In vitro and in vivo evaluation of tegaserod maleate pH-dependent tablets

The purpose of this study was to prepare tegaserod maleate (TM) pH-dependent tablets and evaluate their advantages as a sustained release delivery system. TM, insoluble in water and unstable in gastric milieu, was formulated into pH-dependent tablets coated with combinations of two methacrylic acid copolymers – Eudragit^® L100 and Eudragit^® S100. The influence of core tablet compositions, polymer combination ratios and coating levels on the in vitro release rate of TM from coated tablets was investigated. The optimum formulation was evaluated for in vitro release rate and in vivo bioavailability study on beagle dogs. In addition, physico-chemical properties of the drug, including solubility at different pH and temperatures, and dissociation constant were determined. The results showed that no drug was released in 0.1 mol/L hydrochloric acid within 2 h, and about 90% of the drug was released in the pH 6.8 phosphate buffer within 12 h in a sustained manner. The pharmacokinetic investigation showed that TM pH-dependent tablets exhibited a sustained plasma concentration, a lag time of approximately 2.3 h and a relative bioavailability of 159% compared to plain tablets. A close correlation existed between the in vitro release rate of the pH-dependent system and its in vivo absorption percentage. The results of the present study have demonstrated that the pH-dependent tablet system is a promising vehicle for preventing rapid hydrolysis in gastric milieu and improving oral bioavailability of TM for the treatment of irritable bowel syndrome.     

Polyoxyethylene-polyoxypropylene block copolymer gels as sustained release vehicles for subcutaneous drug administration

Polyoxyethylene-polyoxypropylene surface-active block copolymers (Pluronic^®) were evaluated as a vehicle for subcutaneous administration of drugs using a phenolsulfophthalein (PR) as a tracer. The type of Pluronic^® copolymer (F108 or F127), and their concentrations, and the effect of solutes (NaOH, NaCl or PR) on gelation properties were studied. Sodium hydroxide and sodium chloride decreased the gel-sol transition temperature, whereas the opposite effect was observed with PR. The ‘in vitro’ release rates obtained for PR were inversely proportional to the concentration of Pluronic used and a zero-order release rate was observed in all preparations assayed. Pluronic^® F127/PR preparations were administered subcutaneously (SC) to Wistar rats and PR plasma levels were compared with those reached after SC or intravenous (i.v.) administration of a PR aqueous solution. The gel formulation produced a sustained plateau level within 15 min that lasted 8–9 h. In vivo data analysis was performed with the JANA and PCNONLIN computer programs. The best fittings for experimental data from Pluronic gels were obtained using a zero-order input and first-order output two-compartment model. The results obtained suggest that PF127 aqueous gels may be of practical use as a vehicle for SC administration of drugs.     

Colonic release and reduced intestinal tissue damage of coated tablets containing naproxen inclusion complex

A colonic-release delivery system containing naproxen inclusion complex with 2-hydroxypropyl-β-cyclodextrin (2-HPβCD) was originally proposed. The core tablets consisting of the naproxen inclusion complex and disintegrants (Ac-Di-Sol^®, Primojel^®, Avicel^® or Polyplasdone^®) were formed by direct compression, and then coated with the polymers, either pH-dependent Eudragit^® S100 and/or pH-independent Eudragit^® RS100 with plasticizers like dibutyl sebacate (DBS) and aluminum tristearate (AT). The in vitro release characteristics were evaluated in simulated gastric fluid for 2 h and then subsequently in simulated intestinal fluid for 12 h. The potential histological changes were also evaluated after direct dosing of suspensions of naproxen alone and powdered mixtures of inclusion complex-loaded tablet into rat intestinal segments. No distinct colonic release was observed when disintegrants were excluded in the single-layered coated tablets regardless of coated structures, giving a zero-order fashion over 12 h. The coated tablet with double-layered structures of Eudragit^® S100 and Eudragit^® RS100 was not also applicable. In contrast, colonic release was achieved when the core tablet containing inclusion complex and disintegrant was coated with only Eudragit^® S100 in a single-layered structure. The colonic-release tablet was resistant in gastric fluid for 2 h and for 2–4 h in intestinal fluid, followed by rapid release of the drug after a total of 4–6 h of lag time depending on the type of disintegrants. The lag time was advanced in case of DBS while delayed in case of AT. On histological examination, the inclusion complex-loaded suspension caused less intestinal tissue damage than naproxen alone. Based on these findings, the colonic-release tablet with enteric coatings which contains inclusion complex and disintegrants could be useful to deliver drugs like naproxen to the lower small intestine and upper colon with increased dissolution and reduced intestinal tissue damage.     

Effects of verapamil, diltiazem, nisoldipine and felodipine on sarcoplasmic reticulum

Verapamil, diltiazem, nisoldipine and felodipine, calcium antagonist drugs with different chemical structures, were studied for their effects on activities of sarcoplasmic reticulum (SR) isolated from dog cardiac and rabbit skeletal muscles. Nisoldipine and felodipine exerted biphasic actions on both cardiac and skeletal SR Ca²⁺-ATPase with maximum activation of 40–60% occurring at 20–40 μM for nisoldipine and 30–40% occurring at 15–30 μM for felodipine. At higher drug concentrations, Ca²⁺-ATPase was inhibited. In the presence of oxalate the maximum activation of the Ca²⁺ uptake rates at 5–20 μM nisoldipine were 30–50% for cardiac SR and 80–100 μM of the drug were 300–500% for skeletal SR. Felodipine inhibited the rate of Ca²⁺ uptake by dog cardiac SR, but activated Ca²⁺ uptake by rabbit skeletal SR with a maximum of 30–50% at 12–25 μM. At higher concentrations of the two drugs the rate of Ca²⁺ uptake was inhibited. In the absence of oxalate, i.e., limited tranport, nisoldipine shortened the duration of time that Ca²⁺ was bound to the cardiac and skeletal SR, while the rate of release of Ca²⁺ from skeletal SR was stimulated. Felodipine at low concentrations similarly caused a premature release of Ca²⁺ from skeletal SR at a rapid rate; at high concentrations both drugs did not alter Ca²⁺ binding but delayed Ca²⁺ release. Unlike nisoldipine and felodipine, verapamil and diltiazem inhibited the rates of Ca²⁺ transport both in cardiac and skeletal SR. The two drugs inhibited Ca²⁺-ATPase in cardiac SR but activated the enzyme in skeletal SR. Thus, these drugs caused complex and different effects on cardiac and skeletal SR, possibly resulting from perturbations of the lipid environment of the SR Ca²⁺-ATPase.     

Microencapsulated chitosan nanoparticles for lung protein delivery

It has already been demonstrated that spray drying is a very valuable technique for producing dry powders adequate for pulmonary delivery of drugs. We have developed chitosan/tripolyphosphate nanoparticles that promote peptide absorption across mucosal surfaces. The aim of this work was to microencapsulate protein-loaded chitosan nanoparticles using typical aerosol excipients, such as mannitol and lactose, producing microspheres as carriers of protein-loaded nanoparticles to the lung. The results showed that the obtained microspheres are mostly spherical and possess appropriate aerodynamic properties for pulmonary delivery (aerodynamic diameters between 2 and 3 μm, apparent density lower than 0.45 g/cm³). Moreover, microspheres morphology was strongly affected by the content of chitosan nanoparticles. These nanoparticles show a good protein loading capacity (65–80%), providing the release of 75–80% insulin within 15 min, and can be easily recovered from microspheres after contact with an aqueous medium with no significant changes in their size and zeta potential values. Therefore, this work demonstrated that protein-loaded nanoparticles could be successfully incorporated into microspheres with adequate characteristics to reach the deep lung, which after contact with its aqueous environment are expected to be able to release the nanoparticles, and thus, the therapeutic macromolecule.     

High-throughput determination of OROS drug release rate profile using micro parallel liquid chromatography

A high throughput method with the use of micro parallel liquid chromatography (μPLC) technique was first applied for the determination of drug release profiles in OROS^® tablets. Currently, high-performance liquid chromatography (HPLC) is a preferred analytical tool to analyze samples released from OROS^® tablets. However, it usually takes more than 20 h to analyze a large number of release rate samples and generate a release-rate profile. In this study, with the use of a 24-column Brio cartridge, the μPLC enabled simultaneous analysis of 24 release-rate samples. The total analysis time including the generation of the release-rate profile was greatly reduced to 3 h. Two different OROS^® formulations were used to compare the drug release testing using both μPLC and conventional HPLC. The drug release profiles generated using μPLC were comparable with those obtained by HPLC. In addition, the reproducibility and sensitivity of μPLC analysis were examined. Overall, significant reductions in analysis time and solvent consumption were the major advantages of using μPLC in profiling the drug release rate for a controlled-release dosage.     

High performance liquid chromatographic and thin layer densitometric methods for the determination of risperidone in the presence of its degradation products in bulk powder and in tablets

Two reproducible stability indicating methods were developed for the determination of risperidone (RISP) in presence of its degradation products in pure form and in tablets. The first method was based on reversed phase high performance liquid chromatography (HPLC), on Lichrosorb RP C 18 column (250 mm i.d., 4 mm, 10 μm), using methanol:0.05 M potassium dihydrogen phosphate pH 7 (65:35 (v/v)) as the mobile phase at a flow rate of 1 ml min⁻¹ at ambient temperature. Quantification was achieved with UV detection at 280 nm over a concentration range of 25–500 μg ml⁻¹ with mean percentage recovery of 99.87 ± 1.049. The method retained its accuracy in the presence of up to 90% of RISP degradation products. The second method was based on TLC separation of RISP from its degradation products followed by densitometric measurement of the intact drug spot at 280 nm. The separation was carried out on aluminum sheet of silica gel 60F₂₅₄ using acetonitrile:methanol:propanol:triethanolamine (8.5:1.2:0.6:0.2 (v/v/v/v)), as the mobile phase, over a concentration range of 2–10 μg per spot and mean percentage recovery of 100.1 ± 1.18. The two methods were simple, precise, sensitive and could be successfully applied for the determination of pure, laboratory prepared mixtures and tablets. The results obtained were compared with the manufacturer's method.     

Effect of pharmaceutical excipients on aqueous stability of rabeprazole sodium

The chemical stability of a proton-pump inhibitor, rabeprazole sodium, was evaluated in simulated intestinal fluid (pH 6.8) containing various ‘Generally Recognized As Safe (GRAS)’-listed excipients, including Brij^® 58, Poloxamer 188, Cremophor RH40, Gelucire 44/14 and PEG 6000. After incubation at 37 and 60 °C, the amounts of rabeprazole and its degradation product, thioether-rabeprazole, were quantitated by HPLC analysis. The main degradation product was separated and characterized by LC/MS. The degradation of rabeprazole followed first-order kinetics. In the absence of any excipients, the rate constants (k) obtained at 37 and 60 °C were 0.75 and 2.78 h⁻¹, respectively. In contrast, the addition of excipients improved its stability. Among several excipients tested in this study, Brij^® 58 displayed the greatest stabilizing effect. For instance, at 37 and 60 °C, Brij^® 58 reduced the k values to 0.22 and 0.53 h⁻¹, respectively. The stabilizing mechanisms of these hydrophilic polymeric excipients with optimal HLB values could be partially explained in terms of their solubilizing efficiency and micellar formation for thioether-rabeprazole. In conclusion, rabeprazole formulations that contain suitable excipients would improve its stability in the intestinal tract, thereby maximizing bioavailability.     

LC/ESI-MS method for the determination of trimetazidine in human plasma: application to a bioequivalence study on Chinese volunteers

A rapid liquid chromatography electrospray ionization mass spectrometry (LC/ESI-MS) method with good sensitivity and specificity has been developed and validated for the identification and quantification of trimetazidine in human plasma. Trimetazidine and lidocaine (internal standard) were isolated from plasma samples by protein precipitation with methanol. The chromatographic separation was accomplished on a Xterra MS C₁₈ Column (150 mm × 4.6 mm, 5 μm particle size) with the mobile phase consisting of methanol and water (40:60, v/v) (pH 2.0, adjusted with trifluoroacetic acid), and the flow rate was set at 0.6 mL/min. Detection was performed on a single quadruple mass spectrometer by selected ion monitoring (SIM) mode (m/z 267.0 for trimetazidine and m/z 235.0 for lidocaine) with the retention time at about 3.47 and 5.05 min, respectively. The calibration curve for trimetazidine was satisfactory with regression coefficient 0.9995 over the range of 2.5–100 ng/mL in the plasma. The LOQ (S/N = 10) was accordingly 2.5 ng/mL. The intra-day and inter-day precision expressed as relative standard deviation was 2.83–6.10% and 4.83–5.82%. The method was successfully applied to investigate the bioequivalence between two kinds of tablets (test versus reference product) in 19 healthy male Chinese volunteers. After a single 20 mg dose for the test and reference product, the resulting mean of major pharmacokinetic parameters such as AUC_0–24, AUC_0−∞, C_max, T_max and t_1/2 of trimetazidine were (673.1 ± 117.6 ng h mL⁻¹ versus 652.3 ± 121.9 ng h mL⁻¹), (717.1 ± 120.9 ng h mL⁻¹ versus 692 ± 128.6 ng h mL⁻¹), (74.85 ± 12.13 ng mL⁻¹ versus 71.93 ± 14.32 ng mL⁻¹), (2.312 ± 0.663 h versus 2.211 ± 0.608 h) and (4.785 ± 0.919 h versus 4.740 ± 0.823 h), respectively, indicating that these two kinds of tablets were bioequivalent in the Chinese population.     

Automated system for release studies of salicylic acid based on a SIA method

The aim of this work was to describe a fully automated system for the in vitro release testing of semisolid dosage forms based on SIA technique. The system was tested for monitoring release profiles of different ointments containing 3% of salicylic acid (Belosalic, Diprosalic, Triamcinolone S). The native fluorescence of salicylic acid was used for fluorimetric detection. Phosphate buffer pH 7.4 was the receptor medium; samples were taken at 10 min intervals during 6 h of the release test; and each test was followed by calibration with five standard solutions. The linear calibration range was 0.05–10 μg ml⁻¹ (r = 0.9996, six standards); the maximal SIA sample throughput for this system was 120 h⁻¹, sample volume being 50 μl and flow rate 50 μl s⁻¹. The detection limit for salicylic acid was 0.01 μg ml⁻¹.     

Increasing the oral bioavailability of the poorly water soluble drug itraconazole with ordered mesoporous silica

This study aims to evaluate the in vivo performance of ordered mesoporous silica (OMS) as a carrier for poorly water soluble drugs. Itraconazole was selected as model compound. Physicochemical characterization was carried out by SEM, TEM, nitrogen adsorption, DSC, TGA and in vitro dissolution. After loading itraconazole into OMS, its oral bioavailability was compared with the crystalline drug and the marketed product Sporanox^® in rabbits and dogs. Plasma concentrations of itraconazole and OH–itraconazole were determined by HPLC-UV. After administration of crystalline itraconazole in dogs (20 mg), no systemic itraconazole could be detected. Using OMS as a carrier, the AUC_0–8 was boosted to 681 ± 566 nM h. In rabbits, the AUC_0–24 increased significantly from 521 ± 159 nM h after oral administration of crystalline itraconazole (8 mg) to 1069 ± 278 nM h when this dose was loaded into OMS. T_max decreased from 9.8 ± 1.8 to 4.2 ± 1.8 h. No significant differences (AUC, C_max, and T_max) could be determined when comparing OMS with Sporanox^® in both species. The oral bioavailability of itraconazole formulated with OMS as a carrier compares well with the marketed product Sporanox^®, in rabbits as well as in dogs. OMS can therefore be considered as a promising carrier to achieve enhanced oral bioavailability for drugs with extremely low water solubility.     

A new hydrogel for the extended and complete prednisolone release in the GI tract

The issue of incomplete release of poorly soluble drugs from sustained-release oral formulations is addressed using prednisolone (PDS) as the model drug and a novel highly swelling hydrogel as the rate-controlling material. The hydrogel was formed by heating N-carboxymethylchitosan (CMC) to 80 °C for 24 h. Swelling, alkalimetry, FTIR, DSC, and solid-state NMR studies showed that the treatment produced physical crosslinking, i.e., polymer chain entanglement. A controlled-release system was prepared by coating an inert compacted support of ethylcellulose (50 mg; diameter, 6 mm) with a CMC layer containing dispersed PDS powder (10–50 μm). The system was heated to crosslink the CMC coating, then drug release to simulated GI fluids was studied in vitro. The drug release pattern and term were modulated via the layer mass (LM) (10 or 14 mg cm⁻²) and/or the drug–polymer wt ratio (D/P) (1:5 or 2:5). The rate parameter, K, and the time exponent, n, of the Peppas equation were: K = 26.6 ± 0.3 h⁻ⁿ, n = 0.78 ± 0.02 (LM, 10 mg cm⁻²; D/P, 1:5); K = 24.7 ± 0.7 h⁻ⁿ, n = 0.56 ± 0.02 (LM, 14 mg cm⁻²; D/P, 1:5); K = 20.7 ± 0.3 h⁻ⁿ, n = 0.76 ± 0.01 (LM, 10 mg cm⁻²; D/P, 2:5). Hydrogel swelling was faster than drug release. This was controlled, in a first stage, by drug dissolution–diffusion in the swollen gel, and subsequently, by diffusion. The drug release rate was unaffected by the GI pH variations, and slightly affected by the environmental hydrodynamics. The system promises an extended and complete release of poorly soluble drugs in the GI tract.     

An HPLC method for the determination of atorvastatin and its impurities in bulk drug and tablets

A simple high-performance liquid chromatographic (HPLC) method was developed for the analysis of atorvastatin (AT) and its impurities in bulk drug and tablets. This method has shown good resolution for AT, desfluoro-atorvastatin (DFAT), diastereomer-atorvastatin (DSAT), unknown impurities and formulation excipients of tablets. A gradient reverse-phase HPLC assay was used with UV detection. Some solvent systems prepared using methanol or acetonitrile and water or buffer systems with different pH values were tested. Capacity factors of related substances were calculated at all tested systems. Best resolution has been determined using a Luna C₁₈ column with acetonitrile–ammonium acetate buffer pH 4-tetrahydrofuran (THF) as mobile phase. Samples were eluted gradiently with the mobile phase at flowrate 1.0 ml min⁻¹ and detected at 248 nm. The proposed method was applied to the determination of impurities and were found to contain 0.057–0.081, 0.072–0.097, 0.608–0.664% of the DFAT, DSAT and total impurity, respectively.     

Determination of catecholamines by flow-injection analysis and high-performance liquid chromatography with chemiluminescence detection

A chemiluminescence (CL) detection of catecholamines [norepinephrine (NE), epinephrine (E), dopamine (DA) and l-dopa (LD)] is described for the flow-injection (FI) and high-performance liquid chromatographic (HPLC) determination of these compounds. The detection method is based on the inhibition effect of catecholamines (CAs) on the CL reaction of luminol with iodine in the alkaline medium. The proposed FI method allows the determination of CAs in pharmaceutical preparations for the purpose of drug quality control. The calibration curves show good linearity in the concentration range of: 1.1–20.0 μg l⁻¹ (NE), 0.5–5.0 μg l⁻¹ (E), 0.6–9.0 μg l⁻¹ (DA) and 0.6–10.0 μg l⁻¹ (LD). The limits of detection (defined as a signal-to-noise ratio of 3) are: 0.34 μg l⁻¹ (NE), 0.15 μg l⁻¹ (E) and 0.18 μg l⁻¹ (DA, LD). The HPLC procedure was successfully applied for the determination of catecholamines (NE, E, DA) in human urine after solid-phase extraction (SPE). In a simple run time CAs can be determined in 20 min. The chromatographic linear ranges are: 5.0–72.0 μg l⁻¹ (NE), 5.0–48.0 μg l⁻¹ (E) and 5.0–96.0 μg l⁻¹ (DA). The limits of detection for three urinary CAs are: 0.71 μg l⁻¹ (NE), 0.26 μg l⁻¹ (E) and 0.73 μg l⁻¹ (DA).     

Graft copolymers of ethyl methacrylate on waxy maize starch derivatives as novel excipients for matrix tablets: drug release and fronts movement kinetics

A previous paper deals with the physicochemical and technological characterization of novel graft copolymers of ethyl methacrylate (EMA) on waxy maize starch (MS) and hydroxypropylstarch (MHS). The results obtained suggested the potential application of these copolymers as excipients for compressed non-disintegrating matrix tablets. Therefore, the purpose of the present study was to investigate the mechanism governing drug release from matrix systems prepared with the new copolymers and anhydrous theophylline or diltiazem HCl as model drugs with different solubility. The influence of the carbohydrate nature, drying procedure and initial pore network on drug release kinetics was also evaluated. Drug release experiments were performed from free tablets. Radial drug release and fronts movement kinetics were also analysed, and several mathematical models were employed to ascertain the drug release mechanisms. The drug release markedly depends on the drug solubility and the carbohydrate nature but is practically not affected by the drying process and the initial matrix porosity. A faster drug release is observed for matrices containing diltiazem HCl compared with those containing anhydrous theophylline, in accordance with the higher drug solubility and the higher friability of diltiazem matrices. In fact, although diffusion is the prevailing drug release mechanism for all matrices, the erosion mechanism seems to have some contribution in several formulations containing diltiazem. A reduction in the surface exposed to the dissolution medium (radial release studies) leads to a decrease in the drug release rate, but the release mechanism is not essentially modified. The nearly constant erosion front movement confirms the behaviour of these systems as inert matrices where the drugs are released mainly by diffusion through the porous structure.     

Liquid chromatographic determination of biotin in multivitamin-multimineral tablets

A reproducible reverse phase high pressure liquid chromatography (RP-HPLC) method for the determination of biotin in multivitamin-multimineral tablets has been developed and validated. This method involves reverse phase separation of the component monitored by absorbance at 200 nm wavelength. The method has excellent precision and accuracy with S.D. 0.83 and 2.9%, respectively. The established linearity range was 0.5–2 μg ml⁻¹ (r²>0.9999). The recovery of biotin from spiked placebo was >97% over the linear range. The extraction procedure is simple and the HPLC conditions separate biotin from its degradation products and excipients. The method has been successfully used in determining biotin content in 4 brands of commercially available multivitamin- multimineral tablets.     

Spectrophotometric determination of clobetasol propionate, halobetasol propionate, quinagolide hydrochloride, through charge transfer complexation

Two spectrophotometric procedures are described for the determination of clobetasol propionate(I), halobetasol propionate(II) (corticosteroids) and quinagolide hydrochloride(III) (prolactin inhibitor). For corticosteroid drugs, the procedures are based on the formation of phenyl hydrazones of the corticosteroids which are subsequently subjected to charge transfer complexation reaction with either 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) as π-acceptor or with iodine as σ-acceptor. Prolactin inhibitor was reacted directly with the previous reagents. The molar ratios of the reactants were established and the experimental conditions were studied giving maximum absorption at 588 and 290 nm with DDQ and iodine methods, respectively for the three drugs. The concentration ranges were 20–150, 50–300, and 20–80 μg ml⁻¹ in DDQ method for (I), (II), and (III), respectively and 13–20, 15–40, and 8–32 μg ml⁻¹ in iodine method for (I), (II) and (III), respectively.     

Drug release responses of zinc ion crosslinked poly(methyl vinyl ether-co-maleic acid) matrix towards microwave

The drug release characteristics of beads made of poly(methyl vinyl ether-co-maleic acid) using Zn²⁺ as the crosslinking agent were investigated with respect to the influence of microwave irradiation. The beads were prepared by an extrusion method with sodium diclofenac as a model water-soluble drug. They were subjected to microwave irradiation at 80 W for 5 and 20 min, and at 300 W for 1 min 20 s and 5 min 20 s. The profiles of drug dissolution, drug content, drug–polymer interaction and polymer–polymer interaction were determined by dissolution testing, drug content assay, differential scanning calorimetry and Fourier transform infrared spectroscopy. Treatment of beads by microwave at varying intensities of irradiation can aid to retard the drug release with a greater reduction extent through treating the beads for a longer duration of irradiation. The treatment of beads by microwave induced the formation of multiple polymeric domains of great strength and extent of polymer–polymer and drug–polymer interaction. The release of drug from beads was retarded via the interplay of OH, NH, CH, (CH₂)_n and CO functional groups of these domains, and was mainly governed by the state of polymer relaxation of the matrix unlike that of the untreated beads of which the release of drug was effected via drug diffusion and polymer relaxation. In comparison to Ca²⁺ crosslinked matrix which exhibited inconsistent drug release retardation behavior under the influence of microwave, the extent and rate of drug released from the Zn²⁺ crosslinked beads were greatly reduced by microwave and the release of drug from these beads was consistently retarded in response to both high and low intensity microwaves.     

Stimulus-evoked glutamate release is diminished by acute exposure to uranium in vitro

Uranium is used in civilian applications, in the manufacture of nuclear fuel, and by the military for munitions and armament, but little information is available on its neurotoxicity. Neurological dysfunctions have been observed after chronic exposure in both animals and humans, but the actions of acute exposure on amino acid neurotransmission have not been investigated. The following study was performed to examine the effects of uranyl ion (UO₂^+ 2) on hippocampal glutamatergic and GABAergic function as possible bases for the neurotoxicity and to assess the direct effects on the exocytotic process. Nominal UO₂^+ 2 concentrations were applied to superfused hippocampal synaptosomes to permit estimation of the metal's potency on endogenous transmitter release in the presence and absence of Ca^+ 2. K⁺-evoked glutamate release was diminished in the range of 10 nM–316 μM UO₂^+ 2, resulting in an IC₅₀ of 1.92 μM. In contrast, the potency of UO₂^+ 2 to decrease stimulated GABA release was reduced, producing an IC₅₀ ≈ 2.6 mM. In the absence of Ca^+ 2 in the superfusion medium there was no systematic change in the magnitude of glutamate or GABA release, suggesting that UO₂^+ 2 does not possess Ca^+ 2-mimetic properties. The inhibitory potency of UO₂^+ 2 on glutamate release is similar to the potencies of other multivalent metal ions, suggesting by inference an action exerted on voltage-sensitive Ca^+ 2 channels. The bases for the reduced potency to inhibit GABA release is not known, but differential sensitivity to other heavy metals has been reported for glutamate and GABA neurotransmission. These findings indicate a profile of neurotoxicity not unlike that of other metal ions, and indicate the importance of extending subsequent studies to chronic exposure models.     

Microcalorimetric investigation of the toxic action of ammonium ferric(III) sulfate on the metabolic activity of pure microbes

A series of calorimetric experiments were performed to investigate toxic action of ammonium ferric sulfate (AFS) on Bacillus subtilis, Pseudomonas putida and Candida humicola. The power–time curves of micro-organism metabolism were obtained, and the action of them by addition of AFS was studied. C. humicola, B. subtilis and P. putida were inhibited completely when the concentrations were up to 320.0, 160.0 and 160.0 μg mL⁻¹, respectively. The relationships between growth rate constant (k) and doses of AFS were approximately linear for three microbes, P. putida for 10.0–160.0 μg mL⁻¹ (R = −0.9746), B. subtilis for 0–160.0 μg mL⁻¹ (R = −0.9868) and C. humicola for 10.0–320.0 μg mL⁻¹ (R = −0.9955). The total heat dissipated per milliliter (Q_T) for three microbes remained balance approximately during the lower doses, P. putida and B. subtilis less than the dose of 20.0 μg mL⁻¹, 0.56 ± 0.01 and 0.26 ± 0.01 J mL⁻¹, respectively, C. humicola less than the dose of 40.0 μg mL⁻¹, 0.58 ± 0.03 J mL⁻¹. The biomass and OD₆₀₀ of three micro-organisms growth in the absence of AFS also were obtained. The power–time curve of C. humicola growth coincided with its turbidity curve. It elucidates that microcalorimetric method agreed with the routine microbiology method.