Endocrine Abstracts

Cytochrome P450_arom (aromatase), a marker of granulosa cell differentiation, and CTGF mRNA expression are inversely related in the developing rat follicle, but the cause/effect nature of the relationship is not known. Here, we used semi-quantitative in situ hybridization to analyze the expression of these genes during follicular development in the rat. The effect of CTGF on aromatase enzyme activity in isolated granulosa cells was determined by conversion of testosterone to oestradiol in vitro, and the effect of oestradiol on CTGF mRNA by Northern analysis of granulosa cell total RNA. CTGF mRNA increased gradually from low levels in small preantral (SP) follicles to maximum levels that were 5-foldhigher in large antral (LA) follicles. In preovulatory (PO) follicles, CTGF mRNA was 30% lower than in SP follicles. By contrast, aromatase was low in large preantral and SA follicles, increased only 3-fold in LA follicles, but increased 12-fold in PO follicles. CTGF mRNA intensity across the PO follicle wall showed a gradual increase from the basement membrane to the cumulus oophorus and from mural to antral granulosa cells, with an inverse relationship to aromatase. rhCTGF (1-100 ng/ml)had no effect on aromatase activity in vitro. Oestradiol (10^-7 to 10^-5M) alone caused a 2-fold dose-dependent increase in CTGF mRNA expression. In the presence of FSH (10 ng/ml), which alone reduced CTGF mRNA expression by 35%, oestradiol further reduced expression in a dose-dependent manner to 24% of control values. These results indicate that CTGF gene expression is under local control by oestrogen. Whether oestrogen has a positive or negative effect depends on the presence of FSH, explaining the parallel rise in CTGF and aromatase in the growing follicle and the inverse relationship between the expression of these genes in the PO follicle. Fibrogen, Inc, San Francisco provided the rhCTGF. Supported by MRC Programme Grant 0000066