Effects of Chemical Sympathectomy on Dopamine and Noradrenaline Content of the Dog Gastrointestinal Tract*

Abstract

The content of dopamine and noradrenaline in the mucosa-submucosa and muscular layers of different gastrointestinal areas of the dog, and its modification by 6-hydroxydopamine or pargyline plus 6-hydroxydopamine was studied by means of high pressure liquid chromatography with electrochemical detection. The amounts of dopamine and noradrenaline show a cephalocaudal increase but their physiological levels were rather low when compared with those reported in other tissues. This finding was consistent with the sparse noradrenergic innervation classically described for the gut with histochemical methodologies. On the basis that noradrenergic neurones are considered more susceptible to 6-hydroxydopamine than dopaminergic neurones, a difference abolished by previous treatment with pargyline, our findings did not suggest the existence of dopaminergic neurones in the gastrointestinal tract of the dog. In the muscular layer of the duodenum, jejunum and ileum it was observed that catecholamine depletion by both treatments was smaller than that obtained in the mucosa-submucosa. Due to the resistance to both kinds of chemical sympathectomy exhibited by the dopamine content, the existence of dopamine-containing enterochromaffin cells is proposed in the mucosa-submucosa of different portions of the stomach and small intestine.

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

“…This is further supported by the finding that a considerable amount of Aaad, at least that present in the jejunum, is located in the sparsely innervated mucosa. Another result favouring the view that a considerable amount of the dopamine in the intestinal mucosa is non-neuronal in location is that denervation by 6-hydroxydopamine increases the proportion of dopamine to noradrenaline (Esplugues et al, 1985;Graffner et "1, 1985;Eaker et al, 1988).…”

Dopamine and Renal Function and Blood Pressure Regulation

“…There are dopamine-containing enterochromaffin cells in the mucosa/submucosa of several regions of the stomach and small intestine (164). Significant and detectable quantities of l -DOPA produced by non-neuronal cells that express tyrosine hydroxylase in mesenteric organs (gastrointestinal tract, spleen, and pancreas) are released into the circulation (154).…”

Ontogenic aspects of D1 receptor coupling to G proteins and regulation of rat jejunal Na+, K+ ATPase activity and electrolyte transport

“…The current view of the intestinal dopaminergic system is that of a local non‐neuronal system constituted by epithelial cells of intestinal mucosa, rich in aromatic L‐amino acid decarboxylase (AADC) activity and using circulating or luminal 3,4‐dihydroxyphenylalanine (L‐DOPA) as a source for dopamine (Vieira‐Coelho et al ., 1997). Dopamine is particularly abundant in the mucosal cell layer (Eaker et al ., 1988; Esplugues et al ., 1985). Studies on the formation of dopamine from exogenous L‐DOPA along the rat digestive tract showed that the highest AADC activity is located in the jejunum (Vieira‐Coelho & Soares‐da‐Silva, 1993).…”