Induction of fetal rat enterokinase (enteropeptidase EC. 3.4.21.9) in utero by hydrocortisone and actinomycin D.

Enterokinase activity is first detected in the small intestine of the rat at the 20th day of gestation, whereas sucrase activity first appears in the 14th day of postnatal life. Intraperitoneal injection of hydrocortisone to pregnant rats before the normal appearance of enterokinase in fetuses causes the premature appearance of enterokinase (58 +/- 8 units), but not of sucrase activity. The addition of actinomycin D in the pregnant rat results in supermaximal stimulation of enterokinase activity (229 +/- 25 units). Sucrase activity is stimulated by hydrocortisone when given in the first 3 days of life (118 +/- 0.04 units). The maximal induction occurs 2 days before the normal appearance of the enzyme in untreated animals (7.3 +/- 12 units). The addition of actinomycin D diminished the effect of hydrocortisone on sucrase activity in the neonatal rat (1.4 +/- 2 units versus 1.8 +/- 0.4 units in 3-day-old rats). Thus, enterokinase and sucrase of the small intestine of the fetal and infant rat respond differently to combined hydrocortisone and actinomycin D. The response to hydrocortisone is age dependent and the maximal induction occurs before the time of the natural appearance of the enzymes. No effect is elicited after the normal appearance of enterokinase or sucrase. Glucocoticoids stimulate an early appearance of small intestinal enzymes only before the expected time of the natural development burst of activity. In both, sucrase and enterokinase, glucocorticoids have no effect after the enzymes are fully developed. New enzymes develop in clusters during the late fetal, neonatal, and late sucking periods. The effect of glucocorticoids on the "maturation" of the small intestine is limited to the induction of one phase only; i.e., only before the late fetal period is the precocious appearance of enterokinase possible. The induction of enterokinase activity can serve as an indicator for the early phase of maturation. Whereas the induction of sucrase activity can serve as a marker for late phase of maturation of the small intestine in the rat. The superinduction of enterokinase, but not of sucrase activity, by the addition of actinomycin D to glucocorticoids might be related to the different stability of the mRNA's of these enzymes.