Biochemical changes in the corpus luteum of the cyclic hamster

The corpora lutea (CL) of the hamster secrete progesterone on days 1 and 2 of the oestrous cycle before marked regression at pro-oestrus (day 4) virtually eliminates them from the ovary. Luteal protein and RNA reached their maximum values on day 2 and declined up to day 4. DNA was constant throughout the cycle substantiating the importance of cellular hypertrophy rather than hyperplasia in the growth of the CL. Concentrations of cholesterol and its esters were unchanged between days 1 and 3 but almost doubled in concentration on day 4. Glucose-6-phosphate dehydrogenase activity was maximal on days 2 and 4, apparently associated on these days with steroidogenesis and lipid metabolism, respectively. A significant increase in acid phosphatase activity occurred on day 3 reaching maximal values on day 4, probably accounting for the rapid regression of the CL. The maximal concentration of 3beta-hydroxysteroid dehydrogenase in CL was on day 1, with a gradual decline over the next 3 days.