DEVELOPMENT OF CYTOCHROME-P450 AROMATASE MESSENGER-RNA LEVELS AND ENZYME-ACTIVITY IN OVARIES OF NORMAL AND HYPOGONADAL (HPG) MICE

The cytochrome P450 aromatase (P450(arom)) enzyme is required for bioconversion of androgen to oestrogen. In this study ovarian P450(arom) mRNA and enzyme activity have been measured during development in normal mice and hypogonadal (hpg) mice which lack circulating gonadotrophins. A semi-quantitative reverse transcription-PCR (RT-PCR) technique was used to measure cytochrome P450(arom) mRNA levels and aromatase enzyme activity was measured directly. Using RT-PCR, P450(arom) mRNA was detectable in the adult mouse ovary and also in the uterus, kidney, brain and skeletal muscle but not in cardiac smooth muscle. In the normal mouse, P450(arom) mRNA was detectable in the ovary on the day of birth (day 1) and levels increased significantly up to day 15 with the most marked changes seen between days 1 and 5. Aromatase activity was also detectable at all ages in the ovary and increased significantly between days 1 and 7. In ovaries from hpg mice, normal levels of P450(arom) mRNA were present on day 1 but there P450 was no significant change in P450(arom) mRNA at later ages up to day 15. These results show that in the newborn mouse ovary, which contains only primordial follicles, there is a basal expression of P450 mRNA which is not gonadotrophin-dependent. After 1 day, however, gonadotrophins are required for normal expression of ovarian P450(arom) and this coincides with development of primary and secondary follicles.