Cholesterol synthesis and accretion within various tissues of the fetal and neonatal rat

The rate of cholesterol synthesis is reported to be higher in fetal relative to adult rats. Along with the observation that maternal diets high in fat and cholesterol are unable to alter the rate of cholesterol synthesis in the fetus, this has been taken as indirect evidence that the fetal rat meets its cholesterol needs through de novo synthesis. This study quantified the rates of cholesterol synthesis and accumulation in the liver, brain, intestine, and carcass of the fetal and neonatal rat and the placenta to determine whether these developing tissues are able to support their own cholesterol needs without the uptake of plasma lipoprotein cholesterol. The rate of cholesterol synthesis was determined in vivo using [3H]water. The rate of cholesterol accumulation was determined by calculating the difference in tissue cholesterol content between 2 subsequent days of development. Total fetal body cholesterol synthesis was sufficient to support the rate of cholesterol accumulation. Fetal and neonatal liver synthesized cholesterol at a rate in excess of cholesterol accumulation, suggesting hepatic secretion of cholesterol into the plasma. Before the onset of suckling, the rates of de novo cholesterol synthesis in the intestine, brain, and carcass were also sufficient but not higher than the need for cholesterol accretion. After the establishment of suckling, the rate of cholesterol accumulation in the intestine and carcass was in excess of synthesis, suggesting that neonatal tissues derive some of their cholesterol from dietary milk or liver. These studies suggest that the perinatal rat does not require exogenous cholesterol to support tissue cholesterol accretion. However, the fetal liver may support cholesterol accretion in other tissues through rates of synthesis in excess of accumulation and secretion into plasma. The placenta may derive some cholesterol from the maternal and/or fetal plasma.