Abstract
The activities of hydroxysteroid dehydrogenases (HSDs) were histochemically demonstrated in cultured porcine oocytes, 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. The activities of Δ5-3β-HSD, 17 β-HSD, 20α-HSD and 20β-HSD were observed in 91 to 97% of porcine oocytes soon after collection. The percentages of oocytes showing the activities of Δ5-3β-HSD (using DHA as the substrate), 17β-HSD (testosterone) and 20β-HSD (20β-hydroxyprogesterone) did not change during maturation culture, while those showing the activities of Δ5-3β-HSD (pregnenolone and 17α-hydroxypregnenolone), 17β-HSD (estradiol-17β), 20α-HSD (20α-hydroxyprogesterone) and 20β-HSD (17α-hydroxyprogesterone) decreased as the time of maturation culture was prolonged and reached 4, 0, 0, 2 and 0%, respectively, after 44 h culture. In the oocytes cultured for 22 h with olomoucine, nuclei were all in the germinal vesicle stage, and the activities of Δ5-3β-HSD (pregnenolone and 17α-hydroxypregnenolone), 17β-HSD (estradiol-17β), 20α-HSD (20α-hydroxyprogesterone) and 20β-HSD (17α-hydroxyprogesterone) were observed in 57, 64, 65, 61 and 66% of the treated oocytes, respectively. On the other hand, 10, 2, 10, 7 and 2% of control oocytes respectively showed such HSD activities, demonstrating a significantly lower percentage of oocytes showing the HSD activities, compared with the olomoucine-treated oocytes. From the present findings, it was suggested in porcine oocytes that the metabolic abilities of progesterone, 17α-hydroxyprogesterone, 20α-hydroxyprogesterone, 17α,20β-dihydroxyprogesterone and estradiol-17β in the cytoplasm are closely related to nuclear maturation, and the disappearance of their metabolic abilities could be used as a characteristic for the resumption of meiotic maturation.
