in biological fluids. As 20-HETE was excreted as the glucuronide conjugate, measurement of 20-HETE required treatment of urine with glucuronidase. We measured HETEs in the urine of patients with cirrhosis, and compared these values to those of normal subjects. Urinary excretion rate of 20-HETE was highest in patients with ascites; 12.5+/-3.2 ng/min vs. 5.0+/-1.5 and 1.6+/-0.2 ng/min in cirrhotic patients without ascites and in normal subjects, respectively. Excretion of 16-, 17-, and 18-HETEs was not increased. In patients with cirrhosis, the excretory rate of 20-HETE was several-fold higher than those of prostaglandins and thromboxane, whereas in normal subjects 20-HETE and prostaglandins were excreted at similar rates. Of the eicosanoids, only increased excretion of 20-HETE in subjects with cirrhosis was correlated (r = -0.61; P < 0.01) with reduction of renal plasma flow (RPF).

The hemodynamic abnormalities in short-term insulin deficiency: the role of prostaglandin inhibition.

It has been suggested that the hemodynamic derangements present in diabetic ketoacidosis are the results not only of profound volume depletion but also of the effects of increased production of vasodilating prostaglandins (PGs), principally PGI2, released by adipose tissue. In animal and in vitro models, prostaglandin synthesis is increased during insulin deficiency. We assessed the effects of short-term ketosis on the metabolic and hemodynamic variables of 10 IDDM patients free from long-term complications and of 9 normal control subjects after a 7-day randomized double-blind indomethacin (INDO) (50 mg q.i.d.) or placebo treatment period. Calf blood flow (CBF), postocclusive reactive hyperemia (PORH), and recovery half-time (an index of overall perfusion) after PORH were measured by plethysmography. Left ventricular and myocardial functions were also studied in each different condition during placebo and INDO treatment in IDDM patients. During placebo treatment, the increase in CBF during ketosis was higher (1.75 +/- 0.29 ml / min / 100 ml muscle) than during INDO (0.85 +/- 0.17 ml / min) / 100 ml muscle; P = 0.007). PORH was similar in baseline conditions, during ketosis, and in recovery in both the placebo and INDO arms. Recovery half-time significantly increased during placebo (10 +/- 2; 200%; P < 0.01) but not during INDO (1 +/- 1; 106%; NS) treatment. In normal control subjects, insulin deficiency did not induce any significant effect on hemodynamic variables. In IDDM patients, during placebo treatment, ketosis increased both the cardiac index (from 3.4 +/- 0.7 to 4.1 +/- 0.81 / min / m; P < 0.01) and the stroke index (from 42 +/- 8 to 49 +/- 7 ml/m2; P < 0.01) without changes in left ventricular ejection fraction but with a significant increase in both left and right ventricular end-diastolic volumes. Metabolic recovery induced a normalization of these parameters. INDO treatment significantly blunted these alterations. In summary, we showed that during acute insulin deficiency, INDO-sensitive mechanisms mediate vascular disturbances. Moreover, INDO treatment was capable of completely preventing the cardiac venous return and the left ventricular alterations. INDO does not interfere with the overall ketogenetic process or with insulin-induced metabolic recovery.

Role of atrial natriuretic peptide in the pathogenesis of sodium retention in IDDM with and without glomerular hyperfiltration.

The pathogenetic determinants of sodium retention in IDDM are not fully understood. The aim of this study was to elucidate the action of ANP in 11 IDDM patients with high GFR (greater than or equal to 135 ml.min-1 x 1.73 m-2), referred to here as HF patients; in 10 IDDM patients with normal GFR (greater than 90 and less than 135 ml.min-1 x 1.73 m-2), referred to here as NF patients; and 12 control subjects, here called C subjects, at baseline and during saline infusion administered on the basis of either body weight (2 mmol.kg-1 x 60 min-1; Saline 1) or of ECV (12 mM.ECVL-1 x 90 min-1; Saline 2) during euglycemic insulin-glucose clamp. C subjects and both HF and NF IDDM patients received a second Saline 1 infusion accompanied by ANP infusion (0.02 microgram.kg-1.min-1) at euglycemic levels. HF and NF patients were studied again after 3 mo of treatment with (10 mg/day). Quinapril (CI 906, Malesci, Florence, Italy), an ACE inhibitor without sulfhydryl group. At baseline, both HF and NF IDDM patients had higher plasma ANP concentrations than C subjects (HF, 36 +/- 4, P less than 0.01 and NF, 34 +/- 3, P less than 0.01 vs. C, 19 +/- 3 pg/ml). Plasma ANP and natriuretic response to isotonic volume expansion was impaired both in HF (44 +/- 8 pg/ml, NS vs. base) and NF (40 +/- 7 pg/ml, NS vs. base) compared with C (41 +/- 4 pg/ml, P less than 0.01 vs. base) during Saline 1. On the contrary, plasma ANP response to Saline 2 was similar in HF and NF patients and C subjects, but IDDM patients had still lower urinary sodium excretion rates. The simultaneous administration of ANP and Saline 1 resulted in comparable plasma ANP plateaus in C subjects and HF and NF patients. However, urinary sodium excretion rate was significantly lower in HF and NF patients than in C subjects: HF, 267 +/- 64, P less than 0.01 and NF, 281 +/- 42, P less than 0.01 vs. C, 424 +/- 39 mumol.min-1 x 1.73 m-2. During simultaneous administration of ANP and Saline 1, GFR and FF increased in C subjects, but not in HF and NF patients. HF and NF patients had higher urinary vasodilatory prostanoid excretion rates than C subjects at baseline. Saline infusion did not change urinary excretion rate of prostanoids either in C subjects or IDDM patients (both NF and HF).(ABSTRACT TRUNCATED AT 400 WORDS)

Disagreement between acute and chronic haemodynamic effects of nadolol in cirrhosis: a pathophysiological interpretation.

BACKGROUND: The acute effects of beta-blockers may be different from chronic; mechanisms underlying this difference are poorly elucidated. AIM: To assess portal pressure and its pathophysiological determinants after acute and chronic administration of nadolol. METHODS: In 24 patients with cirrhosis and portal hypertension hepatic venous pressure gradient, portal blood flow and resistance to portal blood flow were measured before, 60-90 min after acute administration of nadolol, and after 1 month. Patients were good-responders if hepatic venous pressure gradient was < or =12 mmHg, or decreased by at least 20%. RESULTS: Eleven and 13 patients were good- and poor-responders to acute administration, respectively. Acute poor-responders showed a lower decrease in portal blood flow (P = 0.04) and a less evident decrease in mean arterial pressure (P < 0.001). Eleven and 13 patients were good- and poor-responders to chronic administration, respectively. Chronic poor-responders showed a larger increase in resistance to portal blood flow compared with good-responders (P = 0.01). Disagreement between acute and chronic effects was seen in 12 patients: six were acute good-responders chronic poor-responders and six were acute poor-responders chronic good-responders. Acute good-responders chronic poor-responders patients had the smallest decreases in portal blood flow and in mean arterial pressure after acute administration, while acute poor-responders chronic good-responders showed the largest (P = 0.05 and 0.01). CONCLUSIONS: Disagreement between acute and chronic effects of nadolol on hepatic venous pressure gradient is common. The mechanism responsible is complex, the acute effect being mainly modulated by arterial hypotension and the chronic effect by changes in portal resistance.

Heme oxygenase-1 transduction in endothelial cells causes downregulation of monocyte chemoattractant protein-1 and of genes involved in inflammation and growth.

Heme oxygenase (HO-1) has been implicated as an anti-inflammatory gene. HO-1 overexpression, transiently and chronically, affects heme protein expression, attenuates TNF-mediated cell death, and decreases adhesion molecules. We assessed the effect of oxidant-mediated agents such as glucose and heme on 8-epi-isoprostane PGF2alpha (8-epi-PGF2alpha) and monocyte chemoattractant protein-1 (MCP-1). Glucose and heme increased both 8-epi-PGF2alpha and MCP-1. Overexpression of HO-1 decreased both 8-epi-PGF2alpha and MCP-1. To identify target genes involved in HO-1-mediated regulation of inflammation, a serial analysis of gene expression mRNA profile was performed in endothelial cells (EC) overexpressing the human HO-1 gene by transduction of a retrovirus carrying the HO-1 gene. Gene arrays (differential displays among 2400 genes) were used to identify known and novel differentially expressed genes. The levels of expression for several genes were confirmed by real time PCR in cells overexpressing the HO-1 gene. In HO-1 overexpressing cells, VEGF and the prostaglandin transporter were greatly increased while MCP-1 levels were decreased by 2.5-fold. The data from this study are relevant to understanding the mechanisms underlying the pathophysiological effects of HO-1 deficiency on endothelial cell injury and inflammation.

Comparison of sublingual captopril and nifedipine in immediate treatment of hypertensive emergencies. A randomized, single-blind clinical trial.

Sublingual captopril (25 mg) was compared with sublingual nifedipine (10 mg) to determine their effectiveness and safety in the treatment of hypertensive emergencies. In nine of 10 patients who received sublingual captopril, mean (+/- SD) systolic blood pressure and diastolic blood pressure dropped from 245 +/- 39 to 190 +/- 25 mm Hg (P less than .0025) and from 144 +/- 8 to 115 +/- 8 mm Hg (P less than .001) at 50 minutes, respectively. The hypotensive effect of the drug was maintained for a mean of 4 hours. In six of nine responders to sublingual captopril, blood pressure-lowering effect was associated with a clear improvement of end-organ failure within 60 minutes. There were no side effects, including a dangerous fall in blood pressure or reflex tachycardia. Sublingual nifedipine lowered diastolic blood pressure and systolic blood pressure in eight of 10 patients. The hypotensive effect of nifedipine was more rapid than that of captopril (10 vs 20 minutes for diastolic blood pressure and 20 vs 30 minutes for systolic blood pressure, respectively), but no difference was observed in the time or in the magnitude of peak hypotensive effect between the two treatments, nor was a difference observed in the duration of hypotensive effect. In six of eight responders to nifedipine therapy, a clear improvement of symptoms and signs of end-organ failure was observed within 60 minutes. In three patients, minor side effects were observed. We conclude that sublingual captopril effectively and safely lowers arterial blood pressure in patients with hypertensive emergencies.

Characterization of a murine model of cardiorenal syndrome type 1 by high-resolution Doppler sonography.

ABSTRACT: Cardiorenal syndrome type 1 (CRS-1) is the acute kidney disfunction caused by an acute worsening of cardiac function. CRS-1 is the consequence of renal vasoconstriction secondary to renin-angiotensin system (RAS) activation. No animal models of CRS-1 are described in literature. PURPOSE: To characterize a murine model of CRS-1 by using a high-resolution ultrasound echo-color Doppler system (VEVO2100). MATERIALS: Post-ischemic heart failure was induced by coronary artery ligation (LAD) in seven CD1 mice. Fifteen and thirty days after surgery, mice underwent cardiac and renal echo-color Doppler. Serum creatinine and plasma renin activity were measured after killing. Animals were compared to seven CD1 control mice. RESULTS: Heart failure with left ventricle dilatation (end diastolic area, p < 0.05 vs. controls) and significantly reduced ejection fraction (EF; p < 0.01 vs. controls) was evident 15 days after LAD. We measured a significant renal vasoconstriction in infarcted mice characterized by increased renal pulsatility index (PI; p < 0.05 vs. controls) associated to increased creatinine and renin levels (p < 0.05 vs. controls). CONCLUSIONS: The mice model of LAD is a good model of CRS-1 evaluable by Doppler sonography and characterized by renal vasoconstriction due to the activation of the renin-angiotensin system secondary to heart failure.

Chronic treatment with tin normalizes blood pressure in spontaneously hypertensive rats.

We have reported that short-term treatment of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats with stannous chloride (SnCl2), which selectively depletes renal cytochrome P450, restores blood pressure to normal in young but not in adult SHR, and is without effect on blood pressure of either young or adult WKY rats. We report in the present study that chronic treatment with SnCl2, begun at age 5 weeks, prevented the development of hypertension in SHR over a period of 15 weeks at which time they were killed. Suspension of SnCl2 treatment after 8 weeks (i.e., at age 13 weeks) did not result in return of blood pressure to hypertensive levels in SHR. Age-matched WKY rats were not affected by tin treatment. These findings provide additional evidence that administration of tin, which stimulates heme oxygenase, thereby producing depletion of cytochrome P450, restores blood pressure to normal levels in SHR.

Effects of iloprost, a prostacyclin analog derivative, on renal plasma flow, renal function, and renin-aldosterone system in humans.

The effects of iloprost, a stable analog derivative of prostacyclin, on heart rate, blood pressure, renal plasma flow (RPF), glomerular filtration rate, filtration fraction, urine flow, fractional excretion of sodium (FENa), proximal fractional sodium reabsorption (PFRNa), fractional sodium resorption at the ascending limb of Henle's loop (HFRNa), plasma renin activity (PRA), and plasma aldosterone concentration (PA) were evaluated in patients with peripheral vascular disease and normal renal function. In 10 patients the drug was administered intravenously for 6 hours daily for 6 days at a rate of 1 ng/kg/min. In 7 patients iloprost was also administered at a dose of 2 ng/kg/min for the same time. There was no significant change in heart rate and blood pressure at both iloprost doses. At the dose of 1 ng/kg/min the drug had no effect on renal hemodynamics and function, PRA, and PA. At the dose of 2 ng/kg/min iloprost significantly increased RPF (p less than 0.025) and FENa (p less than 0.025) and significantly decreased HFRNa (p less than 0.025) without affecting glomerular filtration rate, filtration fraction, urine flow, PFRNa, PRA, and PA. No correlation was found between the increase in RPF and FENa (r = 0.01). We conclude that at a dose of 2 ng/kg/min, but not 1 ng/kg/min, iloprost has a natriuretic effect secondary to inhibition of sodium reabsorption at the ascending limb of the Henle's loop and not related to the renal hemodynamic effect.

Renal cytochrome P-450-dependent metabolism of arachidonic acid in spontaneously hypertensive rats.

Renal cytochrome P-450-dependent monooxygenases metabolize arachidonic acid to products some of which affect vascular tone and (Na+,K+)ATPase activity. We measured these metabolites in spontaneously hypertensive (SHR) and control normotensive Wister-Kyoto (WKY) rats. Systolic tail blood pressure in SHR increased from 112 to 202 mm Hg and in WKY from 97 to 136 mm Hg at 5 and 20 weeks respectively. Renal cortical and outer medullary microsomes were incubated with [14C]arachidonic acid; metabolites formed via the cytochrome P-450 pathway were defined as those dependent on NADPH, inhibited by SKF-525A, and unaffected by indomethacin. The P-450-dependent metabolites were higher in SHR vs WKY at 5, 7 and 11 weeks in the cortex and at 7 and 11 weeks in the outer medulla. In the outer medulla, the formation of these metabolites peaked at 7 weeks. Using reverse-phase HPLC, the cytochrome P-450-dependent metabolites were separated into three radioactive peaks: peak I had a retention time of 17.5 min and comigrated as 11,12-dihydroxyeicosatrienoic acid standard. Peak II had a retention time of 19 min and comigrated with omega-hydroxylation compounds. Peak III had a retention time of 27 min and comigrated with 11,12-epoxyeicosatrienoic acid. In the renal cortex, peak I was higher in SHR vs WKY at 5, 7, and 9 weeks and peak III at 5, 7, 9 and 11 weeks. In the outer medulla, peak I was higher in SHR at 5 and 7 weeks, and peaks II and III at 7 weeks. Cytochrome P-450 content in the renal cortex was always higher in SHR vs WKY. We conclude that renal cytochrome P-450-dependent metabolites of arachidonic acid may participate in the circulatory changes of SHR, particularly during the developmental stage.

Effect of chronic treatment with nadolol plus isosorbide mononitrate on liver blood flow and liver metabolic activity in cirrhosis.

OBJECTIVE: To assess the long-term effect of the addition of long-acting nitrates to beta-blockers on liver blood flow and liver metabolic activity in patients with cirrhosis and portal hypertension. METHODS: Eleven patients with cirrhosis and portal hypertension were investigated by using hepatic vein catheterization and indocyanine green (ICG) constant infusion on baseline conditions, after 1 month of treatment with nadolol, after 3 months of treatment with nadolol plus isosorbide mononitrate, and (in seven cases) after 1 year of combined treatment. RESULTS: The hepatic venous pressure gradient decreased significantly after nadolol, and more so after addition of isosorbide mononitrate. Hepatic blood flow, and ICG intrinsic hepatic clearance did not change significantly, although few cases showed an increase or decrease in either parameter. A significant correlation was found between changes in ICG intrinsic hepatic clearance and in hepatic venous pressure gradient (r = 0.62, P = 0.04). CONCLUSIONS: Liver blood flow and liver metabolic activity are not consistently affected by addition of isosorbide mononitrate to nadolol. Substantial decreases in portal pressure may be associated with a decrease in ICG intrinsic hepatic clearance.

Optimizing the time-frame for the definition of bleeding-related death after acute variceal bleeding in cirrhosis.

OBJECTIVE: To identify the best time-frame for defining bleeding-related death after variceal bleeding in patients with cirrhosis. DESIGN: Prospective long-term evaluation of a cohort of 155 patients admitted with variceal bleeding. SETTING: Eight medical departments in seven hospitals in north-eastern Italy. METHODS: Non-linear regression analysis of a hazard curve for death, and Cox's multiple regression analyses using different zero-time points. RESULTS: Cumulative hazard plots gave two slopes, the first corresponding to the risk of death from acute bleeding, the second a baseline risk of death. The first 30 days were outside the confidence limits of the regression curve for the baseline risk of death. Using Cox's regression analysis, the significant predictors of overall mortality risk were balanced between factors related to severity of bleeding and those related to severity of liver disease. If only deaths occurring after 30 days were considered, only predictors related to the severity of liver disease were found to be of importance. CONCLUSION: Thirty days after bleeding is considered to be a reasonable time-frame for the definition of bleeding-related death in patients with cirrhosis and variceal bleeding.

Role of spleen enlargement in cirrhosis with portal hypertension.

The possible relationships between splenomegaly and portal hypertension have been analysed in patients with cirrhosis. In this condition, splenomegaly is not only caused by portal congestion, but it is mainly due to tissue hyperplasia and fibrosis. The increase in spleen size is followed by an increase in splenic blood flow, which participates in portal hypertension actively congesting the portal system.

Noninvasive grading of the severity of portal hypertension in cirrhotic patients by echo-color-Doppler.

The possibility of estimating portal hypertension combining splenic Doppler pulsatility index (PI), which has been shown strictly to be related to portal resistance, and portal blood flow (PBF) was evaluated. Hepatic venous pressure gradient, and splanchnic Doppler parameters were measured in 40 cirrhotic patients. A formula to assess the severity of portal hypertension from Doppler parameters was calculated in a training group of 19 patients, and then this formula was tested to prospectively predict the degree of portal pressure in 21 further patients. In the training group, the regression of portal resistance over splenic PI was calculated and individual values of estimated portal resistance were obtained for every patient of the test group. From them and from observed values of PBF, an estimated value of portal pressure was calculated. The following formula was obtained [(0.066*splenic PI -0.044)*PBF]. In the second group, predicted and observed portal pressure were well correlated (r = 0.71, p = .0003). A good accuracy for the prediction of mild or severe portal hypertension was obtained.

Novel renal arachidonate metabolites.

Cells of the thick ascending limb of the loop of Henle (TALH) metabolize arachidonic acid (AA) via the cytochrome P450 monooxygenase system to biologically active products that are resolved into two peaks, P1 and P2, on reverse-phase HPLC. Each peak contains materials that have characteristic biological activity. P1 contains a material that relaxes blood vessels and is structurally similar to a vasodilator, the 5,6 epoxyeicosatrienoic acid (EET). P2 contains a material that inhibits cardiac Na+-K+-ATPase, the major component of which has been identified as the 11,12 dihydroxyeicosatrienoic acid. In mTALH cells obtained from rabbits made hypertensive by aortic coarctation, there was a selective increase in P1 and P2 formation compared to other renomedullary cells. We have identified AA metabolites in bovine corneal epithelium with biological properties and chemical features similar to those of mTALH cells. 12(R)hydroxyeicosatetraenoic acid (12(R) HETE) a possible derivative of the 11,12-EET, is produced by the cornea and also has been shown to inhibit Na+-K+-ATPase activity. Renal microsomes obtained from spontaneously hypertensive rats (SHRs) also metabolize AA via a cytochrome P450 monooxygenase pathway to three principal biologically active metabolites that are formed in increased amounts during the developmental phase of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of partial hepatectomy on hepatic and renal heme and cytochrome P450 metabolism.

Partial hepatectomy has been suggested to affect hepatic and renal cytochrome P450 content and the related drug metabolizing enzyme system. In addition, cytochrome P450 and its dependent activities have been shown to be regulated by the availability of cellular heme. We, therefore, studied cytochrome P450 in addition to the level of heme oxygenase, the rate-limiting enzyme of heme catabolism, and delta-aminolevulinic acid (ALA) synthase, the rate-limiting enzyme of heme synthesis, in the remnant liver and intact kidneys of rats after two-thirds hepatectomy. The level of hepatic heme oxygenase was elevated threefold in partially hepatectomized rats as compared to sham-operated rats, while ALA synthase was decreased by 40%. This was reflected in decreased hepatic cytochrome P450 content, ie, from 0.689 +/- 0.175 nmole/mg to 0.505 +/- 0.089 nmole/mg protein and associated decreased drug metabolizing enzymes: aryl hydrocarbon hydroxylase, 7-ethoxycoumarin-O-deethylase, and benzphetamine N-demethylase, by 40%, 40%, and 47%, respectively. In contrast, renal heme oxygenase was not changed after hepatectomy, whereas renal ALA synthase was increased by fourfold. Renal cytochrome P450, aryl hydrocarbon hydroxylase, 7-ethoxycoumarin-O-deethylase, and benzphetamine N-demethylase were increased after partial hepatectomy by 84%, 360%, 165% and 406%, respectively. These data indicate that partial hepatectomy decreases liver cytochrome P450 levels by inducing heme oxygenase and inhibiting ALA synthase activities. In this situation the kidney plays a substitutive role in metabolizing endogenous substrates oxygenated by cytochrome P450 isozymes.