Hemodynamic and electrophysiologic effects of ontazolast in dogs.

OBJECTIVE: To determine whether QT interval is prolonged or sudden death is caused by ventricular fibrillation resulting from torsades de pointes and to identify hemodynamic effects of ontazolast. ANIMALS: 28 Beagles. PROCEDURE: Physiologic variables were measured for 2 hours in conscious dogs given ontazolast (0, 1, or 3 mg/kg of body weight, IV) and for 1 hour in anesthetized dogs given cumulative doses of ontazolast (0, 1, 3, 6, or 8 mg/kg, IV). RESULTS: Ontazolast prolonged QT interval and QT interval corrected for heart rate (QTc) at doses of 6 mg/kg in anesthetized dogs. At 8 mg/kg, both variables remained prolonged but tended to decrease. In conscious dogs, ontazolast increased QT interval and QTc 15 minutes after administration, but both variables returned to reference ranges by 60 minutes. In conscious dogs, ontazolast increased maximum rate of increase of left ventricular pressure and maximal velocity of fiber shortening, indicators of inotropy, and increased tau, indicating a decreased rate of relaxation. One conscious dog receiving 3 mg/kg developed nonfatal torsades de pointes, but another conscious dog developed ventricular fibrillation. Two anesthetized dogs receiving 6 mg/kg developed early afterdepolarizations, and all dogs developed secondary components in theirT waves. CONCLUSION AND CLINICAL RELEVANCE: Ontazolast possesses potent class-III antiarrhythmic properties and induces prolongation of QTc in a dose-dependent fashion. Because there was a clear dose-dependent prolongation of QT interval in all instances, ontazolast may serve as a positive-control compound for studying other compounds that are believed to prolong the QT interval.

Characterization of a microprocessor-controlled tubular multiple metered dose inhaler aerosol generator for inhalation exposures of pharmaceuticals.

A microprocessor-controlled tubular multiple metered dose inhaler (MDI) aerosol generator was constructed for the delivery of pharmaceutical aerosols to inhalation chambers. The MDIs were mounted in four cassettes containing one to four MDIs on a stepped end plate. The MDIs in each cassette were pneumatically activated at intervals that were controlled by the microprocessor. The cassettes permitted easy replacement of each set of MDIs with a fresh set of MDIs whenever necessary. Aerosol concentration was controlled by varying the number of active MDIs in each cassette and the frequency of activations per minute of each row. Aerosol from the MDIs flowed along the long axis of the tube, which provided a path length sufficient to diminish impaction losses. Using a light-scattering device to monitor the aerosol concentration, the pulsatile output from the MDIs in the cassettes was demonstrated to be adequately damped out provided that the dilution/mixing/aging chamber exceeded 3 ft in length. The tube diameter selected was the minimum compatible with mounting the required number of MDIs so that the linear velocity of the aerosol was adequate to efficiently transport the aerosol out of the dilution chamber. Aerosol concentration and particle size data were recorded for a nose-only rodent exposure chamber. Reproducible aerosol concentrations ranging from 0.03 to 0.6 mg/L were generated. Particle sizes ranged from 2- to 3-microm mass median aerodynamic diameter. Thus, the aerosol generated was within the size range suitable for inhalation exposures.

Selective protein arylation and the age dependency of acetaminophen hepatotoxicity in mice.

Male CD-1 mice 1, 1.5, 2, and 3 months old were given 600 mg of acetaminophen (APAP)/kg, po, and liver damage was assessed 12 hr later. The most severe hepatotoxicity was in 3-month-old mice, while the other age groups exhibited little damage. The onset of susceptibility to APAP hepatotoxicity did not correlate with the level of activity of the mixed-function oxidase system as assessed in vitro, since drug metabolizing capability was similar between 2- and 3-month-old mice. Through 4 hr after administration of APAP to 2- and 3-month-old mice in vivo, glutathione (GSH) depletion and both plasma and liver APAP concentrations were similar between ages. Additionally, 24 hr after dosing, 3-month-old mice excreted marginally more APAP-glucuronide conjugate and parent compound in urine than 2-month-old animals, while both age groups excreted similar amounts of the APAP-sulfate and GSH-derived conjugates. Even though the extent of binding of radioactive APAP to macromolecules at 4 hr was similar between 2- and 3-month-old animals, the pattern of immunochemically targetted cytosolic and microsomal proteins was different. Thus, in APAP exposure the extent of binding to specific proteins rather than the overall amount of covalent binding may be the critical determinant of the hepatotoxic response. In the present study, the age-related differences in susceptibility to APAP-induced hepatotoxicity were related to the differences in selective protein arylation.

Gas-chromatographic determination of disopyramide with nitrogen detection.

A sensitive and specific method is presented for the quantification of disopyramide, a new antiarrhythmic agent, in blood plasma or serum. Aminopentamide, a chemically similar compound, is added to the biological fluid, and the two compounds are extracted with chloroform. The concentrated extract is treated with trifluoroacetic anhydride, resulting in the dehydration of the primary amide group of the drug and internal standard to the corresponding nitriles. The dehydrated derivatives are gas chromatographed and detected using a nitrogen-phosphorus detector. The method is applicable to the determination of the drug in plasma in the 1-10 microgram/mL concentration range.

Di-2-ethylhexyl phthalate (DEHP) and mono-2-ethylhexyl phthalate (MEHP) accumulation in whole blood and red cell concentrates.

Plasma DEHP concentrations were measured weekly in whole blood and red cell concentrates (RCC) during 21 days of storage in standard CPD within PL-130 blood bags. In addition, DEHP and MEHP accumulation patterns were investigated in blood stored for 42 days in modified CPD with adenine within PL-146 and BB-69 storage containers. Total per-unit plasma DEHP of RCC units was 49 to 71 per cent of the total in plasma of whole blood units (PL-130). From 28 to 42 days, mean DEHP levels were 12 to 19 per cent higher in whole blood stored in PL-146 than in BB-69. Although MEHP was not found in any blood bag plastic, MEHP accumulated in plasma during whole blood storage. MEHP concentrations were 2.8 to 3.8 times higher in plasma stored in BB-69 than in PL-146. It is postulated that MEHP arises from hydrolysis of DEHP by plasma lipase, even in frozen plasma sample, and that the rate of this reaction is influenced by blood bag plastic surface characteristics.

The prebiotic synthesis of deoxthymidine oligonucleotides. II. Comparison of condensing agents.

A reaction which oligomerizes nucleotides under possible prebiotic conditions has been characterized. Nucleoside monophosphate in the presence of cyanamide at acid pH condenses to form dithymideine pyrophosphate and phosphodiester bonded compounds. Imidazole compounds and activated precursors such as nucleoside triphosphate are not necessary for this ologomerization reaction which produces primarily cyclic ologonucleotides.

Evaluation of T3 coliphage injuries and efficacy of selected materials in preventing them.

A procedure was developed to analyze the inactivation of coliphage T3 during freeze-drying and subsequent rehydration. The amount of gross disruption of the phage as compared with the amount of phage remaining intact was evaluated by cesium chloride density gradient centrifugation. The amount of phage material able to adsorb to host cells and the residual infectivity after the drying were also evaluated. These analyses made it possible to determine the amount of phage material (i) degraded to protein and nucleic acid, (ii) intact or largely intact, (iii) capable of adsorption on host cells, and (iv) infective. The capacities of casein hydrolysate, ascorbic acid, thiourea, bovine albumin, polyethyleneglycol, raffinose, inositol, and lipoproteins to protect T3 bacteriophage from the stress of freeze-drying were investigated.