The plasma clearance of indocyanine green in rats with acute renal failure: Effect of dose and route of administration

The pharmacokinetics of various doses (1–7.5 mg/kg i.v.) of indocyanine green (ICG) have been studied in control rats and rats with glycerol-induced acute renal failure (ARF). The pharmacokinetic changes seen at a dose of 1 mg/kg, after jugular vein administration, were significant decreases in uraemic rats in the rate of entry of ICG into the liver (k₁₂) and in the rate of movement of dye from liver to plasma (k₂₁). Greater and more numerous changes in pharmacokinetic parameters were recorded in experiments conducted using 4.0 and 7.5 mg/kg ICG. The results from these experiments showed that in addition to significant decreases in k₁₂ and k₂₁ there was a significant reduction in the rate constant for transfer of dye from liver to bile (k₂₃). These changes were accompanied by a significant decrease in plasma clearance.In a separate series of experiments steps were taken to reduce the degree of uraemia produced by glycerol injection. The findings from these experiments showed no significant pharmacokinetic differences between control and mildly uraemic animals after administration of a dose of 7.5 mg/kg ICG. This suggests that the kinetic changes described above were a consequence of renal failure and not a direct hepato-toxic effect of glycerol.     

Validation of high-performance liqid chromatography method to determine epirubicin and its pharmacokinetics after intravenous bolus administration in rats

We investigated the pharmacokinetics of epirubicin, an anthracycline derivative antibiotics, after intravenous (i.v.) bolus administration in rats. To analyze epirubicin levels in the plasma, bile, urine and tissue samples, we developed an high-performance liqid chromatography (HPLC)-based method which was validated for a pharmacokinetic study by suitable criteria. The plasma concentration of epirubicin after i.v. bolus administration was rapidly disappeared within 10 min from the blood circulation. The mean plasma half-lives at α phase (t_1/2α) when administered at the dose of 2, 5, 10, 25 and 50 mg/kg were 2.14–2.61 min. The values of t_1/2β at the corresponding doses increased two folds (from 150 to 291 min) with increasing doses. The CL_t values significantly decreased with the increase in dose. In contrast, V_dss values increased about 1.5 times with the increase in dose from 2 to 50 mg/kg. Of the various tissues, epirubicin mainly distributed to the kidney, lung, heart and liver after i.v. bolus administration. The epirubicin concentrations in various tissues at 24 h after i.v. bolus administration were below 1.0 μg/g tissue. Epirubicin was excreted largely in the bile after i.v. bolus administration at the dose of 2, 10 and 50 mg/kg. The cumulative amount of epirubicin in the urine 72 h after dosage represented 20 % of the amount excreted in the bile 12 h after high dosage, indicating that i.v. administered epirubicin was mainly excreted in the bile. In conclusion, epirubicin was rapidly cleared from the blood circulation and transferred to tissues such as the kidney and liver 2 h after i.v. bolus administration. Moreover, the majority of epirubicin appears to be excreted in the bile by 12 h after i.v. bolus administration.     

Plasma pharmacokinetics and urinary and biliary excretion of a new potent tripeptide HIV-1 protease inhibitor,KNI-272, in rats after intravenous administration

The pharmacokinetic (PK) characteristics of KNI-272, a potent and selective HIV-1 protease inhibitor, were evaluated in rats after intravenous (IV) administration. The effect of dose on KNI-272 plasma kinetics, and the urinary and biliary elimination kinetics of KNI-272, were examined. After IV administration of 10.0 mg kg^?1 KNI-272, the mean terminal elimination half-life, t_1/2λz, was 3.49 ± 0.19 (SE) h, the total plasma clearance, CL_tot, was 15.1 ± 1.2 mL min^?1 and the distribution volume at steady state, V_d,ss, was 3790±280 mL kg^?1. On the other hand, after 1.0mg kg^?1 IV administration, t_d,ss, was 3.04±0.11 h, CL_tot was 15.9±0.2mL min^?1, and V_d,ss was 6950±600 mL kg^?1. The PK parameters of KNI-272 after IV administration showed that the disposition of KNI-272 in the rat plasma is linear within the dose range from 1.0 to 10.0mg kg^?1. Using an equilibrium dialysis method, the plasma binding of KNI-272 was measured in vitro. The free fractions were 17.7 ± 0.6%, 12.1±1.5%, and 13.8 ± 1.4% at the total concentration ranges of 9.898 ± 0.097 μg mL^?1, 0.888 ± 0.008 μg mL^?1, and 0.470±0.55 μg mL^?1, respectively. The percentages of the dose excreted into the urine and bile as the unchanged form were 1.20 ± 1.06% and 1.61 ± 0.32% at 1.0mg kg^?1 dose, and 0.164 ± 0.083% and 1.42 ± 0.26% at 10.0 mg kg^?1 dose, respectively. The renal clearance (CL_R) and the biliary clearance (CL_B) were calculated to be 0.191 and 0.256mL min^?1 for 1.0mg kg^?1, and 0.0248 and 0.215 mL min^?1 for 10.0 mg kg^?1, respectively. When comparing these values with the CL_tot values, the urinary and biliary excretion of KNI-272 are minor disposition routes.     

Analysis of the Complicated Nonlinear Pharmacokinetics of Orally Administered Telmisartan in Rats Using a Stable Isotope-IV Method

This study aimed to kinetically analyze the nonlinear absorption and systemic exposure of telmisartan (TEL) after oral administration to rats by using a stable isotope-IV method. Rats were orally administered different dose of TEL, followed by the intravenous injection of 0.005 mg/kg of deuterium-labeled TEL (TEL-d3). Assuming that TEL-d3 shows same pharmacokinetic properties with TEL, systemic clearance (CL_tot), oral bioavailability (F_oral), and intestinal and hepatic availability (F_a*F_g, F_h) of TEL were calculated in each individual rat. AUC_po of TEL increased disproportionately with dose and showed a sigmoid-type relation, indicating the involvement of multi-nonlinear processes in oral absorption of TEL. F_a*F_g of TEL increased with dose at the low-dose range while decreased at the high-dose range. In contrast, F_h increased and CL_tot decreased significantly in the middle range (2 to 6 mg/kg). As main factors of nonlinearity, saturations of solubility, efflux transport in the intestine, and the hepatic uptake of TEL were indicated. In conclusion, this study demonstrated a high possibility of a stable isotope-IV method to characterize complicated pharmacokinetic properties of oral drugs in animals, which can help to consider the future risks in their clinical use.     

Pharmacokinetics and Biliary Excretion of Mitoxantrone in Rats

The objective of this investigation was to compare the observed biliary clearance (CL_b) and % of dose excreted in the bile (PD_b) of mitoxantrone with the predicted values obtained from quantitative structure pharmacokinetic relationship (QSPKR) models. Blood and bile samples were collected from bile duct cannulated rats after an intravenous bolus dose of 0.5 or 2 mg/kg mitoxantrone, and the concentrations were measured by HPLC. Mitoxantrone plasma concentrations exhibited a tri‐exponential profile with systemic clearance of 118 ± 6.8 mL/min/kg. After dosing, 6.08 ± 2.32% and 5.69 ± 0.59% of the dose were excreted into bile in unchanged form after a 3‐h collection. CL_b was 7.20 ± 4.54 and 7.46 ± 0.62 mL/min/kg after the two doses. With the co‐administration of 10 mg/kg GF‐120918, a P‐glycoprotein and BCRP inhibitor, PD_b was reduced to 0.69 ± 0.07%, suggesting that BCRP or P‐glycoprotein may play an important role in the biliary elimination of mitoxantrone. Using QSPKR models developed for the biliary excretion of cations/neutral compounds in rats, CL_b and PD_b of mitoxantrone were predicted as 5.18 mL/min/kg and 7.21%, respectively, suggesting that the models could be used to predict the biliary excretion of mitoxantrone. © 2009 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2502–2510, 2010     

Pharmacokinetics of YJC-10592, a novel chemokine receptor 2 (CCR-2) antagonist,in rats

YJC-10592, a novel chemokine receptor 2 (CCR-2) antagonist, was developed for treating asthma and atopic dermatitis. We studied the pharmacokinetic characteristics of YJC-10592 after intravenous (5, 10 and 20 mg/kg) and oral (100 and 200 mg/kg) administration of the drug to rats. Tissue distribution of YJC-10592 was also evaluated after intravenous administration of YJC-10592, 10 mg/kg, to rats. The pharmacokinetics of YJC-10592 was dose-dependent from 20 mg/kg after intravenous administration to rats. The values of the area under the plasma concentration–time curve from time zero to infinity (AUC) of YJC-10592 were dose-dependent from 20 mg/kg and the time-averaged total body (CL) and nonrenal (CL_NR) clearances of YJC-10592 were significantly lower at dose of 20 mg/kg, suggesting that saturable metabolism may be involved. The absolute bioavailability (F) of YJC-10592 was generally low (<2.55 %) for both oral doses due to incomplete absorption and low urinary excretion. YJC-10592 had a great affinity to all rat tissues studied except brain, which was supported by a relatively high value of the apparent volume of distribution at steady state (V _ss) (890–1385 mL/kg). In conclusion, YJC-10592 showed dose-dependent pharmacokinetics and low F value due to slower elimination and incomplete absorption.     

Metabolic and pharmacokinetic studies of scutellarin in rat plasma, urine, and feces

Aim:

To study the metabolic and pharmacokinetic profile of scutellarin, an active component from the medical plant Erigeron breviscapus (Vant) Hand-Mazz, and to investigate the mechanisms underlying the low bioavailability of scutellarin though oral or intravenous administration in rats.

Methods:

HPLC method was developed for simultaneous detection of scutellarin and scutellarein (the aglycone of scutellarin) in rat plasma, urine and feces. The in vitro metabolic stability study was carried out in rat liver microsomes from different genders.

Results:

After a single oral dose of scutellarin (400 mg/kg), the plasma concentrations of scutellarin and scutellarein in female rats were significantly higher than in male ones. Between the female and male rats, significant differences in AUC, t_max2 and C_max2 for scutellarin were found. The pharmacokinetic parameters of scutellarin in the urine also showed significant gender differences. After a single oral dose of scutellarin (400 mg/kg), the total percentage excretion of scutellarein in male and female rats was 16.5% and 8.61%, respectively. The total percentage excretion of scutellarin and scutellarein in the feces was higher with oral administration than with intravenous administration. The in vitro t_1/2 and CL_int value for scutellarin in male rats was significantly higher than that in female rats.

Conclusion:

The results suggest that a large amount of ingested scutellarin was metabolized into scutellarein in the gastrointestinal tract and then excreted with the feces, leading to the extremely low oral bioavailability of scutellarin. The gender differences of pharmacokinetic parameters of scutellarin and scutellarein are due to the higher CL_int and lower absorption in male rats.     

Leishmanicidal candidate LASSBio-1736, a cysteine protease inhibitor with favorable pharmacokinetics: low clearance and good distribution

Abstract

1.?LASSBio-1736 ((E)-1-4(trifluoromethyl) benzylidene)-5-(2-4-dichlorozoyl) carbonylhydrazine) is proposed to be an oral cysteine protease leishmanicidal inhibitor.

2.?This work aimed to investigate plasma pharmacokinetics, protein binding and tissue distribution of LASSBio-1736 in male Wistar rats.

3.?LASSBio-1736 was administered to male Wistar rats at doses of 3.2?mg/kg intravenously and 12.6?mg/kg oral and intraperitoneal. The individual plasma-concentration profiles were determined by HPLC-UV and evaluated by non-compartmental and population pharmacokinetic analysis (Monolix 2016R1, Lixoft). Tissue distribution was evaluated after iv injection of 3.2?mg/kg drug by non-compartmental approach.

4.?After intravenous administration, Vd_ss (1.79?L/kg), t _½ (23.1?h) and CL_tot (56.1?mL/h/kg) were determined, and they were statistically similar (α?=0.05) to oral and intraperitoneal pharmacokinetic parameters. The plasma profiles obtained after intravenous, oral and intraperitoneal administration of the compound were best fitted to a three-compartment and one-compartment open model with first-order absorption.

5.?The intraperitoneal and oral bioavailability were around 40 and 15%, respectively.

6.?Liver, spleen and skin tissues showed penetration of 340, 130 and 40%, respectively, with t _½ like plasma values.

7.?LASSBio-1736 protein binding was 95?±?2%.

8.?The t _½, CL_tot and tissue distribution of the compound agreed with the desired drug characteristics for leishmanicidal activity.     

Renal Clearance of a Recombinant Granulocyte Colony-Stimulating Factor,Nartograstim, in Rats

Purpose. To clarify the role of the kidney in the elimination of a recombinant human granulocyte colony-stimulating factor, nartograstim, we have investigated its pharmacokinetics in rats with renal failure. Methods. The steady-state clearance (CL_ss) were determined by the intravenous infusion for 4 hr to unilateral renally-ligated and cisplatin-treated rats, whose renal functions were about 50 and 10 % of controls, respectively. Results. CL_ss of nartograstim (27 ml/hr/kg) in the renally-ligated rats at a high infusion rate was significantly lower (25%) than in control rats (p<0.05). CL_ss in these rats, at a low infusion rate was 95 ml/hr/kg, 14 % lower than in control rats. The saturable CL_ss in these rats, 68 ml/hr/kg, was not significantly different from control rats (75 ml/hr/kg, p>0.05). Also, CL_ss in cisplatin-treated rats with extensive renal failure, at a high infusion rate, decreased to 57 % of controls. Furthermore, the total body clearances (CL_tot) of nartograstim after bolus intravenous administration to renally-ligated and cisplatin-treated rats were reduced to 33–49 % of controls. Conclusions. These results suggest that the kidney may be responsible for 40– 50 % of the nonsaturable clearance of nartograstim. Thus, the kidney should make a major contribution to the elimination of nartograstim when rats are given a high dose of nartograstim, which saturates the receptor-mediated clearance.     

Prediction of metabolic clearance of diclofenac in adjuvant-induced arthritis rats using a substrate depletion assay

1.?The purpose of this study was to evaluate drug clearance measured by the metabolic intrinsic clearance (CL_int) in a substrate depletion assay in comparison with the in vivo clearance (CL_tot) observed in adjuvant-induced arthritis (AA) rats. 2.?After intravenous administration of diclofenac as a model drug, CL_tot was 2.8-fold higher in AA rats than in control rats. In two different substrate depletion assays with liver microsomes for glucuronidation and hydroxylation, the CL_int values for glucuronidation was significantly decreased in AA rats to 60% of the value in control rats, whereas the CL_int values for hydroxylation were similar. The unbound fraction of diclofenac in plasma (f_{u, plasma}) was significantly higher (2.8-fold) in AA rats than in control rats. 3.?Hepatic clearance predicted from the CL_int values for both biotransformation pathways and f_{u, plasma} was higher in AA rats than in control rats, with good consistency between predicted and observed values. The same results were obtained for experiments using hepatocytes. 4.?The plasma protein-binding activities, rather than metabolic clearance, in both types of rats would be a determining factor in the pharmacokinetic behaviour differences between control and AA rats. 5.?In summary, substrate depletion assays with liver microsomes and hepatocytes in combination with protein binding assessment can help to predict changes in pharmacokinetics under AA conditions.     

Pharmacokinetic interference of doxorubicin with tolbutamide due to reduced metabolic clearance with increased serum unbound fraction in rats

The study examined the effect of doxorubicin (DOX) on the hepatic expression of CYP2C and its activity for metabolizing tolbutamide (TB), a specific CYP2C substrate, in rats and whether the pharmacokinetics of tolbutamide were altered by doxorubicin exposure. The expression level of hepatic CYP2C11 was depressed 1 day after doxorubicin administration (day 1), and this effect on CYP2C11 was augmented on day 4. However, the expression level of hepatic CYP2C6 remained unchanged. The activity of tolbutamide 4‐hydroxylation in hepatic microsomes was decreased with time following doxorubicin administration. Regarding the enzyme kinetic parameters for tolbutamide 4‐hydroxylation on day 4, the maximum velocity (V_max) was significantly lower in the DOX group than that in the control group, while the Michaelis constant (K_m) was unaffected. On pharmacokinetic examination, the total clearance (CL_tot) of tolbutamide on day 4 was increased, despite the decreased metabolic capacity. On the other hand, the serum unbound fraction (f_u) of tolbutamide was elevated with a reduced serum albumin concentration in the DOX group. Contrary to CL_tot, CL_tot/f_u, a parameter approximated to the hepatic intrinsic clearance of unbound tolbutamide, was estimated to be significantly reduced in the DOX group. These findings indicate that the metabolic capacity of CYP2C11 in the liver is depressed time‐dependently by down‐regulation after doxorubicin exposure in rats, and that the decreased enzyme activity of TB 4‐hydroxylation in hepatic microsomes reflects the pharmacokinetic change of unbound tolbutamide, not total tolbutamide, in serum.     

Comparison of the Pharmacokinetics and Pharmacodynamics of the Aldose Reductase Inhibitors,AL03152 (RS), AL03802 (R), and AL03803 (S)

The pharmacokinetics of AL03152 (RS) and its enantiomers, AL03802 (R) and AL03803 (S), were studied in the Sprague–Dawley rat following intravenous bolus administration. The enantiomers had differing pharmacokinetic profiles, while the racemic compound exhibited pharmacokinetic parameters approximating the mean values of the individual enantiomers. The total clearance (CL_T) values of the two enantiomers were similar, but the intrinsic clearance (Cl_int) was much greater for the S-enantiomer than for the R-enantiomer. The volume of distribution (V_ss) for AL03802 (R) was threefold greater than that for AL03803 (S). The stereoselectivity in V _ss could not be totally accounted for by the slight difference in serum protein binding of the isomers and resulted in a difference in the half-lives of the enantiomers. Only the R-isomer exhibited a persistent terminal elimination phase, consistent with more extensive tissue binding than the S-isomer. AL03152 enantiomers were equivalent in potency assessed from in vitro IC₅₀ values toward rat lens aldose reductase and rat kidney L-hexonate dehydrogenase and lens EC₅₀ values in diabetic rats.     

A predictive biomarker for altered 5‐fluorouracil pharmacokinetics following repeated administration in a rat model of colorectal cancer

The relationship between the plasma ratio of dihydrouracil/uracil (UH2/Ura) and hepatic dihydropyrimidine dehydrogenase (DPD) activity after repeated 5‐fluorouracil (5‐FU) treatment in rats with colorectal cancer (CRC) was investigated. Repeated intravenous 5‐FU bolus injections resulted in a significant decrease in the total clearance (CL_tot) and an increased area under the curve (AUC_0‐∞) in CRC rats. Furthermore, the hepatic DPD levels and the plasma ratio of UH2/Ura decreased significantly and lost their circadian rhythms in CRC rats treated repeatedly with 5‐FU, although significant circadian variation in the two parameters was observed in the control CRC rats. Moreover, a significant correlation was found between the plasma ratio of UH2/Ura and hepatic DPD activity in CRC rats untreated and treated with single or repeated 5‐FU administration (r² = 0.865, p < 0.01). The ratio of UH2/Ura in plasma could be a predictive biomarker of the suppression of hepatic DPD levels during repeated 5‐FU‐based treatment. Furthermore, by plotting the observed pharmacokinetic parameters of 5‐FU against hepatic DPD activity levels predicted by the ratio of UH2/Ura in plasma, AUC_0‐∞, CL_tot and half‐life (t_1/2) were closely linked to predicted hepatic DPD activity levels. These observations suggest that the factor that significantly influences the AUC_0‐∞, CL_tot and t_1/2 of 5‐FU after single or repeated administration of 5‐FU is the hepatic DPD activity and it could be assessed by the ratio of UH2/Ura in plasma. Copyright © 2013 John Wiley & Sons, Ltd.     

Disposition of quinine in rats with induced renal failure

Aetiologically different models of experimental acute renal failure were induced in rats by the administration of glycerol, mercuric chloride and gentamicin, respectively, to different groups. Quinine levels in plasma and urine of the rats with induced renal failure were determined and pharmacokinetic parameters (eliminationt _1/2, CL _p ,V, CL_R AUC_0–) of the drug were derived and compared with values obtained from control rats following intraperitoneal administration of a 10 mg/kg body-weight dose of quinine. Results showed that each of the three compounds caused an up to 25-fold increase in the plasma levels of the drug and a marked decrease in the levels of the metabolite 3-hydroxyquinine. All the pharmacokinetic parameters determined for the rats with renal impairment were markedly different when compared to control. The high plasma quinine levels observed in the rats with renal failure could be largely due to the marked decrease inV and reduced metabolism. Also, in the rats with renal impairment, no correlation was observed between the increased plasma urea levels and plasma quinine levels or disposition of the drug. The results of the study suggest that quinine should be used with caution in patients with renal impairment. The plasma urea levels, as a measure of renal function, might not provide a suitable index for determining quinine dosage.     

Mechanistic Models Describing Active Renal Reabsorption and Secretion: A Simulation-Based Study

The objective of the present study was to evaluate mechanistic pharmacokinetic models describing active renal secretion and reabsorption over a range of Michaelis–Menten parameter estimates and doses. Plasma concentration and urinary excretion profiles were simulated and renal clearance (CL_r) was calculated for two pharmacokinetic models describing active renal reabsorption (R1/R2), two models describing active secretion (S1/S2), and a model containing both processes. A range of doses (1–1,000 mg/kg) was evaluated, and V _max and K _m parameter estimates were varied over a 100-fold range. Similar CL_r values were predicted for reabsorption models (R1/R2) with variations in V _max and K _m. Tubular secretion models (S1/S2) yielded similar relationships between Michaelis–Menten parameter perturbations and CL_r, but the predicted CL_r values were threefold higher for model S1. For both reabsorption and secretion models, the greatest changes in CL_r were observed with perturbations in V _max, suggesting the need for an accurate estimate of this parameter. When intrinsic clearance was substituted for Michaelis–Menten parameters, it failed to predict similar CL_r values even within the linear range. For models S1 and S2, renal secretion was predominant at low doses, whereas renal clearance was driven by fraction unbound in plasma at high doses. Simulations demonstrated the importance of Michaelis–Menten parameter estimates (especially V _max) for determining CL_r. K _m estimates can easily be obtained directly from in vitro studies. However, additional scaling of in vitro V _max estimates using in vitro/in vivo extrapolation methods are required to incorporate these parameters into pharmacokinetic models.     

Pharmacokinetics and metabolic elimination of tolbutamide in female rats: Comparison with male rats

As there are to be known gender differences in the expression profiles of rat hepatic CYP2C, we examined the pharmacokinetic behavior of tolbutamide (TB), a typical probe for CYP2C, and hepatic enzyme activities for metabolizing TB in female rats to compare with male rats. On the pharmacokinetic analysis of TB after intravenous administration to female rats, the elimination rate constant at the terminal phase (k_e), total clearance (CL_tot) and the apparent volume of distribution at steady‐state (Vd_ss) were significantly lower than in male rats. The binding rates of TB to serum protein were similar in male and female rats, indicating that the change in unbound TB concentration in serum is not associated with the difference in the pharmacokinetic disposition of TB. On metabolic examination using hepatic microsomes, the maximum reaction velocity (V_max) of the metabolic conversion from TB to 4‐hydroxytolbutamide (4‐OH‐TB) in female rats was lower than that in male rats, although there was no significant difference in the Michaelis constant (K_m) between genders. Consistent with this, the V_max‐to‐K_m ratio (V_max/K_m) was significantly lower in female rats than in male rats. Therefore, the low in vitro CYP2C‐dependent activity for hepatic TB removal in female rats provided a clear explanation for the lower in vivo elimination clearance of TB. Our findings strongly suggest that there is a gender difference in the metabolic capacity to eliminate drugs that serve as substrates of hepatic CYP2C enzymes in rats.     

Effect of Receptor Up-Regulation on Insulin Pharmacokinetics in Streptozotocin-Treated Diabetic Rats

The present study investigated the mechanism by which the disposition of insulin is altered in streptozotocin (STZ)-treated diabetic rats as compared with 48-hr-fasted normal (control) rats. It was shown by an indocyanine green infusion method that the hepatic plasma flow rate (Q _H) in diabetic rats (1.64 ml/min/g liver) is significantly higher than that in control rats (0.982 ml/min/g liver). The portal injection technique revealed that the unidirectional clearance (CL_on), which represents the binding of A₁₄-¹²⁵ I-insulin to surface receptors in the liver, is significantly elevated in diabetic rats, suggesting an increase in the surface receptor number R _T), i.e., up-regulation in the liver. In both control and diabetic rats, the total-body clearance (CL_tot) and steady-state volume of distribution (Vd _ss) of labeled insulin decreased significantly with a simultaneous injection of unlabeled insulin (8 U/kg), confirming that the disposition of insulin is affected largely by specific, saturable receptor-mediated processes. The CL_tot and Vd _ss increased significantly in diabetic rats, while nonspecific portions of these parameters were not changed. From the increases in CL_tot (80%) and Q _H (67%) in diabetic rats, a pharmacokinetic analysis has revealed a 40% increase in the hepatic intrinsic clearance (CL_{int sp}) of A₁₄-¹²⁵ I-insulin via a specific mechanism in diabetic rats. In conclusion, we have provided in vivo evidence for a small increase in CL_{int sp} of insulin in STZ-diabetic rats compared with control rats, which may be caused by an increase in the surface receptor number in the livers of diabetic rats.     

Mechanism of chlorpromazine prevention of carbon tetrachloride-induced liver necrosis

Chlorpromazine (CPZ) is able to partially prevent the CCl₄-induced liver necrosis in rats 24 hr but not 72 hr after its administration. Preventive effects at 24 hr were still observed when CPZ was given as late as 10 hr after CCl₄. Prevention is not due to variation in CCl₄ concentration in liver. CPZ does not decrease either the covalent binding of CCl₄ reactive metabolites to cellular constituents or lipid peroxidation but causes a marked decrease in the body temperature of the rats. Our results indicate that CPZ only delays the onset of necrosis and suggest that this effect is mediated by the CPZ decreasing effects on body temperature, since the necrosis observed in the CPZ-treated animals injected with CCl₄ and maintained at 37°C is as intense as that observed in the group receiving CCl₄ alone.     

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

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

Pharmacokinetics of guanosine in rats following intravenous or intramuscular administration of a 1:1 mixture of guanosine and acriflavine, a potential antitumor agent

A 1:1 mixture of acriflavine (ACF; CAS 8063-24-9) and guanosine is under evaluation in preclinical studies as a possible antitumor agent. Guanosine is known to potentiate the anti-cancer activity of ACF. We therefore investigated the pharmacokinetics of guanosine following administration of the ACF/guanosine mixture in rats. Rats were given guanosine (1 or 5 mg/kg) or ACF/guanosine (2 or 10 mg/kg) by i.v. bolus; or guanosine (3 or 15 mg/kg) or ACF/guanosine (6 or 30 mg/kg) by i.m. injection. We found that guanosine was rapidly cleared from the blood and transferred to tissues after i.m. administration of ACF/guanosine. The mean plasma half-lives (t_1/2) at the α and β phases were 0.091 and 6.86 h, or 0.09 and 7.51 h at a dose of 1 or 5 mg/kg guanosine, respectively. ACF had no effect on the plasma disappearance of guanosine following either i.v. bolus or i.m. administration of the combination mixture. Moreover, the ACF combination with guanosine did not significantly alter the values of MRT, V_dss, and CL_t of guanosine. Guanosine exhibited linear pharmacokinetics over the dose range from 1 to 5 mg/kg for i.v. doses and 3 to 15 mg/kg for i.m. doses. The bioavailability of guanosine after i.m. administration was 84% for 3 mg/kg dose and 88% for 15 mg/kg dose. ACF had no effects on biliary and urinary excretion of guanosine after i.m. administration. The cumulative amount of guanosine in urine after i.m. administration was about 5-fold larger than that in bile, indicating that guanosine is mostly excreted into the urine. Guanosine was widely distributed in all tissues examined in this study, but was most highly concentrated in the kidney after i.m. administration, followed by slow excretion to bile or urine. ACF had no effect on the tissue distribution of guanosine following i.m. administration. These characterizations of the pharmacokinetics of guanosine after administration of the ACF/guanosine combination will be useful in providing preclinical and clinical bases for the potential application of this combination to the treatment of cancer.