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The effects of norepinephrine and prostaglandin E1 on pharmacokinetics of lidocaine in isolated perfused rat liver
Life Sciences 68 (2001) 2123–2129
The effects of norepinephrine and prostaglandin E1 on pharmacokinetics of lidocaine in isolated perfused rat liver Yasushi Matsuura, Shinichi Nishi*, Nobutaka Kariya, Kazuhisa Shimadzu, Akira Asada Department of Anesthesiology and Intensive Care Medicine, Osaka City University Medical School, 1-5-7, Asahi-machi, Abeno-ku, Osaka, 545-8586, Japan Received 22 March 2000; 20 September 2000
Abstract We hypothesized that depression of liver function by norepinephrine can be improved by prostaglandin E1. Isolated perfused rat liver was selected as an experimental model, since the flow rate can be regulated in it. Twenty-one rats were randomly allocated to three groups: control, norepinephrine, and norepinephrine and prostaglandin E1 groups. The liver was perfused in a recirculating system at a constant flow rate of 20 ml/min. After administration of two milligrams of lidocaine in each group, lidocaine and monoethylglycinexylidide concentrations in the recirculating system were measured. Lidocaine pharmacokinetics were analyzed using the SAAM II® program, including metabolic rate from lidocaine to monoethylglycinexylidide using time-concentration curves. Norepinephrine significantly increased perfusion pressure and the area under the time-concentration curve for lidocaine. Norepinephrine decreased the clearance and the elimination rate constant of lidocaine compared with those in the control group. Although administration of prostaglandin E1 after infusion of norepinephrine did not significantly change perfusion pressure, it significantly (p , 0.05) improved metabolic rate, clearance and the elimination rate constant of lidocaine in the isolated rat liver model. © 2001 Elsevier Science Inc. All rights reserved. Keywords: Two-compartment model; Lidocaine; MEGX; Norepinephrine; Prostaglandin E1
Introduction Many drugs are removed from the blood through metabolism in the liver. It has been reported that high-dose catecholamine administration prior to transplantation can cause nonfunctional liver after liver transplantation [1]. The change of metabolism in liver will lead the unexpected or prolonged effect in some kind of drugs clinically. We previously reported that * Corresponding author. Tel.: 181-6-6645-2186; fax: 181-6-6645-2489. E-mail address: [email protected] (S. Nishi) 0024-3205/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S 0 0 2 4 - 3 2 0 5 ( 0 1 )0 0 9 9 3 -6
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the pharmacokinetics of lidocaine were altered by infusion of norepinephrine in the portal vein, and that norepinephrine inhibited drug metabolism in isolated perfused rat liver (IPRL) [2]. Lenzen et al. [3] also observed intra-hepatic shunting with norepinephrine infusion, using electromicroscopic imaging with dye. Two studies found that prostaglandin E1 (PGE1) had a cytoprotective effect on liver after transplantation, hepatic warm ischemia or reperfusion [4, 5]. However, the mechanisms of cytoprotective effect of PGE1 have not yet been determined. We hypothesized that PGE1 can improve depression of lidocaine metabolism by norepinephrine. Methods Seven-week-old male Sprague-Dawley rats (Nippon Keari Co., Ltd., Tokyo, Japan) were used in this study. Twenty-one rats were randomly allocated to three groups, control (abbreviated as C, n57), norepinephrine (NE, n57) and PGE1 (PGE1, n57) groups. No drug was given to the C group. Norepinephrine was administered at a rate of 131021 mg min21 to the NE group. In the PGE1 group, we administered norepinephrine at the same rate as in the NE group and PGE1 at a rate of 1.631023 mg min21 after norepinephrine infusion. The liver was perfused in situ as described by Lenzen et al [3]. Pentobarbital, 50 mg/kg, was administered intraperitoneally prior to the experiment. A 16 gauge teflon cannula was inserted into the abdominal inferior vena cava. The liver was perfused through the portal vein to the vena cava. A 16 gauge teflon cannula was then inserted into the thoracic inferior vena cava for collection of samples to measure drug concentrations. A nylon catheter was inserted into the bile duct. The IPRL system was started as non-recirculating, but was changed to a recirculating system after the perfusion pressure became stable. The liver was perfused in a non-recirculating system at a flow rate of 20 ml/min with Krebs-Henseleite buffer without hemoglobin and albumin. The buffer was kept at 37 8C and was equilibrated with 5% carbon dioxide in oxygen. Perfusion pressure, oxygen consumption and bile flow were monitored. The oxygen extraction ratio (OER) was selected as an indicator of liver cell viability, and calculated as OER (%) 5100 3 (Cin 2 Cout) / Cin where Cin and Cout are the oxygen contents in the inlet and outlet of the buffer, respectively. The infusion rates of norepinephrine and PGE1 were calculated on the basis of body weight. Two milligrams of lidocaine was injected into the IPRL system. Samples were taken at 5, 10, 15, 30, 45, 60 and 90 minutes after administration and stored at 280 8C until analysis. Lidocaine and monoethylglycinexylidide (MEGX), a major metabolite of lidocaine, were kindly supplied by Astra-Japan Pharmaceuticals Co., Ltd. (Osaka, Japan). We measured lidocaine and MEGX concentrations by fluorescence polarized immunoassay (FPIA) and HPLC [6], respectively. An AC18 column (TSKgel ODS-120T, TOSOH Co., Ltd., Tokyo, Japan) was used for HPLC. The mobile phase consisted of 10 mM phosphate buffer and acetonitrile (80:20) at pH 3. The flow rate was 1.0 ml/min and the UV wavelength used was 214 nm. Fifty ml of 1M sodium hydroxide and 1.5 ml of ethyl acetate were added to 500 ml of sample and shaken on a vortex mixer and reciprocating shaker. One ml of the supernatant was transferred to a glass tube and evaporated after centrifugation at 3000 r.p.m. for 15 min.
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Fig. 1. Two-compartment model of lidocaine. The k21 is a fractional transfer rate constant from medium to liver pools. The kl2 is a fractional transfer rate constant from liver to medium pools. The ke is an elimination rate constant. They were calculated by non-linear regression using the SAAM II® program.
The time-concentration data for lidocaine were fit to a two-compartment model consisting of medium and liver pools (Fig. 1). The model was the same as that reported by Docter et al. [7]. The fractional transfer rate constants, k21 and kl2, from medium to liver and from liver to medium, and ke, the elimination rate constant, were calculated by non-linear regression using the SAAM II® program [8]. The area under the time-concentration curve (AUC0–90) for MEGX was calculated using the trapezoidal rule. The metabolic rate of lidocaine was expressed as AUC0–90(MEGX)/AUC0–90(lidocaine). The AUC in lidocaine pharmacokinetics from zero to infinite time was calculated by SAAM II® program (AUC0–∞). The AUClidocaine in metabolic rate was calculated by trapezoidal rule until the last measured point because the MEGX kinetics could not be assumed to be adequate to fit our measured points to any model. The significance of differences between groups was examined by one-way analysis of variance. The Fisher post-hoc test was performed for group comparisons. P values below 0.05 were considered significant. Results There were no significant differences in either body or liver weights of rats among the three groups. Portal vein pressure significantly (p , 0.05) increased after administrations of norepinephrine in the NE and PGE1 groups; the percent changes of the portal vein pressure before to after administration of norepinephrine were 152% and 144 %, respectively. There were no significant differences in OER among these groups (Table 1). We calculated Akaike’s information criteria (AIC) for evaluating the fitness of the actual data points with a theoretical equation. The AICs in every group were within 29 to zero (Table 2) and our data were fit well to two compartment model (Figs. 2, 3). The concentration of lidocaine in IPRL after 90 minutes was significantly higher than that in the PGE1 and C groups. The concentration of MEGX gradually increased until 30 min and decreased thereafter in every group (Fig. 4). The AUC02∞ for lidocaine was significantly larger in the NE group than that in the C and PGE1 groups. The clearance (CL) and ke in the NE group were significantly
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Table 1 Change of portal vein pressure and oxygen extraction ratio Groups C (n57) NE (n57) PGE1 (n57)
BW (gr)
Liver weight (gr)
Portal vein pressure change (%)
267.1 6 8.20 285.7 6 22.4 275.7 6 19.6
9.0 6 1.6 9.8 6 0.7 9.7 6 1.3
103 6 7.9 152 6 18.0* 144 6 8.6*
OER (%) 62.7 6 4.8 76.9 6 6.9 79.6 6 7.4 (mean 6 SD)
C: Control, NE: Norepinephrine, PGE1: Prostaglandin E1. OER: Oxygen Extraction Ratio. * p , 0.05; compared with control group.
smaller than those in the C and PGE1 groups. There were no significant differences in pharmacokinetic parameters of lidocaine between the C and PGE1 groups. The metabolic rate from lidocaine to MEGX in the NE group was significantly lower than that in the C and PGE1 groups (Table 2). Discussion We used the IPRL system because flow rate can be controlled in it. We used lidocaine as an indicator drug because its metabolism is limited mainly by liver blood flow. When the flow through the liver is regulated in IPRL, the metabolism of lidocaine reflects enzyme function. The two-compartment model was applied in this study to analyze time-concentration data, as in a previous study [7]. We considered the central (V1) and peripheral (V2) compartments in the model to represent the major vessels, and the micro-vascular bed and liver cells, respectively. Norepinephrine increased portal vascular resistance [9] and decreased hepatic uptake of organic anions, bile flow and biliary excretion of taurocholate in IPRL [3]. Beck et al. [10] Table 2 Pharmacokinetic parameters of lidocaine and AIC Groups
AUC0–∞ (mg min ml21)
Clearance (ml min21)
V1 (ml)
V2 (ml)
C NE PGE1
260.7657.0 633.16310.0* 249.3668.1
8.161.4 4.261.8* 8.662.0
189.261.9 209.8614.1 213.4619.8
39.8612.6 39.168.9 40.2624.4
Groups
k12 (31023) (min21)
k21 (31023) (min21)
ke (31023) (min21)
Metabolic rate (%)
C NE PGE1
14.966.5 12.462.2 9.762.1
68.5610.4 67.766.0 65.5617.8
24.26.4 6.164.3* 16.763.8
56.3610.5 29.666.0* 44.263.7
AUC0–∞: Area under the time-concentration curve of lidocaine from zero to infinite time. C: Control, NE: Norepinephrine, PGE1: Prostaglandin E1. AIC: Akaike’s Information Criteria. * p , 0.05; compared with Control or Prostaglandin E1 group.
AIC 22.3861.52 24.3163.51 23.7462.52 (mean6SD)
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Fig. 2. The time-concentration curve of lidocaine. Open circles show the data in control group, closed circles data in NE group, and open triangles data in PGE1 group, respectively. Concentrations in NE group were significantly (p , 0.05) different with those of PGE1 and control groups after 90 minutes, respectively. The curves were theoretical. They were drawn by SAAM II® program.
found two types of liver blood vessels in the liver. Stimulation of alpha-adrenergic nerve resulted in vasoconstriction in the distal region perfused by the 7th to 10th branches of the portal vein, but not in the regions perfused by the 4th to 6th branches of the portal vein. A similar change in intrahepatic circulation was observed following infusion of norepinephrine in denervated rat liver [10]. Kjekshus et al. [11] reported that vascular volume in liver was decreased
Fig. 3. The time-concentration curve of lidocaine with semi-logarithmic scale. Open circles show the data in control group, closed circles data in NE group, and open triangles data in PGE1 group, respectively. The time-concentration data were fit well to two-compartment model using SAAM II® program. The curves were theoretical. They were drawn by SAAM II® program.
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Fig. 4. Time-concentration curve of MEGX. Open circles show the data in control group, closed circles data in NE group, and open triangles data in PGE1 group, respectively. The concentrations of MEGX gradually increased until 30 min, and decreased thereafter. There were no difference in MEGX concentrations at each sampling time in every three group.
by infusion of norepinephrine. Reduction of vascular volume in liver might have been in part responsible for the decrease in metabolic rate of lidocaine by norepinephrine observed in this study. Lenzen et al. [3] reported that norepinephrine induced perfusate shunting at the ultrastructural level in liver. Namely it was mismatch between the blood flow and liver cell. This mismatch would be assumed as intrahepatic shunting. The significant changes in ke, CL and AUC0–∞ in the NE group represented delay in elimination of lidocaine from the medium pool (V1), probably through intrahepatic shunting at the ultrastructural level. Norepinephrine increased the pressure in the portal vein and deteriolated the pharmacokinetic parameters, such as clearance, elimination constant and metabolic rate of lidocaine. On the other hand, PGE1 pharmacokinetically improved lidocaine metabolism depressed by norepinephrine in the IPRL circuit under a constant flow with highly maitained pressure. There are several possible mechanisms to improve lidocaine metabolism under these circumstances. One is the redistribution of the flow in the liver to make the lidocaine metabolism more effective [3]. The second is the improvement of the incorporation of lidocaine into the cell. The third is the improvement of liver enzymes activities concerned with lidocaine metabolism [5,14,15,16]. The fourth is the improvement of the elimination of lidocaine into the bile. We could not measure the concentration of lidocaine in the bile because the amount of the bile was quite small and was not enough to measure precisely. We could not determine the exact mechanism by this experiment including the mechanisms mentioned above. Further study should be needed to elucidate the mechanism. A number of studies have demonstrated cytoprotective effects of prostaglandins in the liver [4, 5, 12, 13 ]. Robert reported that PGE1 improved microcirculation through inhibition of platelet aggregation [12]. Our findings showed that the perfusion pressure after administration of norepinephrine became higher in the NE group than in the C group and that it remained high even after PGE1 administration in the PGE1 group. These results suggest that PGE1 did not par-
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ticipate in the regulation of the portal vein pressure. Shinohara et al. [14] reported that PGE1 had a direct beneficial effect on hepatocytes. Moreover, PGE1 stabilized liver parenchymal cells through change in membrane microviscosity [15]. Xian-en Wang et al. [16] reported that PGE1 exhibited a cytoprotective effect in the liver by inhibiting stellate cell contraction and by increasing hepatic sinusoidal blood flow. Totsuka et al. [5] showed that PGE1 maintained the sinusoids and parenchymal cell mitochondria, which might be destroyed by warm ischemia in liver and reperfusion injury. The pharmacokinetic parameters measured in the present study were significantly decreased by norepinephrine, but were restored to control levels by PGE1. The apparent volumes of distribution (V1, V2) and the rate constant between the two compartments were not altered by these drugs. These results suggested that PGE1 improved lidocaine metabolism through decreasing intrahepatic shunting or through a cytoprotective effect on hepatocytes. The infusion rate of PGE1 in our study, 131021 mg min21, was somewhat higher than that used clinically. Further examination will be required to know how much dose of PGE1 is most effective to improve the liver blood flow decreased by norepinephrine. In conclusion, the change in ke, clearance and AUC in NE group may result from intrahepatic shunting at the ultrastructural level which may be improved by PGE1. References 1. Yamaoka Y, Taki Y, Gubernatis G, et al. Evaluation of the liver graft before procurement. Significance of arterial ketone body ratio in brain—dead patients. Transpl Int. 1990;3(2):78–81 2. Shimadzu K, Nishi S, Kariya N, et al. The phrmacokinetic change of lidocaine by catecholamines using isolated perfused rat liver (IPRL). Life Sci 1996; 62 (26):2399–405. 3. Lenzen R, Funk A, Kolb BV,et al. Norepinephrine-induced cholestasis in the isolated perfused rat liver is secondary to its hemodynamic effects. Hepatology 1990;12 (2):314–21 . 4. Takahashi K, Yamamoto N, Egawa H, et al. Effect of prostaglamdin E1 on preservation injury of canine liver grafts preserved in UW solution. Transpl Int 1993; 6 :245–50 5. Totsuka E, Sasaki M, Takahashi K, et al. The effects of intraportal prostaglandin E1 administration on hepatic warm ischemia and reperfusion injury in dogs. Surgery Today 1995; 25 :421–8 6. Oda Y, Imaoka S, Nakahira Y, et al. Metabolism of lidocaine by purified rat liver microsomal cytochrome p-450 isozymes. Biochem Phrmacol 1989;38(24):4434–44 7. Docter R, Jong MD, Hoek HJ, et al. Development and use of a mathematical two-pool model of distribution and metabolism of 3, 39, 5-triiodothyronine in a recirculating rat liver perfusion system: Albumine dose not play a role in cellular transport. Endocrinology 1990;126(1):451–9 8. SAAM Institute, FL-20, University of Washington Seattle, Washington 98195, USA. 9. Richardson PD, Withrington PG. Responses of the canine hepatic arterial and portal venous vascular beds to dopamine. Eur J Pharmacol 1978;48 :337–49 10. Sungchul Ji, K. Beckh K, K. Jungermnn. Regulation of oxygen consumption and microcirculation by alphasympathetic nerves in isolated perfused rat liver. FEBS Lett 1984;167(1):117–22 11. Kjekshus H, Risoe C, Scholz T, et al. Regulation of hepatic vascular volume. Circulation 1997;96 (12):4415–23 12. Robert A. Cytoprotection by prostaglandins. Gastroenterology 1979;77 (4):761–7 13. Guarner F, Fremont-Smith M, Prieto J. Cytoprotective effect of prostaglandins on isolated rat liver cells. Liver1985;5 :35–9 14. Shinohara H, Tanaka A, Fujimoto T, et al. Prostaglandin E1 resuscitates hepatic organic anion transport independent of its hemodynamic effect after warm ischemia. J Surg Res 1997;68(1):56–62 15. Masaki N, Ohta Y, Shirataki H, et al. Hepatocyte membrane stabilization by prostaglandin E1 and E2: Favorable effects on rat liver injury. Gastroenterology 1992;102 (2):572–6 16. Xian-En Wang, Watanabe S, Oide H, et al. Hepatic stellate cell contraction is inhibited by lipo-prostaglandin E1 in vitro. J Gastroenterol Hepatol 1998;13(Suppl.):S14–18
The effects of norepinephrine and prostaglandin E1 on pharmacokinetics of lidocaine in isolated perfused rat liver Yasushi Matsuura, Shinichi Nishi*, Nobutaka Kariya, Kazuhisa Shimadzu, Akira Asada Department of Anesthesiology and Intensive Care Medicine, Osaka City University Medical School, 1-5-7, Asahi-machi, Abeno-ku, Osaka, 545-8586, Japan Received 22 March 2000; 20 September 2000
Abstract We hypothesized that depression of liver function by norepinephrine can be improved by prostaglandin E1. Isolated perfused rat liver was selected as an experimental model, since the flow rate can be regulated in it. Twenty-one rats were randomly allocated to three groups: control, norepinephrine, and norepinephrine and prostaglandin E1 groups. The liver was perfused in a recirculating system at a constant flow rate of 20 ml/min. After administration of two milligrams of lidocaine in each group, lidocaine and monoethylglycinexylidide concentrations in the recirculating system were measured. Lidocaine pharmacokinetics were analyzed using the SAAM II® program, including metabolic rate from lidocaine to monoethylglycinexylidide using time-concentration curves. Norepinephrine significantly increased perfusion pressure and the area under the time-concentration curve for lidocaine. Norepinephrine decreased the clearance and the elimination rate constant of lidocaine compared with those in the control group. Although administration of prostaglandin E1 after infusion of norepinephrine did not significantly change perfusion pressure, it significantly (p , 0.05) improved metabolic rate, clearance and the elimination rate constant of lidocaine in the isolated rat liver model. © 2001 Elsevier Science Inc. All rights reserved. Keywords: Two-compartment model; Lidocaine; MEGX; Norepinephrine; Prostaglandin E1
Introduction Many drugs are removed from the blood through metabolism in the liver. It has been reported that high-dose catecholamine administration prior to transplantation can cause nonfunctional liver after liver transplantation [1]. The change of metabolism in liver will lead the unexpected or prolonged effect in some kind of drugs clinically. We previously reported that * Corresponding author. Tel.: 181-6-6645-2186; fax: 181-6-6645-2489. E-mail address: [email protected] (S. Nishi) 0024-3205/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S 0 0 2 4 - 3 2 0 5 ( 0 1 )0 0 9 9 3 -6
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the pharmacokinetics of lidocaine were altered by infusion of norepinephrine in the portal vein, and that norepinephrine inhibited drug metabolism in isolated perfused rat liver (IPRL) [2]. Lenzen et al. [3] also observed intra-hepatic shunting with norepinephrine infusion, using electromicroscopic imaging with dye. Two studies found that prostaglandin E1 (PGE1) had a cytoprotective effect on liver after transplantation, hepatic warm ischemia or reperfusion [4, 5]. However, the mechanisms of cytoprotective effect of PGE1 have not yet been determined. We hypothesized that PGE1 can improve depression of lidocaine metabolism by norepinephrine. Methods Seven-week-old male Sprague-Dawley rats (Nippon Keari Co., Ltd., Tokyo, Japan) were used in this study. Twenty-one rats were randomly allocated to three groups, control (abbreviated as C, n57), norepinephrine (NE, n57) and PGE1 (PGE1, n57) groups. No drug was given to the C group. Norepinephrine was administered at a rate of 131021 mg min21 to the NE group. In the PGE1 group, we administered norepinephrine at the same rate as in the NE group and PGE1 at a rate of 1.631023 mg min21 after norepinephrine infusion. The liver was perfused in situ as described by Lenzen et al [3]. Pentobarbital, 50 mg/kg, was administered intraperitoneally prior to the experiment. A 16 gauge teflon cannula was inserted into the abdominal inferior vena cava. The liver was perfused through the portal vein to the vena cava. A 16 gauge teflon cannula was then inserted into the thoracic inferior vena cava for collection of samples to measure drug concentrations. A nylon catheter was inserted into the bile duct. The IPRL system was started as non-recirculating, but was changed to a recirculating system after the perfusion pressure became stable. The liver was perfused in a non-recirculating system at a flow rate of 20 ml/min with Krebs-Henseleite buffer without hemoglobin and albumin. The buffer was kept at 37 8C and was equilibrated with 5% carbon dioxide in oxygen. Perfusion pressure, oxygen consumption and bile flow were monitored. The oxygen extraction ratio (OER) was selected as an indicator of liver cell viability, and calculated as OER (%) 5100 3 (Cin 2 Cout) / Cin where Cin and Cout are the oxygen contents in the inlet and outlet of the buffer, respectively. The infusion rates of norepinephrine and PGE1 were calculated on the basis of body weight. Two milligrams of lidocaine was injected into the IPRL system. Samples were taken at 5, 10, 15, 30, 45, 60 and 90 minutes after administration and stored at 280 8C until analysis. Lidocaine and monoethylglycinexylidide (MEGX), a major metabolite of lidocaine, were kindly supplied by Astra-Japan Pharmaceuticals Co., Ltd. (Osaka, Japan). We measured lidocaine and MEGX concentrations by fluorescence polarized immunoassay (FPIA) and HPLC [6], respectively. An AC18 column (TSKgel ODS-120T, TOSOH Co., Ltd., Tokyo, Japan) was used for HPLC. The mobile phase consisted of 10 mM phosphate buffer and acetonitrile (80:20) at pH 3. The flow rate was 1.0 ml/min and the UV wavelength used was 214 nm. Fifty ml of 1M sodium hydroxide and 1.5 ml of ethyl acetate were added to 500 ml of sample and shaken on a vortex mixer and reciprocating shaker. One ml of the supernatant was transferred to a glass tube and evaporated after centrifugation at 3000 r.p.m. for 15 min.
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Fig. 1. Two-compartment model of lidocaine. The k21 is a fractional transfer rate constant from medium to liver pools. The kl2 is a fractional transfer rate constant from liver to medium pools. The ke is an elimination rate constant. They were calculated by non-linear regression using the SAAM II® program.
The time-concentration data for lidocaine were fit to a two-compartment model consisting of medium and liver pools (Fig. 1). The model was the same as that reported by Docter et al. [7]. The fractional transfer rate constants, k21 and kl2, from medium to liver and from liver to medium, and ke, the elimination rate constant, were calculated by non-linear regression using the SAAM II® program [8]. The area under the time-concentration curve (AUC0–90) for MEGX was calculated using the trapezoidal rule. The metabolic rate of lidocaine was expressed as AUC0–90(MEGX)/AUC0–90(lidocaine). The AUC in lidocaine pharmacokinetics from zero to infinite time was calculated by SAAM II® program (AUC0–∞). The AUClidocaine in metabolic rate was calculated by trapezoidal rule until the last measured point because the MEGX kinetics could not be assumed to be adequate to fit our measured points to any model. The significance of differences between groups was examined by one-way analysis of variance. The Fisher post-hoc test was performed for group comparisons. P values below 0.05 were considered significant. Results There were no significant differences in either body or liver weights of rats among the three groups. Portal vein pressure significantly (p , 0.05) increased after administrations of norepinephrine in the NE and PGE1 groups; the percent changes of the portal vein pressure before to after administration of norepinephrine were 152% and 144 %, respectively. There were no significant differences in OER among these groups (Table 1). We calculated Akaike’s information criteria (AIC) for evaluating the fitness of the actual data points with a theoretical equation. The AICs in every group were within 29 to zero (Table 2) and our data were fit well to two compartment model (Figs. 2, 3). The concentration of lidocaine in IPRL after 90 minutes was significantly higher than that in the PGE1 and C groups. The concentration of MEGX gradually increased until 30 min and decreased thereafter in every group (Fig. 4). The AUC02∞ for lidocaine was significantly larger in the NE group than that in the C and PGE1 groups. The clearance (CL) and ke in the NE group were significantly
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Table 1 Change of portal vein pressure and oxygen extraction ratio Groups C (n57) NE (n57) PGE1 (n57)
BW (gr)
Liver weight (gr)
Portal vein pressure change (%)
267.1 6 8.20 285.7 6 22.4 275.7 6 19.6
9.0 6 1.6 9.8 6 0.7 9.7 6 1.3
103 6 7.9 152 6 18.0* 144 6 8.6*
OER (%) 62.7 6 4.8 76.9 6 6.9 79.6 6 7.4 (mean 6 SD)
C: Control, NE: Norepinephrine, PGE1: Prostaglandin E1. OER: Oxygen Extraction Ratio. * p , 0.05; compared with control group.
smaller than those in the C and PGE1 groups. There were no significant differences in pharmacokinetic parameters of lidocaine between the C and PGE1 groups. The metabolic rate from lidocaine to MEGX in the NE group was significantly lower than that in the C and PGE1 groups (Table 2). Discussion We used the IPRL system because flow rate can be controlled in it. We used lidocaine as an indicator drug because its metabolism is limited mainly by liver blood flow. When the flow through the liver is regulated in IPRL, the metabolism of lidocaine reflects enzyme function. The two-compartment model was applied in this study to analyze time-concentration data, as in a previous study [7]. We considered the central (V1) and peripheral (V2) compartments in the model to represent the major vessels, and the micro-vascular bed and liver cells, respectively. Norepinephrine increased portal vascular resistance [9] and decreased hepatic uptake of organic anions, bile flow and biliary excretion of taurocholate in IPRL [3]. Beck et al. [10] Table 2 Pharmacokinetic parameters of lidocaine and AIC Groups
AUC0–∞ (mg min ml21)
Clearance (ml min21)
V1 (ml)
V2 (ml)
C NE PGE1
260.7657.0 633.16310.0* 249.3668.1
8.161.4 4.261.8* 8.662.0
189.261.9 209.8614.1 213.4619.8
39.8612.6 39.168.9 40.2624.4
Groups
k12 (31023) (min21)
k21 (31023) (min21)
ke (31023) (min21)
Metabolic rate (%)
C NE PGE1
14.966.5 12.462.2 9.762.1
68.5610.4 67.766.0 65.5617.8
24.26.4 6.164.3* 16.763.8
56.3610.5 29.666.0* 44.263.7
AUC0–∞: Area under the time-concentration curve of lidocaine from zero to infinite time. C: Control, NE: Norepinephrine, PGE1: Prostaglandin E1. AIC: Akaike’s Information Criteria. * p , 0.05; compared with Control or Prostaglandin E1 group.
AIC 22.3861.52 24.3163.51 23.7462.52 (mean6SD)
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Fig. 2. The time-concentration curve of lidocaine. Open circles show the data in control group, closed circles data in NE group, and open triangles data in PGE1 group, respectively. Concentrations in NE group were significantly (p , 0.05) different with those of PGE1 and control groups after 90 minutes, respectively. The curves were theoretical. They were drawn by SAAM II® program.
found two types of liver blood vessels in the liver. Stimulation of alpha-adrenergic nerve resulted in vasoconstriction in the distal region perfused by the 7th to 10th branches of the portal vein, but not in the regions perfused by the 4th to 6th branches of the portal vein. A similar change in intrahepatic circulation was observed following infusion of norepinephrine in denervated rat liver [10]. Kjekshus et al. [11] reported that vascular volume in liver was decreased
Fig. 3. The time-concentration curve of lidocaine with semi-logarithmic scale. Open circles show the data in control group, closed circles data in NE group, and open triangles data in PGE1 group, respectively. The time-concentration data were fit well to two-compartment model using SAAM II® program. The curves were theoretical. They were drawn by SAAM II® program.
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Fig. 4. Time-concentration curve of MEGX. Open circles show the data in control group, closed circles data in NE group, and open triangles data in PGE1 group, respectively. The concentrations of MEGX gradually increased until 30 min, and decreased thereafter. There were no difference in MEGX concentrations at each sampling time in every three group.
by infusion of norepinephrine. Reduction of vascular volume in liver might have been in part responsible for the decrease in metabolic rate of lidocaine by norepinephrine observed in this study. Lenzen et al. [3] reported that norepinephrine induced perfusate shunting at the ultrastructural level in liver. Namely it was mismatch between the blood flow and liver cell. This mismatch would be assumed as intrahepatic shunting. The significant changes in ke, CL and AUC0–∞ in the NE group represented delay in elimination of lidocaine from the medium pool (V1), probably through intrahepatic shunting at the ultrastructural level. Norepinephrine increased the pressure in the portal vein and deteriolated the pharmacokinetic parameters, such as clearance, elimination constant and metabolic rate of lidocaine. On the other hand, PGE1 pharmacokinetically improved lidocaine metabolism depressed by norepinephrine in the IPRL circuit under a constant flow with highly maitained pressure. There are several possible mechanisms to improve lidocaine metabolism under these circumstances. One is the redistribution of the flow in the liver to make the lidocaine metabolism more effective [3]. The second is the improvement of the incorporation of lidocaine into the cell. The third is the improvement of liver enzymes activities concerned with lidocaine metabolism [5,14,15,16]. The fourth is the improvement of the elimination of lidocaine into the bile. We could not measure the concentration of lidocaine in the bile because the amount of the bile was quite small and was not enough to measure precisely. We could not determine the exact mechanism by this experiment including the mechanisms mentioned above. Further study should be needed to elucidate the mechanism. A number of studies have demonstrated cytoprotective effects of prostaglandins in the liver [4, 5, 12, 13 ]. Robert reported that PGE1 improved microcirculation through inhibition of platelet aggregation [12]. Our findings showed that the perfusion pressure after administration of norepinephrine became higher in the NE group than in the C group and that it remained high even after PGE1 administration in the PGE1 group. These results suggest that PGE1 did not par-
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ticipate in the regulation of the portal vein pressure. Shinohara et al. [14] reported that PGE1 had a direct beneficial effect on hepatocytes. Moreover, PGE1 stabilized liver parenchymal cells through change in membrane microviscosity [15]. Xian-en Wang et al. [16] reported that PGE1 exhibited a cytoprotective effect in the liver by inhibiting stellate cell contraction and by increasing hepatic sinusoidal blood flow. Totsuka et al. [5] showed that PGE1 maintained the sinusoids and parenchymal cell mitochondria, which might be destroyed by warm ischemia in liver and reperfusion injury. The pharmacokinetic parameters measured in the present study were significantly decreased by norepinephrine, but were restored to control levels by PGE1. The apparent volumes of distribution (V1, V2) and the rate constant between the two compartments were not altered by these drugs. These results suggested that PGE1 improved lidocaine metabolism through decreasing intrahepatic shunting or through a cytoprotective effect on hepatocytes. The infusion rate of PGE1 in our study, 131021 mg min21, was somewhat higher than that used clinically. Further examination will be required to know how much dose of PGE1 is most effective to improve the liver blood flow decreased by norepinephrine. In conclusion, the change in ke, clearance and AUC in NE group may result from intrahepatic shunting at the ultrastructural level which may be improved by PGE1. References 1. Yamaoka Y, Taki Y, Gubernatis G, et al. Evaluation of the liver graft before procurement. Significance of arterial ketone body ratio in brain—dead patients. Transpl Int. 1990;3(2):78–81 2. Shimadzu K, Nishi S, Kariya N, et al. The phrmacokinetic change of lidocaine by catecholamines using isolated perfused rat liver (IPRL). Life Sci 1996; 62 (26):2399–405. 3. Lenzen R, Funk A, Kolb BV,et al. Norepinephrine-induced cholestasis in the isolated perfused rat liver is secondary to its hemodynamic effects. Hepatology 1990;12 (2):314–21 . 4. Takahashi K, Yamamoto N, Egawa H, et al. Effect of prostaglamdin E1 on preservation injury of canine liver grafts preserved in UW solution. Transpl Int 1993; 6 :245–50 5. Totsuka E, Sasaki M, Takahashi K, et al. The effects of intraportal prostaglandin E1 administration on hepatic warm ischemia and reperfusion injury in dogs. Surgery Today 1995; 25 :421–8 6. Oda Y, Imaoka S, Nakahira Y, et al. Metabolism of lidocaine by purified rat liver microsomal cytochrome p-450 isozymes. Biochem Phrmacol 1989;38(24):4434–44 7. Docter R, Jong MD, Hoek HJ, et al. Development and use of a mathematical two-pool model of distribution and metabolism of 3, 39, 5-triiodothyronine in a recirculating rat liver perfusion system: Albumine dose not play a role in cellular transport. Endocrinology 1990;126(1):451–9 8. SAAM Institute, FL-20, University of Washington Seattle, Washington 98195, USA. 9. Richardson PD, Withrington PG. Responses of the canine hepatic arterial and portal venous vascular beds to dopamine. Eur J Pharmacol 1978;48 :337–49 10. Sungchul Ji, K. Beckh K, K. Jungermnn. Regulation of oxygen consumption and microcirculation by alphasympathetic nerves in isolated perfused rat liver. FEBS Lett 1984;167(1):117–22 11. Kjekshus H, Risoe C, Scholz T, et al. Regulation of hepatic vascular volume. Circulation 1997;96 (12):4415–23 12. Robert A. Cytoprotection by prostaglandins. Gastroenterology 1979;77 (4):761–7 13. Guarner F, Fremont-Smith M, Prieto J. Cytoprotective effect of prostaglandins on isolated rat liver cells. Liver1985;5 :35–9 14. Shinohara H, Tanaka A, Fujimoto T, et al. Prostaglandin E1 resuscitates hepatic organic anion transport independent of its hemodynamic effect after warm ischemia. J Surg Res 1997;68(1):56–62 15. Masaki N, Ohta Y, Shirataki H, et al. Hepatocyte membrane stabilization by prostaglandin E1 and E2: Favorable effects on rat liver injury. Gastroenterology 1992;102 (2):572–6 16. Xian-En Wang, Watanabe S, Oide H, et al. Hepatic stellate cell contraction is inhibited by lipo-prostaglandin E1 in vitro. J Gastroenterol Hepatol 1998;13(Suppl.):S14–18