Inducible nitric oxide synthase in P11 cells -: Expression in the presence of interferon-γ, lipopolysaccharide, and modified serum

P11 cells, derived from the transplantable rat pituitary tumor 7315a, have been used previously as a model system to study the regulation of serotonin(2A) (5-HT2A) receptor expression. As our laboratory has been interested in characterizing the interactions between the 5-HT2A receptor and inducible nitric oxide synthase (iNOS), we have analyzed the P11 cell line for iNOS expression. Treatment of P11 cells with interferon-gamma and lipopolysaccharide resulted in a 23-fold increase in nitrite production and induced expression of iNOS protein. The increase in nitrite levels was attenuated by the non-selective nitric oxide synthase (NOS) inhibitor N-G-nitro-L-arginine methyl ester, but not the neuronal NOS inhibitor 7-nitroindazole. Typically, P11 cells have been grown in either charcoal-stripped or dialyzed serum-containing medium. We have observed that P11 cells grown under these culture conditions express basal iNOS activity, as evidenced by a 5-fold increase in nitrite accumulation over a 48-hr period, compared with that in cells grown in non-modified serum, which was inhibited by the selective iNOS inhibitor L-N-6-(1-iminoethyl)-lysine. Conditioned medium from P11 cells was able to stimulate nitrite accumulation in C6 glioma cells, suggesting that the P11 cells may produce a pro-inflammatory-like factor. As pro-inflammatory cytokines have been shown to modify hormone secretion from the anterior pituitary, the P11 cell line may be a useful in vitro model by which to characterize the function of cells from this organ. In addition, our data suggest that alteration of the microenvironment of the anterior pituitary may result in iNOS expression, possibly altering the function of the hypothalamic-pituitary-adrenal axis. (C) 2000 Elsevier Science Inc.