Repeated noninvasive measurement of gastrointestinal transit in rats.

A technique for repeated and noninvasive measurement of oro-cecal transit time in rats and other small animals is described. It is based on the incomplete digestion of carbohydrates such as lactose fed orally to the animals. Since the activity of the enzyme lactase is low in almost all species, lactose is fermented by colonic bacteria after it arrived in the cecum, thus producing hydrogen. Hydrogen is delivered to the lungs via the circulation and exhaled by the animal. An increase in breath hydrogen measured by means of an electrochemical cell or a gas-chromatograph indicates the arrival of the nutrient bolus in the cecum. The method can be used repeatedly in individual animals under various experimental conditions such as investigations of stress effects on gastrointestinal transit.