TY - JOUR T1 - INHIBITION OF NOREPINEPHRINE BIOSYNTHESIS BY α-METHYL AMINO ACIDS IN THE GUINEA-PIG VAS DEFERENS JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 71 LP - 77 VL - 180 IS - 1 AU - NGUYEN B. THOA AU - DAVID G. JOHNSON AU - IRWIN J. KOPIN Y1 - 1972/01/01 UR - http://jpet.aspetjournals.org/content/180/1/71.abstract N2 - In the isolated vas deferens of the guinea pig both α-methyl-m-tyrosine and α-methyldopa decreased formation of norepinephrine from tyrosine-14C. Inhibition was apparent even during the accelerated syntimesis of norepinephrine produced by stimulation of the hypogastric nerves. Both drugs also decreased formation of norepinephrine and dopamine from labeled dopa. In organs treated with the dopa decarhoxylase inhibitor NSD-1055, both α-methyl-m-tyrosine and α-methyldopa decreased the formation of dopa-14C from tyrosine-14C. α-Methyl-m-tyrosine inhibited the uptake of tyrosine-14C into the vas deferens, and α-methyldopa inhibited the uptake of labeled dopa. These results suggest that the α-methylated compounds can inhibit synthesis of norepinephrine in concentrations lower than those necessary to inhibit the enzymes involved in the biosynthesis of norepinephrine. This inhibition may be in part the result of interference with uptake of the labeled precursor amino acids into the sympathetic nerves. © 1972, by The Williams & Wilkins Company ER -