OBJECTIVE To study the intestinal absorption characteristics of insulin in the presence of absorption enhancers and to determine
the advantageous site of intestinal insulin absorption. METHODS The hypoglycemic effects of insulin after administration to the ileum, ascending colon, transverse colon, descending colon and the sigmoid colon were investigated using an
in situ loop method. Insulin solution was administered to the various loops of fasted rats with absorption enhancers such as sodium glycodeoxycholate, disodium ethylenediamine tetraace-tic acid (Na2EDTA), lysolecithin, sodium caprale and sodium salicylate respectively. RESULTS All absorption enhancers promoted the hypoglycemic effect of insulin at all sites. The promotion degree was in the order of 1 % Na2 EDTA > 1 % sodium salicylate > 1 % sodium caprate > 1 % sodium glycodeoxycholate > 1 % lysolecithin. The ileum was the major site of insulin absorption. The colon mucosa was more sensitive, to absorption enhancers than small intestinal mucosa. The most advantageous site of intestinal absorption of insulin with
absorption enhancer was observed in the colon. The absorption promoting effects of various enhancers in the ascending colon and the transverse colon were prior to those in the descending colon and sigmoid colon. CONCLUSION The insulin efficacy could be increased by absorption enhancers more significantly in the colon than in the small intestine.