GLUCOSE UPTAKE AND IRON ABSORPTION BY AN ISOLATED, VASCULARLY AND LUMINALLY PERFUSED PREPARATION OF RAT SMALL INTESTINE

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Abstract
Some characteristics of an isolated vascularly and luminally perfused rat intestinal preparation are described. Over 60 to 90 min perfusion, the vascular perfusion medium (VPM) ‘arterial’ pressure remained stable and between animals it varied between 22 and 47 mmHg while the VPM flow rate remained constant at 1·3 ml/min. Hypersecretion, as monitored by changes in the concentration of phenol red in the luminal perfusion medium (LPM), did not generally occur. Histological examination of the tissue post‐perfusion showed that normal morphology was retained for at least 1 h. Total glucose uptake ranged between 85 and 155, µmol/(g dry wt.h) with greater uptake from the VPM than the LPM. Approximately 50% of the glucose taken up by the intestine appeared as lactate in the perfusion media, most of which was released to the VPM. The addition of phloridzin (5 x 10−4 M) to the LPM significantly reduced the uptake of glucose from the LPM and its transfer to the VPM. Iron absorption was studied by adding FeCl2 (with 59Fe and ascorbate, 100 µg/ml) to the LPM to give a final concentration of 10‐100 µg iron/ml. The appearance of iron in the VPM was investigated over a period of 1 h. At the two lowest concentrations (10 and 25 µg/ml) there was a lag of 20‐40 min before iron appeared in the VPM. At the higher doses (50 and 100 µg/ml) the lag was 10 min. During the final 20 min the appearance of iron in the VPM plateaued to dose‐dependent constant rates. The ratio of the specific radioactivity of 59Fe in the two perfusates (LPM:VPM) was unity when the initial iron concentration was 25 µg/ml or above. At the lowest dose (10 µg/ml) this ratio was 2·5 indicating that during transfer, iron taken up from the LPM had mixed with a small labile endogenous iron pool. Both amounts of iron retained by the intestinal tissue and transferred to the VPM increased exponentially with increasing luminal iron dose. The amount of iron retained by the tissue was always greater than that transferred to the VPM.