Abstract
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 and also the relationship between nuclear maturation and changes in steroid metabolism in the cytoplasm were examined. In mouse oocytes 0 h after human chorionic gonadotrophin (hCG) injection, the activities of Δ5-3β-HSD (with DHA, pregnenolone and 17α-hydroxypregnenolone as the substrates), 17β-HSD (estradiol-17β and testosterone) and 20β-HSD (17α-hydroxyprogesterone and 20β-hydroxyprogesterone) were observed in 87 to 97% of those, but that of 20α-HSD (20α-hydroxyprogesterone) was not. The percentages of oocytes showing the activities of Δ5-3β-HSD, 17β-HSD and 20β-HSD did not change during maturation in vivo or in vitro. Oocytes with 20α-HSD activity appeared 4 h after the hCG injection or after culture for 4 h and the rates of those reached 92 and 100%, respectively, 14 h after the hCG injection or after culture for 14 h. In oocytes cultured for 8 h with olomoucine or 3-isobutyl-1-methylxanthine, nuclei were almost all in the germinal vesicle stage, and activity of 20α-HSD was observed in 84 and 89% of the treated oocytes, respectively. On the other hand, 81% of control oocytes showed 20α-HSD activity, with no significant difference from the rate for the olomoucine- or 3-isobutyl-1-methylxanthine-treated oocytes. The present findings suggested that the metabolic abilities of progesterone, 17α-hydroxyprogesterone, 17α,20β-dihydroxyprogesterone, 20β-hydroxyprogesterone, androgen and estradiol-17β in the cytoplasm are constantly present in mouse oocytes in the process of maturation in vivo and in vitro. The results also suggested that the metabolic ability of 20α-hydroxyprogesterone in mouse oocytes increases during maturation, but the change in the metabolic ability of such a steroid is not related to nuclear maturation.
