Hyperglycaemia is responsible for the inhibited gastrointestinal transit in the early diabetic rat.

The effect of plasma glucose levels on the gastrointestinal motility of the rat was studied. Chronic hyperglycaemia was induced by i.v. injection of streptozotocin 1 week before the motility experiment. Some rats received additional daily insulin therapy (1.25, 2.5 or 10 IU kg-1) after induction of diabetes mellitus. Acute hyperglycaemia was induced by the continuous i.v. infusion of glucose solution (11, 22, 44 or 88 mg kg-1 min-1) 10 min before the motility experiments. The rats were killed 15 min after successful orogastric feeding of a charcoal-contained suspension. Gastrointestinal transit was calculated as the percentage of the overall length of the small intestine to which the charcoal moved during this time period. The diabetic rats were found to have delayed transit compared with controls (mean +/- SEM: 32.2 +/- 2.1% vs. 42.9 +/- 4.2%, P < 0.05). Correction of hyperglycaemia with moderate doses of insulin therapy failed to inhibit transit, whereas hypoglycaemia induced by high-dose insulin treatment enhanced transit. High doses of glucose elicited acute hyperglycaemia and delayed transit when compared with saline infused non-diabetic rats. In early diabetes, hyperglycaemia probably mediates the inhibited gastrointestinal transit, since correction of hyperglycaemia usually restores the delayed transit.