LOW-DENSITY-LIPOPROTEIN CATABOLISM DOES NOT RESPOND TO ESTROGEN IN THE FETAL AND NEWBORN RAT

The elimination of native and methylated low-density lipoprotein (LDL) from serum and the effect of estradiol on the serum LDL-apoB pool, th e uptake of homologoUS [I-125]-LDL into liver and adrenals, and the fr actional catabolic rate (FCR) of[I-125]-LDL was studied in fetal (22nd day of gestation), newborn (15th day postpartum), and adult rats. In fetal rats the receptor-mediated LDL decay accounted only for 47%, whe reas in adults it was calculated to 65%. In the latter, estrogen cause d (1) a diminution of the serum LDL-apoB pool by 85%; (2) an enhanceme nt of the LDL uptake into the liver and the adrenals by 5- and 10-fold , respectively, and (3) an acceleration of the [I-125]-LDL decay in th e serum with a rise of the FCR by 3-fold. In contrast, neither the LDL pool and uptake nor the LDL elimination (FCR) did respond to estrogen in fetal and newborn rats. In summary, the LDL catabolism of the rat is insensitive towards estrogen in the late gestational period and dur ing the first 2 weeks of postnatal life [3].