Hepatic extraction of chenodeoxycholic acid in dogs chronically intoxicated with dimethylnitrosamine

The pharmacokinetics of chenodeoxycholic acid (CDCA) in hepatic dysfunction were evaluated by analyzing the plasma disappearance curves after simultaneous administration of [3H]- and [14C]-CDCA through the femoral and portal veins, respectively, in dogs chronically intoxicated with dimethylnitrosamine (DMN). The plasma concentration-time curve of intravenously administered [3H]-CDCA was best fitted to a three-exponential equation, while that of intraportally administered [14C]-CDCA was fitted to either a two- or a three-exponential equation. In the DMN-intoxicated dogs, significant decreases were observed in total body plasma clearance (CLp), hepatic extraction ratio (EH) and apparent intrinsic clearance (CLint) compared to those of the untreated (control) dogs. The hepatic blood flow (QH), calculated from CLp, CLint and blood-to-plasma concentration ratio (RB) according to the equation reported by Wilkinson and Shand [Clin. Pharmac. Ther. 18, 377 (1975)], was reduced to approximately 70% in the DMN-intoxicated dogs compared to the control dogs. The bindings of CDCA to plasma and liver cytosol fraction were determined by equilibrium dialysis; no significant difference was observed in the unbound fraction between the DMN-treated and control dogs. By comparing both pharmacokinetic parameters obtained from intravenous and intraportal administration, the usefulness of the oral bile acid tolerance test was examined. From these findings, it was suggested that the decrease in the CLp of the DMN-intoxicated dogs was due to both the decrease in QH and that in CLint, and that the decrease in CLint may be due not to an alteration of plasma or cytosol binding but to that of a carrier-mediated transport system. It is also suggested that the measurement of fasting plasma bile acid concentration or the oral bile acid tolerance test is more sensitive for the detection of hepatic dysfunction than the intravenous bile acid tolerance test.     

Hepatic transport of indocyanine green in rats chronically intoxicated with carbon tetrachloride

Hepatic transport of indocyanine green (ICG) and probable factors altering the disposition of ICG were examined in rats chronically intoxicated with carbon tetrachloride. Delays were shown in both plasma disappearance and biliary excretion of ICG in intoxicated rats. No significant difference was shown in the total amount of ICG bound to the plasma proteins. In the intoxicated rats, significant decreases were observed in the pharmacokinetic parameters, k₁₂, k₃₄ and V₂, calculated by a three-compartment model, while a significant increase was observed in k₂₁; V₁ was not altered. In both the control and intoxicated rats, the values of k₁₂·V₁ were significantly smaller than the hepatic plasma flow, and it was suggested that the plasma flow does not play a primary role in the hepatic uptake of ICG. No significant difference was observed in the elution profiles of the 100,000 g supernatant fraction on a Sephadex G-75 column, and ICG bound mainly to the X-fraction in both the control and intoxicated rats. About 90 per cent of the ICG administered intravenously was distributed to the 9000g precipitate fraction by 5 min in both groups of rats. It was concluded that a decrease in the permeability of the sinusoidal plasma membrane of the hepatocyte may explain the decrease of ICG uptake rate by the livers of the intoxicated rats.     

Blood clearances of 99mTc-phytate and indocyanine green in carbon tetrachloride treated dogs.

The comparative study of the blood clearances of 99mTc-phytate (99mTc-P) and indocyanine green (ICG) was carried out in dogs with hepatic injury induced by carbon tetrachloride (CCl4), and the blood clearance of 99mTc-P or ICG was compared with the levels of serum transaminase and bilirubin. The blood clearances of 99mTc-P and ICG in dogs decreased with increase in doses of CCl4 and with elapsed time after CCl4 administration. The decreases were correspondent to the increase in serum transaminase activity and bilirubin level. The blood clearance test of 99mTc-P in dogs showed a equal degree of sensitivity and a higher degree of accuracy for the acute hepatic dysfunction induced by CCl4 as compared with the blood clearance test of ICG.     

A new method to study glutathione adduct formation in periportal and pericentral regions of the liver lobule by micro-reflectance spectrophotometry

A method was developed to measure the formation of glutathione adducts of 1-chloro-2,4-dinitrobenzene (CDNB) and 2,4-dichloro-1-nitrobenzene (DCNB) in periportal and pericentral regions of the liver lobule in the isolated perfused rat liver by surface reflectance spectrophotometry. Conjugates of DCNB and CDNB are released from livers of normal and phenobarbital-treated rats during perfusion in either the anterograde or the retrograde direction at maximal rates around 13-15 mumol/g/hr. The formation of S-(1-chloro-4-nitrophenyl)-glutathione and S-(2,4-dinitrophenyl)-glutathione by the liver decreased the amount of 366-nm light reflected from the liver surface detected with a large-tipped (2 mm) fiberoptic light guide. Initial rates of decrease in reflected light correlated highly with maximal rates of conjugate formation by the liver. Subsequently, micro-light guides were placed on periportal and pericentral regions of the liver lobule. Rates of glutathione adduct formation were calculated from the proportion of the total change in rate of reflected 366-nm light which occurred in each region and the overall rate of product formation by the liver. Changes in the reflectance signal require reduced glutathione (GSH) and were shown to originate from intracellular conjugate formation and not from adducts in the bile canaliculus. Livers from normal rats produced conjugated products from DCNB (100 microM) at maximal rates of 14 and 15 mumol/g/hr in periportal and pericentral regions of the liver lobule, respectively. With CDNB as substrate, changes in reflected light at 366 nm were detected nearly exclusively in periportal regions of the lobule in livers from normal rats. In sharp contrast, CDNB and DCNB were conjugated exclusively in periportal regions of the lobule at rates of 21-22 mumol/g/hr in livers from phenobarbital-treated rats (i.e., the reflectance signal was not altered by these substrates in pericentral areas). When CDNB and DCNB were infused into livers from phenobarbital-treated rats perfused in the retrograde direction, decreases in reflected light at 366 nm were detected initially in pericentral areas followed in about 12 min by changes in periportal regions. Maximal rates of adduct formation in both regions reached 25 mumol/g/hr during perfusion in the retrograde direction. Thus, pericentral regions indeed possess the capacity to conjugate both CDNB and DCNB. When glutathione synthesis was inhibited with L-buthionine sulfoximine treatment (6 mmol/kg), which partially depletes GSH, CDNB was conjugated in both periportal and pericentral regions of the liver lobule in livers from phenobarbital-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)     

A physiologically based model of hepatic ICG clearance: interplay between sinusoidal uptake and biliary excretion

Although indocyanine green (ICG) has long been used for the assessment of liver function, the respective roles of sinusoidal uptake and canalicular excretion in determining hepatic ICG clearance remain unclear. Here this issue was addressed by incorporating a liver model into a minimal physiological model of ICG disposition that accounts of the early distribution phase after bolus injection. Arterial ICG concentration-time data from awake dogs under control conditions and from the same dogs while anesthetized with 3.5% isoflurane were subjected to population analysis. The results suggest that ICG elimination in dogs is uptake limited since it depends on hepatocellular uptake capacity and on biliary excretion but not on hepatic blood flow. Isoflurane caused a 63% reduction in cardiac output and a 33% decrease in the ICG biliary excretion rate constant (resulting in a 26% reduction in elimination clearance) while leaving unchanged the sinusoidal uptake rate. The terminal slope of the concentration-time curve, K, correlated significantly with elimination clearance. The model could be useful for assessing the functions of sinusoidal and canalicular ICG transporters.     

Pharmacokinetic aspects of sulfobromophthalein transport in chronically carbon tetrachlorideintoxicated rats

In order to elucidate the factors affecting the hepatic transport of sulfobromophthalein (BSP) in a pathological condition, the kinetics of the disappearance of BSP from the blood and appearance in the bile were studied in rats chronically intoxicated with carbon tetrachlorde, and the importance of factors that might affect the kinetics, i.e. binding activites of plasma and hepatic cytoplasmic proteins, and glutathione S-transferase activity of Y-fraction, was examined. During chronic intoxication, although plasma protein albumin concentration decreased, no qualitative difference was shown in the high affinity binding site (K₁). A significant decrease was shown in the cytoplasmic protein concentration for the Y- and Z-fractions in intoxicated rats; no significant difference was observed in the number of binding sites for both fractions, but their binding constants decreased. Glutathione S-transferase activity and glutathione (GSH) content were not altered, although a decrease in conjugating activity per rat was expected. The time course for the plasma disappearance and biliary excretion of BSP showed a remarkable delay after CCl₄ intoxication, while no difference was shown in the bile flow rate. It was concluded that hepatic blood flow might play a primary ro)e in the initial plasma disappearance of BSP and that the decrease in the Y-fraetion binding activity might explain the decrease in BSP uptake rate into the liver which was observed in intoxicated rats.     

Effects of fasting on cadmium toxicity, glutathione metabolism, and metallothionein synthesis in rats

Acute oral toxicity of Cd (as cadmium chloride) was enhanced in rats fasted 24 hr, as shown by a markedly decreased LD50. To examine the relationship among Cd toxicity, hepatic glutathione (GSH), and metallothionein (MT) during fasting, rats were administered 75 mg Cd/kg orally 24 hr after fasting and euthanized after a further 4 or 24 hr for various assays. Serum glutamic-pyruvic transaminase activity 24 hr after Cd treatment was higher in fasted rats than in fed rats. Both total GSH and nonprotein sulfhydryl (NPSH) concentrations in liver decreased to 50% of control levels after 28 hr of fasting and returned to 75% of control values by 48 hr. Total hepatic GSH concentration in fed rats decreased 4 and 24 hr after Cd treatment, whereas that in fasted rats remained unchanged at 4 hr and decreased significantly at 24 hr. Cd uptake by the liver (both concentration and content) 24 hr after Cd treatment was higher in fasted rats than in fed rats. Hepatic MT concentration was markedly increased by Cd treatment and higher in fasted rats than in fed rats. There was no relationship between Cd toxicity and hepatic thiobarbituric acid (TBA) value, an indicator of lipid peroxidation. Fasting had no effect on hepatic GSH peroxidase and GSH reductase activities. These enzymes probably are not involved in Cd toxicity. On histological examination, focal degenerative and necrotic changes were observed from the midlobular to the pericentral region in the livers of fed rats 24 hr after Cd treatment. These changes were enhanced by fasting, diffusing from the pericentral to the periportal region. Histochemical examination revealed a heterogeneous distribution of GSH in the livers of fed rats, with strong staining of GSH in the periportal region. This heterogeneous distribution of GSH in liver was not observed in fed rats 4 hr after Cd treatment or in fasted rats at 24 hr. The present results suggest that hepatic GSH plays an important role in protection against Cd toxicity before the onset of MT synthesis. Animals in bad condition, such as that resulting from interruption of nutrient supply, cannot be protected against Cd toxicity even if the hepatic MT level is high.     

The effect of acute renal failure on the pharmacokinetics of indocyanine green in the rat

The pharmacokinetics of indocyanine green (ICG) have been studied in control rats and rats with acute renal failure (ARF). Three models of ARF were investigated, and these were produced in the following ways: by bilateral ureteral ligation (surgical model), or by parenteral injection of either uranyl nitrate or glycerol. In both control and uraemic rats, from all three models of ARF, the plasma disappearance of ICG was biexponential and from the plasma disappearance curves the rate constants for transfer from plasma to liver (k₁₂), liver to plasma (k₂₁); and liver to bile (k₂₃) were calculated. The initial removal of ICG from plasma was significantly slowed and k₁₂ significantly decreased in male rats with surgically or uranyl nitrate-induced ARF. The plasma clearance of ICG was not affected by surgically-induced ARF but clearance was reduced in the uranyl nitrate model. More complex changes occurred in male rats with glycerol-induced ARF as k₁₂, k₂₁, k₂₃ and plasma clearance of ICG were all significantly decreased. Female rats with glycerol-induced ARF showed significant decreases in k₁₂, and plasma clearance, but these changes were much smaller than in uraemic males.Of the three models of ARF studied the glycerol model was preferred because surgery alone had a pronounced effect upon the kinetics of ICG and wet liver weight was significantly decreased in the uranyl nitrate model. These changes complicated interpretation of the results from the surgical and uranyl nitrate models. The results from the glycerol model suggest that the hepatic uptake of ICG, and possibly its biliary excretion, were reduced in rats with ARF. In addition, liver function in female rats appears to be more resistant than that in males to the effects of glycerol-induced ARF.     

Glucuronidation of 7-hydroxycoumarin in periportal and pericentral regions of the lobule in livers from untreated and 3-methylcholanthrene-treated rats

Rates of production of 7-hydroxycoumarin glucuronide were measured in specific zones of the liver lobule using micro-light guides placed on periportal and pericentral regions on the surface of livers from untreated and 3-methylcholanthrene-treated rats. Livers were perfused with sulfate-free buffer under normoxic conditions and fluorescence of free 7-hydroxycoumarin was monitored. The formation of nonfluorescent 7-hydroxycoumarin glucuronide was then inhibited completely by perfusion with N2-saturated perfusate containing 20 mM ethanol. The difference between fluorescence readings under normoxic and hypoxic conditions was used to calculate rates of glucuronidation. Maximal rates of glucuronidation (11.9-13.5 mumol/g/hr) did not differ significantly in periportal and pericentral regions in livers from either 3-methylcholanthrene-treated or untreated rats. In all regions of the liver lobule, glucuronidation was half-maximal with about 20 microM 7-hydroxycoumarin. Glucuronosyltransferase assayed in lyophilized tissue sections with saturating concentrations of UDPGA (9 mM) was 2.3-fold greater in pericentral than in periportal areas in livers from untreated rats. In livers from 3-methylcholanthrene-treated rats, activities were similar in periportal and pericentral regions but were 4- to 7-fold higher than values from untreated rats. In addition, glucuronosyltransferase activity assayed in native microsomes with physiological concentrations of UDP-glucuronic acid (UDPGA) (0.4 mM) with UDP-N-acetylglucosamine (0.3 mM) was 2-fold higher in preparations from 3-methylcholanthrene-treated than untreated rats. Thus, 3-methylcholanthrene treatment increased glucuronosyltransferase activity in vitro but did not alter rates of glucuronide formation in periportal and pericentral regions of the liver lobule of intact liver. Infusion of epinephrine (50 nM) into perfused livers from untreated and 3-methylcholanthrene-treated rats increased rates of glucuronidation by about 35%. Since epinephrine probably acts by increasing the supply of the cofactor UDPGA due to increased breakdown of glycogen, it follows that UDPGA supply limits rates of glucuronidation in perfused livers from both untreated and 3-methylcholanthrene-treated rats.     

Selective depletion and measurement of glutathione in periportal and pericentral regions in the perfused rat liver

A method was developed to selectively deplete and measure glutathione (GSH) in periportal and pericentral regions of the liver lobule based on the formation of chlorodinitrobenzene-glutathione (CDNB-GSH) adducts. Using microlight guides, we demonstrated that small pulses of CDNB caused reflected light at 366 nm to decline only in upstream regions of the liver lobule. This indicates that GSH was only depleted in upstream periportal or pericentral regions following perfusions in the anterograde or retrograde direction, respectively. Infusion of repeated pulses of CDNB in alternating directions of perfusion (up to eight) allowed selective and complete depletion of GSH in specific sublobular regions. Summation of local rates of adduct formation indicated that GSH content averaged 3.6 +/- 0.8 mumol/g in periportal regions and was 3.3 +/- 0.8 mumol/g in pericentral areas. Total values for GSH calculated from GSH-CDNB adduct formation were nearly identical to levels of GSH measured chemically. This new method may be useful in evaluating the mechanism of toxic chemicals which interact with GSH in discrete regions of the liver lobule.     

Oxidative stress occurs in perfused rat liver at low oxygen tension by mechanisms involving peroxynitrite

Ethanol increases free radical formation; however, it was recently demonstrated that it also causes extensive hypoxia in rat liver in vivo. To address this issue, it was hypothesized that peroxynitrite formed in normoxic periportal regions of the liver lobule has its reactivity enhanced in hypoxic pericentral regions where the pH is lower. Via this pathway, peroxynitrite could lead to free radical formation in the absence of oxygen. Livers from fed rats were perfused at low flow rates for 75 min. Under these conditions, periportal regions were well oxygenated but pericentral areas became hypoxic. Low-flow perfusion caused a significant 6-fold increase in nitrotyrosine accumulation in pericentral regions. During the last 20 min of perfusion, the spin-trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone was infused and adducts were collected for electron-spin resonance analysis. A six-line radical adduct signal was detected in perfusate. Direct infusion of peroxynitrite produced a radical adduct with identical coupling constants, and a similar pattern of nitrotyrosine accumulation was observed. Retrograde perfusion at low rates resulted in accumulation of nitrotyrosine in periportal regions. Although the magnitude of the radical in perfusate was increased by ethanol, it was not derived directly from it. Both nitrotyrosine accumulation and radical formation were reduced by inhibition of nitric oxide synthase with N-nitro-L-arginine methyl ester, but not with the inactive D-isomer. Radical formation was decreased nearly completely by superoxide dismutase and N-nitro-L-arginine methyl ester, consistent with the hypothesis that the final prooxidant is a derivative from both NO. and superoxide (i.e., peroxynitrite). These results support the hypothesis that oxidative stress occurs in hypoxic regions of the liver lobule by mechanisms involving peroxynitrite.     

Menadione causes selective toxicity to periportal regions of the liver lobule

Infusion of increasing concentrations (0.2-1 mM) of the quinone, menadione, caused step-wise increases in oxygen uptake in perfused livers from fasted rats presumably due to oxygen-dependent redox cycling. Maximal increases in oxygen uptake of about 40 mumol/g/h were observed with 0.8 to 1.0 mM menadione. This increase in oxygen uptake was confined to periportal areas of the liver lobule suggesting that redox cycling due to menadione occurs exclusively in cells localized around the portal triad. After 60 min of infusion of menadione (1 mM), lactate dehydrogenase was released from the liver at rates between 60 to 70 U/g/h. Under these conditions, trypan blue was taken up by virtually all hepatocytes in periportal regions of the liver lobule. In contrast, dye was not taken up by cells in pericentral areas. It is concluded that menadione is selectively toxic to hepatocytes located in oxygen-rich periportal regions of the liver lobule.     

Protection against hepatic injury by a novel spiropiperidine derivative

The evaluation of a novel hepatoprotective agent, Y-8845 (8(2-dimethylaminoethyl)-3-oxo-4-phenyl-1-thia-4,8-diazaspiro [4,5]decane dihydrochloride monohydrate), against carbon tetrachloride (CCl4)- and endotoxin-induced acute and chronic hepatic injury was carried out in rats. This compound, in a dose-dependent way, markedly reduced the increases in serum transaminase activities, the extent of liver cell necrosis, and the delay in indocyanine green (ICG) disappearance produced by a single toxic dosage of CCl4. This protective effect was observed even at doses of Y-8845 lower than 10 mg/kg po. It was also shown to protect the liver against injury induced by endotoxin. Furthermore, in the chronic liver injury induced by repeated administrations of CCl4 for 12 weeks, significant reductions of the increases in serum enzyme activities, liver fibrosis, and liver enlargement, and improvement in the ICG retention rate, were recognized in the Y-8845-treated groups at 10 mg/kg po or less. These findings indicate that this new agent has a remarkable protective effect, and possibly a therapeutic effect on liver injury.     

Liver damage following paraquat in selenium-deficient and diethyl maleate-pretreated mice

Human paraquat poisoning often includes a transient impairment of liver function before death due to pulmonary edema and fibrosis. The purpose of this study was to examine the effect of paraquat on liver function in mice fed normal lab chow, in mice fed a selenium (Se)-deficient diet for 5 weeks, and in diethyl maleate-pretreated mice (1.2 ml/kg). Liver function was determined by evaluating plasma activity of glutamic-pyruvic transaminase (SGPT), hexobarbital sleeping time, and plasma disappearance of indocyanine green (ICG). Paraquat, in doses as high as the LD50 (30 mg/kg, ip) did not alter hexobarbital sleeping time or SGPT activity in lab chow-fed mice. Selenium-deficient, paraquat-treated mice, however, had significantly elevated SGPT activity (31 units in control mice, > 1000 units in treated group), had longer hexobarbital sleeping times (from 30 min to > 180 min), and retained ICG in plasma (15-min plasma ICG concentrations of 8.4 mg/100 ml in Se-deficient paraquat-treated group vs 1.3 mg/100 ml in controls). Liver damage in Se-deficient treated mice was also observed histologically. In mice treated with paraquat, diethyl maleate pretreatment produced similar, but not as marked, effects as Se deficiency. The results suggest that paraquat alone is not hepatotoxic in mice; however, Se deficiency or diethyl maleate pretreatment may shift the organ specific toxicity of paraquat toward the liver.     

Glucuronidation of 7-hydroxycoumarin in periportal and pericentral regions of the liver lobule

Rates of glucuronidation were measured at high substrate concentrations in specific zones of the liver lobule using micro-light guides placed on periportal and pericentral regions on the surface of livers from phenobarbital-treated rats. Livers were perfused with sulfate-free buffer under normoxic conditions, and fluorescence of free 7-hydroxycoumarin was monitored in the tissue. The formation of nonfluorescent 7-hydroxycoumarin glucuronide was then inhibited completely by perfusion with N2-saturated perfusate containing 20 mM ethanol. Under these conditions, fluorescence recorded from the surface of the liver was directly proportional to the concentration of substrate infused. The difference in 7-hydroxycoumarin fluorescence between N2 plus ethanol and normoxic perfusion was due to glucuronidation. Maximal rates of glucuronidation in periportal and pericentral regions of the liver lobule calculated with this new method were 9.6 and 35 mumoles/g/hr, respectively. Glucuronidation was half-maximal with 25-50 microM 7-hydroxycoumarin in both regions. Glucuronosyltransferase activity assayed in microdissected, freeze-dried tissue samples in vitro was 3-fold greater in pericentral areas than in periportal areas. This activity was half-maximal with 0.2 mM UDP-glucuronic acid and 54 microM 7-hydroxycoumarin in both regions of the liver lobule. Thus, the maximal capacity of the glucuronidation system determined in vitro is about 3-fold greater in pericentral than in periportal regions of the liver lobule, a difference which correlates well with measured rates of glucuronidation of 7-hydroxycoumarin in the two zones of the lobule in the intact, perfused liver.     

Mechanism of zone-specific hepatic steatosis caused by valproate: inhibition of ketogenesis in periportal regions of the liver lobule

Microvacuolar steatosis in periportal regions of the liver lobule was produced by injection of fasted rats with a single dose of valproate (500 mg/kg, subcutaneously). In livers perfused in the absence of exogenous fatty acids, ketone body (acetoacetate + beta-hydroxybutyrate) production was decreased by valproate (500 microM) maximally by 67%. Concomitantly, NADH fluorescence detected from the liver surface declined about 30% with a time course similar to that of the inhibition of ketogenesis. Valproate had little effect on oxygen uptake but caused an elevation of the steady state level of catalase-H2O2 corresponding to an increase in H2O2 production of about 6 mumol/g/hr. In addition, valproate decreased the rate of oxidized glutathione release into bile by 45% but had little effect on bile flow. In the presence of oleate (250 microM), valproate inhibited ketone body production by 46% and decreased NADH fluorescence by 39%. Rates of ketogenesis in periportal and pericentral regions of the liver lobule were calculated from changes in NADH fluorescence detected with micro-light guides during infusion of valproate in the presence and absence of fatty acids. In the absence of valproate, endogenous ketogenesis was about 35 mumol/g/hr in both regions of the liver lobule. In the presence of oleate, however, rates were significantly higher in pericentral regions (89 +/- 2 mumol/g/hr) than in periportal areas (71 +/- 3 mumol/g/hr). In the presence of added oleate, valproate decreased rates of ketogenesis to 34 +/- 4 mumol/g/hr in periportal regions and 51 +/- 3 mumol/g/hr in pericentral areas. We conclude, therefore, that fat accumulates in periportal areas because valproate depresses ketogenesis to a greater extent in hepatocytes localized around the portal triad.     

Effect of 2-methylaminoethyl-4,4'-dimethoxy-5,6,5',6'-dimethylenedioxybiphenyl-2-carboxylic acid-2'-carboxylate monohydrochloride (DDB-S) on indocyanine green (ICG) clearance in rats

The clearance of ICG, a known hepatic blood flow marker was investigated in rats in order to examine whether DDB-S influences hepatic blood flow. The effect of DDB-S on the protein binding and blood-to-plasma partition of ICG was measured. The steady-state plasma concentration of ICG was monitored before and after co-administration of various concentration of DDB-S, and ICG clearance was estimated from the steady-state concentration and the infusion rate of ICG. There was no significant difference in protein binding and blood-to-plasma partition of ICG with and without addition of DDB-S (10, 20, and 40 microg/mL). When ICG was infused into DDB-S pretreated rats, the steady-state concentrations of ICG decreased and the calculated ICG clearance increased. However, no dose-dependency of ICG Css on DDB-S Css was observed. Since DDB-S did not affect the protein binding and blood-to-plasma partition of ICG, the increased clearance of ICG with co-administration of DDB-S seems to be due to the increased hepatic blood flow by DDB-S.     

The effect of ranitidine on the plasma clearance and hepatic extraction of indocyanine green in patients with chronic liver disease.

Since hepatic clearance of ICG is reduced by H2-receptor antagonists in normal subjects, it has been suggested that they reduce liver blood flow. We have studied the effect of intravenous ranitidine on ICG clearance in twelve patients with chronic liver disease. Wedged and free hepatic venous pressure were measured before and after intravenous ranitidine in nine of the patients, and the hepatic extraction of ICG was determined in six patients. ICG clearance fell by 22 +/- 11% (s.e. mean) 60 min after ranitidine. In patients in whom ICG clearance fell after intravenous ranitidine the hepatic extraction of ICG was also reduced. There was no significant change in the gradient between wedged and free hepatic venous pressure after ranitidine. It is therefore unlikely that ranitidine lowers liver blood flow.     

Hepatic Blood Flow Measurements and Indocyanine Green Kinetics in a Chronic Dog Model

The objective of this study was to compare hepatic blood flow measurements using ultrasonic flow probes and ICG in a conscious dog model and to evaluate whether ICG can be used to estimate relative change in hepatic blood flow. Seven mongrel dogs (3 M, 4 F, BW = 21 ± 1.8 kg, Hct = 0.39 ± 0.05) were used in the study. Catheters were surgically inserted into carotid artery and portal, hepatic and jugular vein. Transit-time ultrasonic flow probes were implanted around the portal vein and hepatic artery. After two weeks of recovery, a single i.v. bolus dose of ICG (0.5 mg/kg) was administered to each dog. The disposition profiles for ICG in the four catheters were measured for 15 minutes and the hepatic blood flow reading from the probes recorded. Jugular vein ICG blood clearance (Cl = 5.9 ± 1.1 ml/min/kg) was low compared to the electronically measured hepatic blood flow rate (Q = 27.8 ± 9.1 ml/min/kg). Extraction ratios (E = 0.15 ± 0.05) estimated using data from the inlet and the outlet of the liver were consistent with the clearance values, suggesting that ICG is not highly extracted by dog livers. Three dogs were used in experiments where liver blood flow was increased by food intake. Consistent with characteristics of low extraction ratio drugs, ICG was insensitive to blood flow changes while there was an overall increase in electronically measured liver blood flow of 30%. Therefore, ICG is a poor indicator of hepatic blood flow and the present dog model permits continuous and reliable measurements of hepatic blood flow and can be a useful tool in studying the effects of hepatic hemodynamics on pharmacokinetics.