Search PubMed⌕ Search

Biomedical subjects

C E Lunte

Publications and source records attributed to C E Lunte.

65 records · Page 4Linked to original sources
PubMed1990

Microdialysis sampling for determination of plasma protein binding of drugs.

The use of microdialysis sampling to study the binding of drugs to plasma proteins was evaluated. Microdialysis sampling is accomplished by placing a short length of dialysis fiber in the sample and perfusing the fiber with a vehicle. Small molecules in the sample, such as drugs, diffuse into the fiber and are transported to collection vials for analysis. Larger molecules, such as proteins and protein-bound drugs are excluded by the dialysis membrane. Microdialysis was found to give values for in vitro protein binding in plasma equivalent to those determined by ultrafiltration. Microdialysis offers advantages in terms of maintaining equilibria and experimental versatility. Microdialysis sampling also provides potential use for in vivo determinations of protein binding.

Blood Proteins↗
PubMed1989

Identification of 9-hydroxylamine-1,2,3,4-tetrahydroacridine as a hepatic microsomal metabolite of tacrine by high-performance liquid chromatography and electrochemistry.

Amperometric detection using a dual-electrode thin-layer cell in the series configuration can aid in the identification of unknown components in complicated samples by voltammetric characterization. This is shown by studying the metabolism of tacrine by rat hepatic microsomes using high-performance liquid chromatography with electrochemical detection. The major metabolite detected in microsomal incubations did not co-elute with any standard acridine available and was produced in too small a quantity for mass spectral characterization. Tentative identification of this metabolite as 9-hydroxylamine-1,2,3,4-tetrahydroacridine was made by electrochemical characterization. The electrochemistry of the metabolite was compared to that of the hydroxylamine produced and studied by cyclic voltammetry.

Aminoacridines↗
PubMed1989

Microdialysis-perfusion sampling for the investigation of phenol metabolism.

In vivo methods provide several advantages for the study of metabolism relative to the commonly used in vitro techniques. The integrity of the organism and actual physiological conditions are maintained to reflect more accurately the processes occurring on exposure to a xenobiotic compound. Experimental precision is improved because each animal serves as its own control and can be used to generate a complete pharmacokinetic experiment. This may result in the added benefit that fewer experimental animals will be needed for a metabolic investigation using in vivo techniques. The technique of microdialysis perfusion was characterized for the in vivo study of the hepatic metabolism of phenol and conjugation by glutathione. In this study, in vivo experiments were conducted by implanting a microdialysis probe into the intact, in-place liver of a killed rat. These results were compared to in vitro experiments using liver homogenate and liver-microsomal protein. Substantial differences were observed between the in situ experiments and those performed in vitro.

Animals↗
PubMed1988

Electrochemical determination of N-oxidized procainamide metabolites and functional assessment of effects on murine cells in vitro.

Because of the implication of N-oxidized metabolites of procainamide in the induction of drug-related lupus, we have studied the electrochemical behavior of these metabolites and developed an electrochemical synthesis of nitrosoprocainamide. This synthesis was developed using procainamide hydroxylamine as the starting material which was oxidized to the nitroso species at an applied potential of 700 mV vs Ag/AgCl using a carbon packed bed bulk electrolysis flow cell. Conversion efficiencies of greater than 95% were achieved with this method. Subsequent studies with a chemically diverse series of biocompounds were used to investigate possible reactions between the procainamide hydroxylamine and nitroso species and these selected molecules. Only antioxidants such as cysteine, glutathione and ascorbic acid were found to react with the nitroso compound as determined by electrochemical methods, and this reaction was characterized as primarily a simple redox reaction at physiological pH. Animal studies conducted with murine spleen cells incubated with mitogens and various procainamide compounds demonstrated that the N-oxidized metabolites are the active immunopharmacologic agents.

Acecainide↗
PubMed1984

Determination of quinonoid dihydrobiopterin by liquid chromatography and electrochemical detection.

Tetrahydrobiopterin (BH4) is a required cofactor for the hydroxylation of the amino acids phenylalanine, tyrosine and tryptophan. Quinonoid dihydrobiopterin (q-BH2) is the natural product of the oxidation of BH4 in these enzymatic reactions. This report describes a method based on liquid chromatography and electrochemical detection for the determination of q-BH2 in synthetic and biological samples. This methodology is used to study the electrochemistry of q-BH2 formed by oxidation of BH4 and in the hydroxylation of phenylalanine by phenylalanine hydroxylase.

Animals↗
PubMed1984

Determination of phenylalanine hydroxylase activity by liquid chromatography/electrochemistry.

An assay method is presented for the determination of phenylalanine hydroxylase activity in biological samples. The procedure is rapid and requires little sample. Multiple components of the enzyme system are determined and therefore serve as internal checks of the assay system. Liquid chromatography/electrochemistry is employed to follow the oxidation of the tetrahydropterin cofactor to the dihydropterin and to follow the formation of tyrosine. The KM and Vmax values of both phenylalanine and 6-methyl-5,6,7,8-tetrahydropterin were determined for mouse liver phenylalanine hydroxylase. Determination of the stoichiometry of the reaction showed that 1 mol of dihydropterin and 1 mol of tyrosine are formed per mole of tetrahydropterin that is oxidized. The reaction rate was linear for several minutes and over a wide range of enzyme (protein) concentrations.

Animals↗
PubMed1983

The determination of pterins in biological samples by liquid chromatography/electrochemistry.

A method is presented for determining the concentrations of several oxidized pterins in a variety of biological samples. This methodology employs reverse-phase "ion-pair" liquid chromatography with electrochemical detection. Detection limits below a picomole have been achieved with responses linear over four orders of magnitude. This methodology was employed to study the excretion pattern of pterins in human urine. The concentration of several pterins in mouse brain and liver samples were also determined. The direct detection of tetrahydrobiopterin was demonstrated.

Animals↗
PubMedDate not supplied

[An improved method for microdialysis study of noradrenaline level in rat myocardium].

A level of myocardial norepinephrine (NE) is considered as one of the meaningful parameters in the estimation of myocardium functioning. Long lasting changes of myocardial NE appear to be not only a sequence of pathologic processes in myocardium, but could also be a factor responsible for some diseases. An improved microdialysis sampling technique with HPLC-ED analysis was developed to measure in vivo NE content in a rat myocardial interstitium. Linear polyacrylonitryl 5 mm probes were flushed with methanol while being immersed in water. In vitro NE recovery with the flow rate of perfusate was found at the level 67.9 + 0.4%. Probes were implanted into the rat myocardium under the general anaesthesia. Myocardial dialysate was collected during 20 min into plastic vials, containing 10 microliters of 0.1 M perchloric acid. Low noise, high sensitivity dual electrochemical detection was used for the determination of NE amount in the samples. Overall sensitivity threshold was found about 0.3 pg of NE in 20 microliters. Steady state concentration of NE in myocardial dialysate was found 54 + 7 pg/ml. 20 min before cardiac arrest the concentration of NE in myocardial dialysate was found to be increased 4-5 times. 40 min after cardiac arrest further increase in NE content was registered up to 1-4 ng per ml of perfusate. It is suggested that the method will be useful for routine study of myocardial NE.

Animals↗