Lipid metabolism in regressing rat corpora lutea of pregnancy.

Lipid accumulation is a hallmark of corpus luteum regression and we characterized lipids stored in rat corpora lutea of pregnancy between days 21 and 24 post coitum, the period of luteolysis. A 10-fold rise in lutein triglyceride concentrations occurred between days 21 and 24, which represented the major alteration in luteal lipid metabolism during luteolysis, coinciding with the appearance of numerous lipid droplets in the luteal cells. The fatty acid composition of luteal triglycerides was altered between days 20 and 23 in a pattern consistent with the influx of blood triglyceride fatty acids. No evidence for increased de novo fatty acid synthesis by luteal tissue between days 21 and 24 post coitum was obtained using in vitro methods. [14C]Acetate incorporation into lipids declined between days 16 and 24 and label was preferentially introduced into long chain polyunsaturated fatty acids. Rates of tritium incorporation into fatty acids from tritiated water were relatively low. [14C]Glucose was predominantly incorporated into the glycerol moiety of luteal lipids and incorporation of label into this fraction was augmented between days 21 and 23 post coitum. The incorporation of [14C]palmitate into triglycerides of luteal tissue during in vitro incubation also increased between days 21 and 23. In vitro lactate production, [14C]glucose oxidation, and [14C-palmitate oxidation to 14CO2 increased significantly during this time. We conclude that specific biochemical alterations occur in regressing corpora facilitating uptake and storage of blood glyceride fatty acids as triglycerides. The physiological significance of this triglyceride accumulation remains to be elucidated.