GASTRO-INTESTINAL SITES OF FUROSEMIDE ABSORPTION IN RATS

The rate of absorption of [35S]furosemide from the lumen of the gastrointestinal tract of rats, in situ, was studied by following the disappearance of radioactivity from the lumen and its appearance in plasma, urine, and bile. Absorption appeared to be most rapid and efficient in the stomach at pH 3.5 and least rapid and efficient in the jejunum at pH 5.4. To confirm these preliminary results, a fluorimetric assay was utilized to study furosemide disappearance from various segments of the rat gastrointestinal tract, in situ, at various pHs. The most rapid absorption was found to occur from the stomach at pH 3.0 (t 1 2 = 2.5 ± 0.3 h). Absorption was slower from the duodenum at pH 5.0 (t 1 2 = 3.1 ± 0.4 h); even slower from the duodenum + 30 cm of jejunum at pH 5.0 (t 1 2 = 11.7 ± 2.2 h). In intact rats the absorption process following gastric gavage in fasted animals was found to be biexponential, and the results were consistent with an absorption model in which rapid absorption occurs from the stomach and slower absorption occurs from the small intestine. Preliminary experiments in non-fasted intact rats suggested that oral absorption of furosemida with food in the stomach was slower but more complete than in the absence of food. © 1979.