Changes of steroid metabolism in mouse oocytes during meiotic maturation

"The activities of hydroxysteroid dehydrogenases (HSDs) were histochemically demonstrated in mouse oocytes in the process of maturation in vivo and in vitro, and the changes in steroid metabolism during meiotic maturation were examined. In mouse oocytes soon after collection, the activities of D**5-3beta-HSD, 17beta-HSD and 20alpha-HSD were observed in 87 to 97% of those, while the activity of 20alpha-HSD was not. The percentages of oocytes showing the activities of D5-3beta-HSD (using DHA, pregnenolone and 17alpha-hydroxypregnenolone as the substrates), 17beta-HSD (estradiol-17beta and testosterone) and 20beta-HSD (17alpha-hydroxyprogesterone and 20beta-hydroxyprogesterone) did not change during maturation in vivo and in vitro. The oocytes with the activity of 20alpha-HSD (20alpha-hydroxyprogesterone) appeared 4 hrs after the hCG injection or after culturing for 4 hrs and the rates of those reached 92 and 100%, respectively, 14 hrs after the hCG injection or after culturing for 14 hrs. In the oocytes cultured for 8 hrs with olomoucine, an inhibitor of cyclin-dependent kinase, nuclei were almost in the germinal vesicle stage, and the activity of 20alpha-HSD (20alpha-hydroxyprogesterone) was observed in 84% of the treated oocytes. On the other hand, 81% of control oocytes also showed such the HSD activity, showing no difference from the rate of the treated oocytes. From the present findings, it was suggested that the metabolic abilities of progesterone, 17alpha-hydroxyprogesterone, 17alpha, 20beta-dihydroxyprogesterone, 20beta-hydroxyprogesterone, estradiol-17beta and androgen are constantly present in mouse oocytes in the process of maturation in vivo and in vitro. And it was also suggested that the metabolic ability of 20alpha-hydroxyprogesterone in mouse oocytes varies with maturation, while the change in the metabolic ability of such steroid is not related to nuclear maturation."