Relative importance of corticosterone and thyroxine in the postnatal development of sucrase and maltase in rat small intestine.

Both corticosterone and T4 have been previously implicated as causal factors in the ontogenic increases in jejunal sucrase and maltase activities during the third week of life in the rat. Furthermore, it is known that the administration of exogenous T4 during the developmental period causes significant increases in serum corticosterone concentrations. To determine whether the effects of T4 on sucrase and maltase are secondary to the corticosterone rise, we examined the effect of T4 administration in adrenalectomized (adX) pups. Serum corticosterone was measured in all operated animals. Some of the adX pups had substantial concentrations of circulating corticosterone. In adX pups with serum corticosterone levels below 0.1 microgram/dl, there was no effect of T4 on either maltase or sucrase activity. We also studied the effect of propylthiouracil-induced hypothyroidism on sucrase and maltase. At 21 days of age, both enzyme activities were significantly reduced in hypothyroid pups. Injections of either T4 or cortisone acetate were equally effective in restoring activities to normal. For sucrase, there was no further increase in activity when both hormones were administered. For maltase, the combined treatment gave activities that were significantly higher than those with either hormone alone. We conclude that for both sucrase and maltase, the effects of changes in thyroid status are primarily due to the accompanying changes in serum corticosterone. The normal rate of development of both enzymes appears to be principally under glucocorticoid control, although for maltase, T4 may have a facilitory action.