The involvement of P-glycoprotein (P-gp) in pentazocine (PTZ) transport at the blood–brain barrier (BBB) in rats was evaluated by means of an in vivo study using the brain uptake index (BUI) method. ...The amount of radioactivity in the brain was estimated at different intervals (up to 240 s) after carotid injection in rats. The apparent elimination rate constant (ktest) due to efflux of PTZ from the brain was calculated as 0.22 min−1. The observed BUI values of 3H-PTZ (0.35 μM) were not significantly different between 5 and 15 s after the carotid injection. The concentration-dependent uptake of PTZ by the brain was increased gradually by increasing the concentration (0.01—1 mM) of PTZ in the injection solution. The apparent uptake of PTZ by the brain increased in the presence of P-gp inhibitors such as cyclosporin A, quinidine, verapamil and vinblastine after the carotid injection. These results suggest that the increment of PTZ uptake by the brain could be explained by the saturable efflux transport system involving a P-gp-mediated efflux mechanism of PTZ transport at the BBB.
Transport characteristics of 17beta-estradiol 17beta-D-glucuronide (E217betaG), a dual substrate of the transporters for cellular uptake (organic anion-transporting polypeptide 1 or oatp1) and ...cellular excretion (multidrug resistance-associated protein 1or MRP1), in the rat choroid plexus were studied in vivo and in vitro. The uptake of E217betaG into isolated choroid plexus was mediated by an energy-dependent system with a Km of 3.4 microM. Together with the previous finding that oatp1 is localized on the apical membrane of choroid plexus, these results suggest that oatp1 is responsible for the uptake of this ligand. After intracerebroventricular administration, elimination of E217betaG from cerebrospinal fluid was probenecid sensitive and much more rapid than that of inulin; less than 2% of the administered E217betaG and 40 to 50% of inulin remained in the cerebrospinal fluid 20 min after intracerebroventricular administration. In addition, the amount of E217betaG associated with choroid plexus at 20 min was negligible, suggesting the presence of an efficient excretion system on the basolateral membrane of choroid plexus. Expression of MRP1 was detected in choroid plexus. Semiquantitative reverse transcription-polymerase chain reaction and Western blot analyses indicated that the expression level of MRP1 in choroid plexus is about four or five times higher than that in the lung, one of the tissues exhibiting high expression of MRP1. Together with the in vivo vectorial transport of E217betaG, these results can be accounted for by assuming that there is basolateral localization of MRP1 in choroid plexus. Combined, oatp1 and MRP1 may synergistically mediate the efficient transcellular transport of E217betaG across choroid plexus.
The influx transport mechanism of pentazocine (PTZ) at the blood-brain barrier (BBB) was investigated in rats using the carotid injection technique. The uptake kinetics of PTZ into the rat brain ...exhibited saturability, which occurred by both nonsaturable and carrier-mediated transport processes. The in vivo kinetic parameters were estimated as follows: the maximal uptake rate (Jmax), 3.6±1.2 μmol/min/g brain and the apparent Michaelis constant (Kt), 3.7±1.7 mM for the saturable component of PTZ into the brain, and the nonsaturable uptake rate constant (Kd), 0.06±0.04 ml/min/g brain. The uptake of PTZ by the brain was strongly inhibited by lidocaine, imipramine and propranolol, and also by H1-antagonists such as mepyramine, diphenhydramine. In addition, narcotic-antagonist analgesic (buprenorphine, butorphanol or eptazocine) and an opioid antagonist (naloxone) significantly inhibited PTZ transport. These results suggest that PTZ permeates into the brain via a carrier-mediated transport system, which may widely recognize the cationic drugs.
Nifedipine-containing calcium phosphate cement (CPC) was prepared, and nifedipine (NF) release from this preparation was evaluated by the shaking method (SK), Japanese Pharmacopoeia XIV (JPXIV) ...paddle method (PD), and JPXIV flow-through cell method (FT). The release of NF from the CPC preparation continued for 7 d or longer by all these methods. This suggests that the release of NF can be controlled by preparing NF-containing CPC. The release pattern of NF from CPC in these tests was found to follow the Higuchi equation. However, the Higuchi constant differed among the three dissolution tests, probably because the apparent tortuosity of capillary system (τ) varied.
The effect of naloxone, a potent and specific opioid antagonist, on cerebral glucose utilization was investigated in conscious rat. For quantitative evaluation of the functional activity in brain, ...the regional cerebral metabolic rate for glucose (rCMRglc) was measured by the double tracer technique, using 14C2-deoxyglucose and 3H3-O-methylglucose. Intravenous administration of naloxone significantly increased rCMRglc in the medulla and thalamus at a dose of 1 or 10 mg/kg, and in the cerebral cortex, midbrain and cerebellum at a dose of 10 mg/kg. Our findings strongly suggest that naloxone by itself affects the cerebral functional activity within 10 min of administration.
A remarkable feature of the pharmacokinetics of polypeptide hormones is the contribution of specific binding sites (receptors) to the polypeptide hormone distribution and clearance in the body. The ...concept of "transport receptor" is now well established, and receptor-mediated endocytosis (RME) is recognized as a general mechanism in the uptake of biologically important peptide hormones. This article focuses on the kinetic analysis of the RME of polypeptides, based mainly upon the observations of the kinetics of epidermal growth factor in the liver. The following points are emphasized: (1) How can we determine the existence and the kinetic constants of polypeptide RME in vivo and in the perfused liver system? A liver perfusion method, the single-pass multiple-indicator dilution technique, has been shown to be suitable for analyzing the dynamics of interaction of peptide hormones with their cell surface receptors. (2) What is the importance of down-regulation of transport receptors to the overall kinetics of polypeptides in vivo? Time profiles of polypeptide plasma concentrations and their surface receptors in the liver after iv administration of epidermal growth factor were simulated with a physiologic pharmacokinetic model that includes kinetic constants representing the interaction of polypeptides and their receptors.
To clarify the contribution of P-glycoprotein to the biliary excretion of vincristine in rats, the effects of induction of hepatic P-glycoprotein by a phenothiazine treatment on the biliary excretion ...of
3Hvincristine were investigated. Immunoblot analysis using C219, a monoclonal antibody to P-glycoprotein, demonstrated that the phenothiazine treatment increased the P-glycoprotein level in isolated bile canalicular membrane vesicles approximately 6.5-fold. Transport of
3Hvincristine to canalicular membrane vesicles from the phenothiazine-treated and control rats revealed ATP-dependency, with an overshoot that results from the consumption of medium ATP. The maximum ATP-dependent uptake was increased in canalicular membrane vesicles from the phenothiazine-treated rats approximately 2-fold compared to the control. The biliary excretion of
3Hvincristine was further studied using an indicator dilution method in a single-pass perfused liver. The ratios of the cumulative amount of
3Hvincristine excreted into the bile to the amount of
3Hvincristine taken up by the liver at 15, 30 and 90 min were significantly increased in the phenothiazine-treated rats by 60, 45 and 25%, respectively, compared to the control rats. Furthermore, the corrected mean residence time of
3Hvincristine in hepatocytes in the phenothiazine-treated rats was reduced to 21 min from that in the control rats (30 min), supporting the contention that the induction of hepatic P-glycoprotein accelerates the biliary excretion of
3Hvincristine. The present results suggest that P-glycoprotein on the bile canalicular membrane functions as a transporter not only in the isolated membrane but also in the more physiological perfused liver system. One must be cautious in the interpretation of the data, however, since phenothiazine can induce other proteins which might affect the behavior of
3Hvincristine.
The effects of buprenorphine (BNP, 10-200 μg/kg, i.v.) and pentazocine (PTZ, 2.5-10 mg/kg, i.v.) on the regional cerebral metabolic rate for glucose (rCMRglc) were analyzed in nine anatomically ...discrete areas of the conscious rat brain by the simultaneous use of 14C2-deoxyglucose, the glucose analogue that can be phosphorylated in the brain, and 3H3-O-methylglucose, a nonmetabolizable glucose analogue. Originally, this method was developed by Gjedde and Diemer in the rat and in humans. The rCMRglc was significantly decreased by BNP (100 or 200 μg/kg) in most of the brain regions investigated, except the cerebellum. In contrast, PTZ (10 mg/kg) significantly increased rCMRglc in the cerebral cortex and medulla. In the cerebral cortex and medulla, the direction of the effect on rCMRglc was opposite for BNP (22% decrease at the dose of 200 μg/kg) and PTZ (22% increase at the dose of 10 mg/kg). These findings strongly suggest that the discrepancies between the marked effects of BNP (a partial μ agonist and κ antagonist) and PTZ (a μ antagonist and κ agonist) on rCMRglc reflect the selectivity of agonist action at the different types of opioid receptors, μ and κ receptors, in the rat brain.
The relstionship between the pharmacokinetics and the pharmacodynamics of eptazocine, a narcotic-antagonist analgesic, was investigated in rats. The analgesic effect of eptazocine (2.5, 5 and 10 ...mg/kg) following intravenous (i.v) administration was evaluated by both the Randall-Selitto method and the D'Amour-Smith method. The analgesic effects were determined before and at designed intervals for a period of 120 min after eptazocine administration, and are expressed as area under the effect-time curve (AUCE). The plasma concentration of eptazocine was determined by fluorescence HPLC and was analyzed with a two compartment open model using the nonlinear least-squares method. Eptazocine produced a dose-dependent analgesic effect. It was demonstrated that eptazocine has a linear relationship between AUCE and the area under the plasma concentration-time curve (AUC) following i.v. administration for three different doses ranging from 2.5 to 10 mg/kg.
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