IMMUNOLOCALIZATION OF STEROIDOGENIC ENZYMES P450SCC, 3-BETA-HSD, P450C17 AND P450AROM IN THE CORPUS-LUTEUM OF THE HOKKAIDO BROWN BEAR (URSUS-ARCTOS YESOENSIS) IN RELATION TO DELAYED IMPLANTATION

The objective was the immunocytochemical localization of steroidogenic enzymes in the corpus luteum of Hokkaido brown bears during the perio d of delayed implantation. Cholesterol side-chain cleavage cytochrome P450 (P450scc), 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), 17 a lpha-hydroxylase cytochrome P450 (P450c17) and aromatase cytochrome P4 50 (P450arom) were localized as biosynthetic sites of pregnenolone, pr ogesterone, androgens, and oestrogens, respectively. Ovaries containin g corpora lutea were obtained from three mature bears during the expec ted delayed implantation period and ovarian sections were immunostaine d by the avidin-biotin-peroxidase complex method using polyclonal anti bodies generated against steroidogenic enzymes of mammalian origin. P4 50scc and 3 beta HSD were localized in all luteal cells, whereas P450c 17 (0.4-5.1% of 1000 cells) and P450arom (7.1-11.2% of 1000 cells) wer e localized in only a few luteal cells. These data suggest that luteal cells contain steroidogenic enzymes required for progesterone synthes is but also have a minimum capability for synthesizing androgen and oe strogen during the delayed implantation period in Hokkaido brown bears .