Biosynthesis of Cholesterol XI. Biosynthesis of Cholesterol and Fatty Acids in Pregnant Rats. ∗

Summary

These investigations do not bear out the assumed similarity between the biosynthesis of cholesterol in pregnant rats with the same process in tumor bearing animals. During pregnancy there is apparently no appreciable impairment or other change in rate of biosynthesis in the mother liver although total amounts of cholesterol produced increase with the increase of weights of the livers during pregnancy and more considerably so during lactation, when milk production requires the synthesis of large amounts of fat. It is doubtful whether the early embryonal cell produces any cholesterol from acetate at all or accumulates it. However, at the end of pregnancy the liver of the fetus synthesizes this substance at least at a similar rate as the adult animal, in contrast to the observation that cells of the Yoshida ascites tumor do not make cholesterol from acetate. The degradation of cholesterol in the fetal liver at the day before birth seems to be much less than in the normal controls or the pregnant mothers, thus causing the apparently tremendous incorporation of C¹⁴ from acetate into fetal liver cholesterol. The experiment shows that only a very minute transfer of this substance from the mother through the placenta takes place. At the day before birth gastrointestinal tracts and carcasses of the fetuses accumulate much higher radioactivities than in the mothers. Synthesis of fatty acids increases during pregnancy in the mothers'tissues and reaches high levels during lactation. At the day before birth the tissues of the fetus show very high levels of radioactivity in the fatty acids.