Dopamine formation, from its immediate precursor 3,4‐dihydroxyphenylalanine, along the rat digestive tract

Abstract

The formation of dopamine, from L-3,4-dihydroxyphenylalanine (L-dopa), in fragments of non-glandular and glandular stomach, duodenum, jejunum, ileum and proximal and distal colon of the rat was examined. The deamination of newly-formed dopamine into 3,4-dihydroxyphenylacetic acid (dopac) was also studied. The synthesis of dopamine in tissues incubated with 500 microM L-dopa for 20 min in conditions of catechol-O-methyltransferase (Comt) inhibition was found to be in the duodenum, jejunum and ileum 2-fold that in the proximal colon, 6-fold that in the glandular stomach and 120-fold that in the non-glandular stomach and distal colon. The formation of dopac in these tissues followed the pattern of amine formation. In the jejunum, the formation of dopamine and dopac was found to be dependent on the concentration of L-dopa (50 to 5000 microM) used. In another set of experiments, it was found that the formation of dopamine in jejunal segments loaded with increasing concentrations of L-dopa (50, 100 and 500 microM) was a time-dependent process. The rate constant (k) of formation of dopamine as a function of time was found to be similar (0.050 +/- 0.005) with either concentration of L-dopa; the rate constant of dopac formation in these experiments was, in contrast, found to be greater at the highest concentrations of L-dopa (100 and 500 microM). Aromatic L-amino acid decarboxylase (Aaad) activity determined in homogenates of the jejunal mucosa was found to be twice that observed in homogenates of the remaining jejunal wall (muscular).(ABSTRACT TRUNCATED AT 250 WORDS)

Sources and Physiological Significance of Plasma Dopamine Sulfate

“…M-PST could also function to delimit the actions of dopamine as an autocrine-paracrine factor in the gastrointestinal tract (51). Mesenteric organs express dopamine receptors (27), and administration of drugs that alter occupation of dopamine receptors affects bicarbonate secretion and sodium-hydrogen ion exchange in the gastrointestinal tract (52) in a manner consistent with the gastroprotective actions of dopamine (53,54).…”

Trace Amines and Their Receptors

“…However, it should be borne in mind that AADC expression is not restricted to neuronal cells. AADC is present in a number of other cell types, including glia (Li et al, 1992b;Juorio et al, 1993), blood vessels , and cells of the gastrointestinal tract (Lauweryns and Van Ranst, 1988;Vieira-Coelho and Soares-da-Silva, 1993), kidney (Christenson et al, 1970;Lancaster and Sourkes, 1972;Aperia et al, 1990;Hayashi et al, 1990), liver (Bouchard and Roberge, 1979;Ando-Yamamoto et al, 1987;Dominici et al, 1987), lungs (Lauweryns and Van Ranst, 1988;Linnoila et al, 1993), pancreas (Lindström and Sehlin, 1983;Furuzawa et al, 1994;Rorsman et al, 1995), and stomach (Lichtenberger et al, 1982). In such cells, it can reasonably be expected that AADC will convert any precursor amino acids present into the corresponding trace amine(s).…”

The Dopaminergic System in Autoimmune Diseases

“…Another peripheral source of dopamine is the gut (8). Gastrointestinal (GI) dopamine is produced by aromatic amino acid decarboxylase (AADC) expressed in epithelial cells in the gut lumen and luminal l -DOPA (9). There are three additional sources of dopamine: immune cells synthesizing and releasing dopamine, the peripheral nervous system (PNS), and the central nervous system (CNS).…”

“…Additional studies have shown that TH, dopamine, and DAT immunoreactivities colocalize in subsets of neurons from mouse intestines, known to be resistant to extrinsic denervation, thus strongly suggesting that enteric dopaminergic neurons are intrinsic (94). On the other hand, dopamine may be synthesized by epithelial cells of the intestinal mucosa, which show high AADC activity and are exposed both to circulating or luminal l -DOPA (9). Interestingly, inflamed mucosa from CD and UC patients shows a marked reduction of dopamine content (95), which may alter the activation or differentiation status of DAR-expressing immune cells, such as inflammatory T cells, Tregs, B cells, macrophages, NK cells, and DCs.…”