Chronic lactose intake modifies the gastric emptying of monosaccharides but not of disaccharides in weanling rats

Ninety-six weanling male Wistar rats were fed for four weeks one of two different chows: a normal rat chow containing 55.5 percent (w/w) starch (control group, N = 48) or a rat chow in which starch was partially replacced by lactose, in such a way that the experimental group (N = 48) received 35.3 per cent (w/w) starch and 20 percent (w/w) lactose. The gastric emptying of fluid was then studied by measuring the gastric retention of four test meals containing lactose (5 percent or 10 percent, w/v) or glucose + galactose (5 percent or 10 percent, w/v). Homogenates of the small intestine were assayed for lactase activity. The gastric retention values were obtained 15 min after orogastric infusion of the liquid meals. The median values for gastric retention of the 5 percent lactose solutions were 37.7 percent for the control group and 37.0 percent for the experimental group (P>0.02) For the 10 percent lactose solution the median values were 51.2 percent and 47.9 percent (P>0.02) for the control and experimental groups, respectively. However, for the 2.5 percent glucose + 2.5 percent galactose meal the median gastric retention was lower (P0.05). These results suggest that the prolonged ingestion of lactose by young adult rats changes the gastric emptying of a solution containing 5 percent monosaccharides. This adaptation may reflect the desensitization of intestinal nutrient receptors, possibly by an osmotic effect of lactose present in the chow. (AU)