Water absorption from the pig proximal colon: relations with feeding and flow of digesta

Net water absorption from the proximal colon was determined at 2 h intervals for 10 h after a meal in four pigs chronically fitted with two cannulas in the proximal colon (1st and 2nd coil) and a catheter in the ileum. Water flux was measured by infusing a marker (51Cr-EDTA) at a constant rate into the ileum and by sampling colonic content through the cannulas. Two hours after the meal water was absorbed by the colonic segment situated between the two cannulas at a rate of 0.7 +/- 0.1 ml/min. Then the net water absorption increased progressively and reached a maximum (1.7 +/- 0.3 ml/min) 8 h after eating. These postprandial changes in water absorption were positively correlated (r = 0.63, n = 40) with changes in the flow of digesta at the level of the proximal cannula. The concentration of volatile fatty acids and the osmolality of the digesta, as well as the transit time of a marker (phenolsulphonphthalein) between the two cannulas, did not significantly fluctuate after the meal and were not correlated with water absorption. Antibiotic treatment for 3 days (neomycin, 15 g/day, continuously infused into the ileum) induced a 90% decrease in volatile fatty acid concentration but did not modify colonic water absorption nor its postprandial changes. These results show a postprandial pattern of colonic water absorption which is mainly controlled by the flow of digesta into the colon.