PubMed Health⌕ Search

Biomedical subjects

G Ricciarello

Publications and source records attributed to G Ricciarello.

12 recordsLinked to original sources
PubMed1998

Age-related alteration of the adenosine/dopamine balance in the rat striatum.

An antagonistic interaction between adenosine A2A- and dopamine D2-receptors has been described. Radioligand binding experiments showed a predominant reduction in the number of D2 vs. A2A-receptors in the striatum of aged compared to young rats. The A2A-receptor-mediated antagonistic modulation of D2-receptor binding remained unchanged in aged animals. In striatal homogenates a significant increase in adenosine and no change in dopamine content was found in aged vs. young rats. These results reveal the existence of an age-dependent imbalance of adenosine vs. dopamine in favor of adenosine, which involves both presynaptic and postsynaptic mechanisms.

Adenosine↗
PubMed1995

Adenosine A2A receptor stimulation enhances striatal extracellular glutamate levels in rats.

The influence of CGS 21680, an adenosine A2A receptor agonist, on striatal glutamate extracellular levels was tested in a microdialysis study in rats. CGS 21680 (10 mu M), infused intrastriatally through the microdialysis probe, greatly enhanced glutamate extracellular levels. These results show that striatal adenosine A2A receptors are involved in the regulation of striatal glutamate extracellular levels. They also suggest that adenosine A2A receptor antagonists may possess neuroprotective effects in models of striatal excitotoxicity.

Adenosine↗
PubMed1994

Simultaneous high-performance liquid chromatographic determination of adenosine and dopamine in rat striatal tissue with combined ultraviolet absorbance and electrochemical detection.

A method is described for the simultaneous determination of biogenic amines, adenosine and their metabolites in rat striatal tissue using high-performance liquid chromatography with ultraviolet spectrophotometric and electrochemical detection. Peaks in the chromatograms of striatal tissue extracts were identified by retention times and by on-line analysis of peak spectra for adenosine and its metabolites, and by comparing current ratios of the dual-electrode coulometric detector for monoamines and metabolites. The assay gives a linear response over the concentration range of 0.15-0.60 micrograms/ml for biogenic amines, 0.5-2.0 micrograms/ml for serotonin, 5-20 micrograms/ml for hypoxanthine, adenosine and N-methyladenosine, and 10-40 micrograms/ml for inosine. The limit of detection for striatal homogenates was 3.5 ng/g for monoamines, 9 ng/g for serotonine, 140 ng/g for hypoxanthine, 290 ng/g for inosine and 80 ng/g for adenosine. The recovery ranged from 88.5% for vanillylmandelic acid to 110.3% for dopamine. The method was used to measure biogenic amines, adenosine and related metabolites in rat striatal tissues.

Adenosine↗
PubMed1994

Different effects of harmine on plasma concentrations of L-dopa and on cerebral dopamine metabolism in rabbits and rats.

The effects of short-term intravenous administration of harmine, a monoamine oxidase inhibitor, on the plasma concentrations of L-Dopa and on dopamine levels in the brain striata of rats and rabbits after L-Dopa administration were studied. Harmine affects the L-Dopa plasma concentrations in rabbits but not in rats: in fact in the former species the area under the concentration-time curve observed after administration of L-Dopa alone increased significantly when animals were pretreated with harmine. Dopamine striatal levels increased in concert with plasma L-Dopa concentrations after administration of L-Dopa in rats and rabbits. However pretreatment with harmine resulted in a significant increase of dopamine levels in the brain striata of rabbits only. These results suggest that harmine or one of its metabolites affect the brain dopamine system not merely as a type A monoamine oxidase inhibitor but with a modulatory effect, without a precise indication of site or mode of action of harmine.

Animals↗
PubMed1993

Determination of nicotine and four metabolites in the serum of smokers by high-performance liquid chromatography with ultraviolet detection.

A simple and reliable reversed-phase high-performance liquid chromatographic method with ultraviolet detection is described for the quantitation of nicotine and its metabolites cotinine, trans-3'-hydroxycotinine, norcotinine and cotinine N-oxide in human serum. The analytes and the internal standard, N-ethylnorcotinine, were extracted by solid-phase extraction before chromatography. Two different columns and mobile phases with gradient systems were used. The detection limit of the assay was 10 ng/ml for nicotine, 3 ng/ml for cotinine N-oxide and 5 ng/ml for cotinine, trans-3'-hydroxycotinine and norcotinine. The concentrations of nicotine and its metabolites in the serum of 12 cigarette smokers are reported.

Chromatography, High Pressure Liquid↗
PubMed1992

High-performance liquid chromatography-electrochemical detection of 3-methylhistidine in human urine.

A reversed-phase high-performance liquid chromatographic method is described for the determination of 3-methylhistidine content in human urine using pre-column derivatization with phenylisothiocyanate, isocratic elution with 15 mM sodium acetate-acetonitrile (92:8, v/v) and electrochemical detection. The limit of quantitation was 0.1 pmol. The method has been applied in routine analyses of 3-methylhistidine in both clinical and research work.

Chromatography, High Pressure Liquid↗
PubMed1992

Simultaneous high-performance liquid chromatographic analysis of buspirone and its metabolite 1-(2-pyrimidinyl)-piperazine in plasma using electrochemical detection.

A selective and sensitive high-performance liquid chromatographic method with coulometric detection is described for the quantitation of buspirone and its active metabolite, 1-(2-pyrimidinyl)piperazine, in plasma samples of mice treated orally with buspirone (10 mg/kg body weight). The analytes are extracted with a carboxylic acid solid-phase extraction column before chromatography. A dual-electrode electrochemical detector is used. The limit of detection is 50 pg for buspirone and 35 pg for 1-(2-pyrimidinyl)piperazine.

Administration, Oral↗
PubMed1991

Determination of naltrexone and 6 beta-naltrexol in plasma by high-performance liquid chromatography with coulometric detection.

A simple and reliable reversed-phase high-performance liquid chromatographic method with coulometric detection is described for the quantitation of naltrexone and its metabolite, 6 beta-naltrexol, in plasma samples of healthy volunteers who received orally 50 mg of naltrexone. The analytes and the internal standard, naloxone, are extracted with an octadecyl solid-phase extraction column before chromatography. The mobile phase is 0.01 M potassium phosphate (pH 3)-acetonitrile (85:15, v/v) and it is pumped at 0.8 ml/min. The coulometric detector is formed by two electrodes set at +0.20 V and +0.70 V, with a palladium reference electrode. The limit of quantitation observed was 5 ng/ml for both naltrexone and 6 beta-naltrexol. This method can be used to investigate pharmacokinetic parameters of different pharmaceutical preparations of this opioid antagonist.

Chromatography, High Pressure Liquid↗
PubMed1991

High-performance liquid chromatographic determination of L-3-(3,4-dihydroxyphenyl)-2-methylalanine (alpha-methyldopa) in human urine and plasma.

A procedure is described for the determination of alpha-methyldopa (MD) [L-3-(3,4-dihydroxyphenyl)-2-methylalanine], its metabolite and catecholamines in the urine and plasma of patients undergoing MD therapy, by high-performance liquid chromatography with dual working electrode coulometric detection. An efficient sample preparation procedure is presented for the isolation of endogenous MD, its metabolite and catecholamines from plasma or urine. After deproteinization of a plasma sample with methanol containing 2% of 0.5 M perchloric acid and dilution of a urine sample (1:200), MD, dihydroxyphenylacetic acid (DOPAC), 3-O-methylmethyldopa (3-OMMD) and homovanillic acid (HVA) were separated with a Supelcosil LC-18 column. Catecholamines were extracted from the supernatant of deproteinized plasma or from urine by ion exchange on a Sephadex CM-25 column and subsequent adsorption on alumina. The use of the same mobile phase for the concurrent assay of MD, its metabolite and catecholamines increased considerably the efficiency of sample separation. Recoveries were close to 100% for MD, DOPAC, 3-OMMD and HVA and 70% for catecholamines. The effects of various experimental parameters related to mobile phase composition on chromatographic performance are reported. The purity of the eluted compounds was tested by recording both the first detector response (oxidation current) and the second detector response (reduction current). The ratio of the detector responses yielded a chemical reversibility ratio for the detected compound. A number of applications such as monitoring data from patients under MD therapy are presented.

Chromatography, High Pressure Liquid↗
PubMed1990

Simultaneous measurement of L-dopa, its metabolites and carbidopa in plasma of parkinsonian patients by improved sample pretreatment and high-performance liquid chromatographic determination.

A procedure is described for the determination of L-3,4-dihydroxyphenylalanine (L-DOPA), its metabolites and carbidopa (CD) in plasma of Parkinsonian patients by high-performance liquid chromatography with dual working-electrode coulometric electrochemical detection. An efficient sample preparation scheme is presented for the isolation of L-DOPA, its metabolites and the catecholamines from the same plasma aliquot. After a simple deproteinization with methanol containing 2% of 0.5 M perchloric acid and evaporation of the solvent, L-DOPA, its metabolites and CD were separated with a 5-micron Nucleosil C18 column. Catecholamines were extracted from the supernatant of the deproteinized plasma by ion exchange on small columns and adsorption on alumina. Recoveries were close to 100% for L-DOPA, its metabolites and CD and 70% for catecholamines. The use of the same mobile phase for the concurrent assay of L-DOPA, its metabolites and catecholamines considerably increased the throughput of samples in the chromatographic system. The dual-electrode coulometric detector afforded peak identification by comparing current ratios. Monitoring of data from patients under L-DOPA therapy is reported.

Carbidopa↗
PubMed1988

Improved high-performance liquid chromatographic analysis with double detection system for L-dopa, its metabolites and carbidopa in plasma of parkinsonian patients under L-dopa therapy.

An analytical method is described for measuring L-3,4-dihydroxyphenylalanine (L-DOPA), 3-O-methyl-DOPA, dihydroxyphenylacetic acid, free catecholamines and the peripheral DOPA decarboxylase inhibitor, carbidopa, in plasma samples of Parkinsonian patients by using high-performance liquid chromatography. A sample preparation method is presented for the isolation of the catecholamines and L-DOPA with its metabolites. Catecholamines are extracted by weak cation exchange on small columns and subsequent adsorption on alumina. L-DOPA, 3-O-methyl-DOPA, dihydroxyphenylacetic acid and carbidopa contained in the column effluents are directly injected in the chromatographic system. The eluates are separated on a reversed-phase column, monitored by both a coulometric electrochemical detector and a fluorescence detector, connected in series. Chromatographic peaks were identified on the basis of their retentions and response ratios of the two detectors. Two examples are presented of therapeutic drug monitoring in Parkinsonian patients treated with oral doses and continuous intravenous infusion of L-DOPA.

Carbidopa↗