| Popis: |
Sucrose feeding is known to increase the activity of sucrase-isomaltase, the hydrolytic enzyme responsible for surface membrane hydrolysis of this disaccharide. However, the precise mechanism by which this increase occurs remains unknown. Rats that had been maintained on carbohydrate-free pelleted diet were divided into two groups, one of which was fed a diet containing 68% sucrose. The control group continued to consume a carbohydrate-free diet of the same total caloric content. Maximal increase in sucrase activity occurred only 12 h after initiation of the sucrose diet (98 ± 7 mU/mg protein vs. 38 ± 5 for the carbohydrate-free controls). Maximal activity patterns for isomaltase paralleled those for sucrase. The time-course of the rise in sucrase activity was further studied by force feeding rats sucrose; a significant increase in sucrase activity (p 3 H]leucine precursor was administered intraperitoneally, incorporation into brush border sucrase, recovered by specific immunoprecipitation, was two times greater for sucrose-fed than for control rats. Thus, the main mechanism of the early sucrose effect appears to be stimulation of de novo synthesis. Separation of villus and crypt cells 12 h after the beginning of sucrose feeding revealed a parallel increase of sucrase activity along the villus-crypt axis, indicating that the sucrosemediated increase in sucrase activity, rather than acting preferentially on crypts, occurs over the entire villus-crypt unit. |
