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 tw o different chows: a normal rat chow containing 55.5% (w/w) starch (co ntrol group, N = 48) or a rat chow in which starch was partially repla ced by lactose, in such away that the experimental group (N = 48) rece ived 35.5% (w/w) starch and 20% (w/w) lactose. The gastric emptying of fluid was then studied by measuring the gastric retention of four tes t meals containing lactose (5% or 10%, w/v) or glucose + galactose (5% or 10%, w/v). Homogenates of the small intestine were assayed for lac tase activity. The gastric retention values were obtained 15 min after orogastric infusion of the liquid meals. The median values for gastri c retention of the 5% lactose solutions were 37.7% for the control gro up and 37.0% for the experimental group (P>0.02). For the 10% lactose solution the median values were 51.2% and 47.9% (P>0.02) for the contr ol and experimental groups, respectively. However, for the 2.5% glucos e + 2.5% galactose meal the median gastric retention was lower (P<0.02 ) in the group fed a lactose-enriched chow (38.5%) than in the control group (41.6%). For the 5% glucose + 5% galactose solution the median values were not statistically different between groups, 65.0% for the control group and 58.8% for the experimental group. The median values of the specific lactase activity in the small intestine homogenate was 0.74 U/g in the control group and 0.91 U/g in the experimental group. These values were not statistically different (P>0.05). These results suggest that the prolonged ingestion of lactose by young adult rats c hanges the gastric emptying of a solution containing 5% monosaccharide s. This adaptation may reflect the desensitization of intestinal nutri ent receptors, possibly by an osmotic effect of lactose present in the chow.