In vivo cholesterol synthesis by the rat digestive tract. II. A study of turnover.

In the main organs of the digestive tract of rats fed a semi-purified diet containing 0.5% cholesterol, cholesterol activity was measured 70 min and 8, 24 and 48 h after subcutaneous impulsion of 14C-acetate or intravenous injection of tritiated water. Cholesterol synthesized in the stomach and caecum-colon was not significantly renewed during the 48-hour experiment. On the contrary, cholesterol synthesized in situ in the intestine disappeared with a mean rate constant of 4% X h-1. The rate constant (K) varied (6% X h-1 in the duodenum and jejunum and about 3% X h-1 in the distal ileum) according to the site of the enterocytes in the small intestine. Cell sloughing could not account for the major part of the decrease in cholesterol radioactivity, particularly in the first three quarters of the small intestine. In the proximal half of the gut internal cholesterol secretion via lipoproteins poured into the lymph might play a role.