Biosynthesis of phosphatidic acid by liver and lung of maternal and fetal rabbits

Labelled lipids distribution following [3H]glycerol injection to pregnant rabbits

1. The time dependent variation in specific activity of serum triglycerides and phospholipids has been studied following an intravenous pulse-labelling with 2-[3H]glycerol to pregnant rabbits. 2. The specific activity of triglycerides varied according to the gestation time and the maximal values of specific activity shifted to shorter times when gestation progressed to term. 3. The specific activity of serum phospholipids was higher in pregnant animals and increased with gestation time. 4. Concentrations and specific activities of both triglycerides and phospholipids were investigated in serum of pregnant and fetal rabbits at term. Concentrations of both lipid classes were notably higher in the fetal blood than in the maternal one. 5. The results were discussed on the basis of changes in hepatic biosynthesis of phosphatidic acid. Also, it was suggested a high drainage of either lipids or their degradation products by the feto-placental unit at the end of pregnancy. 6. Levels and specific activities of maternal and fetal lipids from liver and lung were also examined. The different metabolic roles of the main tissues involved in triglyceride and phospholipid metabolism were discussed.

Postnatal development of some membrane-bound enzymes of rat liver and kidney

1. The development of rat liver acyl-CoA:sn-glycerol-3-phosphate-O-acyl-transferase (EC 2.3.1.15) is characterized by an increase and decrease in activity during the neonatal period, followed by a second increase and decrease during the late weaning period. Kidney acyltransferase exhibits a similar peak in activity during the neonatal period before increasing to adult levels of activity during the late weaning period. 2. Nucleosidediphosphatase activity increases rapidly during the neonatal period and thereafter gradually rises to adult levels in both liver and kidney. The latency of the enzyme increases rapidly after birth and thereafter shows little change with age. The enzyme appears to be more latent in the liver than in the kidney at all ages studied. 3. NADPH-cytochrome c reductase of liver has a single steep maximum and minimum in activity during the neonatal period, before increasing again to adult levels during the late weaning period. The enzyme in kidney shows a similar developmental pattern but at much lower levels of specific activity. 4. sn-Glycerol-3-phosphate acyltransferase activity was significantly higher in rough than in smooth membranes throughout the neonatal period of rapid smooth membrane proliferation. This distribution of enzyme activity is unlike that reported by others in phenobarbital-induced smooth membrane proliferation and suggests a major role for rough membranes in phospholipid synthesis during the neonatal period. 5. The qualitative similarity in development in rough and smooth microsomal subfractions for each of these enzymes is in distinct contrast with results previously reported for glucose-6-phosphatase.