Dietary sucrose-mediated changes in jejunal sucrase activity of rats.

Abstract

The sites of stimulation of dietary sucrose-mediated changes in jejunal sucrase activity was investigated in rats refed on 5 g of a high sucrose diet following a 2-day fast. Actinomycin D was injected into rats 7.5 hr prior to, just before or 15 hr after the beginning of refeeding. Regardless of actinomycin D injection and respective periods, jejunal sucrase specific activity (sucrase activity per mg of mucosa protein) of rats 24 hr after the beginning of refeeding was significantly increased, but the significant increase in the segmental sucrase activity, sucrase activity per 15 cm segment, was remarkably inhibited by actinomycin D injection 7.5 hr prior to and just before refeeding. There was no difference in time-course changes in the sucrase specific activity after the beginning of refeeding between rats receiving actinomycin D injection 7.5 hr prior to refeeding and treated with saline injection in the same period. However, the significant rise of the segmental sucrase activity between 15 and 24 hr after the beginning of refeeding was remarkably inhibited by the actinomycin D injection. Hydroxyurea (a karyorrhexis agent) injection just before the beginning of refeeding affected neither the increase in jejunal sucrase specific activity nor that in the segmental sucrase activity, but the hydroxyurea injection 3 hr prior to refeeding caused a significant reduction of increases in the sucrase specific activity and the segmental sucrase activity. The significant increase in segmental sucrase activity 24 hr after the beginning of refeeding was not affected by a massive addition of surface-active agents into the refed diet and drinking water during the initial period of refeeding. These experimental results lent strong support to the idea that the stimulation of the response of jejunal sucrase activity to dietary sucrose in rats was produced in the crypt cell during the initial period of refeeding.