1. Intestinal absorption of sorbitol was studied in a duodeno-jejunal loop of anaesthetized rats. The acute effects of exogenous sorbitol on glucose homeostasis were also evaluated in male and female rats.2. In the presence of lumen concentrations of sorbitol ranging from lfiM to 2 0 0 m~, a fairly constant low percentage (about 12%) of the loop's contents was absorbed after 30 min. This amount increased only slightly with time, but this was not due to sorbitol accumulation in the mucosal layer of the loop.3. 3-O-methylglucose was absorbed much more quickly than sorbitol, but did not interfere with sorbitol absorption. The latter was not impaired by omission of lumen sodium ions nor by phloridzin, both of which inhibited 3-O-methylglucose absorption.
4.Gastric administration of sorbitol did not affect plasma glucose or insulin levels. Glucose or sucrose administration caused a similar rise in plasma glucose, but the increase in plasma insulin levels was larger after glucose than after sucrose administration.5. Intravenous administration of sorbitol slightly increased plasma glucose and insulin levels. These changes were, however, considerably smaller than those occurring after glucose administration.6. In the normal rat, intestinal absorption of sorbitol is passive and proceeds at a low rate. Acute oral administration of sorbitol does not affect glucose homeostasis, which is only slightly disturbed by a large intravenous load of sorbitol.Sorbitol was first proposed as an alternative sweetener more than 50 years ago (Thannhauser & Meyer, 1929). Two advantages over glucose and sucrose have been emphasized repeatedly to justify its wide use: (1) slow and only partial intestinal absorption, (2) rapid metabolism, largely independent of insulin (Forster, 1974;Mehnert et al. 1975;Brunzell, 1978).The opinion that sorbitol is only slowly absorbed rests on the studies carried out in rats and in man (Mehnert & Forster, 1961;Mehnert et al. 1975). However, these studies contradicted earlier measurements (Wick et al. 1951) and were not confirmed by very recent ones (Ertel et al. 1983), which suggested that a substantial proportion of sorbitol can be absorbed within 1 h of ingestion. Furthermore, all these experiments were performed with one single, high amount of intestinal sorbitol.In the present study, we therefore have re-evaluated the intestinal absorption of sorbitol in anaesthetized rats. The measurements were carried out in the presence of a wide range of lumen concentrations of sorbitol, at different sites of the intestine and under conditions permitting an insight into the mechanism of its absorption. To study the effects of exogenous sorbitol on glucose homeostasis, plasma glucose and insulin levels were measured after acute oral and intravenous administration of sorbitol. They were compared with the changes brought about by glucose or sucrose administration.