SUMMARY

Subcutaneous injection of cortisol (10 \g=m\g/gbody wt daily for 5 days) into normal neonatal rats increased the activity ofstomach pepsinogen after day 5. l-Thyroxine (T4; 0\m=.\2\g=m\g/gbody wt daily for 5 days) alone did not affect the activity but it somewhat enhanced the effect of cortisol. Even before day 5, when no effect of cortisol alone was observed, T4 plus cortisol increased pepsinogen activity. In adrenalectomized, thyroidectomized neonatal rats, injection of cortisol alone did not induce enzyme activity but cortisol together with T4 did induce it. Moreover, the increase in pepsinogen activity was depressed in rats thyroidecto-mized on day 10 but not in those thyroidectomized on day 15. These results suggest that T4 does not have a direct effect on the stomach but plays an important role in making the stomach responsive to glucocorticoids, resulting in increased pepsinogen activity