Methodological problems in the use of indocyanine green to estimate hepatic blood flow and ICG clearance in man

Quantitative liver SPECT/CT is a novel tool to assess liver function, prognosis, and response to treatment in cirrhosis

Background

Functional liver reserve is an important determinant of survival in cirrhosis. The traditional indocyanine green test (ICG) is cumbersome. Hence, we developed and validated a novel liver imaging, a hybrid of SPECT and CT (Q-SPECT/CT), for evaluating disease severity, outcomes, and response to treatment in decompensated cirrhosis (DC).

Methods

We recruited a cohort of DC patients at a tertiary institute between 2016-2019. First, we standardized the Q-SPECT/CT across a predefined range of volumes through phantom experiments. Then we performed clinical and laboratory evaluations, ICG test (retention at 15 min), and Q-SPECT/CT at baseline and 12 months of granulocyte colony-stimulating factor (G-CSF) and standard medical treatment (SMT).

Results

In 109 DC patients, 87.1% males, aged 51 ± 10 years, MELD: 14 (7-21), the percent quantitative liver uptake (%QLU) on Q-SPECT/CT exhibited a strong correlation with CTP (r = -0.728, p < 0.001), MELD (r = -0.743; p < 0.001) and ICG-R-15 (r = -0.720, p < 0.001) at baseline. %QLU had the maximum discrimination (AUC: 0.890-0.920), sensitivity (88.9-90.3%), specificity (81.2-90.7%), and accuracy (85.8-89.4%) than liver volumes on Q-SPECT/CT or ICG test for classifying patients in CTP/MELD based prognostic categories. A significant increase in %QLU (26.09 ± 10.06 to 31.2 ± 12.19, p = 0.001) and improvement in CTP/MELD correlated with better survival of G-CSF treated DC patients (p < 0.05). SMT did not show any improvement in Q-SPECT/CT or clinical severity scores (p > 0.05). %QLU > 25 (adj.H.R.: 0.234, p = 0.003) and G-CSF treatment (adj.H.R.: 0.414, p = 0.009) were independent predictors of better 12-months survival in DC.

Conclusion

Q-SPECT/CT (%QLU) is a novel non-invasive, diagnostic, prognostic, and theragnostic marker of liver reserve and its functions in cirrhosis patients.

Clinical trial registration

Clinicaltrials.gov, NCT02451033 and NCT03415698.

Physiologically Based Modeling of the Effect of Physiological and Anthropometric Variability on Indocyanine Green Based Liver Function Tests

Accurate evaluation of liver function is a central task in hepatology. Dynamic liver function tests (DLFT) based on the time-dependent elimination of a test substance provide an important tool for such a functional assessment. These tests are used in the diagnosis and monitoring of liver disease as well as in the planning of hepatobiliary surgery. A key challenge in the evaluation of liver function with DLFTs is the large inter-individual variability. Indocyanine green (ICG) is a widely applied test compound used for the evaluation of liver function. After an intravenous administration, pharmacokinetic (PK) parameters are calculated from the plasma disappearance curve of ICG which provide an estimate of liver function. The hepatic elimination of ICG is affected by physiological factors such as hepatic blood flow or binding of ICG to plasma proteins, anthropometric factors such as body weight, age, and sex, or the protein amount of the organic anion-transporting polypeptide 1B3 (OATP1B3) mediating the hepatic uptake of ICG. Being able to account for and better understand these various sources of inter-individual variability would allow to improve the power of ICG based DLFTs and move toward an individualized evaluation of liver function. Within this work we systematically analyzed the effect of various factors on ICG elimination by the means of computational modeling. For the analysis, a recently developed and validated physiologically based pharmacokinetics (PBPK) model of ICG distribution and hepatic elimination was utilized. Key results are (i) a systematic analysis of the variability in ICG elimination due to hepatic blood flow, cardiac output, OATP1B3 abundance, liver volume, body weight and plasma bilirubin level; (ii) the evaluation of the inter-individual variability in ICG elimination via a large in silico cohort of n = 100,000 subjects based on the NHANES cohort with special focus on stratification by age, sex, and body weight; (iii) the evaluation of the effect of various degrees of cirrhosis on variability in ICG elimination. The presented results are an important step toward individualizing liver function tests by elucidating the effects of confounding physiological and anthropometric parameters in the evaluation of liver function via ICG.

Hepatic blood volume is decreased in patients with cirrhosis and does not decrease further after a meal like in healthy persons

BACKGROUND & AIMS

The aim was to measure fractional hepatic blood volume (HBV) and hepatic blood flow (HBF) before and after a meal in patients with cirrhosis (n = 7) and healthy persons (n = 6).

METHODS

Catheters were placed in a radial artery and a hepatic vein for blood sampling and a peripheral vein for indocyanine green (ICG) infusion. A 6-min positron emission tomography (PET) liver scan was performed after inhalation of 1000 MBq ¹⁵O-CO and repeated after ingestion of a standard meal. HBV was calculated as the ¹⁵O-CO concentration in liver tissue (PET) divided by that in arterial blood. HBF was calculated from ICG infusion rate and arterial and hepatic venous blood concentrations according to Fick's principle.

RESULTS

Mean fasting HBV was 14 mL blood/100 mL liver tissue in patients with cirrhosis and 21 mL blood/100 mL liver tissue in healthy subjects (p < .01). Mean HBV did not change postprandially in patients with cirrhosis (13 mL blood/100 mL liver tissue) but decreased in healthy subjects (17 mL blood/100 mL liver tissue; p = .02). Mean fasting HBF was 1.5 L blood/min in patients with cirrhosis and 1.1 L blood/min in healthy subjects and increased in both groups of subjects to 1.8 L blood/min.

CONCLUSIONS

Fasting HBV was lower in patients with cirrhosis and did not decrease postprandially as it did in the healthy controls although the HBF increased equally. Patients with cirrhosis thus have a disturbed hemodynamic response to normo-physiological changes such as a meal.

Hepatic bile acid transport increases in the postprandial state: A functional 11C-CSar PET/CT study in healthy humans

Background & Aims

It is not known how hepatic bile acids transport kinetics changes postprandially in the intact liver. We used positron emission tomography (PET)/computed tomography (CT) with the tracer [N-methyl-¹¹C]cholylsarcosine (¹¹C-CSar), a synthetic sarcosine conjugate of cholic acid, to quantify fasting and postprandial hepatic bile acid transport kinetics in healthy human participants.

Methods

Six healthy human participants underwent dynamic liver ¹¹C-CSar PET/CT (60 min) during fasting and from 15 min after ingestion of a standard liquid meal. Hepatobiliary secretion kinetics of ¹¹C-CSar was calculated from PET data, blood samples (arterial and hepatic venous) and hepatic blood flow measured using indocyanine green infusion.

Results

In the postprandial state, hepatic blood perfusion increased on average by 30% (p <0.01), and the flow-independent hepatic intrinsic clearance of ¹¹C-CSar from blood into bile increased by 17% from 1.82 (range, 1.59–2.05) to 2.13 (range, 1.75–2.50) ml blood/min/ml liver tissue (p = 0.042). The increased intrinsic clearance of ¹¹C-CSar was not caused by changes in the basolateral clearance efficacy of ¹¹C-CSar but rather by an upregulated apical transport, as shown by an increase in the rate constant for apical secretion of ¹¹C-CSar from hepatocyte to bile from 0.40 (0.25–0.54) min⁻¹ to 0.67 (0.36–0.98) min⁻¹ (p = 0.03). This resulted in a 33% increase in the intrahepatic bile flow (p = 0.03).

Conclusions

The rate constant for the transport of bile acids from hepatocytes into biliary canaliculi and the bile flow increased significantly in the postprandial state. This reduced the mean ¹¹C-CSar residence time in the hepatocytes.

Lay summary

Bile acids are important for digestion of dietary lipids including vitamins. We examined how the secretion of bile acids by the liver into the intestines changes after a standard liquid meal. The transport of bile acids from liver cells into bile and bile flow was increased after the meal.

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Following a meal, the active transport of bile acids from hepatocytes into bile is increased significantly.

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A meal also increases bile flow out of the liver.

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The postprandial changes are induced shortly after intake of a meal.

Exploring the Link Between Hepatic Perfusion and Endotoxemia in Hemodialysis

Introduction

The liver receives gut-derived endotoxin via the portal vein, clearing it before it enters systemic circulation. Hemodialysis negatively impacts the perfusion and function of multiple organs systems. Dialysate cooling reduces hemodialysis-induced circulatory stress and protects organs from ischemic injury. This study examined how hemodialysis disrupts liver hemodynamics and function, its effect on endotoxemia, and the potential protective effect of dialysate cooling.

Methods

Fifteen patients were randomized to receive either standard (36.5°C dialysate temperature) or cooled (35.0°C) hemodialysis first in a two-visit crossover trial. We applied computed tomography (CT) liver perfusion imaging to patients before, 3 hours into and after each hemodialysis session. We measured hepatic perfusion and perfusion heterogeneity. Hepatic function was measured by indocyanine green (ICG) clearance. Endotoxin levels in blood throughout dialysis were also measured.

Results

During hemodialysis, overall liver perfusion did not significantly change, but portal vein perfusion trended towards increasing (P = 0.14) and perfusion heterogeneity significantly increased (P = 0.038). In addition, ICG clearance decreased significantly during hemodialysis (P = 0.016), and endotoxin levels trended towards increasing during hemodialysis (P = 0.15) and increased significantly after hemodialysis (P = 0.037). Applying dialysate cooling trended towards abrogating these changes but did not reach statistical significance compared to standard hemodialysis.

Conclusion

Hemodialysis redistributes liver perfusion, attenuates hepatic function, and results in endotoxemia. Higher endotoxin levels in end-stage renal disease (ESRD) patients may result from the combination of decreased hepatic clearance function and increasing fraction of liver perfusion coming from toxin-laden portal vein during hemodialysis. The protective potential of dialysate cooling should be explored further in future research studies.

Obeticholic acid improves hepatic bile acid excretion in patients with primary biliary cholangitis

BACKGROUND & AIMS

Obeticholic acid (OCA) is an agonist of the nuclear bile acid receptor farnesoid X receptor, which regulates hepatic bile acid metabolism. We tested whether OCA treatment would influence hepatic transport of conjugated bile acids in patients with primary biliary cholangitis (PBC) who responded inadequately to treatment with ursodeoxycholic acid (UDCA).

METHODS

Eight UDCA-treated patients with PBC with alkaline phosphatase ≥1.5 times the upper limit of normal range participated in a double-blind, placebo-controlled study. While continuing on UDCA, the patients were randomised to two 3-month crossover treatment periods with placebo and OCA, in random order, separated by a 1-month washout period without study treatment. After each of the two treatment periods, we determined rate constants for transport of conjugated bile acids between blood, hepatocytes, biliary canaliculi, and bile ducts by positron emission tomography of the liver using the conjugated bile acid tracer [N-methyl-¹¹C]cholylsarcosine (¹¹C-CSar). The hepatic blood perfusion was measured using infusion of indocyanine green and Fick's principle.

RESULTS

Compared with placebo, OCA increased hepatic blood perfusion by a median of 11% (p = 0.045), the unidirectional uptake clearance of ¹¹C-CSar from blood into hepatocytes by a median of 11% (p = 0.01), and the rate constant for secretion of ¹¹C-CSar from hepatocytes into biliary canaliculi by a median of 73% (p = 0.03). This resulted in an OCA-induced decrease in the hepatocyte residence time of ¹¹C-CSar by a median of 30% (p = 0.01), from group median 11 min to 8 min.

CONCLUSIONS

This study of UDCA-treated patients with PBC showed that, compared with placebo, OCA increased the hepatic transport of the conjugated bile acid tracer ¹¹C-CSar, and thus endogenous conjugated bile acids, from hepatocytes into biliary canaliculi. As a result, OCA reduced the time hepatocytes are exposed to potentially cytotoxic bile acids.

LAY SUMMARY

Primary biliary cholangitis is a chronic liver disease in which the small bile ducts are progressively destroyed. We tested whether the treatment with obeticholic acid (OCA) would improve liver excretion of bile acids compared with placebo in 8 patients with primary biliary cholangitis. A special scanning technique (PET scan) showed that OCA increased the transport of bile acids from blood to bile. OCA thereby reduced the time that potentially toxic bile acids reside in the liver by approximately one-third.

Hepatobiliary transport kinetics of the conjugated bile acid tracer 11C-CSar quantified in healthy humans and patients by positron emission tomography

BACKGROUND & AIMS

Hepatobiliary secretion of bile acids is an important liver function. Here, we quantified the hepatic transport kinetics of conjugated bile acids using the bile acid tracer [N-methyl-¹¹C]cholylsarcosine (¹¹C-CSar) and positron emission tomography (PET).

METHODS

Nine healthy participants and eight patients with varying degrees of cholestasis were examined with ¹¹C-CSar PET and measurement of arterial and hepatic venous blood concentrations of ¹¹C-CSar.

RESULTS

Results are presented as median (range). The hepatic intrinsic clearance was 1.50 (1.20-1.76) ml blood/min/ml liver tissue in healthy participants and 0.46 (0.13-0.91) in patients. In healthy participants, the rate constant for secretion of ¹¹C-CSar from hepatocytes to bile was 0.36 (0.30-0.62)min^-1, 20 times higher than the rate constant for backflux from hepatocytes to blood (0.02, 0.005-0.07min^-1). In the patients, rate constant for transport from hepatocyte to bile was reduced to 0.12 (0.006-0.27)min^-1, 2.3times higher than the rate constant for backflux to blood (0.05, 0.04-0.09). The increased backflux did not fully normalize exposure of the hepatocyte to bile acids as mean hepatocyte residence time of ¹¹C-CSar was 2.5 (1.6-3.1)min in healthy participants and 6.4 (3.1-23.7)min in patients. The rate constant for transport of ¹¹C-CSar from intrahepatic to extrahepatic bile was 0.057 (0.023-0.11)min^-1 in healthy participants and only slightly reduced in patients 0.039 (0.017-0.066).

CONCLUSIONS

This first in vivo quantification of individual steps involved in the hepatobiliary secretion of a conjugated bile acid in humans provided new insight into cholestatic disease.

LAY SUMMARY

Positron emission tomography (PET) using the radiolabelled bile acid (¹¹C-CSar) enabled quantification of the individual steps of the hepatic transport of bile acids from blood to bile in man. Cholestasis reduced uptake and secretion and increased backflux to blood. These findings improve our understanding of cholestatic liver diseases and may support therapeutic decisions.

CLINICAL TRIAL REGISTRATION NUMBER

The trial is registered at ClinicalTrials.gov (NCT01879735).

Glucagon-to-insulin ratio is pivotal for splanchnic regulation of FGF-21 in humans

BACKGROUND & AIMS

Fibroblast growth factor 21 (FGF-21) is a liver-derived metabolic regulator induced by energy deprivation. However, its regulation in humans is incompletely understood. We addressed the origin and regulation of FGF-21 secretion in humans.

METHODS

By determination of arterial-to-venous differences over the liver and the leg during exercise, we evaluated the organ-specific secretion of FGF-21 in humans. By four different infusion models manipulating circulating glucagon and insulin, we addressed the interaction of these hormones on FGF-21 secretion in humans.

RESULTS

We demonstrate that the splanchnic circulation secretes FGF-21 at rest and that it is rapidly enhanced during exercise. In contrast, the leg does not contribute to the systemic levels of FGF-21. To unravel the mechanisms underlying the regulation of exercise-induced hepatic release of FGF-21, we manipulated circulating glucagon and insulin. These studies demonstrated that in humans glucagon stimulates splanchnic FGF-21 secretion whereas insulin has an inhibitory effect.

CONCLUSIONS

Collectively, our data reveal that 1) in humans, the splanchnic bed contributes to the systemic FGF-21 levels during rest and exercise; 2) under normo-physiological conditions FGF-21 is not released from the leg; 3) a dynamic interaction of glucagon-to-insulin ratio regulates FGF-21 secretion in humans.

Regional metabolic liver function measured in patients with cirrhosis by 2-[¹⁸F]fluoro-2-deoxy-D-galactose PET/CT

BACKGROUND & AIMS

There is a clinical need for methods that can quantify regional hepatic function non-invasively in patients with cirrhosis. Here we validate the use of 2-[(18)F]fluoro-2-deoxy-d-galactose (FDGal) PET/CT for measuring regional metabolic function to this purpose, and apply the method to test the hypothesis of increased intrahepatic metabolic heterogeneity in cirrhosis.

METHODS

Nine cirrhotic patients underwent dynamic liver FDGal PET/CT with blood samples from a radial artery and a liver vein. Hepatic blood flow was measured by indocyanine green infusion/Fick's principle. From blood measurements, hepatic systemic clearance (Ksyst, Lblood/min) and hepatic intrinsic clearance (Vmax/Km, Lblood/min) of FDGal were calculated. From PET data, hepatic systemic clearance of FDGal in liver parenchyma (Kmet, mL blood/mL liver tissue/min) was calculated. Intrahepatic metabolic heterogeneity was evaluated in terms of coefficient-of-variation (CoV, %) using parametric images of Kmet.

RESULTS

Mean approximation of Ksyst to Vmax/Km was 86% which validates the use of FDGal as PET tracer of hepatic metabolic function. Mean Kmet was 0.157 mL blood/mL liver tissue/min, which was lower than 0.274 mL blood/mL liver tissue/min, previously found in healthy subjects (p<0.001), in accordance with decreased metabolic function in cirrhotic livers. Mean CoV for Kmet in liver tissue was 24.4% in patients and 14.4% in healthy subjects (p<0.0001). The degree of intrahepatic metabolic heterogeneity correlated positively with HVPG (p<0.05).

CONCLUSIONS

A 20-min dynamic FDGal PET/CT with arterial sampling provides an accurate measure of regional hepatic metabolic function in patients with cirrhosis. This is likely to have clinical implications for the assessment of patients with liver disease as well as treatment planning and monitoring.

Hepatic galactose metabolism quantified in humans using 2-18F-fluoro-2-deoxy-D-galactose PET/CT

Accurate quantification of regional liver function is needed, and PET of specific hepatic metabolic pathways offers a unique method for this purpose. Here, we quantify hepatic galactose elimination in humans using PET and the galactose analog 2-(18)F-fluoro-2-deoxy-d-galactose ((18)F-FDGal) as the PET tracer.

METHODS

Eight healthy human subjects underwent (18)F-FDGal PET/CT of the liver with and without a simultaneous infusion of galactose. Hepatic systemic clearance of (18)F-FDGal was determined from linear representation of the PET data. Hepatic galactose removal kinetics were determined using measurements of hepatic blood flow and arterial and liver vein galactose concentrations at increasing galactose infusions. The hepatic removal kinetics of (18)F-FDGal and galactose and the lumped constant (LC) were determined.

RESULTS

The mean hepatic systemic clearance of (18)F-FDGal was significantly higher in the absence than in the presence of galactose (0.274 ± 0.001 vs. 0.019 ± 0.001 L blood/min/L liver tissue; P < 0.01), showing competitive substrate inhibition of galactokinase. The LC was 0.13 ± 0.01, and the (18)F-FDGal PET with galactose infusion provided an accurate measure of the local maximum removal rate of galactose (V(max)) in liver tissue compared with the V(max) estimated from arterio-liver venous (A-V) differences (1.41 ± 0.24 vs. 1.76 ± 0.08 mmol/min/L liver tissue; P = 0.60). The first-order hepatic systemic clearance of (18)F-FDGal was enzyme-determined and can thus be used as an indirect estimate of galactokinase capacity without the need for galactose infusion or knowledge of the LC.

CONCLUSION

(18)F-FDGal PET/CT provides an accurate in vivo measurement of human galactose metabolism, which enables the quantification of regional hepatic metabolic function.

Hepatic blood perfusion measured by 3-minute dynamic 18F-FDG PET in pigs

There is an unmet clinical need for an imaging method for quantification of hepatic blood perfusion. The purpose of the present study was to develop and validate a PET method using blood-to-cell clearance (K(1)) of (18)F-FDG, 3-O-(11)C-methylglucose ((11)C-MG), or 2-(18)F-fluoro-2-deoxy-D-galactose ((18)F-FDGal) as a measure of hepatic blood perfusion without the need for portal venous blood samples. We aimed to make the method as simple as possible with the prospect of future application to clinical studies. For this purpose, we examined the possibility of using a 3-min data acquisition and a model-derived dual input calculated from measurements of radioactivity concentrations in a peripheral artery.

METHODS

Pigs (40 kg) underwent dynamic PET of the liver with (18)F-FDG, (11)C-MG, or (18)F-FDGal with simultaneous measurements of time-activity curves in blood sampled from a femoral artery and the portal vein (PV); blood flow rates were measured in the hepatic artery (HA) and PV by transit-time flow meters. Two input functions were compared: A measured dual input and a model-derived dual input, the latter with the PV time-activity curve estimated from the measured arterial time-activity curve and a previously validated 1-parametric PV model. (K(1)) was estimated for each tracer by fitting compartmental models to the data, comparing 3-min and 60-min data acquisitions and the 2 dual-input time-activity curves.

RESULTS

Agreement between (K(1)) estimated using the measured and the model-derived dual input was good for all 3 tracers. For (18)F-FDG and (11)C-MG, (K(1)) (3-min data acquisition, model-derived dual input, and 1-tissue compartmental model) correlated to the measured blood perfusion (P = 0.01 and P = 0.07, respectively). For (18)F-FDGal, the correlation was not significant.

CONCLUSION

A simplified method for quantification of hepatic blood perfusion using 3-min dynamic (18)F-FDG PET or (11)C-MG PET with blood sampling from only a peripheral artery was developed. Parametric (K(1)) images were constructed and showed homogeneous blood perfusion in these normal livers.

Pulse dye densitometry and indocyanine green plasma disappearance in ASA physical status I-II patients

BACKGROUND

Indocyanine green plasma disappearance rate (ICG-PDR) is used to evaluate hepatic function. Although hepatic failure is generally said to occur with an ICG-PDR <18%/min, ICG disappearance rate is poorly defined in the healthy population, and a clear cutoff value of ICG-PDR that discriminates between normal hepatic function and hepatic failure has not yet been described. We therefore defined the ICG disappearance rate in an otherwise healthy patient population. In addition, we evaluated the noninvasive measurement of ICG-PDR (transcutaneously by pulse dye densitometry [PDD] at the finger and the nose) and compared these with the simultaneously performed invasive measurements of ICG-PDR (in arterial blood).

METHODS

In patients without signs of liver disease, scheduled for elective nonhepatic surgery, 10 mg ICG was administered IV and ICG-PDR measured by PDD (DDG-2001, Nihon Kohden, Tokyo, Japan). In a subset of patients, arterial blood samples were gathered to compare PDD with invasive ICG measurements. Methods were compared using Bland-Altman analysis. The results of our study and reported studies on discriminative use of ICG-PDR in assessing liver failure were used to construct receiver operating characteristic curves.

RESULTS

Forty-one patients were studied: 33 using the finger probe and 8 using the nose probe. The mean +/- SD noninvasive ICG-PDR in this patient population is 23.1% +/- 7.9%/min (n = 41) with a range of 9.7% to 43.2%/min. Bias (+/-2 sd, limits of agreement) for ICG-PDR measured by PDD compared with those measured in arterial blood were 1.6%/min (-5.2% to 8.3%/min) for the finger probe and -6.0%/min (-15.5% to 3.4%/min) for the nose probe.

CONCLUSION

ICG-PDR values in a population without liver failure ranged well below 18%/min, cited as the cutoff value for hepatic failure. This cutoff value needs reconsideration. In addition, we conclude that the ICG concentration is adequately determined noninvasively by PDD.

Hepatic ethanol elimination kinetics in patients with cirrhosis

OBJECTIVE

To address the question of whether increased ethanol elimination in alcoholics can be ascribed to increased metabolism via alcohol dehydrogenase (ADH; K(m) around 0.2 mM) or the microsomal ethanol-oxidizing system (MEOS; K(m) 10 mM) by kinetic analysis of hepatic ethanol elimination in recently drinking patients with alcoholic cirrhosis and healthy subjects. A further objective was to investigate whether systemic clearance of ethanol at low arterial ethanol concentrations can be used as a measure of hepatic blood flow.

MATERIAL AND METHODS

Six patients with alcoholic cirrhosis were enrolled after 2 days of abstinence, along with 6 healthy subjects. Ethanol was administered as 6 successive infusions in increasing doses. Arterial and hepatic venous blood concentrations of ethanol were measured; hepatic blood flow was measured simultaneously. Kinetic parameters were calculated according to the sinusoidal perfusion model of enzymatic elimination by the intact liver.

RESULTS

Mean hepatic K(m) for ethanol was 0.16 mM (range 0.09-0.36) in healthy subjects and 0.36 mM (range 0.16-0.69) in patients with cirrhosis (p>0.3), both compatible with the K(m) for ADH. The two groups of subjects had similar V(max) values (p>0.3). Extrahepatic elimination of ethanol accounted for more than 50% of total elimination in both groups, which precludes the use of systemic clearance as a measure of hepatic blood flow.

CONCLUSIONS

The results support the hypothesis that ADH remains the main pathway for hepatic elimination of ethanol in recently drinking patients with alcoholic cirrhosis. We interpret this as evidence against a significant contribution of MEOS in vivo.

Sildenafil does not influence hepatic venous pressure gradient in patients with cirrhosis

AIM

To investigate if sildenafil increases splanchnic blood flow and changes the hepatic venous pressure gradient (HVPG) in patients with cirrhosis. Phosphodiesterase type-5 inhibitors are valuable in the treatment of erectile dysfunction and pulmonary hypertension in patients with end-stage liver disease. However, the effect of phosphodiesterase type-5 inhibitors on splanchnic blood flow and portal hypertension remains essentially unknown.

METHODS

Ten patients with biopsy proven cirrhosis (five females/five males, mean age 54 +/- 8 years) and an HVPG above 12 mmHg were studied after informed consent. Measurement of splanchnic blood flow and the HVPG during liver vein catheterization were done before and 80 min after oral administration of 50 mg sildenafil. Blood flow was estimated by use of indocyanine green clearance technique and Fick's principle, with correction for non-steady state.

RESULTS

The plasma concentration of sildenafil was 222 +/- 136 ng/mL 80 min after administration. Mean arterial blood pressure decreased from 77 +/- 7 mmHg to 66 +/- 12 mmHg, P = 0.003, while the splanchnic blood flow and oxygen consumption remained unchanged at 1.14 +/- 0.71 L/min and 2.3 +/- 0.6 mmol/min, respectively. Also the HVPG remained unchanged (18 +/- 2 mmHg vs 16 +/- 2 mmHg) with individual changes ranging from -8 mmHg to +2 mmHg. In seven patients, HVPG decreased and in three it increased.

CONCLUSION

In spite of arterial blood pressure decreases 80 min after administration of the phosphodiesterase type-5 inhibitor sildenafil, the present study could not demonstrate any clinical relevant influence on splanichnic blood flow, oxygen consumption or the HVPG.

Indocyanine green plasma disappearance rate during the anhepatic phase of orthotopic liver transplantation

Non-invasive pulse spectrophotometry to measure indocyanine green (ICG) elimination correlates well with the conventional invasive ICG clearance test. Nevertheless, the precision of this method remains unclear for any application, including small-for-size liver remnants. We therefore measured ICG plasma disappearance rate (PDR) during the anhepatic phase of orthotopic liver transplantation using pulse spectrophotometry. Measurements were done in 24 patients. The median PDR after exclusion of two outliers and two patients with inconstant signal was 1.55%/min (95% confidence interval [CI]=0.8-2.2). No correlation with patient age, gender, body mass, blood loss, administration of fresh frozen plasma, norepinephrine dose, postoperative albumin (serum), or difference in pre and post transplant body weight was detected. In conclusion, we found an ICG-PDR different from zero in the anhepatic phase, an overestimation that may arise in particular from a redistribution into the interstitial space. If ICG pulse spectrophotometry is used to measure functional hepatic reserve, the verified average difference from zero (1.55%/min) determined in our study needs to be taken into account.

The adaptive response of the reticuloendothelial system to major liver resection in humans

OBJECTIVE

To evaluate the contribution of the liver to total circulatory reticuloendothelial system (RES) phagocytosis capacity in patients undergoing liver resection and to compare it with values in end-stage chronic liver disease.

SUMMARY BACKGROUND DATA

The mechanism whereby major liver resection is associated with a high incidence of infection is unknown. Significant impairment of RES phagocytosis has been described in liver failure, rendering such patients susceptible to infection; and we hypothesized that similar impairment might occur following major liver resection.

METHODS

A prospective study was conducted in which Tc-albumin microspheres blood clearance served as a parameter for RES phagocytosis and was studied together with indocyanine green blood clearance, actual liver volume measured by three-dimensional image analysis, and a clinical score of hepatic dysfunction in 17 patients undergoing liver resection and in 8 patients with end-stage chronic liver disease assessed for liver transplantation.

RESULTS

When expressed relative to volume unit of residual liver, microspheres clearance increased significantly in the immediate postoperative period (day 1) following major (0.009% versus 0.022% min(-1) mL(-1), P < 0.001), but not minor liver resection. In contrast, the absolute rate of microsphere clearance decreased following major resection (15% min(-1) versus 10% min(-1), P < 0.001) and was comparable with the rate observed in end-stage chronic liver disease (9% min(-1)). This decrease in circulatory microspheres clearance after resection paralleled a decrease in indocyanine green clearance (R2 = 0.511, P = 0.006), and there was a trend for those with moderate liver dysfunction to have lower microspheres clearance rates (P = 0.068).

CONCLUSION

Preservation of a minimum volume of functioning liver is a prerequisite for adequate RES phagocytosis capacity, and failure of this system may predispose patients undergoing major liver resection to infection as observed in clinical studies.

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.

Capillarization of the sinusoids in liver fibrosis: noninvasive assessment with contrast-enhanced MRI in the rabbit

Sinusoidal capillarization induces microcirculatory changes in liver cirrhosis and fibrosis. The purpose of this study was to assess whether contrast-enhanced MRI can be used to demonstrate the effects of sinusoidal capillarization in liver fibrosis. Dynamic MRI after injection of a low-molecular-weight contrast agent of 0.56 kDa (Gd-DOTA), and two high-molecular-weight contrast agents of 6.47 kDa and 52 kDa (P792 and P717) was performed in rabbits with liver fibrosis induced by cholesterol and diethylstilbestrol. The hepatic distribution volume accessible to the high-molecular-weight agents decreased in the rabbits with liver fibrosis (P792: 7.8% +/- 1.7% vs. 10.1% +/- 1.8% in normal rabbits, P =.038; P717: 6.2% +/- 2.1% vs. 9.7% +/- 1.6% in normal rabbits, P =.007), whereas the hepatic mean transit time (MTT) of the low-molecular-weight agent was increased (15.9 +/- 8.0 s vs. 8.8 +/- 2.6 s in normal rabbits, P =.015). In rabbits with liver fibrosis, the clearance of indocyanine green (ICG) was correlated with the volume accessible to the high-molecular-weight agents (P792: r = 0.810, P =.015; P717: r = 0.857, P =.007). The collagen content of the liver was inversely correlated with the distribution volume of P717 (r = -.833, P =.010) and with the ICG clearance (r = -.810, P =.015). It was concluded that the microcirculatory changes induced by sinusoidal capillarization in liver fibrosis can be demonstrated noninvasively with MRI.

Metabolic effects of interleukin-6 in human splanchnic and adipose tissue

Interleukin-6 (IL-6) was infused intravenously for 2.5 h in seven healthy human volunteers at a dose giving rise to a circulating IL-6 concentration of approximately 35 ng l(-1). The metabolic effects of this infusion were studied in subcutaneous adipose tissue on the anterior abdominal wall and in the splanchnic tissues by the Fick principle after catheterizations of an artery, a subcutaneous vein draining adipose tissue, and a hepatic vein, and measurements of regional adipose tissue and splanchnic blood flows. In control studies without IL-6 infusion subcutaneous adipose tissue metabolism was studied by the same technique in eight healthy subjects. The net release of glycerol and fatty acids from the subcutaneous abdominal adipose tissue remained constant in the control experiment. IL-6 infusion gave rise to increase in net glycerol release in subcutaneous adipose tissue while the net release of fatty acids did not change significantly. In the splanchnic region IL-6 elicited a pronounced vasodilatation, and the uptake of fatty acids and the gluconeogenic precursors glycerol and lactate increased significantly. The splanchnic net output of glucose and triacylglycerol did not change during the IL-6 infusion. It is concluded that IL-6 elicits lipolytic effects in human adipose tissue in vivo, and that IL-6 also has effects on the splanchnic lipid and carbohydrate metabolism.

Attenuated hepatosplanchnic uptake of lactate during intense exercise in humans

We evaluated whether the increase in blood lactate with intense exercise is influenced by a low hepatosplanchnic blood flow as assessed by indocyanine green dye elimination and blood sampling from an artery and the hepatic vein in eight men. The hepatosplanchnic blood flow decreased from a resting value of 1.6 +/- 0.1 to 0.7 +/- 0.1 (SE) l/min during exercise. Yet the hepatosplanchnic O2 uptake increased from 67 +/- 3 to 93 +/- 13 ml/min, and the output of glucose increased from 1.1 +/- 0.1 to 2.1 +/- 0.3 mmol/min (P < 0.05). Even at the lowest hepatosplanchnic venous hemoglobin O2 saturation during exercise of 6%, the average concentration of glucose in arterial blood was maintained close to the resting level (5.2 +/- 0.2 vs. 5.5 +/- 0.2 mmol/l), whereas the difference between arterial and hepatic venous blood glucose increased to a maximum of 22 mmol/l. In arterial blood, the concentration of lactate increased from 1.1 +/- 0.2 to 6.0 +/- 1.0 mmol/l, and the hepatosplanchnic uptake of lactate was elevated from 0.4 +/- 0.06 to 1.0 +/- 0.05 mmol/min during exercise (P < 0.05). However, when the hepatosplanchnic venous hemoglobin O2 saturation became low, the arterial and hepatosplanchnic venous blood lactate difference approached zero. Even with a marked reduction in its blood flow, exercise did not challenge the ability of the liver to maintain blood glucose homeostasis. However, it appeared that the contribution of the Cori cycle decreased, and the accumulation of lactate in blood became influenced by the reduced hepatosplanchnic blood flow.

Decreased splanchnic oxygen uptake and increased systemic oxygen uptake in cirrhosis are normalized after liver transplantation

The aim of this study is to (1) characterize the impact of orthotopic liver transplantation (OLT) on splanchnic and systemic oxygen uptake (VO(2)) in patients with liver cirrhosis, and (2) investigate possible influencing factors, as well as metabolic consequences, of reduced splanchnic VO(2) in patients with cirrhosis. Therefore, we measured systemic VO(2) (indirect calorimetry), portal pressure (hepatic venous pressure gradient), hepatic blood flow (HBF; primed continuous infusion of indocyanine green), and hepatic turnover (arteriohepatic venous concentration differences multiplied by HBF) of oxygen, glucose, free fatty acids (FFAs), and aromatic amino acids (AAAs) in 52 patients with advanced cirrhosis and 16 patients with a clinically stable long-term course after OLT. Systemic VO(2) was significantly increased in patients with cirrhosis (261 +/- 7 mL/min) and normalized after OLT (216 +/- 8 mL/min; P < .001). Arterial and hepatic venous oxygen saturation and splanchnic oxygen extraction (in percent) were not different between patients with cirrhosis and after OLT. Splanchnic VO(2) was decreased in patients with cirrhosis (41 +/- 3 mL/min, representing 16% +/- 1% of systemic VO(2)) and normalized after OLT (69 +/- 6 mL/min; P < .001, representing 32% +/- 3% of systemic VO(2); P < .001). In patients with cirrhosis, a decrease in HBF was associated with decreased splanchnic VO(2) (r = 0.74; P < .001). Conversely, decreased splanchnic VO(2) reflected a decrease in hepatic glucose production (r = 0.34; P = .01) and hepatic extraction of FFAs (r = 0.40; P < .01) and AAAs (r = 0.30; P < .05). These results show that (1) splanchnic and systemic VO(2) normalize after OLT, indicating correction of hepatic and extrahepatic metabolic derangements; (2) in cirrhosis, HBF becomes limiting for hepatic oxygen supply; and (3) impaired splanchnic VO(2) reflects a decrease in metabolic liver function.

Laboratory assessment of hepatic hemodynamics

Although the study of hepatic circulation is complicated by the dual blood supply and complex anatomy of the liver, many distinct methods are available to facilitate its study. Before embarking on an investigation of hepatic hemodynamics, the investigator must be familiar with the available methods and their applications. All methods have their own attributes and limitations. No one method is superior to the others, but, depending on the aspect of hepatic hemodynamics to be investigated, a particular methodology may yield distinct advantages.

Sorbitol as a marker for drug-induced decreases of variable duration in liver blood flow in healthy volunteers

OBJECTIVE

Sorbitol has been suggested as a suitable marker to assess liver blood flow (LBF), after it was shown to adequately reflect prolonged changes in LBF but changes of a shorter duration have not been investigated. We therefore used sorbitol to evaluate drug-induced decreases in LBF of variable duration with i.v. infusions of somatostatin and its synthetic analogue octreotide.

METHODS

In a double-blind, placebo controlled, randomised study, six healthy males received sorbitol for 170 min. At sorbitol steady state, which was at 45 min after the start of the infusion (t=0), somatostatin or octreotide was infused for 30 min. Sampling for sorbitol assay and echo-Doppler hepatic portal vein flow measurements were done regularly and treatments were compared using ANOVA.

RESULTS

The sorbitol AUC over the 30-min intervention period was 15% (95% C.I.: +4, +22%) and 13% (+5, +24%) higher compared to placebo after somatostatin and octreotide respectively. The decline of sorbitol levels after termination of the intervention was faster for somatostatin compared to octreotide, demonstrated by the difference in the AUC (0-2 h) with placebo which was 8% (-3, +19%) lower after somatostatin, and 15% (+5, +26%) after octreotide. Portal venous blood flow decreased during the 30-min interventions; after somatostatin 27% (-14, -40%) and after octreotide 29% (-17, -42%). Portal flow was lower than placebo during the entire experiment after octreotide 30% (-10, -50%), but not after somatostatin 13% (-33, +7%). Changes in sorbitol levels and portal venous blood flow occurred simultaneously and were well correlated for each individual, making it likely that the interventions did not interfere with metabolism.

CONCLUSION

Sorbitol can be used to adequately assess decreases in LBF of variable duration in healthy volunteers.

Splanchnic metabolism of fuel substrates in acute liver failure

BACKGROUND/AIMS

This study aimed to characterize the exchange of fuel substrates in the splanchnic circulation in acute liver failure.

METHODS

Liver vein catheterization was used in 22 patients with acute liver failure after development of hepatic encephalopathy grade III-IV Healthy controls, patients with cirrhosis and patients with acute on chronic liver disease were also studied.

RESULTS

In acute liver failure there was splanchnic removal of glucose (0.21+/-0.44 mmol/min), release of lactate (0.34+/-0.37 mmol/min), pyruvate (0.08+/-0.06 mmol/min) and ketone bodies (0.04+/-0.02 mmol/min), while extraction of amino acids and free fatty acids was insignificant. In the acute liver failure group, a normal hepatic venous oxygen saturation (0.69+/-0.12) and normal pyruvate/lactate ratio suggested absence of hypoxia even though the acetoacetate/beta-hydroxybutyrate ratio was decreased. Only in the acute liver failure group did the measured splanchnic oxygen content difference exceed what could be accounted for even by hypothesizing complete oxidation of all extracted blood-borne fuel substrates; oxidation of endogenous substrates may be quantitatively important in this condition.

CONCLUSION

Acute liver failure was associated with a state of accelerated glycolysis in the splanchnic region, leading to release of lactate in the absence of splanchnic hypoxia.

Effect of liver blood flow and function on hepatic indocyanine green clearance measured directly in a cirrhotic animal model

BACKGROUND

Peripheral blood clearance of indocyanine green (ICG) has been used as a test of liver function but gives little information on biliary excretion. Hepatic ICG uptake and clearance can be measured directly by near-infrared spectroscopy (NIRS). Direct ICG measurement has not previously been correlated with liver blood flow and function in cirrhosis.

METHODS

Two groups of New Zealand white rabbits (n = 12) underwent laparotomy for liver exposure. Cirrhosis was induced by feeding animals (n = 6) with a high-cholesterol (2 per cent) diet for 16 weeks. Hepatic blood flow and microcirculation were measured. Hepatic ICG concentration was measured directly using NIRS probes on the liver surface. From the ICG concentration-time curve, hepatic ICG uptake and excretion rates were calculated by a non-linear least square curve fitting method.

RESULTS

There was a significant reduction in ICG uptake rate (mean(s.d.) 0.300(0.130) versus 2.040(0.420) min-1; P = 0.0001) and ICG excretion rate (0.007(0.009) versus 0.227(0.096) min-1; P = 0. 002) in cirrhotic animals. The hepatic ICG uptake rate correlated with hepatic blood flow and flow in the microcirculation (r = 0.81, P = 0.002; r = 0.92, P < 0.001, respectively). The hepatic ICG excretion rate was significantly associated with indicators of impaired liver function including bilirubin (r = - 0.86, P = 0.0004), aspartate aminotransferase (r = - 0.81, P = 0.001) and lactate dehydrogenase (r = - 0.83, P = 0.0008).

CONCLUSION

ICG uptake measured directly by NIRS reflects the reduced liver blood flow and perfusion in cirrhosis and its excretion correlates with the degree of liver parenchymal dysfunction. This technique may allow a more accurate method of liver function assessment than peripheral blood ICG clearance.

13C-phenylalanine and 13C-methacetin breath test to evaluate functional capacity of hepatocyte in chronic liver disease

BACKGROUND

To grade liver damage, Child-Pugh classification is used but these tests do not reflect the quantitative functional hepatic reserve.

AIMS

13C-Phenylalanine Breath Test and 13C-Methacetin Breath Test are evaluated as possible tools, being both safe and easy to perform, to quantify functional hepatic reserve in chronic liver disease patients.

PATIENTS

Both tests were performed in 48 healthy volunteers and 48 chronic liver disease patients.

METHODS

Breath samples were collected after taking 13C-Phenylalanine (100 mg) and 13C-Methacetin (75 mg). 13CO2 enrichment was measured using mass spectrometry

RESULTS

Both tests discriminated the hepatic function, decreasing results of the 13CO2 enrichment agreeing with the increasing severity of the hepatic patient (13C-Phenylalanine Breath Test multiple correlation coefficient: 0.72, global p<0.001; Methacetin Breath Test: 0.73, p<0.001). Correlation between 13C-Phenylalanine Breath Test and Methacetin Breath Test was 0.63, p<0.001. If both tests were pathological, the sensitivity for the diagnosis of hepatic dysfunction was high (98%), although the specificity decreased to 60%. Best results were obtained at 30 minutes with 13C-Phenylalanine Breath Test and at 10 minutes with Methacetin Breath Test.

CONCLUSIONS

Both 13C-Phenylalanine Breath Test and Methacetin Breath Test are safe and easy tests to perform and both are able to discriminate the hepatic functional capacity between the different groups studied.

Influence of respiration and portal pressure on transabdominal duplex Doppler ultrasound measurement of portal blood flow: a porcine model for experimental studies

Transabdominal duplex Doppler ultrasonography (TDDU) is commonly used for measuring hepatic blood flow (HBF) in clinical practice. Flow velocity and the cross-sectional area (CSA) of vessels are obtained separately and used to compute blood flow. Respiration and changes in portal pressure are known to cause variations in the CSA of the portal vein, but the impact of these parameters on TDDU measurement of portal blood flow is unclear. Eight Yorkshire pigs (20.7-25.1 kg) were used for the study. TDDU determination of portal blood flow was carried out using CSA of the portal vein obtained at inspiration (maximal) and at expiration (minimal) for computation, and the differences obtained were compared. Determination of HBF was carried out simultaneously on the same animals using diisopropyliminodiacetic acid (DISIDA) clearance. A physiological increase in portal pressure was then created by 50% hepatectomy and TDDU measurement similarly carried out on the second postoperative day. Computing portal blood flow in the intact liver using maximal and minimal CSA gave rise to a mean difference of 7.0 ml kg(-1) min(-1) (P < 0.001). A significant correlation was obtained between HBF and portal flow computed from maximal CSA (Pearson's correlation = 0.85, P < 0.033). The respiratory index of the portal vein (maximal CSA/minimal CSA) decreased from 1.5 to 1.2 after hepatectomy, which also caused a 90% increase in portal pressure. Respiration and portal pressure thus significantly impact on TDDU determination of HBF, and in this porcine model, computation using maximal CS more accurately reflects HBF.

The effect of increasing blood pressure with dopamine on systemic, splanchnic, and lower extremity hemodynamics in patients with acute liver failure

BACKGROUND

Arterial hypotension occurs frequently in patients with acute liver failure (ALF). Treatment with epinephrine and norepinephrine in patients with ALF has been associated with a decrease in whole-body (systemic) oxygen consumption. We aimed to investigate the effect of increasing blood pressure with dopamine on whole-body (systemic), splanchnic, and lower extremity hemodynamics and oxygen consumption in patients with acute liver failure and hepatic encephalopathy grade III or IV.

METHODS

In seven patients with ALF cardiac output (CO) was measured with the thermodilution technique, and hepatic blood flow (HBF) was estimated with infusion of sorbitol as test compound, liver vein catheterization, and calculations on the basis of Fick's principle. Lower-extremity blood flow was measured with strain-gauge plethysmography.

RESULTS

During infusion of dopamine (5 +/- 2 microg kg(-1) min(-1)) mean arterial pressure (MAP) increased from 68 +/- 5 to 85 +/- 8 mmHg. CO increased from 6.8 +/- 0.8 to 9.0 +/- 2.4 l/min (P < 0.05), systemic oxygen delivery from 45 +/- 7 to 63 +/- 19 mmol/min (P < 0.05), systemic oxygen consumption from 10.2 +/- 2.0 to 11.5 +/- 3.3 mmol/min (NS). HBF increased from 2.2 +/- 0.7 to 2.7 +/- 1.0 l/ min (P < 0.05), splanchnic oxygen delivery from 14.4 +/- 5.3 to 18.5 +/- 7.2 mmol/min (P < 0.01), and splanchnic oxygen consumption decreased from 3.9 +/- 1.1 to 2.9 +/- 0.6 mmol/min (P < 0.05). No significant changes in lower extremity flow and oxygenation variables were found.

CONCLUSIONS

The use of dopamine in patients with ALF to increase MAP was associated with increases in systemic and splanchnic oxygen delivery. A concomitant decrease in splanchnic oxygen consumption was observed.

Glucose production during exercise in humans: a-hv balance and isotopic-tracer measurements compared

The present study compared the arteriohepatic venous (a-hv) balance technique and the tracer-dilution method for estimation of hepatic glucose production during both moderate and heavy exercise in humans. Eight healthy young men (aged 25 yr; range, 23-30 yr) performed semisupine cycling for 40 min at 50.4 +/- 1.5(SE)% maximal O(2) consumption, followed by 30 min at 69.0 +/- 2.2% maximal O(2) consumption. The splanchnic blood flow was estimated by continuous infusion of indocyanine green, and net splanchnic glucose output was calculated as the product of splanchnic blood flow and a-hv blood glucose concentration differences. Glucose appearance rate was determined by a primed, continuous infusion of [3-(3)H]glucose and was calculated by using formulas for a modified single compartment in non-steady state. Glucose production was similar whether determined by the a-hv balance technique or by the tracer-dilution method, both at rest and during moderate and intense exercise (P > 0. 05). It is concluded that, during exercise in humans, determination of hepatic glucose production can be performed equally well with the two techniques.

Liver volume, portal vein flow, and clearance of indocyanine green and antipyrine in hyperthyroidism before and after antithyroid treatment

BACKGROUND

The aim of the study was to examine liver volume, portal vein flow, and indocyanine green (ICG) and antipyrine clearance in hyperthyroidism before and after antithyroid drug treatment.

METHODS

Liver volume and blood flow in the portal vein were investigated in nine fasting patients with hyperthyroidism by means of computed tomography scan and Doppler ultrasound, respectively. ICG clearance was estimated by bolus injection of ICG (0.5 mg/kg body weight) and antipyrine clearance with a one-sample technique. All patients were investigated before and after 3 months of antithyroid treatment, when euthyroidism had been achieved. The Wilcoxon matched-pairs test was used for statistical analysis.

RESULTS

The median liver volume increased by 238 (155-289) ml (median, 95% confidence interval), corresponding to 19%, and the weight by 5.0 (0.0-8.0) kg (8%), and the antipyrine clearance decreased by 8 (3.1-34.4) ml/min (16%). These changes were all significant (P < 0.05). The relation between liver volume and body weight increased from 19.9 (16.5-23.7) ml/kg to 21.4 (17.1-21.9) ml/kg (P = 0.11). The liver blood flow as estimated by ICG clearance and Doppler ultrasound was not altered significantly after the treatment period (P = 0.07 and 0.77, respectively).

CONCLUSIONS

The liver volume increased by 19% in nine hyperthyroid patients during treatment with antithyroids. Antipyrine clearance was reduced by 16%, whereas liver blood flow, as estimated by ICG clearance and Doppler ultrasound examination of portal vein flow, was not significantly altered. A differential regulation of liver volume and oxidative metabolic capacity in hyperthyroidism was seen.

Splanchnic haemodynamics after intravenous terlipressin in anaesthetised healthy pigs

BACKGROUND/AIMS

Terlipressin is used for the treatment of bleeding oesophageal varices. We evaluated the effects of terlipressin on hepatic haemodynamics, with special focus on the interactions between portal venous flow and hepatic arterial flow over time. Secondly, we evaluated the estimated hepatic blood flow by the ICG clearance method against direct measurements of hepatic blood flow.

METHODS

Eight healthy anaesthetised pigs received terlipressin 1 mg or placebo intravenously in a randomised, blind, cross-over design. Hepatic arterial flow, portal venous flow, systemic haemodynamics, and portal vein diameter were recorded simultaneously. Portal venous flow and hepatic arterial flow were measured by transit time ultrasound flowmetry. Estimated hepatic blood flows at baseline and after terlipressin were compared with the sum of the portal venous flow and hepatic arterial flow.

RESULTS

Portal venous flow decreased significantly 5 min after administration of terlipressin (p<0.05). At 30 min it had decreased by 34% (p<0.01) and the hepatic arterial flow had increased by 81% (p<0.01). The estimated hepatic blood flow and the hepatic blood flow decreased by 23% (p<0.015). At baseline the estimated hepatic blood flow and the hepatic blood flow correlated significantly (r=0.85, p<0.01), but this correlation disappeared after administration of terlipressin (r=0.06, p=ns). The hepatic blood flow was 12% higher than the estimated hepatic blood flow before and after terlipressin.

CONCLUSIONS

Terlipressin decreased the portal venous flow, hepatic blood flow, and estimated hepatic blood flow significantly and was accompanied by a substantial increase in hepatic arterial flow. The estimated hepatic blood flow and hepatic blood flow were strongly correlated at baseline, but after terlipressin the correlation disappeared.

Hepatic blood flow and splanchnic oxygen consumption in patients with liver failure. Effect of high-volume plasmapheresis

Liver failure represents a major therapeutic challenge, and yet basic pathophysiological questions about hepatic perfusion and oxygenation in this condition have been poorly investigated. In this study, hepatic blood flow (HBF) and splanchnic oxygen delivery (DO2, sp) and oxygen consumption (VO2,sp) were assessed in patients with liver failure defined as hepatic encephalopathy grade II or more. Measurements were repeated after high-volume plasmapheresis (HVP) with exchange of 8 to 10 L of plasma. HBF was estimated by use of constant infusion of D-sorbitol and calculated according to Fick's principle from peripheral artery and hepatic vein concentrations. In 14 patients with acute liver failure (ALF), HBF (1.78 +/- 0.78 L/min) and VO2,sp (3.9 +/- 0.9 mmol/min) were higher than in 11 patients without liver disease (1.07 +/- 0.19 L/min, P <.01) and (2.3 +/- 0.7 mmol/min, P <.001). In 9 patients with acute on chronic liver disease (AOCLD), HBF (1.96 +/- 1.19 L/min) and VO2,sp (3.9 +/- 2.3 mmol/min) were higher than in 18 patients with stable cirrhosis (1.00 +/- 0.36 L/min, P <.005; and 2.0 +/- 0.6 mmol/min, P <.005). During HVP, HBF increased from 1.67 +/- 0.72 to 2.07 +/- 1.11 L/min (n=11) in ALF, and from 1.89 +/- 1.32 to 2.34 +/- 1.54 L/min (n=7) in AOCLD, P <.05 in both cases. In patients with ALF, cardiac output (thermodilution) was unchanged (6.7 +/- 2.5 vs. 6.6 +/- 2.2 L/min, NS) during HVP. Blood flow was redirected to the liver as the systemic vascular resistance index increased (1,587 +/- 650 vs. 2, 020 +/- 806 Dyne. s. cm-5. m2, P <.01) whereas splanchnic vascular resistance was unchanged. In AOCLD, neither systemic nor splanchnic vascular resistance was affected by HVP, but as cardiac output increased from 9.1 +/- 2.8 to 10.1 +/- 2.9 L/min (P <.01) more blood was directed to the splanchnic region. In all liver failure patients treated with HVP (n=18), DO2,sp increased by 15% (P <.05) whereas VO2,sp was unchanged. Endothelin-1 (ET-1) and ET-3 were determined before and after HVP. Changes of ET-1 were positively correlated with changes in HBF (P <.005) and VO2,sp (P <.05), indicating a role for ET-1 in splanchnic circulation and oxygenation. ET-3 was negatively correlated with systemic vascular resistance index before HVP (P <.05) but changes during HVP did not correlate. Our data suggest that liver failure is associated with increased HBF and VO2, sp. HVP further increased HBF and DO2,sp but VO2,sp was unchanged, indicating that splanchnic hypoxia was not present.

Mesenteric, coeliac and splanchnic blood flow in humans during exercise

1. Exercise reduces splanchnic blood flow, but the mesenteric contribution to this response is uncertain. 2. In nineteen humans, superior mesenteric and coeliac artery flows were determined by duplex ultrasonography during fasting and postprandial submaximal cycling and compared with the splanchnic blood flow as assessed by the Indocyanine Green dye-elimination technique. 3. Cycling increased arterial pressure, heart rate and cardiac output, while it reduced total vascular resistance. These responses were not altered in the postprandial state. During fasting, cycling increased mesenteric, coeliac and splanchnic resistances by 76, 165 and 126 %, respectively, and it reduced corresponding blood flows by 32, 50 and 43 % (by 0.18 +/- 0.04, 0.42 +/- 0.03 and 0.60 +/- 0.04 l min-1). Postprandially, mesenteric and splanchnic vascular resistances decreased, thereby elevating regional blood flow, while the coeliac circulation was not influenced. Postprandial cycling did not influence the mesenteric resistance significantly, but its blood flow decreased by 22 % (0.46 +/- 0.28 l min-1). Coeliac and splanchnic resistance increased by 150 and 63 %, respectively, and the corresponding regional blood flow decreased by 51 and 31 % (0.49 +/- 0.07 and 0.96 +/- 0.28 l min-1). Splanchnic blood flow values assessed by duplex ultrasound and by dye-elimination techniques were correlated (r = 0.70; P < 0.01). 4. During submaximal exercise in humans, splanchnic resistance increases and blood flow is reduced following a 50 % reduction in the hepato-splenic and a 25 % reduction in the mesenteric blood flow.

No effect of diltiazem on the hepatic clearance of indocyanine green in the rats

In order to investigate the effect of the pretreatment with various doses of diltiazem (DTZ) on the pharmacokinetics of indocyanine green (ICG) at steady state, especially the hepatic blood clearance due to the change of hepatic blood flow, the following experiments were carried out with ICG, a hepatic function test marker, not metabolized in liver and only excreted in bile. The intravenous bolus injection (3,780 micrograms/kg) and the constant-rate infusion (10,100 micrograms/kg/hr) of ICG into the left femoral vein were made in order to check the steady-state plasma concentration (Css of 10 micrograms/ml) of ICG at 20, 25 and 30 min. Following a 90-min washout period, the intravenous bolus injection (108, 430, 860 and 1,720 micrograms/kg) and the constant-rate infusion (108, 433, 866 and 1,730 micrograms/kg/hr) of DTZ into the right femoral vein were made and the achievement of the steady-state plasma levels (Css of 50, 200, 400 and 800 ng/ml) of DTZ were conformed at 60, 70 and 80 min. During the steady state of DTZ, the intravenous bolus injection (3,780 micrograms/kg) and the constant-rate infusion (10,200 micrograms/kg/hr) of ICG into the left femoral vein were made and also the steady-state plasma concentration of ICG was checked at 20, 25 and 30 min. The plasma concentrations of DTZ and ICG were determined using a high performance liquid chromatographic technique. At the steady state, the hepatic blood clearance of ICG was obtained from the plasma concentration and blood-to-plasma concentration ratio (RB) of ICG. The pretreatment with various doses of DTZ did not influence the plasma concentrations, RB and plasma free fraction (fp) of ICG. So the hepatic blood clearance of ICG was independent of concentration of DTZ. The hepatic blood clearance of ICG could be affected by both hepatic blood flow and hepatic intrinsic clearance. But there was no change of the hepatic blood clearance of ICG between the control and the DTZ-pretreated rats in this study. So it may be suggested that DTZ does not influence hepatic blood flow.

Sorbitol as a test substance for measurement of liver plasma flow in humans

The objective of this study was to evaluate whole-body removal kinetics of sorbitol, the use of extrarenal sorbitol clearance to estimate hepatic plasma flow in humans, and to compare measurements of liver flow by Fick's principle using either indocyanine green (ICG) or sorbitol. A sorbitol bolus (5 mmol/kg) was given intravenously to 6 controls for determination of sorbitol elimination capacity (SEC) and distribution volume, V(sorb)d. Sorbitol infusion (287 micromol/ min) was given to 17 liver patients and 11 controls. Extrarenal sorbitol clearance (V(sorb)x was calculated as infusion rate (corrected for renal excretion and accumulation in V(sorb)d) divided by arterial concentration. Liver flow (Q(ICG)) was calculated from the ICG infusion and arterial and hepatic venous ICG concentrations by Fick's principle. Average SEC was 73 micromol/min/kg, V(sorb)d was 0.16 L plasma per kilogram, and in vivo V(sorb)d was 3 mmol/L. Renal sorbitol excretion rate was 0.03 to 0.31 of infusion rate. Extrahepatic extrarenal removal was not significantly different from zero but varied considerably. Hepatic extraction fraction of sorbitol, (E(sorb)), measured by liver vein catheterization, was 0.35 to 1.04 (median, 0.86) in cirrhotic patients and 0.90 to 0.98 (0.86) in controls. The requirements for using Cl(sorb)x as an estimate of Q(ICG) was not violated by the data in controls, Cl(sorb)x/Q(ICG) 0.70 to 1.55 [median, 1.08]), whereas there was a systematic underestimation in cirrhotic patients (0.72-1.08 [0.85]). Liver flow calculated by Fick's principle using either sorbitol or ICG agreed well. E(sorb) > E(ICG) in each individual except one. Curvilinear relationship between E(sorb) and E(ICG) was in agreement with different kinetic parameters for sorbitol and ICG, and did not require additional assumption of intrahepatic shunts.

Assessment of the hepatic circulation in humans: new concepts based on evidence derived from a D-sorbitol clearance method

D-Sorbitol (SOR) is safe, is easy to measure, and has an exceptionally high extraction ratio in the normal liver of 0.93+/-0.05 (mean+/-SD). Together with the general interest in hepatic hemodynamics, these facts motivated us to review the usefulness of this compound for the assessment of liver plasma flow in humans. We concluded that in subjects without liver disease the nonrenal clearance of SOR-measured noninvasively-very closely approximates hepatic plasma flow. Because of its lower and more variable extraction ratio, indocyanine green should no longer be used without hepatic vein catheterization. Even in patients with cirrhosis, SOR exhibits higher hepatic extraction ratios than indocyanine green. To fully explore the potential of SOR in the evaluation of such patients attention needs to be paid to the complex changes in architecture and function occurring in this disease. In cirrhotics the noninvasively measured nonrenal clearance of SOR presumably approximates the flow through intact and capillarized sinusoids (functional flow) and reflects the amount of blood having functional contact with hepatocytes. The theoretic background of the method, its accuracy, further research needs, and potentials of various approaches are discussed in detail.

Hepatic plasma flow estimated according to Fick's principle in patients with hepatic encephalopathy: evaluation of indocyanine green and D-sorbitol as test substances

The magnitude of hepatic plasma flow in patients with liver failure and hepatic encephalopathy (HE) is unknown because a reliable flow estimate has not been available. The purpose of this study was to estimate hepatic plasma flow in patients with HE and to evaluate indocyanine green (ICG) and sorbitol as test compounds. Fourteen patients with acute liver failure (ALF) and nine patients with chronic liver failure (CLF), all with HE grade II or more, were studied. After hepatic vein catheterization, hepatic plasma flow was estimated by use of constant infusion, simultaneous arterial and hepatic vein concentration measurements, and calculated according to Fick's principle. The hepatic extraction fraction of D-sorbitol 0.179+/-0.144 (mean+/-SD) was higher than the hepatic extraction fraction of ICG 0.054+/-0.085 (P < .001). The low hepatic extraction fraction of ICG rendered this compound unfit for estimation of hepatic plasma flow in these patients. In contrast, by using D-sorbitol the hepatic plasma flow could be estimated in 21 of 23 patients with a median SD of 8.4% (range, 2.6% to 29%). The D-sorbitol estimated hepatic plasma flow was 1.2+/-0.5 L/min (n = 12) in patients with ALF and 1.4+/-0.9 L/min (n = 9) in patients with CLF. These values are higher than what has been reported in normal subjects and in patients with cirrhosis without HE. An elevated hepatic flow should increase oxygen delivery and may enhance the failing liver's ability to remove substances from the blood. At the same time, hepatic first pass metabolism is reduced. We conclude that an elevated hepatic flow in these patients is of clinical importance.

L-[1-(13)C] Phenylalanine oxidation as a measure of hepatocyte functional capacity in end-stage liver disease

BACKGROUND

Liver disease is associated with impaired metabolism of these amino acids phenylalanine and tyrosine. Decreased metabolism of these amino acids leads to abnormal plasma elevations and impaired clearance rates. We have developed a noninvasive breath test that measures hepatic cytosolic enzyme activity.

METHODS

The rate of hepatic phenylalanine metabolism was quantitatively calculated from the appearance of 13CO2 in the breath using the nonradioactive tracer L-[1-(13)C]phenylalanine.

RESULTS

Normal controls (n = 47) oxidized phenylalanine more than twice that of end-stage liver disease patients (n = 117). Significant differences in the percent of phenylalanine oxidized per hour (mean +/- SEM) were found between controls (7.08% +/- 0.33%, 95% CI: 6.42%-7.74%) and Child Pugh classification patients, class A (4.96% +/- 0.69%, 95% CI: 3.50%-6.42%), class B (2.88% +/- 0.13, 95% CI: 2.39%-3.38%) and class C (1.75% +/- 0.13, 95% CI: 1.50%-2.01%). The phenylalanine breath test score significantly correlated with albumin levels, prothrombin time and total bilirubin.

CONCLUSION

We have demonstrated that phenylalanine oxidation is significantly decreased with end-stage liver disease and is correlated with the best clinical measures of liver disease.

Relationship between hepatic blood flow, liver tests, haemodynamic values and clinical characteristics in patients with chronic liver disease

Although hepatic blood flow (HBF) has been measured in patients with liver disease for many years, the results of these studies have not provided clear information concerning the usefulness of this measurement. Hepatic blood flow was measured in 392 patients with either cirrhosis (n = 356) or hepatic fibrosis (n = 36). The control group included 59 subjects with normal liver architecture. Hepatic clearance of indocyanine green (ICG) was markedly reduced in patients with cirrhosis and hepatic fibrosis compared with controls (182 +/- 5, 276 +/- 22 and 421 +/- 25 mL/min, respectively). In patients with cirrhosis, ICG clearance and extraction were significantly correlated, but were not correlated to HBF. Although HBF did not differ between patients with cirrhosis and controls (1.26 +/- 0.04 vs 1.35 +/- 0.07 L/min, respectively), patients with hepatic fibrosis had lower HBF (1.04 +/- 0.07 L/min; P < 0.05). In patients with cirrhosis, no correlation was observed between HBF and cardiac output, mean arterial pressure, azygos blood flow, the hepatic venous pressure gradient or Pugh's score. However, a significant difference in HBF was observed in patients with and without hepatic encephalopathy (1.00 +/- 0.09 vs 1.28 +/- 0.03 L/min, respectively; P < 0.05). In conclusion, the present study shows that, in patients with cirrhosis, HBF is normal and is not related to other haemodynamic values or liver tests. These results discourage the measurement of HBF in the evaluation of patients with cirrhosis.

A simple and rapid method for the determination of D-sorbitol in plasma using the Cobas Mira S

The standard enzymatic assay for quantification of D-sorbitol in plasma was adapted to the automatic analyzer Cobas Mira S. In the assay, NAD (reagent) in the presence of sorbitoldehydrogenase (SDH; start reagent) converts D-sorbitol to fructose with formation of NADH, which was detected automatically as the difference between the first and last readings at 340 nm. The sample blank values for each specimen were subtracted to exclude both endogenous D-sorbitol and sugars, which also react as substrates for SDH. The method is simple, rapid (40 samples/h), precise down to endogenous concentrations (coefficient of variation < 5%; limit of determination: 0.38 mg/L) and linear up to 100 mg/L. Samples with higher D-sorbitol concentrations were estimated after dilution. The method was used to measure disposition curves of sorbitol in volunteers after a single intravenous dose of 0.8 g sorbitol.

The kinetics of continuously infused indocyanine green in the pig

Indocyanine green (ICG) is used in cardiology and hepatology for the estimation of cardiac output, liver function, and splanchnic blood flow. ICG is bound to plasma proteins and ultimately excreted by the liver. We studied the whole body kinetics of ICG during constant infusion in pigs weighing 30-40 kg. The conventional kinetic model (backflux model) assumes that deviations from one-compartmental linear kinetics is caused by backflux from a liver storage to plasma, and that no extravascular, extrahepatic distribution takes place. This model was tested against an alternative (redistribution) model postulating that temporary redistribution of ICG into an extrahepatic extravascular storage was responsible for the deviations while the hepatic uptake was a one-way first-order process. A mathematical analysis of the two models showed that they predicted different time courses of the hepatic extraction fraction of ICG. Thus, with blood sampling from both a peripheral artery and a hepatic vein, a discriminative model-testing experiment was possible. This test required a first-order steady-state hepatic removal of ICG which was confirmed in 7 experiments with infusion rates varied in a stepwise fashion (0.133 +/- 0.003, 0.269 +/- 0.010, 0.547 +/- 0.020 and 0.130 +/- 0.003 mumol.min-1). In the model-testing experiments (n = 10) ICG was infused at a constant rate of 0.135 +/- 0.07 mumol.min-1. The mean concentration in peripheral artery (microM) was well fitted by the biexponential function C(t) = 0.476.(1-0.632.e-0.216.1-0.368.e-0.0172.1). The time course of the observed hepatic extraction fraction was significantly different (p = 0.004) from that predicted from the backflux model but in agreement (p = 0.98) with the new model assuming hepatic removal to be a one-way process and implying temporary ICG redistribution into an extrahepatic, extravascular storage with an apparent volume of 0.144 +/- 0.023 L.Kg-1. Accordingly, extravascular ICG was demonstrated in a number of different tissues after 4-hr infusion (n = 3). If ICG is used to estimate hepatic blood flow according to Fick's principle, the use of a backflux model to correct for non-steady-state conditions will lead to an overestimation of hepatic blood flow of 28% after 25-min infusion, 16% after 50 min, and 6% after 100 min. The study indicated that distribution of ICG between plasma and tissues is not instantaneous, and that the time course of the redistribution itself significantly influences whole body kinetics. Comparison with a previously published study by Ott, Keiding, and Bass of ICG kinetics after bolus injection suggested that a two-compartment model was insufficient and that the kinetics for the exchange of ICG between plasma and the redistribution space may be nonlinear. The study demonstrates how blood sampling on both sides of the eliminating organ can expose the influence of redistribution. The discriminative model test for constant infusion experiments is novel and may be useful with other ligands.

Exposure to high environmental temperature in the sauna does not change plasma indocyanine green (ICG) clearance in healthy subjects

Indocyanine green (ICG) was given intravenously (0.5 mg kg-1) to seven healthy male volunteers in random order during a control session and a session in the sauna bath. The sauna bathing session consisted of three 10 min. stays in the sauna (temperature 85-95 degrees, relative humidity 25-30%), separated by two 5-min. periods of resting at 22 degrees. Blood samples were taken for 60 min. in order to calculate ICG plasma clearance (CI), volume of distribution (Vss) and elimination half-life (t1/2 beta). The mean +/- S.E.M. values of ICG plasma clearance, Vss and t1/2 beta for the control session and the sauna bathing session were 0.47 +/- 0.08 1 min.-1 versus 0.39 +/- 0.04 1 min.-1, 2.4 +/- 0.4 1 versus 2.3 +/- 0.2 1 and 3.9 +/- 0.3 min. versus 4.4 +/- 0.3 min., respectively. No statistically significant differences in the CI, t1/2 beta or Vss of ICG were detected between the control and sauna bathing sessions. The results suggest that short-term exposure to high ambient temperatures during sauna bathing does not affect hepatic blood flow. Consequently, short-term hyperthermia and associated changes in hepatic blood flow are assumed to have little, if any, effect on the hepatic clearance of drugs.

Review article: quantitative tests of liver function

The search continues for a single reliable test of liver function that provides accurate prognostic information in chronic liver disease, in acute liver failure, and about graft function following orthotopic liver transplantation. Although transaminases, the commonly used markers of hepatocellular injury, have a high sensitivity in screening for liver disease, they do not provide any information about prognosis. Rational assessment of liver function using bilirubin, serum albumin and prothrombin-time is limited by the relative lack of sensitivity of these measurements and their inability to identify the functional reserve of the liver. Dynamic liver function tests are an improvement on the static tests but are generally cumbersome. The ideal liver function test would be cheap, easy to perform and analyse, safe, have a simple pharmacokinetic profile with minimal drug interactions, have a high predictive value and provide quick results. Numerous quantitative liver function tests have been developed and have shown promise in some studies. The aim of this review is to assess the place of these tests in the practical management of liver disease.

Glucose homeostasis during exercise in humans with a liver or kidney transplant

To investigate the role of liver nerve activity on hepatic glucose production during exercise, liver-transplant subjects (LTX, n = 7, 25-62 yr, 4-18 mo postoperative) cycled for 40 min, 20 min at 52 +/- 3% (SE) maximal O2 consumption (VO2max) and 20 min at 83 +/- 1% VO2max, respectively. Kidney-transplant (KTX) and healthy control subjects (C) matched for sex and age exercised at the same %VO2max as LTX. VO2max was lower in both LTX (1.59 +/- 0.12 l/min) and KTX (1.59 +/- 0.07) than in C (2.60 +/- 0.26). At rest plasma renin and insulin were higher and plasma adrenocorticotropic hormone and cortisol lower in transplant corticosteroid-treated subjects compared with C. In LTX, hepatic glucose production (Ra) increased from 11.9 +/- 0.9 (rest) to 17.6 +/- 1.8 and 25.5 +/- 1.8 mumol.min-1.kg-1 at 52 and 82% VO2max, respectively. Peripheral glucose uptake was similar to Ra, and glucose remained at basal postabsorptive levels. During exercise the Ra increase as well as norepinephrine, insulin, and growth hormone responses were similar in LTX compared with both KTX and C. The increase in epinephrine was smaller in LTX than in C, the only group showing an increase in cortisol. The increase in plasma renin activity during exercise was attenuated in KTX compared with LTX and C. During exercise blood lactate rose more and plasma glycerol and free fatty acid levels were lower in LTX and KTX compared with C.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of liver metabolic function. Clinical implications

Inter- and intraindividual variability in pharmacokinetics of most drugs is largely determined by variable liver function as described by parameters of hepatic blood flow and metabolic capacity. These parameters may be altered as a result of disease affecting the liver, genetic differences in metabolising enzymes, and various types of drug interactions, including enzyme induction, enzyme inhibition or down-regulation. With the now known large number of drug metabolising enzymes, their differential substrate specificity, and their differential induction or inhibition, each test substance of liver function should be used as a probe for its specific metabolising enzyme. Thus, the concept of model test-substances providing general information about liver function has severe limitations. To test the metabolic activity of several enzymes, either several test substances may be given (cocktail approach) or several metabolites of a single test substance may be analysed (metabolic fingerprint approach). The enzyme-specific analysis of liver function results in a preference for analysis of the metabolites rather than analysis of the clearance of the parent test substance. There are specific methods to quantify the activity of cytochrome P450 enzymes such as CYP1A2, CYP2C9, CYP2C19MEPH, CYP2D6, CYP2E1, and CYP3A, and phase II enzymes, such as glutathione S-transferases, glucuronyl-transferases or N-acetyltransferases, in vivo. Interactions based on competitive or noncompetitive inhibition should be analysed specifically for the cytochrome P450 enzyme involved. At least 5 different types of cytochrome P450 enzyme induction may result in major variability of hepatic function; this may be quantified by biochemical parameters, clearance methods, or highly enzyme-specific methods such as Western blot analysis or molecular biological techniques such as mRNA quantification in blood and tissues. Therapeutic drug monitoring is already implicitly used for quantification of the enzyme activities relevant for a specific drug. Selective impairment of hepatic enzymes due to gene mutations may have an effect on the pharmacokinetics of certain drugs similar to that caused by cirrhosis. Assessment of this heritable source of variability in liver function is possible by in vivo or ex vivo enzymological methods. For genetically polymorphic enzymes and carrier proteins involved in drug disposition, molecular genetic methods using a patient's blood sample may be used for classification of the individual into: (i) the impaired or poor metaboliser (homozygous deficient); (ii) the extensive (homozygous active) metaboliser group; and (iii) the moderately extensive metaboliser (heterozygous) group. For hepatic blood flow determinations, galactose or sorbitol given at relatively low doses may be much better indicators than the indocyanine green.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of dehydration and hyperosmolal hydration on lignocaine and metabolites disposition in conscious rabbits

1. The present study aimed to investigate the effect of dehydration and hyperosmolal hydration on the disposition of lignocaine and two of its metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX). 2. Lignocaine was infused to three groups of conscious rabbits: controls, rabbits previously deprived of water for 48 h and rabbits receiving an infusion of 2.5% NaCl. 3. In dehydrated and hyperosmolal-hydrated rabbits, plasma osmolality was 321 +/- 1 and 313 +/- 1 mOsm kg-1, respectively (P < 0.01 compared to controls, 285 +/- 1 mOsm kg-1). In dehydrated animals, baseline values of plasma arginine vasopressin (AVP) concentrations and plasma renin activity (PRA) were higher than in controls, i.e. 12.4 +/- 1.4 pg ml-1 and 15.4 +/- 1.7 ng AI ml-1 h-1 vs. 3.4 +/- 0.2 pg ml-1 (P < 0.01), and 5.1 +/- 0.6 ng AI ml-1 h-1 (P < 0.01), respectively; atrial natriuretic peptide (ANP) decreased from 55 +/- 11 to 32 +/- 4 pg ml-1 (P < 0.05). Compared to controls, hyperosmolal hydration only increased AVP to 15.5 +/- 0.7 pg ml-1 (P < 0.01). 4. Under both experimental conditions, lignocaine plasma concentrations were almost double (P < 0.01) those in controls, due to a lower systemic clearance, e.g. 54 +/- 3 and 59 +/- 1 vs. 96 +/- 5 ml min-1 kg-1, respectively. Plasma levels of MEGX increased (P < 0.01) only in dehydrated animals, although GX plasma concentrations were augmented (P < 0.01) about three fold in both groups of animals. The changes in lignocaine plasma concentrations were correlated with AVP levels (R2 = 0.5168, P<0.001).5. To document the effect of AVP on hepatic plasma flow, another group of rabbits received on separate occasions two doses of AVP (17 and 84 ng kg-1) while receiving an infusion of in docyanine green. AVP reduced hepatic plasma flow from 38.9 +/-2.7 ml min-1 to 19.6 +/-2.5 ml min-1 (P<0.01).The predicted maximal AVP-induced decrease in hepatic plasma flow was 19.6 ml min-1 kg- 1(Emax), and AVP concentration eliciting 50% of Em.. (ED50) was 28.7 pg ml-1.6 It is concluded that both dehydration and hyperosmolal hydration alter the disposition of lignocaine and two of its metabolites.