Relative secretion of cholesterol-4-¹⁴C in the bile and upper and lower small intestinal washings of the bile fistula rabbit

The secretion of circulating labeled cholesterol by a total biliary fistula, by the isolated upper half of the small intestine, and by the isolated lower half of the small intestine was measured in 21 anesthetized rabbits over an average time of 13 hours. From the secreted radioactivity, ratios were calculated and the three key average radioactivity excretion ratios were: bile counts per minute (cpm)/combined total number of counts per minute (bile counts per minute + upper small intestinal counts per minute + lower small intestinal counts per minute), 0.5470; bile counts per minute/total number of small intestinal counts per minute, 1.4948; and jejunal-ileal counts per minute/distal ileal counts per minute, 1.6031. The measured average jejunal-ileal/ distal ileal length ratio was 1.338. It is concluded that in the rabbit under the acute conditions of this experiment: (1) the cholesterol that is secreted in the bile is 1 1 2 times the amount secreted by the small intestinal mucosa. (2) Small bowel mucosal cholesterol secretion, on the basis of comparison of the jejunal-ileal/distal ileal counts per minute and length ratios, does not appear to be localized to either the upper or the lower half of the small intestine. (3) Bowel mucosal cholesterol secretion is independent of the presence of bile salts in the intestinal lumen.