L‐methionine

Pearce, Larry A.; Waterbury, L. David

doi:10.1212/wnl.24.7.640

Cited by 9 publications

(3 citation statements)

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“…The absorption of levodopa across the blood-brain barrier as well as the small intestinal mucosa is governed by stereospecific active transport mechanisms for which other L-amino acids are also substrates (Daniel et al, 1976;Wade et al, 1973). Thus Pearce & Waterbury (1974) demonstrated that L-methionine antagonised the clinical effect of levodopa, and Mena & Cotzias (1975) reported that low-protein diets enhanced its efficacy and reduced the severity of fluctuations. More recently Nutt et al (1984) have investigated the effects of high-protein meals.…”

Section: -Ome Dopamentioning

confidence: 99%

The pharmacokinetics of intravenous and oral levodopa in patients with Parkinson's disease who exhibit on‐off fluctuations.

Hardie¹,

Malcolm²,

Lees³

et al. 1986

Brit J Clinical Pharma

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We have studied the clinical effects and pharmacokinetics of levodopa infusions and oral therapy in seven patients with Parkinson's disease. They all showed on‐off fluctuations whilst receiving long‐term treatment with levodopa in combination with a peripheral decarboxylase inhibitor. Intravenous infusion at a constant rate for up to 16 h resulted in a smoother clinical response, and maintained plasma levodopa concentrations within narrower limits compared with conventional oral therapy. Following infusion rates of 32‐80 mg h‐1 (0.5‐1.3 mg kg‐1 h‐1) the plasma concentration associated with optimum therapeutic response lay between 0.3 and 1.6 mg l‐1. There was considerable variation in the oral absorption and elimination of levodopa, both within and between subjects. The concentration of 3‐OMe dopa in plasma hardly increased during each day's levodopa therapy. In all cases levels were greater than the maximum concentrations of levodopa, sometimes by as much as a factor of 10. In contrast to most previous reports on the pharmacokinetics of levodopa, the data presented here are consistent with a two‐compartment kinetic model. It is not known whether the difference in pharmacokinetics is due to chronic therapy or whether it is specific to those patients who show on‐ off phenomena, but such changes might be related in some way to the development of fluctuations in clinical response.

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Section: -Ome Dopamentioning

confidence: 99%

The pharmacokinetics of intravenous and oral levodopa in patients with Parkinson's disease who exhibit on‐off fluctuations.

Hardie¹,

Malcolm²,

Lees³

et al. 1986

Brit J Clinical Pharma

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“…Whilst the specific central action of methionine remains obscure, there is evidence that L-DOPA acts as a competitive inhibitor of methionine uptake by nerve endings in homogenates of rat brains (Baldessarini & Karobath, 1972). Furthermore, methionine appears to reverse the clinical effectiveness of L-DOPA in Parkinsonism (Pearce & Waterbury, 1974 …”

Section: Discussionmentioning

confidence: 99%

EFFECTS OF l‐TRYPTOPHAN AND l‐METHIONINE ON ACTIVITY IN THE RAT

Taylor

1976

British J Pharmacology

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I The effects of an intraperitoneal dose of 20 mg/kg L-tryptophan and doses of 100 and 150 mg/kg of L-methionine were investigated on activity in the rat. 2 Activity was measured by a time sampling behaviour categorization procedure, and began 15 min after compound administration, lasting for a total of one hour. 3 Total active behaviour in the first half hour was reduced after 20 mg/kg tryptophan, 100 or 150 mg/kg methionine. Only 20 mg/kg tryptophan led to a significant reduction in active behaviour during the second half hour. 4 Administration of 100 mg/kg methionine plus 20 mg/kg tryptophan, and 150 mg/kg methionine plus 20 mg/kg tryptophan had no discernible effect on activity. 5The results draw attention to the role of another amino acid in the modification of the behavioural effects of tryptophan.

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“…Since S-adenosylmethionine in both brain and adrenal medulla tissue is lowered by levodopa, Pearce et al (1971) studied the effect of methionine in Parkinsonism. Since S-adenosylmethionine in both brain and adrenal medulla tissue is lowered by levodopa, Pearce et al (1971) studied the effect of methionine in Parkinsonism.…”

Section: L-methioninementioning

confidence: 99%