Abstract
Abstract The oxyntic glands of rat and mouse stomachs contain argyrophil "enterochromaffin-like" endocrine cells that synthesize and store histamine and also have APUD ability—they can take up exogenous L-5-hydroxytryptophan (5-HTP), can decarboxylate it to 5-hydroxytryptamine (5-HT, serotonin) by the enzyme DOPA decarboxylase, and can store the amine. Previous cytochemical studies have suggested that these cells correspond to both the ECL and A-like cells, the two predominant endocrine cells identified by electron microscopy in rat and mouse oxyntic glands. The purpose of this study was to identify by EM radioautography the APUD and thereby the enterochromaffin-like cells in the oxyntic glands of these rodents. Pieces of rat and mouse gastric mucosa were incubated in organ culture with H3-5-HTP, H3-5-HTP and carbidopa (an inhibitor of DOPA decarboxylase), and H3-5-HT and were processed for LM and EM radioautography. Additional pieces of rat gastric mucosa were incubated with 5-HTP, freeze-dried, and processed by the Falck-Hillarp technique to permit the detection of 5-HT by fluorescence microscopy. After H3-5-HTP incubations, the EeL cells of both the rat and mouse oxyntic glands were labeled by EM radioautography, but the A-like cells of only the mouse were so labeled. Since this labeling was inhibited by carbidopa and since exogenous H3-5-HT failed to label endocrine cells, the labeling must have resulted from the uptake of exogenous H3-5-HTP and its intracellular conversion to H3-5-HT. The failure of some rat oxyntic endocrine cells to form and store 5-HT from exogenous 5-HTP was also demonstrated by the Falck-Hillarp technique and by LM radioautography. Thus, this study demonstrates that only the ECL and not the A-like cell of rat oxyntic glands is an APUD and therefore enterochromaffin-like cell, and that despite their morphologic similarities, the A-like cells of the rat and mouse have metabolic differences.
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