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P H Redfern

Publications and source records attributed to P H Redfern.

At least 19 recordsLinked to original sources
PubMed1979

Surfactant ion-pair high-performance liquid chromatography of tryptophan and some of its metabolites in biological fluids.

A rapid, sensitive assay for tryptophan and some of its metabolites in urine, plasma and saliva has been developed using sodium dodecylsulphate as a pairing ion in a surfactant ion-pair high-performance liquid chromatography technique. The method is highly selective for tryptophan which is separated from its main indoleamine metabolites, 5-hydroxytryptophan, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid, and from kynurenine. The usefulness of the assay has been demonstrated in plasma level and urinary excretion studies of orally administered tryptophan.

Biological Availability↗
PubMed1978

The mechanism of the hypothermic effect of amantadine in rats and mice.

Amantadine (25--100 mg kg-1, i.p.) given to rats at an ambient temperature of 4 degrees, or mice at 21 degrees, caused a marked fall in rectal temperature. Prior administration of pimozide (1--2 mg kg-1, s.c.) did not block hypothermia due to amantadine in rats or mice; in contrast, hypothermia due to apomorphine (2 mg kg-1, i.p.) and piribedil (10--40 mg kg-1, i.p.) in rats was blocked by pimozide pretreatment. Amphetamine (5 mg kg-1, i.p.) given 2 h after reserpine (2 mg kg-1, i.p.) caused a reversal of the hypothermic effect of reserpine in mice, but a reversal was not obtained with amantadine (50 mg kg-1, i.p.). Direct injection of amantadine (4--8 mg kg-1) into the cerebral ventricles (i.c.v.) of mice caused marked hypothermia which was not blocked by pimozide, but intravenous injection of the same dose of amantadine did not cause hypothermia. Rimantadine, a congener of amantadine but without anti-parkinsonian activity, also caused pimozide insensitive hypothermia in mice at doses of 50 mg kg-1, intraperitoneally or 2--4 mg kg-1, intracerebroventricularly. The main conclusion drawn from these results is that in causing hypothermia amantadine acts in the cns but not on dopamine receptors.

Amantadine↗
PubMed1977

Twenty-four hour rhythms in serum and brain indoleamine concentrations: tryptophan-5-hydroxylase and monoamine oxidase activity in the rat.

The relationship between the 24 h rhythm in 5-hydroxy-tryptamine (5HT) levels in rat brain, the availability of precursors of 5HT and the concentration of its major metabolite, 5-hydroxyindole acetic acid (5HIAA) has been investigated. Serum total and "free" tryptophan (TRY) levels and brain TRY levels all show a 24 h rhythm with highest concentrations in the middle of the dark phase i.e. 12 h displaced from that of the 5HT rhythm. No 24 h variation in either tryptophan-5-hydroxylase or monoamine oxidase activity was detected, nor did brain 5-hydroxytryptophan (5HTP) levels vary with clock hour. Changes in 5HIAA concentration paralleled those of 5Ht. The uptake of 14C-5HTP, 14C-TRY and 14C-5HT into homogenates of the septal region of rat brain did not display a circadian rhythm, although there was evidence that uptake of 14C-TRY in an isolated synaptosomal preparation from the same region was greater during the light phase, indicating the possibility that uptake of the precursor into the nerve ending may be, in part, responsible for the 24 h rhythm in brain 5HT. It is concluded that brain 5HT levels are independent of the serum or brain TRY concentrations measured. Since changes in 5HT with clock hour are paralleled by changes in 5HIAA, it also seems unlikely that the increase in brain 5HT during the light phase is caused by a decreased release of 5HT from nerve endings.

5-Hydroxytryptophan↗
PubMed1976

Brain acetylcholine concentration and acetylcholinesterase activity in selectively-bred strains of rats.

Significant differences in whole brain and in brain area acetylcholine concentration have been observed between the two strains of rats selectively bred for differences in speed of acquisition of conditioned avoidance. Brain acetylcholinesterase activity was similar in the strains. The strain showing poor conditioned avoidance behaviour possessed the highest brain concentration of acetylcholine. The finding supports a theory which describes a central cholinergic inhibitory system which may be active in the control of certain types of learning behaviour.

Acetylcholine↗
PubMed1976

Studies on the mechanism of action of amantadine.

1 The effect of amantadine hydrochloride on various aspects of catecholamine metabolism in the rat brain has been investigated. 2 Amantadine failed to have any significant effect on brain concentrations of dopamine or noradrenaline even when administered daily for 9 days. 3 Amantadine had no effect on the rate of decline of noradrenaline and dopamine concentrations after alpha-methyl-p-tyrosine. 4 In vitro amantadine inhibited dopamine uptake into synaptosomes only at high concentrations, and caused little release of dopamine from synaptosomes. 5 There is no evidence from these results to suggest that the anti-Parkinsonian effect of amantadine is related to an action on dopaminergic mechanisms.

Amantadine↗