Effects of follicle stimulating hormone on estradiol-17β production and P-450 aromatase (CYP19) activity and mRNA expression in brown trout vitellogenic ovarian follicles in vitro

Abstract

In order to determine whether follicle stimulating hormone (FSH) regulates P-450 aromatase (P-450 arom) in salmonid fish, we investigated the in vitro effects of FSH on estradiol (E2) production and P-450 arom activity and expression in brown trout (Salmo trutta) vitellogenic ovarian follicles. Brown trout ovarian follicles were incubated in the presence of coho salmon FSH and the production of E2 into the medium was measured by RIA, the activity of P-450 arom by the tritiated water release assay and the expression of P-450 arom by Northern blotting using a homologous cDNA probe obtained by RT-PCR. Results from this study indicate that the dose- and time-dependent stimulatory effects of FSH on E2 production are dependent on new RNA and protein synthesis. The basal and FSH-stimulated E2 production was completely blocked by fadrozole, a specific aromatase inhibitor. FSH was capable of stimulating P-450 arom activity but this stimulation was only detectable with short incubation times (30 min) since longer incubation times with FSH resulted in the inhibition of P-450 arom activity. In addition, FSH increased the steady-state P-450 arom mRNA levels. In conclusion, our results indicate, for the first time in teleost fish, that FSH stimulates the expression of P-450 arom, as well as its activity, albeit after a short-term treatment with FSH, and that FSH plays a fundamental role in the regulation of the production of E2 in the salmonid ovary