Abstract
This study aimed to ascertain whether the dietary fat-dependent modification of the distribution of intestinal HMG-CoA reductase activity in rats is related to differences in the site of absorption of dietary fat. Either [3H]triolein or [3H]tripalmitin and [14C]β-sitosterol were used as an absorbable and a non-absorbable marker and the absorption site was estimated by comparing the [3H]/[14C] ratio in the lumen of the gastrointestinal tract with that of the diet. The small intestine was divided into four segments of equal length. When triolein was used, the marker ratio ([3H]/[14C]) was essentially comparable up to the jejunum, and reduced significantly in the upper ileum where mucosal radioactivity was also fairly high. When [3H]tripalmitin was used, the luminal marker ratio was slightly increased as the digest moved down to the ileum. A distinct decrease of the ratio was also observed in the upper ileum but to a lesser extent than in the case of triolein. Incorporation of radioactivity into the mucosa was most substantial in the upper ileum. Although the digestibility differed somewhat, both triolein and tripalmitin were considered to be absorbed mainly in the ileum. Hence the distribution of HMG-CoA reductase activity along the small intestine was not always consistent with the localization of the site of fat absorption. This study did not indicate the stimulatory effect of dietary fat on intestinal cholesterogenesis and the production of chylomicrons to process the absorbed fat.
