Active absorption of hypoxanthine by lamb jejunum in vitro.

The kinetics of [3H]hypoxanthine entry into lamb mid-jejunum were measured using 2-min mucosal exposures. Mucosal hypoxanthine uptake occurred by a Na+- and energy-dependent saturable mechanism indicating that a carrier-mediated active transport process is involved. Inhibitory measurements indicate that hypoxanthine, adenosine, uracil and thymine complete for a common entry mechanism. Adenine, uric acid, allantoin and thymidine produced no significant inhibition of hypoxanthine entry. In additional experiments hypoxanthine was transported against a high concentration gradient from the mucosal to the serosal side of everted sacs of mid-jejunum. Therefore hypoxanthine appears to be absorbed by active transport from the lamb jejunum.