An Electron Microscopic Radioautographic Identification of the APUD Endocrine Cells in the Rat Gastric Pyloric Glands

Abstract

The rat stomach was shown some years ago to contain numerous endocrine cells with APUD ability--cells that could take up the amino acids L-5-hydroxytryptophan (5-HTP) or L-dihydroxyphenylalanine (L-DOPA) and could decarboxylate them to their respective amines, 5-hydroxytryptamine (5-HT, serotonin) and dopamine, by means of the enzyme DOPA-decarboxylase. In a recent study, most of the APUD endocrine cells in the rat oxyntic mucosa were shown by electron microscopic radioautography to be the enterochromaffinlike cells, while the A-like cells were shown to lack APUD ability. To identify the APUD cells in the pyloric mucosa, pieces of rat pylorus were incubated in organ culture with 3H-5-HTP and were processed for light microscopic and electron microscopic radioautography. Additional specimens were incubated with 3H-5-HTP and carbidopa, an inhibitor of DOPA-decarboxylase, used to block the decarboxylation of 3H-5-HTP to 3H-5-HT, or with 3H-5-HT, used to determine where exogenous 3H-5-HT localizes in the pyloric mucosa. The 3H-5-HTP labeled all three types of endocrine cells identified within the pyloric glands--the G, enterochromaffin, and D cells. As this labeling was inhibited by carbidopa, and as exogenous 3H-5-HT labeled these cells only lightly, the labeling must have resulted from the uptake and intracellular conversion of the 3H-5-HTP of 3H-5-HT. Thus despite their morphologic differences, all rat pyloric endocrine cells possess APUD ability, a property shared by many, but not all, of the peptide- and amine-producing endocrine cells located throughout the body.