EXPRESSION OF 17-BETA-HYDROXYSTEROID DEHYDROGENASE IN THE RAT OVARY DURING FOLLICULAR DEVELOPMENT AND LUTEINIZATION INDUCED WITH PREGNANT MARE SERUM GONADOTROPIN AND HUMAN CHORIONIC-GONADOTROPIN

Antibodies against human placental 17 beta-hydroxysteroid dehydrogenas e (17-HSD) and 17-HSD cDNA were used to study the expression of the co rresponding enzyme in the immature rat ovary during follicular develop ment and luteinization,which were induced by treating the animals with pregnant mare serum gonadotrophin (PMSG) or with PMSG followed by hum an chorionic gonadotrophin (hCG). Immune-blot analysis indicated that the M(r) of the 17-HSD expressed in rat granulosa cells was 35 000, as previously shown for the human placental enzyme. In immunohistochemic al studies of untreated immature rat ovaries, only the granulosa cells from small antral follicles were stained. One day after PMSGtreatment , strong expression of 17-HSD was observed in the granulosa cells ofgr owing Graafian follicles. A marked decrease in enzyme expression was o bserved in preovulatory follicles on day 2 of PMSG treatment, starting from the basal layers of granulosa cells and progressing toward the l uminal cells. No 17-HSD expression was detected in luteinized follicle s or corpora lutea 22 h afterhCG injection. The stroma and theca cells were negative for 17-HSD staining. In Northern hybridization analyses , two 17-HSD mRNAs were detected (1.4 and 1.7 kb). The strongest expre ssion for both mRNAs was detected after 1 day of PMSG treatment, coinc iding with maximal immunostaining of the enzyme protein. Down-regulati on of 17-HSD observed by immunohistochemistry was reflected in a simil ar decrease in mRNA expression and the signals were almost undetectabl e 22 hafter hCG injection. Our data suggest that 17-HSD expression in rat granulosacells is up-regulated during follicular development and, thereafter, the enzyme expression is down-regulated during luteinizati on.