Influence of bloodflow on the absorption of theophylline from the jejunum of the rat.

The influence of the jejunal bloodflow on the absorption of theophylline was investigated. The bloodflow through a segment under investigation was varied by changing the systemic blood pressure by means of a donor blood infusion into the jugular vein or by an infusion of isoprenaline or levarterenol into a femoral vein, and was measured by collecting the venous outflow from the intestinal segment. Above a bloodflow of approximately 0.40 µl/min/cm the flux/ flow ratio is reduced, and it is proposed that above this flow the intestinal epithelium provides the rate limiting step in the absorption of theophylline. When the bloodflow was held low for a prolonged time, the flux of theophylline decreased. The absorptive site bloodflow was calculated to be 18 % of the total bloodflow through the segment under investigation.