INDUCTION OF PRECOCIOUS PEPSINOGEN SYNTHESIS BY GLUCOCORTICOIDS IN FETAL-RAT GASTRIC EPITHELIUM IN ORGAN-CULTURE - IMPORTANCE OF MESENCHYMEFOR EPITHELIAL DIFFERENTIATION

Glucocorticoids significantly affect both proliferation and differenti ation of gastric epithelial cells in vivo. Here we examined the mechan ism of action of glucocorticoids on the cells in vitro, with special r eference to the epithelial-mesenchymal interaction. When 16.5-day feta l rat gastric explants were maintained in organ culture, the epithelia l cells began to invaginate into mesenchyme on days 3 to 4, and formed glandular structures on days 5 to 6 in culture. Immunohistochemical a nalysis with specific antibodies revealed that pepsinogen-synthesizing cells first appeared on day 2, and they increased in number with epit helial morphogenesis to about 20%-30% of total epithelial cells on day s 4 to 6, and that these cells were localized at the base of glandular structures in control media. When the explants were treated with hydr ocortisone (1 mu g/ml), epithelial morphogenesis was mostly suppressed , but epithelial cytodifferentiation was significantly stimulated, ind icating that epithelial morphogenesis is not necessary for their cytod ifferentiation. In glucocorticoid-treated explants, pepsinogen-synthes izing cells first appeared on day 1, and more than 90% of the cells we re positively stained with the antibodies from days 3 to 5 in culture. Biochemical analysis showed that much higher acid protease activity c ould be detected in glucocorticoid-treated explants than in controls f rom days 2 to 6 in culture, and analysis by zymography indicated that the synthesis of pepsinogen 1 but not cathepsin E was stimulated by th e hormone. Northern blotting analysis showed that the level of pepsino gen 1 mRNA was greatly increased by glucocorticoids. Examination of th e effect of the hormone on the epithelial proliferation showed that hy drocortisone (1 mu g/ml) significantly inhibited the epithelial growth from days 1 to 3 in culture. To investigate the role of epithelial-me senchymal interaction in the glucocorticoid-induced differentiation of the gastric epithelial cells, effects of the hormone on the prolifera tion and differentiation of the cells in the absence of mesenchyme wer e examined, using a recently established primary culture system. The e pithelial cells synthesized cathepsin E but not pepsinogen in cell cul ture, irrespective of glucocorticoid treatment, and the level of acid protease activity was not affected by the hormone, indicating that mes enchyme is necessary for the hormone to induce pepsinogen gene express ion in the epithelial cells. In the cell culture system, glucocorticoi ds did not inhibit but significantly stimulated epithelial proliferati on. This suggests that the hormone indirectly inhibited epithelial pro liferation in organ culture, probably via mesenchyme. The mechanism of action of glucocorticoids on the epithelial-mesenchymal interaction i n the fetal glandular stomach is discussed.