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Studies on normal and precocious appearance of jejunal sucrase in suckling rats
Insights
Hydrocortisone induces sucrase in infant rat jejunum, but only in proliferative enterocytes. This hormone
Area of Science:
- Gastroenterology
- Developmental Biology
- Molecular Endocrinology
Background:
- Sucrase activity in the jejunum of infant rats is developmentally regulated.
- Glucocorticoids, like hydrocortisone, are known to influence intestinal enzyme expression.
Purpose of the Study:
- To investigate the cellular and molecular mechanisms underlying sucrase appearance in infant rat jejunum.
- To determine the role of cell proliferation and migration in glucocorticoid-induced sucrase expression.
Main Methods:
- Administration of hydrocortisone and Actinomycin D to infant rats.
- Assay of jejunal sucrase activity in tissue homogenates and cryostat sections.
- Analysis of enzyme activity localization along the intestinal villi.
Main Results:
- Actinomycin D significantly inhibited hydrocortisone-induced sucrase activity.
- Hydrocortisone-induced sucrase initially appeared at the villus base and spread with cell migration.
- Enterocyte responsiveness to hydrocortisone increased with age during the first two postnatal weeks.
Conclusions:
- Glucocorticoid action on enterocytes requires the cells to be in their proliferative phase.
- Cell migration plays a crucial role in the distribution of induced sucrase activity.
- The ontogeny of jejunal sucrase induction is linked to increasing enterocyte responsiveness to glucocorticoids.
Abstract:
Some of the cellular and molecular events involved in the normal and precocious appearance of sucrase in jejunum of infant rats have been studied. Actinomycin D has been shown to inhibit (by 79%) the rise in sucrase activity usually seen after administration of hydrocortisone to 9-day-old rats. The precocious appearance of sucrase has also been studied with respect to the cytological localization of enzyme activity in the intestinal mucosa. Tissue was sectioned in a cryostat (transverse to the villi) and sucrase was assayed in homogenates prepared from the sections. By 24 h after administration of hydrocortisone to 9-day-old animals, sucrase was detectable only at the bases of the villi. During the subsequent 72 h the enzyme activity increased and spread along the villi at a rate consistent with that of cell migration. These data have lead to the conclusion that the action of glucocorticoids on enterocytes can occur only when the cells are in their proliferative phase. An ontogenic study of the ability of hydrocortisone to elicit jejunal sucrase showed that the tissue becomes increasingly responsive to the hormone with increasing age through the first and second postnatal weeks. Various hypotheses to explain this increase have been examined.