Design and characterization of electrochemical detector for high-performance liquid chromatography and application to the determination of biogenic amines

Vitamin E status in a normal population: the influence of age

Plasma vitamin E levels and age have been positively correlated up to the sixth decade of life. Since antioxidants protect biomembranes in vivo against oxidative damage, it has been hypothesized that free radical scavengers such as vitamin E may have protective effects against aging. In the present study, plasma vitamin E and lipids were determined in 95 healthy volunteers [mean age (+/- S.D.) 55.9 +/- 24.5 yr]. Special attention was focused on vitamin E status in the elderly: 23 individuals were older than 80 years. A significant age effect (p less than 0.005) was observed for both vitamin E and cholesterol, both being increased in the middle-aged group (40-59 yr) and decreased in the elderly (greater than or equal to 80 yr). Since a high plasma cholesterol represents a major risk factor for ischemic heart disease, decreasing levels of plasma cholesterol with advancing age in a healthy population-sample appears to be the result of negative selection. Plasma vitamin E concentration was correlated (p less than 0.001) with total cholesterol, triglyceride, and total lipid. Since vitamin E is mainly transported by plasma lipoproteins, these strong correlations suggest that changes in vitamin E should be considered as an epiphenomenon of altered plasma transport capacity. The determination of plasma vitamin E is therefore a poor indicator of the real tissue vitamin E activity.

Simultaneous assay of 3,4-dihydroxyphenylalanine, catecholamines and O-methylated metabolites in human plasma using high-performance liquid chromatography

We devised a procedure for the simultaneous determination of 3,4-dihydroxyphenylalanine, catecholamines and O-methylated metabolites using a reversed-phase liquid chromatographic system. Detection is achieved by an electrochemical detector and a fluorescence detector connected in series. Sample preparation is kept to a minimum, and involves precipitation of proteins with trichloroacetic acid and perchloric acid, and subsequent neutralization, thus omitting the commonly adopted adsorption step. Chromatographic peaks were identified on the basis of retention behaviour and the ratio of responses at several oxidation potentials. The method was applied to the quantitative determination of 3,4-dihydroxyphenylalanine, catecholamines and O-methylated metabolites in human plasma.

Degradation study of catecholamines, indole amines and some of their metabolites in different extraction media by chromatography and electrochemical detection

Optimal conditions for the extraction from brain tissue and the simultaneous quantification of catechol and indole derivatives were determined after a systematic degradation study in water and perchloric acid. The roles of three parameters, namely temperature, presence of antioxidant agents, and time, were considered. Adrenaline, noradrenaline, dopamine, homovanillic acid, 5-hydroxytryptophan, 5-hydroxyindole acetic acid, serotonin, and epinephrine were separated by HPLC and detected electrochemically. The results indicated a great instability of the indole derivatives at an ambient temperature, in an acid medium, and in the absence of a protective agent. Therefore, when perchloric acid has to be used for deproteinization, the lowest concentration (0.1 M) is preferable. The samples have to be kept on ice, in darkness, and protected by ascorbic acid and sodium ethylenediamine tetracetate.

Uptake, storage and secretion of 5-hydroxytryptamine and its amino acid precursor by dispersed rat pancreas acinar cells

Rat pancreas acinar cells contain 5-hydroxytryptamine (5-HT; 10.86 +/- 2.52 ng/i.u. amylase), all of which can be accounted for by the 5-HT recovered from the zymogen granule fraction of these cells (10.70 +/- 3.06 ng/i.u. amylase). When incubated with [14C]5-HT dispersed acinar cells take up the amine and concentrate it in zymogen granules. These cells will also take up [14C]5-HTP (5-hydroxytryptophan), decarboxylate it and store the [14C]5-HT so produced in zymogen granules. 5-HTP itself is not taken up by the granules. 5-HT is incorporated into zymogen granules early in their formation; no amine is accumulated by mature zymogen granules and the amine within the mature granule is not exchangeable with extragranular amine. When dispersed acinar cells pre-labelled with [14C]5-HT and [3H]leucine are stimulated with caerulein, there is a synchronous increase in amylase activity and secretion of [14C]5-HT and [3H]protein; the ratios of [3H]protein/[14C]5-HT in zymogen granules and in the secretory products are identical. Pancreas acinar cells take up L-DOPA, decarboxylate it and store the dopamine produced in zymogen granules but the dopamine is not retained by the granules (t1/2 approximately equal to 90 min) and dopamine secretion from cells exposed to caerulein could not be demonstrated. It is concluded that 5-HT is a normal component of rat pancreas acinar cell zymogen granule. The granular amine has a turnover rate similar to that of granular protein and is released when the cells are stimulated to secrete protein. All the 5-HT released from the cell originates in zymogen granules.

Differential effects of alpha-, beta- and gamma-endorphins on dopamine metabolism in the mouse brain

The effects of intracerebral injection of alpha-, beta- and gamma-endorphins on the mouse brain dopamine (DA) metabolism were contrasted in relation to the previously identified patterns of behavior. alpha-Endorphin (20 micrograms) decreased the content of homovanillic acid (HVA) in the striatum, while gamma-endorphin (10 micrograms) the contents of DA, 3,4-dihydroxyphenylacetic acid and HVA. beta-Endorphin (1 and 2 micrograms) had no effects on the mouse DA metabolism in the brain. The changes in the DA metabolism induced by alpha- and gamma-endorphins were readily reversed by the pretreatment with naloxone (1 mg/kg). Results suggested: (1) the patterns of behavior in mice treated with endorphins are mediated by these differences in DA metabolism; (2) changes in DA metabolism induced by alpha- and gamma-endorphins occur via opiate receptors in the mouse brain.

Simultaneous determination of norepinephrine, dopamine and serotonin in rat brain regions by ion-pair liquid chromatography on octyl silane columns and amperometric detection

A highly sensitive and specific ion-pair liquid chromatography-electrochemical detection method is described for the simultaneous determination of rat brain regional norepinephrine, dopamine and serotonin levels using octylsilane (C8) columns. These amines were first isolated from tissue homogenates by adsorption on Amberlite CG-50 resin followed by separation on RP-8 columns with a mobile phase consisting of 0.05 M NaH2PO4 (pH 3.0) 0.02 mM EDTA, 1 mM heptanesulphonate-methanol (92:8, v/v) at 1.8 ml/min. Using 3,4-dihydroxybenzylamine as the internal standard, tissue recoveries (mean +/- S.D.) for norepinephrine, dopamine and serotonin were 87.5 +/- 2.6%, 61.8 +/- 10.5% and 72.9 +/- 7.5%, respectively. Assay sensitivities were sufficient for reliable quantitation of at least 200 pg of these compounds in a brain sample. The procedure is readily adaptable to determination of brain epinephrine and normetanephrine levels, as well. Finally, the reversed-phase system employed is highly flexible in that the same column and mobile phase conditions may be used for assay of biogenic amine metabolites.

High performance liquid chromatography (HPLC) determination of endogenous serotonin released from aggregating platelets

High performance liquid chromatography with electrochemical detection was developed for the determination of serotonin (5-hydroxytryptamine) in rabbit platelet and plasma. A peak from tissue extract (peak a) was identified as serotonin based on retention time on the chromatogram, using a potential that gave limiting current on both a current-potential curve and gas chromatography-mass spectrum, as compared with that of authentic serotonin. For the assay of serotonin, 5-hydroxy-N-methyltryptamine was used as an internal standard and the extraction recovery of the serotonin added to the platelet-rich plasma was almost total. Furthermore, using this highly sensitive method, it has been demonstrated that the release of endogenous serotonin from rabbit platelets occurs during collagen-induced platelet aggregation but not during adenosine diphosphate-induced platelet aggregation. The procedures described should prove to be simple and useful for pharmacological and physiological investigations on the relationship between platelet aggregation and release reaction.

Determination of plasma and urine levels of a new anti-inflammatory agent, 4,5-bis-(4-methoxyphenyl)-2-(2-hydroxymethylsulfinyl)-imidazole, by high-performance liquid chromatography and electrochemical or ultraviolet detection

The determination of a new anti-inflammatory substance, 4,5-bis-(4-methoxyphenyl)-2-(2-hydroxyethylsulfinyl)-imidazole, in plasma and urine by high-performance liquid chromatography is described. Ultraviolet and electrochemical detection modes are compared and special consideration is given to the mechanism of the electrochemical reaction. The site of oxidation in the molecule seems to be an aliphatic hydroxyl group yielding a carboxyl function in a four-electron transfer reaction. Plasma levels and urinary excretion after an oral dose of 250 mg to two male volunteers have been measured.

Regional distribution of a novel analgesic dipeptide kyotorphin (Tyr-Arg) in the rat brain and spinal cord

Using high performance liquid chromatography, we measured kyotorphin content in discrete regions of the rat brain and spinal cord in an attempt to clarify its physiological significance. Higher concentrations of the dipeptide were found in the midbrain, pons plus medulla oblongata and dorsal cord, which are the most sensitive sites for the microinjection of morphine and/or electrical stimulation-induced analgesia. Kyotorphin may play a physiological role in pain control in the central nervous system.