665 INTESTINAL REDIFFERENTIATION IN THE INFANT RAT: IN VIVO EVIDENCE OF AN INTRINSIC PROGRAM

Abstract

The enteric epithelium of the suckling rat undergoes dramatic functional and cytokinetic changes at the time of weaning. Evidence suggesting that this redifferentiation is preprogrammed and intrinsic has been obtained by surgical transplants of fetal intestines. In an attempt to alter this redifferentiation a 60% proximal intestinal resection was performed on suckling rats at 10 days of age. Animals surviving for 2 months were compared with sex and weight matched littermates who had undergone laparotomy or laparotomy with transection. The residual intestine was increased in diameter and weight per unit length, but not significantly lengthened. The segmental increase in weight was primarily accomplished by hyperplasia as evidenced by parallel increases in total protein and DNA content. This increase in cell number was associated with a modest increase in the segmental sucrase and maltase activities in the residual ileum. However, when expressed as activity per unit DNA, sucrase and maltase concentrations in the residual ileum were indistinguishable from control ileal segments. Lactase activity virtually disappeared from all segments of the residual intestine in resected animals. These results lend in vivo support to the concept of a fixed intrinsic program of enteric redifferentiation.