Abstract
Dopamine (DA) metabolism was compared in rat superior cervical ganglion, coeliac ganglion, mesenteric ganglion and adrenal medulla. Substantial amounts of DA, 3–4 dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were found in all the above structures. The proportion of DA metabolites over total adrenergic compounds increased from the superior cervical (22 ± 2.2%) to the mesenteric ganglia (37 ± 1.4%) and was much higher in ganglia (30 ± 1.6%) than in adrenal medulla (1.1 ± 0.3%). The turnover rates of DOPAC and HVA were calculated in sympathetic ganglia after pargyline (75 mg/kg i.p.) or probenecid (200–500 mg/kg i.p.). After pargyline, the DOPAC levels decreased faster than HVA levels in all ganglia. The corresponding half-lives and calculated turnover rates were: about 4 and 10 min and 100 and 40 pmol/mg protein per h for DOPAC and HVA respectively. No differences were observed between the three ganglia. After probenecid, DOPAC accumulated in all the ganglia in a dose-dependent way; HVA accumulated in the superior cervical and coeliac ganglia but not in the mesenteric ganglion. As in central areas, the turnover rates of DOPAC and HVA calculated on the basis of the greatest accumulation of acidic levels after probenecid were much smaller than those obtained after pargyline. Probenecid increased DOPAC levels in adrenal medulla, but the concomitant changes in DA and epinephrine (E) amounts suggest that probenecid was able to enhance adrenomedullary activity. Together these data demonstrate that sympathetic ganglia are relevant peripheral dopaminergic structures, with a rostrocaudal enrichment in DA cells, great turnover and fast elimination of free DOPAC and HVA, only partially due to a probenecid sensitive mechanism. DA metabolism, and possibly the DA functional role, are quite different in sympathetic ganglia and adrenal medulla, but share common features with those previously reported for brain dopaminergic areas.
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