Interleukin-6 decreases estrogen production and messenger ribonucleic acid expression encoding aromatase during in vitro cytodifferentiation of rat granulosa cell

To elucidate the influence of interleukin-6 (IL-6) on the maturation of rat granulosa cell (GC), we have established a differentiation model of rat GC in vitro and examined the expression of IL-6 and its receptors, and its possible actions during GC maturation. Bioactive IL-6 was detectable in the conditioned media of GC at similar to 2.5 ng/ml/24 h per 5 x 10(5) cells. Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that messenger RNAs encoding components of functional IL-6 receptor, namely both ligand-binding subunit (IL-6R) and gp130, were expressed in GC. Treatment of GC with IL-6 for 72 h during the process of in vitro GC maturation dose-dependently inhibited the accumulation of estradiol-17 beta (E-2) and the expression of cytochrome P450 aromatase (P450arom). IL-6 did not change nitric oxide (NO) production and inducible NO synthase expression, implying that IL-6-induced suppression on E-2 levels is dissociated with NO expression. Further, GC which had been incubated with neutralizing anti-IL-6 antibody showed a distinct increase in the levels of P450arom mRNA. These results suggest that IL-6 may attenuate E-2 production partially by inhibiting the expression of aromatase mRNA as an intraovarian regulator for suppressing GC maturation. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.