Pulmonary Delivery of Low Molecular Weight Heparins

PURPOSE: To investigate if pulmonary delivery of low molecular weight heparin (LMWH) formulated with tetradecyl-beta-maltoside (TDM) or dimethyl-beta-cyclodextrin (DMbetaCD) could be a feasible alternative to subcutaneous injections for the treatment of pulmonary embolism. METHODS: The pulmonary absorption of two LMWHs and unfractionated heparin formulated with TDM or DMbetaCD was studied in cell culture and rodent model. The in vitro study was performed by measuring the transport of radiolabeled enoxaparin and mannitol across human bronchial epithelial cells (Calu-3) in the presence or absence of varying concentrations of TDM or DMbetaCD. The changes in transepithelial electrical resistance (TEER) and enoxaparin metabolic stability were also investigated using Calu-3 cells. In vivo absorption studies were performed by measuring plasma anti-factor Xa activity after pulmonary administration of enoxaparin, dalteparin, or unfractionated heparin to anesthetized rats. RESULTS: In vitro experiments conducted in Calu-3 cells suggest that the addition of TDM or DMbetaCD to the apical chamber results in a significant increase in 3H-enoxaparin and 14C-mannitol permeability and a decrease in TEER across the Calu-3 cell monolayer. Enoxaparin incubated in Calu-3 cell extracts was stable for 8 h. In vivo studies indicate that both TDM and DMbetaCD enhance pulmonary absorption of LMWH. However, TDM was found to be more potent than DMbetaCD in both in vitro transport and in vivo absorption studies. CONCLUSIONS: TDM and DMbetaCD enhance pulmonary absorption of LMWH both in vitro and in vivo, with TDM being more efficacious than DMbetaCD. Both agents increase drug transport by acting mainly on the membrane rather than interacting with the drug.     

Transdermal Delivery of Timolol and Atenolol Using Electroporation and Iontophoresis in Combination: A Mechanistic Approach

PURPOSE: The purpose of this work was to study the effect of electroporation on iontophoretic transport of two beta-blockers, timolol (lipophilic) and atenolol (hydrophilic), and to have a better understanding of the mechanism of combination. METHODS: The transdermal delivery of these beta-blockers through human stratum corneum was studied in three-compartment diffusion cells. The transport of mannitol was evaluated to assess the electroosmotic flow. RESULTS: The iontophoretic transport of timolol was decreased by electroporation because the high accumulation of the lipophilic cation timolol in the stratum corneum resulted in a decrease of electroosmosis. In contrast, electroosmosis was not affected by atenolol, and the iontophoretic transport of atenolol was increased by electroporation. CONCLUSIONS: Using two different beta-blockers, we showed that lipophilicity and positive charges affect the electrotransport of drugs. Understanding the effect of the physicochemical properties of the drug, as well as the electrical parameters, is thus essential for the optimization of transdermal drug delivery by a combination of electroporation and iontophoresis.     

Reversal of tumor-induced immunosuppression by TGF-beta inhibitors

The immune system is responsible for the early detection and destruction of newly transformed malignant cells. Some transformed cells become immunologically invisible by passive avoidance of immune surveillance (i.e., when tumor cells are immunologically indistinguishable from normal cells). Other transformed cells actively secrete cytokines that effectively blind the immune system to the presence of abnormal antigens on the tumor cell surface. Transforming growth factor- (TGF-), which is expressed by a majority of malignant tumors, is the most potent immunosuppressor and therefore, the most likely cytokine to be responsible for the latter phenomenon. In addition to playing a key role in tumor-induced immunosuppression, TGF- stimulates angiogenesis. Interestingly, tumor cells eventually become refractory to TGF--mediated growth arrest, either due to loss of TGF- receptors or due to dysregulation in TGF- signaling pathways. Neutralization of TGF- or inhibition of its production is an effective method of cancer treatment in variety of animal models. Several agents targeting TGF- are in the early stages of development and include anti-TGF- antibodies, small molecule inhibitors of TGF-, Smad inhibitors and antisense gene therapy. Since tumors may express more than one isoform of TGF-, these new drugs should target all three TGF- isoforms produced by human tumors. The effects of therapies targeting TGF- are likely to be synergistic with cytotoxic chemotherapy and immunotherapy. Reversal of TGF--induced immunosuppression is a new and promising approach to cancer therapy, with potential applications in other diseases such as AIDS.     

Thermodynamics of Binding of Neutral Molecules to Sulfobutyl Ether β-Cyclodextrins (SBE-β-CDs): The Effect of Total Degree of Substitution

Purpose. To understand the role of degree of substitutionon binding of molecules to -Cyclodextrins (-CDs) with varyingdegrees of sulfobutyl ether (SBE) substitution. Methods. Using UV spectroscopy, complexation constants ofmolecules to SBE--CDs were estimated as a function of temperature,allowing for calculation of thermodynamic parameters, including the enthalpyand entropy of binding. Results. Binding constants of various molecules toSBE--CDs did not show a uniform trend to total degree of SBEsubstitution. However, a distinct pattern was observed with the enthalpy andentropy of complexation. The results showed the complexation of substratesto SBE--CDs to be more entropy-favored as the number of SBE groupsincreased. This favorable entropy of interaction was compensated by a lessfavorable enthalpy of interaction. Conclusions. Enthalpy and entropy of complexation providedadditional insight into the role that the alkylsulfonate groups may play inthe complexation of molecules with SBE--CDs.     

Nasal Absorption Enhancement of 17β-Estradiol by Dimethyl-β-Cyclodextrin in Rabbits and Rats

A new formulation for nasal administration containing 17-estradiol (E₂) with dimethyl--cyclodextrin (DMC) as a solubilizer and absorption enhancer is described. Nasal administration of this E₂-DMC formulation gave a significantly higher E₂ absorption than an E₂ suspension in both rabbits and rats. Relative to an intravenous injection of the E₂-DMC formulation, absolute bioavailabilities of 94.6 and 67.2% were calculated for the nasal E₂-DMC formulation in rabbits and rats, respectively. Differences in bioavailability may have resulted from differences in experimental animal conditions. The effects on human nasal ciliary activity of the E₂-DMC formulation were studied with an in vitro method. The formulation was found to exert only a minor effect on ciliary beat frequency. Thus, nasal delivery of E₂, using a cyclodextrin inclusion formulation, may have potential for clinical application, e.g., in the therapy of postmenopausal disorders.     

Genetic Immunization Using Nanoparticles Engineered from Microemulsion Precursors

Purpose. Genetic immunization using naked plasmid DNA (pDNA) has been shown to elicit broad humoral and cellular immune responses. However, more versatile and perhaps cell-targeted delivery systems are needed. To this end, a novel process to engineer cationic nanoparticles coated with pDNA for genetic immunization was explored. Methods. Cationic nanoparticles were engineered from warm oil-in-water microemulsion precursors composed of emulsifying wax as the oil phase and cetyltrimethylammonium bromide (CTAB) as the cationic surfactant. Plasmid DNA was coated on the surface of the cationic nanoparticles to produce pDNA-coated nanoparticles. An endosomolytic lipid and/or a dendritic cell-targeting ligand (mannan) were incorporated in or deposited on the nanoparticles to enhance the in vitro cell transfection efficiency and the in vivo immune responses after subcutaneous injection to Balb/C mice. The IgG titer to expressed -galactosidase and the cytokine release from isolated splenocytes after stimulation were determined on 28 days. Results. Cationic nanoparticles (around 100 nm) were engineered within minutes. The pDNA-coated nanoparticles were stable at 37°C over 30 min in selected biologic fluids. Transmission electron microscopy showed the nanoparticles were spherical. Plasmid DNA-coated nanoparticles, especially those with both an endosomolytic lipid and dendritic cell-targeting ligand, resulted in significant enhancement in both IgG titer (over 16-fold) and T-helper type-1 (Th1-type) cytokine release (up to 300% increase) over naked pDNA. Conclusion. A novel method to engineer pDNA-coated nanoparticles for enhanced in vitro cell transfection and enhanced in vivo immune responses was reported.     

Radioreceptor Assay of Metoprolol in Human Plasma: Comparison with an Enantiospecific High-Performance Liquid Chromatographic (HPLC) Procedure

Plasma concentrations of metoprolol after acute and repetitive administration of R/S-metoprolol to healthy volunteers were measured by a -adrenoceptor subtype-specific radioreceptor assay (RRA) and by an enantiospecific high-performance liquid chromatographic (HPLC) method. In the RRA, R/S-metoprolol showed a 20-fold ₁-subtype selectivity: the S-( – )-enantiomer was 35-fold more potent than the R-( + )-enantiomer. A comparison between S-( – )-metoprolol concentrations detected in the plasma samples by HPLC and those detected by RRA yielded a 1/1 relationship, indicating that active metabolites are not present to a significant extent. These results were independent of the widely scattering metabolic clearance of metoprolol (with the potential of differences in the rate and extent of formation of active metabolites) in the volunteers. In general, HPLC methods can be validated by comparison with RRA in order to clarify whether active metabolites are present and—on the basis of the K_i value from RRA—whether the detection limit of the physicochemical procedure is sufficient to cover the therapeutically relevant range.     

The metabolism of the amyloid precursor protein and its relevance to Alzheimer's disease

Summary The pathology of Alzheimer's disease is primarily characterized by the deposition of -amyloid/A peptide as the major component of senile or neuritic plaques. The A peptide is produced as a result of proteolytic cleavage of the transmembrane protein precursor, APP, during its normal cellular metabolism. The free amino terminus of the A peptide is generated by an endopeptidic cleavage between Met⁶⁷¹-Asp⁶⁷² by a protease termed -secretase. Increased cleavage at this site takes place in a rare, inherited double mutation (Lys⁶⁷⁰-Met⁶⁷¹ to Asn⁶⁷⁰-Leu⁶⁷¹), leading to increased A production and consequent development of Alzheimer's disease on an accelerated time scale in the affected individuals, underscoring the pathological importance of -secretase activity. Cellular studies provide direct evidence that inhibition of -secretase activity would appear to be effective in inhibiting A production as a rational approach to developing therapeutics for the disease.     

The Pharmacokinetics of β-Cyclodextrin and Hydroxypropyl-β-cyclodextrin in the Rat

Hydroxypropyl--cyclodextrin was analyzed by HPLC using postcolumn complexation with phenolphthalein and negative colorimetric detection, with a detection limit of 20 µg/ml. The pharmacokinetics of -cyclodextrin and of hydroxypropyl--cyclodextrin were studied after intravenous administration to permanently cannulated rats. The pharmacokinetic behavior of both cyclodextrins was similar to that of inulin, showing rapid distribution over extracellular fluids. Elimination occurred through glomerular filtration. When a dose of 200 mg/kg -cyclodextrin was administered the elimination rate was decreased, probably as a result of nephrotoxicity of -cyclodextrin. Within 24 hr after administration most of the cyclodextrin dose was recovered unchanged in urine. After oral administration, only insignificant amounts of intact -cyclodextrin were absorbed from the gastrointestinal tract.     

The effect of isoprenaline on plasma concentrations of immunoreactive β-endorphin and β-lipotropin in the conscious rat

Summary The effect of the -adrenoceptor agonist isoprenaline on the plasma concentrations of -endorphin (-E) and -lipotropin (-LPH) was investigated in conscious rats. Isoprenaline (i.m.) elevated plasma -endorphin-like immunoreactivity (-EI) as measured by radioimmunoassay of unextracted plasma, with peak values 24 min after drug administration. This effect was dose-dependent. The lowest effective dose of isoprenaline was 15 g kg^–1; 240 g kg^–1 exerted a maximum effect, raising plasma -EI about ten-fold above control values. Plasma vasopressin concentrations also increased in response to isoprenaline following a timecourse identical to that of plasma -EI. (±)-Propranolol (1 mg kg^–1) but not phentolamine (10 mg kg^–1) rendered isoprenaline (240 g kg^–1) injections almost ineffective. Because of the cross-reactivity of -LPH in the radioimmunoassay used, plasma was extracted by means of a cation exchange resin and subjected to gel chromatography on a Sephadex G-50 column, avoiding artefactual degradation of the peptides. In isoprenaline-treated rats about 50% of the -EI behaved similar to human -LPH, whereas 45% co-migrated with human -E; immunoreactivity corresponding to -LPH or -E comprised about 70% or 30%, respectively, in the plasma extract of vehicle-treated rats. Dexamethasone pretreatment reduced the isoprenaline-induced increase in plasma -EI by 87%, but left the simultaneous elevation of plasma vasopressin concentrations unchanged.These data demonstrate that isoprenaline stimulates -LPH and -E release in vivo. The possibility of an interrelationship between vasopressin and -E release is discussed.     

Analysis of the β-receptor mediated effect on fast-contracting skeletal muscle in vitro

Summary Subtetanic contractions of the isolated extensor digitorum longus (EDL) of the guinea-pig, a fast-contracting muscle, were evoked by transmural field stimulation. Isoprenaline, adrenaline, terbutaline, and noradrenaline each caused a dose-dependent increase in the force of contraction, their potencies decreasing in that order. Tyramine was without effect in this respect. Curare depressed the contractions of EDL by about 20% but did not appreciably change the response to the -adrenoceptor agonists. The effects of isoprenaline and noradrenaline were blocked by propranolol (unselective) and H 35/25 (1-(p-tolyl)-2-isopropylamino-1-propanol, ₂-selective) but not by practolol (₁-selective). Moreover, the increase in the force of subtetanic contractions of EDL produced by noradrenaline was unaffected by phentolamine. It is concluded that the adrenoceptor mediating the increase in the force of contraction of the isolated EDL is of the ₂-type and that the site of action is direct on the muscle. Its similarity to the receptor mediating the inverse effect on the slow-contracting soleus-muscle is pointed out.Subsidiary to AB Astra, Sweden     

Differences between full and partial α-adrenoceptor agonists in eliciting phasic and tonic types of responses in the longitudinal smooth muscle of the rat portal vein

Summary The aim of the present investigation was to study, taking into account both quantitative and qualitative differences, the influence of full and partial -adrenoceptor agonists on spontaneous myogenic activity in the rat portal vein.We found that the -adrenoceptor agonists cirazoline, adrenaline, noradrenaline, phenylephrine, St 587, Sgd 101/75, B-HT 920 and UK-14,304 could increase the amplitude of the phasic myogenic contractions in the rat portal vein with apparent differences in EC₅₀ and E_max values. In addition to an increase in phasic myogenic activity, the -adrenoceptor agonists cirazoline, adrenaline, noradrenaline, and phenylephrine were also able (in higher concentrations) to increase the basal tone of the rat portal vein preparation, again with apparent differences in EC₅₀ and E_max values. Changing the extracellular Ca²⁺ concentration from 0.9 mmol/l to 2.5 mmol/1 had no influence on the phasic character and the concentration range in which St 587 and UK-14,304 increased spontaneous myogenic activity, although changes in amplitude and frequency of the spontaneous myogenic contractions were less pronounced at a higher extracellular Ca²⁺ concentration (2.5 mmol/1). By the use of Schild analysis with the competitive a-adrenoceptor antagonists prazosin (pA₂ = 8.74) and 5-methyl-urapidil (pA₂ = 8.37), it was established that the contractile responses to St 587 were mediated by the same ₁-adrenoceptor subtype as the phasic and tonic type of contraction elicited by phenylephrine as described in a previous study. The concentration-response curve of UK-14,304 was significantly shifted to the right by low concentrations of prazosin (3 nmol/1–30 nmol/1), indicating stimulation of ₁-adrenoceptors by UK-14,304 in the rat portal vein. The -adrenoceptor antagonists phenoxybenzamine and chloroethylclonidine irreversibly blocked the contractile responses to St 587. Based on the method of receptor alkylation with phenoxybenzamine an affinity constant was calculated for St 587 (pK_a = 5.91). Phenoxybenzamine was approximately 1000-fold more potent in inactivating ₁-adrenoceptors than chloroethylclonidine.In conclusion there appeared to be a divergence in the excitation-contraction coupling of ₁-adrenoceptors in the rat portal vein, which is reflected by two types of contraction (phasic versus tonic). The extent to which both the phasic and tonic types of contraction are stimulated by agonists depends on the affinity and intrinsic efficacy for each of the receptor-coupled effector pathways. Thus, partial and full agonism can only meaningfully be discussed if confined to one particular effector pathway. Send offprint requests to H. R. Schwietert at the above address     

Intrinsic sympathomimetic activity ofβ-adrenoceptor blocking agents

Summary The pharmacological methods used to assess the intrinsic sympathomimetic activity (ISA) of -blockers are discussed. The clinical relevance of ISA to respiratory function, peripheral resistance and cardiac function is reviewed. It appears doubtful whether ISA is always of predominant clinical significance and an alternative explanation is offered for many clinical effects observed with certain -blockers, e.g. pindolol, oxprenolol, tolamolol, metoprolol, etc. Some effects of these -blockers resemble those of labetalol, a new drug with both - and -blocking activity. Some clinical effects of certain -blockers are more likely to be due to -blocking activity than to their ISA.     

Vasopressin stimulates release of β-lipotropin and β-endorphin in conscious rats as measured by radioimmunoassay of unextracted plasma

Summary Using a newly developed radioimmunoassay to determine the -endorphin-like immunoreactivity (-EI) in unextracted plasma, the effect of vasopressin injections on plasma -EI was investigated in conscious rats. Arginine vasopressin caused a dose-dependent increase of plasma -EI from 34.5±7.8 fmol ml^–1 (n=6) in vehicle-treated animals to 205.0±36.1 fmol ml^–1 (n=7) after injection of the highest vasopressin dose employed (486 ng/100 g b.w.). In view of the appreciable cross-reactivity of -lipotropin (-LPH) in the radioimmunoassay used, plasma was extracted and subjected to gel chromatography on a Sephadex G-50 column. On average, about 70% of the -EI co-eluted with human -LPH and about 30% with human -endorphin in plasma extracts obtained from both control and vasopressin-treated rats. No peripheral conversion of human -LPH occurred under the experimental conditions, since after i.v. bolus injection of human -LPH 97% of the -EI comigrated with human -LPH during gel filtration. A similar blood pressure increase to that induced by the vasopressin injections, when elicited by noradrenaline or angiotensin II i.v., was not followed by an elevation of plasma -EI.These data indicate that vasopressin stimulates -lipotropin and -endorphin release into the systemic circulation in vivo.     

Isomerisation of β-acetyldigoxin in a buffered alkaline solution

Summary Dilution and incubation of two batches of -acetyldigoxin tablets (Novodigal^®) in a weakly alkaline solution at 37° C yields amounts of -acetyldigoxin increasing with time. Thus, within 60 min the percentage of -acetyldigoxin was approximately 60 and 70% for lot A and lot B, respectively. The rate of isomerisation does not control the rate at which acetyldigoxin is absorbed in the intestinal tract.Supported by Deutsche Forschungsgemeinschaft.     

Comparison of Single-Dose and Steady-State Nadolol Plasma Concentrations

The pharmacokinetics of nadolol have been previously reported to be linear between single and steady-state dosing. Data from a study in our laboratory suggested greater than expected -blockade with nadolol at steady state. Because the early potency studies were single-dose studies, we hypothesized there was a nonlinearity in nadolol pharmacokinetics which produced higher than expected plasma concentrations at steady state. Six normal volunteers from the previous study (steady state) volunteered to participate in the single-dose study. Plasma concentrations were determined for 24 hr following a single dose of nadolol, 80 mg. A simple, inexpensive, and accurate method for determination of nadolol in plasma or serum by HPLC with fluorometric detection is described. The AUC_o–tau at steady state was greater than the AUC_0– following a single dose in five of the six subjects. The mean ratio of AUC_ss/AUC_sd was 2.54. This value would be unity in the presence of linear pharmacokinetics. We conclude that the principle of superposition is not applicable for nadolol.     

The β-adrenergic receptor-adenyl-cyclase system of rat reticulocytes

Summary Non-nucleated red blood cells from rats contain adenyl cyclase, the activity of which is predominantly localized in the reticulocytes. Basal enzyme activities in membrane preparations from reticulocyte-rich blood (pretreatment of rats with acetyl-phenylhydrazide: about 60% reticulocytes) are about 5 times higher than in preparations from reticulocyte-poor blood (untreated animals: 2–3% reticulocytes). The enzyme activities are stimulated 10-fold by sodium fluoride (10^–2 M) and 6 to 8-fold by isoprenaline (10^–4 M).Adenyl cyclase activities in membrane preparations from reticulocyte-rich and reticulocyte-poor blood can be ascribed to identical enzymes since identical apparent K _m (ATP; 3×10^–4 M), K _a (isoprenaline; 3×10^–6 M) and K _i (propranolol vs. isoprenaline; 3×10^–7 M) values were obtained in both preparations.Besides NaF, only phenylethanolamine derivatives with -adrenergic receptor stimulant properties were effective as stimulators of adenyl cyclase activity. The affinities (apparent K _a values) of the investigated compounds decreased in the order isoprenaline—hexoprenaline—fenoterol—salbutamol—adrenaline—terbutaline—noradrenaline—phenylephrine. For maximal intrinsic activity, the catechol structure was essential; the relative intrinsic activities of resorcinol derivatives did not exceed 0.6.The isoprenaline-stimulated adenyl cyclase activities in erythrocyte membrane preparations were competitively inhibited by -adrenergic blocking drugs, the affinities (apparent K _i values) decreasing in the order prindolol—penbutolol—propranolol—practolol. The dextrorotatory enantiomers of penbutolol and propranolol were 1/100 to 1/200 as active as the resp. levorotatory enantiomers.From experiments with -adrenergic agonists (e.g. phenylephrine) and antagonists (e.g. phentolamine), it is concluded that -adrenergic receptors do not interfere with the -adrenergically-mediated cAMP formation in these particular membranes.A variety of hormones and drugs known to stimulate adenyl cyclase activities in various tissues, e.g. ACTH, glucagon, STH, erythropoietin, prostaglandin E ₁ etc. did not affect adenyl cyclase activity in reticulocyte-rich erythrocyte membrane preparations.In contrast to adenyl cyclase activity, phosphodiesterase activities in erythrocyte membrane and cytoplasmic fractions were only twice as high in reticulocyterich as in reticulocyte-poor preparations.From the experiments described, it is obvious that the adenyl cyclase of the rat reticulocyte is subject to monovalent-hormonal, i.e. -sympathomimetic stimulation. Moreover, the premature red blood cell provides a useful model for quantitative studies of the interaction of drugs with the -adrenergic receptor.This study was supported by the Deutsche ForschungsgemeinschaftPreliminary accounts were presented at meetings of the Deutsche Pharmakologische Gesellschaft (Gauger et al., 1972; Gauger and Palm, 1973; Quiring et al., 1974a).     

Cotransport of Estradiol and Ethanol Through Human Skin in Vitro: Understanding the Permeant/Enhancer Flux Relationship

The thermodynamic and kinetic limits of ethanol-enhanced estradiol skin transport have been investigated by studying the relationship between estradiol and ethanol steady-state flux in the cotransport of permeant and enhancer in situations in which there exists an enhancer solvent gradient across the skin (asymmetric configuration). For aqueous ethanol solution saturated with estradiol, the flux of estradiol across the human epidermal membrane is empirically observed to be linear with the ethanol flux. A physical model approach has been used to determine the basis of this empirical linearity and to predict permeant/enhancer transport across the skin for the asymmetric configuration. Enhancement factors, determined with a balanced ethanol concentration across the skin (symmetric configurations), are used to predict fluxes in the asymmetric configurations. The model demonstrates that ethanol enhances the stratum corneum transport of estradiol and of itself by increasing the respective diffusion coefficients at lower concentrations (<50%) and by both increasing the diffusion coefficients and decreasing the membrane activity coefficients at moderate concentrations (50 to 75%). The model also demonstrates that the permeant flux, in general, is not linear with the cotransported enhancer flux.     

Dissociation between the attentional effects of infusions of a benzodiazepine receptor agonist and an inverse agonist into the basal forebrain

The effects of infusions of the benzodiazepine receptor (BZR) full agonist chlordiazepoxide (CDP) or the full inverse agonist -CCM into the basal forebrain on behavioral vigilance were tested. Vigilance was measured by using a previously characterized task that requires the animals to discriminate between visual signals of variable length and non-signal events. Measures of performance included hits, misses, correct rejections, false alarms, side bias, and errors of omission. Following the infusion of saline (0.5 µl/hemisphere), the relative number of hits varied with signal length. In response to shorter signals, the number of hits decreased over time, indicating a vigilance decrement. Infusions of CDP (20, 40 µg/hemisphere) initially decreased the relative number of hits in response to shorter signals and, later in the course of the test sessions, to longer signals as well. CDP did not affect the relative number of correct rejections. In contrast, infusions of the inverse agonist -CCM (1.5, 3.0 µg/hemisphere) did not affect the relative number of hits but decreased the relative number of correct rejections (i.e., increased the number of false alarms). These data suggest that the basal forebrain mediates the attentional effects of BZR ligands. As systemic or intrabasalis administration of BZR agonists and inverse agonists was previously demonstrated to decrease and augment, respectively, activated cortical acetylcholine (ACh) efflux, their effects on behavioral vigilance are hypothesized to be mediated via their effects on cortical ACh.     

Hepatic clearance of drugs. II. Experimental evidence for acceptance of the “well-stirred” model over the “parallel tube” model using lidocaine in the perfused rat liverin situ preparation

Theoretical analysis of two models of hepatic drug clearance revealed that one powerful discriminator between them is the effect of changes of hepatic blood flow on either the emergent drug concentration or the availability of a highly extracted compound when operating under linear conditions. Lidocaine (extraction ratio 0.997) was employed in the discriminatory studies. The behavior of this drug under linear conditions (input lidocaine concentrations < 5 mg/ liter) to changes in hepatic blood flow rate (10–16 ml/min per liver) was examined in the perfused rat liver in situpreparation. The steady-state output lidocaine concentration in the blood leaving the liver was predicted better by a well-stirred model than by a parallel tube model. As anticipated, the clearance of a poorly extracted compound, antipyrine (extraction ratio 0.08),was unaltered by changes in hepatic blood flow. These experimental findings, and the data from the literature, point to the acceptance of the well-stirred model, which describes the liver as a well-stirred compartment with the drug in the hepatic venous blood being in equilibrium with that in the liver.Supported in part by National Institutes of Health Grant GM 16496 and the Patent Fund, Graduate Division, University of California, San Francisco.Abstracted in part from a dissertation submitted by K. Sandy Pang to the Graduate Division, University of California, San Francisco, California, in partial fulfillment of the Doctor of Philosophy degree requirements.