Quantitative studies on the fetal lipid metabolism in rats: liver fatty acid esterification and conversion into carbon dioxide, and hepatic output of triglycerides and phospholipids into serum.

Fetal lipid metabolism was studied quantitatively using the 14C-1-palmitate in vivo tracer technique and compartment analysis, and in vitro incorporation experiments. The following conclusions can be drawn from our experiments. Fetal serum free fatty acids (FFA) exchange so rapidly with the FFA of another compartment that the FFA of both compartments can be considered as one homogeneous FFA compartment. The turnover time of this compartment was calculated to be 0.76 mumol FFA/min/l through this compartment. The incorporation of fetal serum FFAs into fetal liver triglyceride fatty acids (TG-FA) and phospholipid fatty acids (PL-FA) was calculated to be 0.05 and 0.14 mumol FFA/min/l, respectively. Thus, only 16% of the fetal serum FFA is incorporated into fetal liver lipids. The fetal serum TG-FA most likely originate in the fetal liver. The fetal liver puts out 0.025 mumol TG-FA/min/l and 0.10 mumol PL-FA/min/l into the fetal serum. The turnover times of fetal serum TG-FA and PL-FA are 100 and 39 min, respectively. The fetal liver conversion rate of fatty acids (FA) into CO2 determined in vitro (0.06 mumol FA/min/l) amounts to about 25% of the rate seen in the whole rat fetus.