Search PubMed⌕ Search

Biomedical subjects

T Eriksson

Publications and source records attributed to T Eriksson.

At least 91 records · Page 5Linked to original sources
PubMed1986

Rat brain concentration of administered amino acids: dependence on time of day for administration.

Several large neutral amino acids (LNAA) (e.g. L-DOPA and L-tryptophan) are used as therapeutic agents. To reach the brain they have to compete with the naturally occurring large neutral amino acids for the saturable, carrier mediated transport into the brain. Since the concentration of LNAA in plasma demonstrates a diurnal rhythm, this competition could be expected to vary accordingly. To investigate if this variation could influence the brain concentration of a certain administered amino acid we injected three groups of rats with L-DOPA, L-tryptophan or saline in the afternoon when the rat plasma concentration of LNAA is at its lowest. Three other groups of rats received the same treatments at 3 a.m., when the concentration of LNAA is reported to be at a maximal level. The brain concentrations of the administered amino acids were significantly higher and LNAA in plasma lower in the groups injected in the afternoon compared with those injected during the night. These findings support the hypothesis that the time of the day when an amino acid is administered is of importance to the concentration of the administered amino acid in the brain.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1985

Isolation and Partial Purification of Prophenoloxidase from Daucus carota L. Cell Cultures.

The enzyme, phenoloxidase, was isolated and partially purified as an inactive enzyme, a proenzyme, from plant cell cultures of Daucus carota, Nicotiana tabacum, and Haplopappus gracilis. The prophenoloxidase was found to be specifically activated by Ca(2+) or Mn(2+) ions in concentrations above 1 millimolar. Calmodulin was not involved in this activation. Concentrations of Ca(2+) or Mn(2+) below 1 millimolar could not induce activation of the prophenoloxidase, but if trypsin was added simultaneously with Ca(2+) or Mn(2+) at a concentration of 1 millimolar or below, the proenzyme was converted to its active form. The inactive form of phenoloxidase was found to be a soluble enzyme, whereas after activation the enzyme aggregated, and a significant amount of the enzyme activity could become pelleted.

Journal Article↗
PubMed1984

"On-off" phenomenon in Parkinson's disease: correlation to the concentration of dopa in plasma.

To investigate the relation between "on-off" fluctuations in symptomatology and bioavailability of dopa in patients with Parkinson's disease, five Parkinsonian patients with pronounced "on-off" symptoms were studied. Continuously during the study the degree of disability in the patients was registered. Every one hour, and in addition, whenever there was a change from "on" to "off" or vice versa, a blood sample was collected for dopa determination. Since dopa is transported from plasma into the brain by a saturable carrier for which it has to compete with endogenous large neutral amino acids (LNAA), the concentrations of these competitors were measured too. In four of the patients there were considerable oscillations in the plasma dopa concentration during the day; in one of these patients the highest value was as much as 12 times higher than the lowest value. These dramatic fluctuations in the absolute concentration of dopa in plasma had a major influence on the relative dopa concentrations (calculated as the ratio dopa/sum of LNAA) as the fluctuations in the concentrations of LNAA in plasma were much less pronounced. Consequently, the absolute and the relative concentrations of dopa in plasma were highly parallelled. In four of the five patients "on"-periods began within one hour after a peak in the concentration of dopa in plasma and in the fifth patient five out of seven "on"-periods were preceded by a rise in plasma dopa concentration within the same time interval. From the present data it could be concluded that the "on-off" phenomenon in Parkinson's disease, at least partly, is due to oscillations in the concentration of dopa in plasma. A reduction in the variations of the concentration of dopa in plasma seems to be necessary to overcome the "on-off" problem. The introduction of a slow release preparation of dopa is therefore urgently warranted. The concentration of LNAA in plasma must, however, also be considered in this context.

Aged↗
PubMed1984

Toluene-induced decrease in rat plasma concentrations of tyrosine and tryptophan.

The organic solvent toluene is demonstrated to cause a decrease in rat plasma concentrations of tyrosine and tryptophan both after intraperitoneal injections and after inhalation. Tyrosine and tryptophan are precursors to neurotransmitters and are transported from plasma into the brain. As the concentrations of these amino acids in plasma could influence the monoamine synthesis in the brain, this phenomenon might be of importance for the pathophysiology behind solvent-induced effects on brain function.

Animals↗
PubMed1984

Beta-adrenergic influence on brain concentrations of monoamine precursors.

The beta-adrenergic agonist isoprenaline: Causes a decrease in most amino acids in plasma. Changes the relation between the large neutral amino acids in plasma in favor of tyrosine and Try. Causes an increase in brain concentrations of tyrosine and Try. Causes an increase in brain concentrations of DOPA and Try after the administration of these amino acids. The reported effects might be of clinical importance in the treatment of mental depression and other diseases where amino acids are used as therapeutic agents.

Amino Acids↗
PubMed1983

Influence of supply of heat to cobalt-chromium frameworks during soldering and subsequent hardening heat treatment of wrought clasps.

Retentive clasp arms of wrought gold alloy wire were soldered to frameworks made of three dental cobalt-chromium alloys. The clasps were then subjected to a conventional hardening heat treatment. Microstructure and hardness of the cobalt-chromium alloys were determined before and after these operations. The results reveal that the supply of heat during soldering and hardening heat treatment of the clasp does not influence the microstructure and hardness of the cobalt-chromium alloys.

Chromium Alloys↗
PubMed1982

Adrenergic influence on rat plasma concentrations of tyrosine and tryptophan.

Isoprenaline given to rats in doses between 0.08 and 10 mg/kg intraperitoneally caused a significant decrease in plasma concentrations of tyrosine and tryptophan. Low doses of adrenaline (0.04 - 0.16 mg/kg, intraperitoneally) caused a 30 per cent decrease in plasma concentrations of tyrosine, while high doses (0.63 - 1.25 mg/kg, intraperitoneally) caused an increase in plasma tyrosine to nearly 200 per cent of the controls. High doses of noradrenaline (0.63 - 2.5 mg/kg, intraperitoneally) caused a similar increase in plasma tyrosine concentration. The decrease in plasma amino acids caused by these catecholamines is inhibited by propranolol, suggesting that this effect is mediated via adrenergic beta-receptors, while the increasing effect is inhibited by phenoxybenzamine, which suggests that this effect is caused by an alpha-adrenergic mechanism.

Animals↗
PubMed1982

Isoprenaline increases brain concentrations of administered L-dopa and L-tryptophan in the rat.

A small dose of isoprenaline or saline was administered intraperitoneally to rats 20 min before the administration of one of the amino acids L-dopa or L-tryptophan. Isoprenaline caused a marked increase in the brain concentration of the administered amino acid. Isoprenaline has previously been shown to cause a decrease in at least some of those plasma amino acids which compete with L-dopa and tryptophan for carrier-mediated transport into the brain. The effect of isoprenaline on the concentrations of dopa and tryptophan in the brain is suggested to be at least partly caused by a change in the relationship between endogenous and administered amino acids. It is also possible that a direct effect of isoprenaline on the blood-brain barrier transport system contributes to the effect. The reported finding might be of clinical interest in view of the therapeutic importance of aromatic amino acids with a central site of action.

Animals↗
PubMed1981

Effects of pentobarbital and diazepam on rat plasma amino acid patterns.

Intraperitoneal injections with pentobarbital and diazepam caused an increase in the concentration of most plasma amino acids in rat. In contrast, tryptophan was significantly decreased after treatment with pentobarbital. The tyrosine level showed no change and was thus actually reduced after pentobarbital treatment in relation to the total pool of large neutral amino acids. The possibility should be considered that these changes in plasma amino acid patterns may lead to reduced transport of e.g. tryptophan and tyrosine into the brain, which in turn might retard the synthesis of monoaminergic neurotransmitters. The transport and action of several aromatic amino acids used as therapeutic agents may also be influenced.

Amino Acids↗
PubMed1981

Effects of hypophysectomy, adrenalectomy and (-)-propranolol on ethanol-induced decrease in plasma amino acids.

In previous studies we have demonstrated that an acute dose of ethanol cause an immediate decrease in most plasma amino acids in both man and rat. This effect of ethanol is partly inhibited by the beta-adrenergic antagonist (-)-propranolol, partly by adrenalectomy or hypophysectomy and almost completely by a combination of adrenalectomy with (-)-propranolol. This finding suggests an involvement of both beta-adrenergic mechanisms and steroids from the adrenal cortex in the ethanol-induced decrease in plasma amino acids.

Adrenalectomy↗
PubMed1980

Ethanol-induced increase in brain concentrations of administered neutral amino acids.

Ethanol 2 g kg-1 i.p. to rat increased the concentrations in the brain of administered large neutral amino acids (tyrosine, tryptophan, 5-hydroxytryptophan and alpha-methyldopa). We have previously found a similar effect of ethanol on administered L-Dopa, resulting in increased brain/plasma ratios of dopa. Since large neutral amino acids are known to complete with each other for the carrier-mediated transport into the brain we suggest that the increased concentrations of the administered amino acids in the brain are at least partly the consequence of the ethanol-induced decrease in plasma amino acids observed previously.

Amino Acids↗
PubMed1977

Readaptation time after photo stress. Alcohol-induced acute and post-alcohol 'hangover' changes in ocular readaptation time.

The effect of alcohol intake on readaptation time (RAT) after photo stress is studied. Ten healthy subjects were given 0.72 g alcohol per kg body weight to be consumed within 20 min. The tests were made during a total period of 11-12 h. The findings demonstrate that moderate blood alcohol concentrations induce definite changes in RAT. An average RAT-prolongation of 60-70% was seen during the acute phase of intoxication. RAT-prolongation ended before the blood alcohol concentration had reached zero, but did not have the same downward slope. Following a period of reduction, a new prolongation of RAT was observed. The lack of congruence between the RAT-curve and the blood alcohol curve in the acute phase of intoxication and the post-alcohol increase are discussed. It is concluded that the alcohol-induced RAT-changes probably are CNS-effects and that the equipment used constitutes a sensitive method of estimating these effects.

Adaptation, Ocular↗