Evolution of some biochemical characteristics of the intestinal mucosa during the first postnatal weeks in C57 mice. Effects of thyroxine and putrescine.

In C57 mice, during the third week after birth, there is a rapid conversion of the intestinal epithelium from fetal to mature adult status. Some characteristics (lactase, maltase, diamine oxidase, and sucrase activity; putrescine, spermine and spermidine concentrations; mitotic index) have been analyzed for the proximal, middle, and distal parts of the intestine in mice of different ages: 8, 15, 19, and 60 days. The most important observations recorded were as follows: (a) sucrase- and maltase-specific activities as well as spermine and spermidine contents increased abruptly on the 19th postnatal day and then decreased; (b) decrease of lactase and diamine oxidase-specific activity was recorded between the 15th and 19th postnatal days, (c) later, diamine oxidase-specific activity increased, whereas putrescine content decreased in the proximal part of the intestine; and (d) mitotic index was not significantly different when estimated for the crypts on days 11 and 19. No similar variations of these biochemical parameters were observed over a period of 3 days when mice were injected with thyroxine on the 8th day or when mice received putrescine per os on the 9th day, as explained in the text. Only a slight but significant variation in sucrase- or maltase-specific activity with thyroxine and a variation of the lactase or DAO-specific activity of the distal part of the intestine with putrescine were recorded.