Characterization of voltage-gated calcium currents in freshly isolated smooth muscle cells from rat tail main artery.

The aim of the present study was to characterize voltage-gated Ca2+ currents in smooth muscle cells freshly isolated from rat tail main artery in the presence of 5 mmol L(-1) external Ca2+. Calcium currents were identified on the basis of their voltage dependencies and sensitivity to nifedipine, Ni2+ and cinnarizine. In the majority of the cells studied, T- and L-type currents were observed, while the remaining cells showed predominantly L-type currents. In the latter group of cells, holding potential change from -50 to either -70 or -90 mV increased the corresponding inward current amplitude while its voltage activation threshold remained unchanged. The steady state inactivation of L-type Ca2+ channels showed half-maximal inactivation at -38 mV. A Ca2+-dependent inactivation was also evident. Nifedipine (3 micromol L(-1)) blocked L-type but not T-type Ca2+ currents. Ni2+ (50 micromol L(-1)) as well as cinnarizine (1 micromol L(-1)) suppressed the nifedipine-resistant, T-type component of the currents. At higher concentrations, both Ni2+ (0.3-1 mmol L(-1)) and cinnarizine (10 micromol L(-1)) blocked the net inward current. Replacement of Ca2+ with 10 mmol L(-)1 Ba2+ significantly increased the amplitude of L-type Ca2+ currents. These results demonstrate that smooth muscle cells freshly isolated from rat tail main artery may be divided into two populations, one expressing both L- and T-type and the other only L-type Ca2+ channels. Furthermore, this report shows that in arterial smooth muscle cells cinnarizine potently inhibited T-type currents at low concentrations (1 micromol L(-1)) but also blocked L-type Ca2+ currents at higher concentrations (10 micromol L(-1)).

Cytochrome P450-dependent N-dealkylation of L-deprenyl in C57BL mouse liver microsomes: effects of in vivo pretreatment with ethanol, phenobarbital, beta-naphthoflavone and L-deprenyl.

The monoamine oxidase inhibitor L-deprenyl [(-)-deprenyl, selegiline] is an effective therapeutic agent for improving early symptoms of idiopathic Parkinson's disease. It appears to exert this action independently of its inhibition of monoamine oxidase B (MAO-B) and some of its metabolites are thought to contribute. Cytochrome P450 (CYP) activities are known to give rise to L-deprenyl metabolites that may affect the dopaminergic system. In order to clarify the interactions of L-deprenyl with these enzymes, C57BL mice were treated with L-deprenyl, ethanol, phenobarbital or beta-naphthoflavone to induce different CYP isozymes. After preincubation of L-deprenyl with liver microsomes from control or treated mice, the metabolites were analysed by a GLC method. L-deprenyl (10 mg/kg i.p. for 3 days) caused a significant decrease in total CYP levels (0.315+/-0.019, L-deprenyl; 0.786+/-0.124, control, nmol/mg protein) and CYP2E1-associated p-nitrophenol hydroxylase activity (0.92+/-0.04 vs. 1.17+/-0.06 nmol/min/mg). Both phenobarbital and ethanol increased the N-depropynylation activity towards L-deprenyl that leads to the formation of methamphetamine (4. 11+/-0.64, phenobarbital; 4.77+/-1.15, ethanol; 1.77+/-0.34, control, nmol/min/mg). Ethanol alone increased the N-demethylation rate of L-deprenyl, that results in formation of nordeprenyl (3.99+/-0.68, ethanol; 1.41+/-0.31, control, nmol/min/mg). Moreover, the N-dealkylation pathways of deprenyl are inhibited by 4-methylpyrazole and disulfiram, two CYP2E1 inhibitors. None of the other treatments modified L-deprenyl metabolism. These findings indicate that mainly CYP2E1 and to a lesser extent CYP2B isozymes are involved in L-deprenyl metabolism. They also suggest that, by reducing CYP content, L-deprenyl treatment may impair the metabolic disposition of other drugs given in combination regimens.

Potentiation of mitochondrial Ca2+ sequestration by taurine.

The effects of taurine (2-aminoethanesulphonic acid) and its analogues, 2-aminoethylarsonic acid, 2-hydroxyethanesulphonic (isethionic) acid, 3-aminopropanesulphonic acid, 2-aminoethylphosphonic acid, and N,N-dimethyltaurine, were studied on the transport of Ca2+ by mitochondria isolated from rat liver. Taurine enhanced Ca2+ uptake in an apparently saturable process, with a Km value of about 2.63 mM. Taurine behaved as an uncompetitive activator of Ca2+ uptake, increasing both the apparent Km and Vmax values of the process. This effect was not modified in the presence of cyclosporin A (CsA). N,N-Dimethyltaurine also stimulated Ca2+ uptake at higher concentrations, but there was no evidence that the process was saturable over the concentration range used (1-10 mM). Aminoethylarsonate was a weak inhibitor of basal Ca2+ uptake, but inhibited that stimulated by taurine in an apparently competitive fashion (Ki = 0.05 mM). The other analogues had no significant effects on this process. Taurine either in the presence or the absence of CsA had no effect on Ca2+ release induced by 200 nM ruthenium red. Thus, the mechanism of taurine-enhanced Ca2+ accumulation appears to involve stimulation of Ca2+ uptake via the uniport system rather than inhibition of Ca2+ release via the ion (Na+/Ca2+ and/or H+/Ca2+) exchangers or by taurine modulating the permeability transition of the mitochondrial inner membrane. Overall, these findings indicate an interaction of taurine with an as yet unidentified mitochondrial site which might regulate the activity of the uniporter. The unique role of taurine in modulating mitochondrial Ca2+ homeostasis might be of particular importance under pathological conditions that are characterised by cell Ca2+ overload, such as ischaemia and oxidative stress.

2,5-Di-t-butyl-1,4-benzohydroquinone induces endothelium-dependent relaxation of rat thoracic aorta.

The aim of this work was to clarify the mechanism by which 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ) induces relaxation of rat thoracic aorta. In particular, the role of endothelium-derived nitric oxide (NO) was investigated. BHQ concentration dependently (0.1-10 microM) relaxed rat aorta rings precontracted with phenylephrine. This effect was dependent on the intactness of the endothelium, suppressed by preincubation with 100 microM N(omega)-nitro-L-arginine methyl ester and antagonised by 3-30 microM methylene blue. The 10 microM BHQ-induced relaxation, however, was followed by the gradual and slow return to phenylephrine-induced tone. Superoxide dismutase (250 U/ml) increased the BHQ-induced relaxation, while preincubation with 3 mM diethyldithiocarbamate inhibited it in a time-dependent fashion. BHQ gave rise to superoxide anion formation which was markedly inhibited by the addition of superoxide dismutase (250 U/ml), either in the presence or in the absence of aorta rings. The non-specific blocker of Ca2+ channels, Ni2+, concentration dependently attenuated the BHQ relaxing effect. BHQ did not modify the relaxation induced by the NO donor 3-morpholino-sydnonimine in endothelium-deprived rings. In conclusion, BHQ induces endothelium-dependent relaxation and gives rise, by auto-oxidation, to the formation of superoxide anion. The former effect results from the enhanced synthesis of NO rather than from its enhanced biological activity; NO synthase is presumed to be stimulated by BHQ-induced activation of Ca2+ influx through Ni2+-sensitive Ca2+ channels.

Myorelaxant activity of 2-t-butyl-4-methoxyphenol (BHA) in guinea pig gastric fundus.

This study investigates the mechanism whereby the antioxidant 2-t-butyl-4-methoxyphenol (BHA) relaxes guinea pig gastric fundus smooth muscle. In circular smooth muscle strips, 10 microM cyclopiazonic acid, a specific inhibitor of sarcoplasmic reticulum Ca2+-ATPase, induced a prolonged rise in tension which depended on the presence of extracellular Ca2+. BHA (pIC50 = 5.83), sodium nitroprusside (6.85), isoproterenol (7.69) and nifedipine (8.02), but not 2,6-di-t-butyl-4-methoxyphenol (DTBHA) (up to 30 microM), relaxed muscle strips contracted with cyclopiazonic acid. Methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyri dine-5-carboxylate (Bay K 8644) (1 microM) antagonised the nifedipine- but not the BHA-induced relaxation. Nifedipine and isoproterenol (10 microM) caused a decrease in spontaneous tone, but did not counteract the subsequent rise in tension elicited by 10 microM cyclopiazonic acid. Conversely, 100 microM BHA and 100 microM sodium nitroprusside not only significantly reduced spontaneous tone but also markedly impaired the response of the muscles to cyclopiazonic acid. DTBHA failed to show either effect. When added to preparations completely relaxed by 100 microM BHA, 10 mM tetraethylammonium still elicited nifedipine-sensitive tonic and phasic contractions in the presence or absence of 10 microM cyclopiazonic acid. BHA and DTBHA inhibited, in a concentration-dependent manner, the Ca2+-promoted contraction of strips depolarised by 10 mM tetraethylammonium. The BHA antagonism showed a non-competitive profile while that of DTBHA was competitive. In muscle strips at rest, 10 microM BHA caused a significant increase in tissue cAMP concentration, leaving cGMP unmodified. To conclude, the myorelaxant action of BHA on gastric fundus smooth muscle appears to be mediated partly by an increase in cAMP levels and partly by inhibition of Ca2+ influx from the extracellular space.

Effects of 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ) on rat aorta smooth muscle.

To characterise the pharmacological activity of 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ) on vascular smooth muscle, the different effects of BHQ on rat aorta were investigated under several experimental conditions. In aortic rings at rest or depolarised with 80 mM K+ in the presence of 1 microM nifedipine, BHQ evoked a slow tonic contraction which was antagonised by 1 mM Ni2+. Depolarised rings contracted in response to addition of 1 mM Ca2+, with an EC50 value of 32.4+/-1.0 mM for K+. At 20 mM K+, Ca2+-induced contraction was enhanced by BHQ. This effect was antagonised by 1 mM Ni2+, but not by 1 microM nifedipine. By contrast, at 40, 80 and 128 mM K+, BHQ antagonised Ca2+-induced contraction. This effect was partially reversed by 1 microM methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyri dine-5-carboxylate (Bay K 8644) or by increasing extracellular Ca2+ concentration. In the presence of nifedipine and Ni2+, depolarised rings (80 mM K+) contracted in response to addition of 1 microM phenylephrine; this response was fast and then slowly decreased. When the preparations were preincubated with BHQ, the phenylephrine-induced contraction was transient and antagonised in a concentration-dependent manner by BHQ. These results indicate that the myotonic effect of BHQ on rat aortic rings depends on activation of Ca2+ influx via a Ni2+-sensitive pathway, whereas its myolytic activity is due either to antagonism of Ca2+ entry via L-type Ca2+ channels or depletion of intracellular Ca2+ stores.

Measurement of synthetic phenolic antioxidants in human tissues by high-performance liquid chromatography with coulometric electrochemical detection.

The antioxidants, 2-tert.-butyl-4-methoxyphenol (BHA) and its oxidative peroxidation product 2,2'-dihydroxy-3,3'-di-tert.-butyl-5,5'-dimethoxybiphenyl (di-BHA), 3,5-di-tert.-butyl-4-hydroxytoluene (BHT) and propyl gallate, were measured in plasma and tissue homogenates by HPLC and electrochemical detection, with a sensitivity down to 0.2 (BHA), 0.1 (di-BHA), 0.4 (BHT) and 1 (propyl gallate) ng ml(-1) of plasma or tissue homogenate. The data demonstrate that in man, at the current level of exposure to dietary antioxidants, significant amounts of BHA, BHT and propyl gallate are accumulated in the omentum. Furthermore, they provide the first evidence that the peroxidase-catalysed oxidation of BHA is operative in man.

Rat tissue concentrations of chlorimipramine, chlorpromazine and their N-demethylated metabolites after a single oral dose of the parent compounds.

A single oral dose of 90 mg kg-1 chlorimipramine or chlorpromazine, corresponding to 54.5 or 55.9 mumol, respectively, was given to male Sprague-Dawley rats and concentrations of parent drugs and their N-desmethyl metabolites measured by gas chromatography in plasma and major organs (brain, liver, lung, kidney, heart, spleen and peritoneal fat). In the case of chlorimipramine, N-desmethyl metabolite levels were consistently higher than those of the parent drug for the entire observation period of 24 h in all tissues except fat, while lower N-desmethyl metabolite/parent compound ratios were observed for chlorpromazine. N-Desmethyl metabolite kinetics of chlorimipramine appeared to be elimination-rate limited, while those of chlorpromazine were formation-rate limited. In all analysed organs, the maximu detectable drug+metabolite concentrations accounted for only 2.3 and 4.6% of the initial dose of chlorimipramine and chlorpromazine. Chlorpromazine treatment gave rise to an area under the total amount-time curve (AUC0-24) for parent drug+metabolites, 3.9-fold that for chlorimipraine. Closer scrutiny discloses a conversion ratio of parent compound to N-desmethyl metabolite of 1.1 for chlorpromazine and of 2.2 for chlorimipramine, indicating the greater efficiency of chlorimipramine metabolism in all compartments. The expected high conversion index found in the liver (2.3) reaches its maximum of 5.4 in the lung. Fractional data analysis of chlorimipramine and chlorpromazine distribution patterns revealed greater organ transfer for the N-desmethyl metabolites than for the more stably-located parent compounds. The N-desmethyl metabolites of chlorimipramine apparently moved from liver to lung, kidney and spleen, whereas N-desmethylchlopromazine moved preferentially to the brain and lung tissue. This single dose study of chlorimipramine and chlorpromazine kinetics, highlights the two distinct dispositional processes at work in the rat in all likelihood, attributable to different absorption patterns, to a slower metabolism and, thus, to the longer persistence of chlorpromazine.

Inhibition of interleukin-1 beta-induced pyresis in the rabbit by peptide 204-212 of lipocortin 5.

The intracerebroventricular administration of interleukin-1 beta (12.5 ng/kg) in rabbits caused a prompt rise of prostaglandin E2 concentration (+ 632.6 +/- 243.9%) in the cerebrospinal fluid followed by hyperthermia (+ 1.61 +/- 0.14 delta degrees C). The intracerebroventricular administration of an anti-inflammatory nonapeptide (amino acids 204-212, SHLRKVFDK) derived from lipocortin 5, thereafter referred to as lipocortin 5-(204-212)-peptide, inhibited in a significant manner both the increase in cerebrospinal fluid [prostaglandin E2] and the febrile response induced by the cytokine. This inhibitory effect is probably due to interference by the peptide with phospholipase A2 activity. A control peptide (FKRVHDLKS) formed by the same amino acids in a randomly shuffled sequence had no effect. These results show that, in addition to the anti-inflammatory effect previously reported, the peptide 204-212 of lipocortin 5 possesses, like glucocorticoids, anti-pyretic activity. The research on lipocortin-derived peptides may lead to the development of novel anti-inflammatory and anti-pyretic compounds.

Increase of extracellular brain calcium involved in interleukin-1 beta-induced pyresis in the rabbit: antagonism by dexamethasone.

1. This study investigates the role of extracellular brain calcium in the hyperthermia induced by interleukin-1 beta (IL-1 beta). 2. Intracerebroventricular (i.c.v.) injection of IL-1 beta (12.5 ng kg-1) in rabbits caused a prompt and sustained rise in cerebrospinal fluid (CSF) Ca2+ concentration ([Ca2+]) followed by enhanced prostaglandin E2 (PGE2) release and hyperthermia. 3. A linear and significant correlation was observed between the increase in [Ca2+] induced by IL-1 beta and the rise in body temperature. 4. Ventriculo-cisternal perfusion with artificial CSF containing the calcium chelator EGTA (1.3 mM) blocked the IL-1-induced PGE2 release and countered the febrile response. 5. I.c.v. administration of dexamethasone (Dex) (2.4 and 24 micrograms kg-1) 100 min prior to IL-1 beta, dose-dependently antagonized the cytokine-induced Ca2+ increase, the PGE2 release and the febrile response. 6. These results suggest that changes in extracellular brain calcium are involved in the regulation of body temperature. In this light, the antipyretic action of Dex may be related to its effect on Ca2+ uptake.

Interactions of monoamine oxidase inhibitors, N-acetylenic analogues of tryptamine, with rat liver microsomal cytochrome P450.

Interactions between some novel and potent monoamine oxidase inhibitors (MAOIs), acetylenic analogues of tryptamine, and rat liver microsomal cytochrome P450 (P450) as evidenced by visible spectra analysis were analysed. Compounds with a secondary aliphatic amine moiety throughout induced type II difference spectra and exhibited the highest affinity for P450, whereas tertiary amines induced type I spectral changes and showed diminished affinity. P450 dependent aniline hydroxylase activity was inhibited by all compounds in an irreversible time-dependent manner. Only tertiary aliphatic amines constituted the substrate for P450-dependent N-demethylase activity, with comparable kinetic parameters. The N-demethylated metabolites were identified by thin-layer chromatography and mass-spectrometric analyses. These findings describe the role of P450-dependent microsomal mono-oxygenase systems in the metabolism of some MAOI acetylenic tryptamine derivatives and the possible hepatic contribution to adverse interactions between MAOIs, endobiotics and sympathomimetic compounds.

Interactions between substituted tryptamine analogues, MAO inhibitors and cytochrome P-450.

The effects of some MAO inhibitors, N-acetylenic analogues of tryptamine, on rat liver microsomal cytochrome P-450 (cyt P-450) have been investigated. All the compounds tested interacted with cyt P-450 with Ks values ranging between 14 and 358 microM (clorgyline Ks = 10.5 microM). Compounds with a tertiary amine and those possessing a secondary amine group in the acetylenic side chain exhibited type I and type II difference spectra, respectively. Aniline hydroxylase activity was inhibited irreversibly and in a time-dependent fashion by all compounds tested with IC50 ranging between 7 x 10(-5) and 7 x 10(-3) M (clorgyline 10(-4) M).

Pharmacokinetics of chlorimipramine, chlorpromazine and their N-dealkylated metabolites in plasma of healthy volunteers after a single oral dose of the parent compounds.

A single oral dose of 0.7 mg kg-1 chlorimipramine (n = 18) and chlorpromazine (n = 16) was given to each subject 45 days apart and plasma concentrations of parent drugs and their monodesmethyl and didesmethyl metabolites were measured by GC. Ingestion of chlorimipramine resulted in an area under the plasma concentration-time curve (AUC0-24) for parent drug plus metabolites 5-fold higher than that observed in the same subjects following chlorpromazine intake (600 +/- 87 and 124 +/- 14 ng mL-1, respectively). Plasma chlorimipramine levels reached a mean peak value of 43.8 ng mL-1, which occurred 2 h after administration. Desmethyl metabolite kinetics of chlorimipramine appeared to be elimination rate-limited and those of chlorpromazine appeared to be formation-rate-limited. The response to single doses of these two drugs in healthy subjects highlights the two distinct dispositional processes involved, thus offering pharmacokinetic explanation of the hitherto empirical discrepancy in dosage levels in chronic treatment.

Calcium antagonist and antiperoxidant properties of some hindered phenols.

1. The calcium antagonist and antioxidant activities of certain synthetic and natural phenols, related to BHA (2-t-butyl-4-methoxyphenol), were evaluated in rat ileal longitudinal muscle and in lipid peroxidation models respectively. 2. Compounds with a phenol or a phenol derivative moiety, with the exception of 2,2'-dihydroxy-3,-3'-di-t-butyl-5,5'-dimethoxydiphenyl (di-BHA), inhibited in a concentration-dependent manner the BaCl2-induced contraction of muscle incubated in a Ca(2+)-free medium. Calculated pIC50 (M) values ranged between 3.32 (probucol) and 4.96 [3,5-di-t-butyl-4-hydroxyanisole (di-t-BHA)], with intermediate activity shown by khellin < gossypol < quercetin < 3-t-butylanisole < BHA < nordihydroguaiaretic acid (NDGA) < 2,6-di-t-butyl-4-methylphenol (BHT) and papaverine. 3. The Ca2+ channel activator Bay K 8644 overcame the inhibition sustained by nifedipine, BHA and BHT, while only partially reversing that of papaverine. 4. BHA, BHT, nifedipine and papaverine also inhibited in a concentration-dependent fashion CaCl2 contractions of muscle depolarized by a K(+)-rich medium. This inhibition appeared to be inversely affected by the Ca(2+)-concentration used. 5. The inhibitory effects of nifedipine, papaverine, BHA and BHT were no longer present when muscle contraction was elicited in skinned fibres by 5 microM Ca2+ or 500 microM Ba2+, suggesting a plasmalemmal involvement of target sites in spasmolysis. 6. Comparative antioxidant capability was assessed in two peroxyl radical scavenging assay systems. These were based either on the oxidation of linoleic acid initiated by a heat labile azo compound or on lipid peroxidation of rat liver microsomes promoted by Fe2+ ions. Across both model systems,di-t-BHA, NDGA, BHT, di-BHA, BHA and quercetin ranked as the most potent inhibitors of lipid oxidation, with calculated pICso (M) values ranging between 7.4 and 5.7.7. Of the 32 compounds studied only 15 phenolic derivatives exhibited both antispasmogenic andantioxidant activity. Within this subgroup a linear and significant correlation was found betweenantispasmogenic activity and antioxidation. These bifunctional compounds were characterized by the presence of at least one hydroxyl group on the aromatic ring and a highly lipophilic area in the molecule.8. Di-t-BHA is proposed as a lead reference compound for future synthesis of new antioxidants combining two potentially useful properties in the prevention of tissue damage after ischaemia reperfusion injury.

Toxic injury to rat gut musculature following intraperitoneal administration of 2-t-butyl-4-methoxyphenol.

The 100-fold increase in toxicity of intraperitoneal (i.p.) rather than orally administered 2-t-butyl-4-methoxyphenol (BHA) is adduced to the depressive effect which this compound exerts on the contractility of the gut musculature. A structure/activity relation study shows the t-butyl group on the benzene ring as being the major determinant of i.p. BHA toxicity. Contractile activity, elicited by field electrical stimulation, acetylcholine or Ba2+, of the ileum longitudinal muscle preparation from BHA-treated rats was greatly reduced 30 min after i.p. injection, and almost absent during the subsequent 48 h. Electron-microscope examination of ileum longitudinal muscle also showed partial destruction of cell membranes 4 h after BHA administration with subsequent mitochondrial swelling and destruction of cristae, myofibrillar fragmentation and cell necrosis. Comparable suppression of contractile activity and morphological damage were observed in BHA or t-butylbenzene incubated ileum segments where longitudinal smooth muscle contractility was irreversibly depressed in a time- and dose-dependent manner. These convergent findings point to the toxic effect of i.p. BHA on gut musculature with consequent impairment of intestinal transit.

HPLC determination of inorganic cation levels in CSF and plasma of conscious rabbits.

An HPLC method is described using conductimetric detection for the quantitative determination of sodium, potassium, magnesium, and calcium in cerebrospinal fluid (CSF) and plasma of conscious rabbits. This method enabled the four cations to be estimated with rapidity, sensitivity, accuracy, and precision. The mean millimolar concentrations +/- SD found in CSF and (plasma) of 15 untreated animals were as follows: sodium, 146.96 +/- 17.84 (135.06 +/- 20.11); potassium, 3.32 +/- 0.56 (4.57 +/- 1.03); magnesium, 0.90 +/- 0.20 (0.72 +/- 0.13); and calcium, 1.47 +/- 0.19 (3.32 +/- 0.59).

Dehalogenation and N-dealkylation of chlorpromazine as revealed by plasma concentrations of metabolites in a population of chronically medicated schizophrenics.

Dehalogenaton and N-demethylation of chlorpromazine (CPZ) were studied in twelve psychotic inpatients orally treated for four weeks with a daily CPZ dose of 6.4 +/- 1.1 (S.E.) mg/kg body weight (1.5-14.1, range). Weekly drug and metabolite plasma concentrations were measured by a gas liquid chromatography-nitrogen/phosphorus detector method (GLC/NPD). Plasma concentrations of the parent compound CPZ, of the dehalogenated metabolite promazine (PZ) and of the N-dealkylated metabolites N-monodemethylated chlorpromazine (CPZ-nor1) and N-didemethylated chlorpromazine (CPZ-nor2) had already reached a steady state by the end of the first week of treatment. During the entire treatment period the major plasma component was found to be PZ. Patients (N = 6) on a low dose regimen (3.7 +/- 0.2 mg/kg body weight) showed significantly lower mean plasma concentrations of CPZ and nor metabolites than patients (N = 6) on a higher dose regimen (8.6 +/- 0.7 mg/kg body weight). PZ mean plasma concentrations, however, were not significantly different in the two groups of patients, indicating that the yield of the CPZ dechlorination pathway, as opposed to that of the N-demethylation pathway, was already maximal at the CPZ concentrations attained under the low dose regimen. Male patients (N = 5) exhibited significantly higher mean PZ plasma concentrations over the 4 week period of the study than female patients (N = 7).