Linked Life Data

2901461

Source:http://linkedlifedata.com/resource/pubmed/id/2901461

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PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4
pubmed:dateCreated
1988-10-19
pubmed:abstractText
To elucidate the source and physiological significance of plasma 3,4-dihydroxyphenylalanine, the immediate product of the rate-limiting step in catecholamine biosynthesis, plasma 3,4-dihydroxyphenylalanine was quantified in conscious rats after administration of reserpine, desipramine, clorgyline, or forskolin, treatments that affect tyrosine hydroxylase activity. Plasma 3,4-dihydroxyphenylalanine was also examined during infusions of norepinephrine with or without clorgyline, reserpine, or desipramine pretreatment. After reserpine, the plasma 3,4-dihydroxyphenylalanine level decreased by 22% and then increased by 40%, a result consistent with modulation of tyrosine hydroxylase activity first by an increased axoplasmic norepinephrine content and then by depletion of norepinephrine stores. After desipramine, the plasma 3,4-dihydroxyphenylalanine level decreased by 20%, reflecting the depressant effect of neuronal uptake blockade on norepinephrine turnover. Forskolin increased the plasma 3,4-dihydroxyphenylalanine level by 30%, consistent with activation of tyrosine hydroxylase by cyclic AMP-dependent phosphorylation. Acute administration of clorgyline was without effect on the plasma 3,4-dihydroxyphenylalanine level. Norepinephrine infusions decreased the plasma 3,4-dihydroxyphenylalanine concentration, as expected from end-product inhibition of tyrosine hydroxylase. Pretreatment with desipramine prevented the norepinephrine-induced decrease in plasma dihydroxyphenylalanine content, indicating that inhibition of tyrosine hydroxylase required neuronal uptake of norepinephrine. Both reserpine and clorgyline augmented the norepinephrine-induced decrease in plasma 3,4-dihydroxyphenylalanine level, suggesting that retention of norepinephrine in the axoplasm--due to inhibition of norepinephrine sequestration into storage vesicles or catabolism--caused further inhibition of tyrosine hydroxylase. Changes in plasma 3,4-dihydroxyphenylalanine concentration during norepinephrine infusions were negatively correlated with those in plasma 3,4-dihydroxyphenylglycol level, a finding consistent with modulation of tyrosine hydroxylase activity by axoplasmic norepinephrine. In reserpinized animals, clorgyline and norepinephrine infusion together decreased the plasma 3,4-dihydroxyphenylalanine content by 50%, a result demonstrating that hydroxylation of tyrosine was depressed by at least half. The results indicate that quantification of plasma 3,4-dihydroxyphenylalanine can provide a simple and direct approach for examination of the rate-limiting step in catecholamine biosynthesis.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Oct
pubmed:issn
0022-3042
pubmed:author
pubmed:issnType
Print
pubmed:volume
51
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
1204-13
pubmed:dateRevised
2003-11-14
pubmed:meshHeading
pubmed:year
1988
pubmed:articleTitle
Source and physiological significance of plasma 3,4-dihydroxyphenylalanine in the rat.
pubmed:affiliation
Clinical Neuroscience Branch, National Institute of Neurological and Communicative Disorders and Stroke; Bethesda, Maryland.
pubmed:publicationType
Journal Article