title: Oral load of tyrosine or L-dopa and plasma levels of free and sulfoconjugated catecholamines in healthy men.
abstract: The levels of free and sulfoconjugated catecholamines were measured in the plasma of fasting, recumbent normal subjects before and after an oral load of the catecholamine precursors tyrosine or L-dopa. Basal values of sulfoconjugated catecholamines, measured in plasma samples diluted 1:100 were 7998 +/- 540 pg/ml for dopamine sulfate, 2938 +/- 281 pg/ml for norepinephrine sulfate, and 2958 +/- 288 pg/ml for epinephrine sulfate (n = 37 tests in 15 men); these basal values are higher than those reported previously. Neither free nor sulfoconjugated catecholamine concentrations were changed by a tyrosine load (100 mg/kg) that induced a doubling of the plasma tyrosine level or by a meal low in phenylalanine and tyrosine (but otherwise supplying constituents of normal nourishment) that induced a greater than 50% reduction in the plasma tyrosine concentration. After an oral load of L-dopa (125 mg) the following were observed. (1) An extremely large increase (greater than 100-fold) in dopamine sulfate levels was noted, an increase that was less marked in the same subjects given L-dopa (125 mg) plus the peripheral dopa-decarboxylase inhibitor carbidopa (12.5 mg); as expected, free dopamine concentration also was increased. (2) Neither free nor sulfoconjugated norepinephrine concentrations were altered. (3) Epinephrine sulfate but not free epinephrine concentration was increased (more than ten-fold) after L-dopa ingestion alone; this result was unexpected and has to be confirmed before considering its physiological meaning, if any.
mesh_terms: D000284:Administration, Oral; D002395:Catecholamines / Q000097:blood*; D006801:Humans; D007980:Levodopa / Q000008:administration & dosage*; D008297:Male; D008676:Metanephrine / Q000097:blood; D010649:Phenylalanine / Q000008:administration & dosage; D014443:Tyrosine / Q000008:administration & dosage* / Q000097:blood
chemical_list: D002395:Catecholamines; D014443:Tyrosine; D007980:Levodopa; D010649:Phenylalanine; D008676:Metanephrine