The ontogeny and site of intestinal lipid and lipoprotein synthesis

The developmental aspects of characteristic intestinal lipoprotein synthesis, chlomicrons (CM), very low density lipoproteins (VLDL) and high density lipoproteins (HDL), are unknown. Our objective was to determine the ontogeny of intestinal lipid and lipoprotein synthesis in both the jejunum and the ileum. Explants of the jejunum and the ileum from fetal (F) (18-19 days of gestation), suckling (S) (5 days old) and weaning (W) (23 days old) rats were cultured in the presence of [14C]-oleic acid to examine lipid synthesis. The results indicate the following. (1) The incorporation of oleic acid is higher for the fetal explants. However, the efficiency of esterification of free fatty acids (FFA) into triglycerides (TG) in the jejunum increases with age (33% F, 37% S, 48% W) (P less than 0.05, by ANOVA). (2) The same profile is found at the ideal site for the incorporation of oleic acid. However, the capacity for the synthesis of TG is more intense at the suckling period (34% F, 54% S, 42% W) (P less than 0.05, by ANOVA). (3) The relative content of TG in CM changes with age: F, 90-93%; S, 80-84%; W, 33-40%. (4) A low percentage of TG content is found in CM at the weaning period while high levels are detectable in VLDL (40-42%). (5) A most significant difference is noted between the jejunum and the ileum in TG synthesis at the suckling period. The ileum synthesizes 53% more TG than the jejunum (P less than 0.025). (6) HDL particles contain substantial amounts of FFA. Nevertheless, they were also found to be able to transport TG mainly in the suckling rat. Thus, this study demonstrates that with growth the rat is able to synthesize CM, VLDL and HDL. Our findings indicate changes in the synthesis of intestinal lipids and lipoproteins, depending on both the development and the site, which suggests an ontogeny. These modifications can be attributed to dietary and hormonal influences present during the period of development.