Differential effects of thyroxine and cortisone on jejunal sucrase expression in suckling rats

Effects of thyroxine (T4) and cortisone (C) on developmental expression of jejunal immunoreactive sucrase-isomaltase (S-I) and sucrase activity in suckling rats were studied to determine whether these hormones have distinctive actions. Immunoreactive S-I and sucrase activity were absent in infant rats and appeared simultaneously on days 16-18, when cells expressing S-I protein were detected at the villus base. By day 22, the entire jejunal mucosal surface was covered by new cells expressing immunoreactive S-I. Jejunal S-I content surged to adult levels on day 22, whereas the sucrase activity of immunoreactive S-I protein increased continuously until day 32. Administration of 12.5 nmol of T4 or 1.25 mumol of C on day 12 induced precocious expression of jejunal sucrase activity on day 15. T4 also induced sucrase activity in adrenalectomized rats without increasing serum corticosterone concentrations. Both T4 and C appeared to exert their effects in crypt cells, since immunoreactive S-I protein appeared only...