Ontogenic development continues after birth in mammalian enteric epithelium as an adaptive mechanism to extrauterine life. In the rat, particularly significant developmental changes in enteric structure, function, and cytokinetic properties occur over a short critical period (usually between 16 and 20 days of age), preparatory to dietary change with weaning. Surgical bypass of ileal segments was performed on suckling rats of 12-14 days of age, and the effect on subsequent intestinal development was studied in both the bypassed and the shortened segment remaining in continuity. The bypassed segment, although achieving normal maturational patterns of active sucrase appearance and maltase accumulation, continued to maintain coincident immature patterns of high lactase activity and low cell turnover times. The intestine in continuity showed precocious appearance of active sucrase and accumulation along with maltase to greater than control levels, accompanied by a normal coincident decline in lactase activity and enterocyte life-span. Involvement of intraluminal influences on various parameters of enteric ontogenic development is thus indicated with the effects expressed by a delay in the excluded (bypassed) segment and by stimulation in the shortened segment in continuity. Data are presented in further support of the hypothesis that the life-span of the enterocyte serves postnatally as a primary determinant of enteric lactase levels.
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