SUCRASE-ISOMALTASE ONTOGENY - SYNERGISM BETWEEN GLUCOCORTICOIDS AND THYROXINE REFLECTS INCREASED MESSENGER-RNA AND NO CHANGE IN CELL-MIGRATION

During postnatal maturation of the rat small intestine, glucocorticoid hormones (GC) and thyroxine (T-4) act synergistically to elicit a pre cocious increase of sucrase activity. The current work shows that the synergistic effect on sucrase activity is paralleled by increased stea dy-state levels of sucrase-isomaltase mRNA. The enhancing effects of T -4 on dexamethasone (DEX)-induced sucrase activity was seen even after prolonged treatment (9 days). Moreover, when the location of sucrase- bearing cells was examined after 2 days of hormone treatment, there wa s distinctly stronger immunostaining of sucrase in the presence of T-4 , and the sucrase-bearing cells were located on the lower quarter of t he intestinal villi regardless of whether the animals received DEX or T-4 plus DEX. Thus, despite predictions from the literature, there was no evidence for increased migration in the presence of T-4. Instead, we conclude that the synergism between the two hormones is due to grea ter accumulation of sucrase-isomaltase per epithelial cell. (C) 1998 A cademic Press.