Induction of intestinal differentiation by systemic and not by luminal corticosterone in adrenalectomized rat pups

Potential effects of corticosterone (cort) from maternal milk on intestinal differentiation were studied using adrenalectomized (adx) rat pups fed a formula containing differing amounts of cort. Formula cort concentrations in the range found in milk (0.1-0.5 micrograms/ml) increased the survival of adx rats, but did not induce intestinal differentiation. Formulae containing 1.0-50.0 micrograms/ml cort caused a dose-dependent elevation of serum cort concentrations and jejunal maltase activity and precocious jejunal sucrase induction. Adx rats receiving the formula containing 10 micrograms/ml cort showed serum cort concentrations similar to those in day 15 control rats and jejunal sucrase and maltase activities equivalent to those in day 18-20 control rats, suggesting that the rise in serum cort that occurs during postnatal development suffices to modulate intestinal differentiation. To distinguish between direct local and systemic effects of luminal cort on intestinal differentiation, expression of sucrase was determined in jejunal isografts and in host jejunum from adx rats fed luminal cort. Jejunal isografts and host jejunum expressed similar sucrase activities and showed similar immunofluorescent staining. Moreover, administration of cort by continual ip infusion was more effective than continual intragastric infusion in inducing intestinal sucrase and maltase activities. These data imply that luminal cort is absorbed and transported into the systemic circulation before inducing intestinal epithelial cell differentiation through the systemic route.