The use of a Thiry-Vella loop of jejunum to study the intestinal absorption of calcium and inorganic phosphate in the conscious pig

1. Pigs, each surgically prepared with a Thiry-Vella jejunal loop were used to study the absorption of calcium and inorganic phosphate from the intestine.2. The loops were perfused daily for 6–8 h with a nutrient solution and absorption from the perfusate was measured.3. The technique employed minimized atrophy of the jejunal mucosa and enabled the measurement of hourly or daily changes in absorption rate of components of the luminal fluid.4. No differences were observed when polyethylene glycol (PEG; molecular weight 4000), [14C]PEG or 51Cr-EDTA were used as markers of net water movement.5. Increasing the concentration of Ca in the perfusate resulted in the demonstration of a two-component relationship between net absorption rate of Ca and intraluminal Ca concentration. An initial rapid absorption rate from 0 to 4 mm was found, then a slower rate from approximately 5 mm upwards which did not saturate at the highest concentration tested (25 mm).6. Increasing the concentration of phosphate in the perfusion solution increased the net absorption of phosphate from that solution. Although a two-component system, similar to that for Ca, was not evident, net absorption of phosphate was not saturated at the highest concentration tested (50 mm).7. The absorption of Ca was unaffected by the presence of phosphate in the solution but Ca (2.5 mm) enhanced the absorption of phosphate.