Precursors and Metabolites of Norepinephrine in Sympathetic Ganglia of the Dog

Abstract

3,4-Dihydroxyphenylalanine, dopamine, epinephrine, 3,4-dihydroxyphenylglycol, and 3,4-dihydroxyphenylacetic acid as well as norepinephrine were measured in dog lumbar sympathetic ganglia. The responses of these compounds to several classes of stimuli were investigated using an isolated time-resolved superfusion system. Nonselective (i.e., amphetamine and high K+) and receptor-mediated selective (oxotremorine) stimuli were used to evoke releases. The overflows of all compounds were measured by HPLC with electrochemical detection. The efficiency of each stimulus was estimated by normalizing the amount of evoked release to the total neurotransmitter pool when the stimulus was applied; i.e., fractional release was calculated. Overflows of all compounds except 3,4-dihydroxyphenylalanine were enhanced by a 10-min 100 .mu.M amphetamine stimulus, and each of the catecholamine pools (dopamine, norepinephrine and epinephrine) was effected to the same degree. By contrast, the 3,4-dihydroxyphenylalanine and dopamine pools were more readily releasable than the norepinephrine pool with a 10 min 80 mM K+ stimulus, and these releases were Ca2+ dependent. Epinephrine was released in preference to norepinephrine by a 10-min1 mM oxotremorine stimulus. The data suggest the existence of at least three types of neurons in dog lumbar ganglia and are consistent with previous histological observations.