BIOCHEMICAL CHANGES IN THE CORPORA LUTEA OF PREGNANT AND LACTATING HAMSTERS

Abstract

SUMMARY Progesterone was secreted by hamster corpora lutea between days 1 and 15 of pregnancy; on day 14, the concentration in the peripheral plasma reached a maximum. A pronounced fall in luteal weight began on the day after parturition and the corpora lutea had virtually disappeared by days 4–5 post partum. The concentration of protein and the weights of the corpora lutea reached peak levels on days 12 and 14 respectively. The highest levels of luteal RNA were reached on days 12–13. The concentration of DNA in the corpora lutea was constant throughout pregnancy, indicating that hypertrophy rather than hyperplasia accounted for the increase in luteal weight. Luteal concentrations of cholesterol and its esters were unchanged between days 1 and 14 of pregnancy except for a significant decline in the level of cholesteryl ester on days 8 and 13. During the final stages of regression of the corpora lutea during lactation, the luteal concentrations of free and esterified cholesterol rose to three and ten times respectively, the values obtained on day 2 of pregnancy. A significant increase in the concentration of acid and alkaline phosphatase began on day 16 of pregnancy correlated with the onset of structural luteolysis. The activity of luteal glucose-6-phosphate dehydrogenase peaked on days 2 (comparable to the value on day 2 of the oestrous cycle) and 13 of pregnancy and day 3 of lactation. The high levels on these days may be associated either with luteal steroidogenesis during pregnancy or with lipid metabolism during the post-partum involutional phase. The activity of luteal 3β-hydroxysteroid dehydrogenase was relatively constant except for significant decreases on days 10 and 13 of pregnancy. The results indicate that the activities of all of the biochemical variables in the corpora lutea of pregnancy were highest between days 11 and 13.