Interleukin-1 beta induces nitric oxide production by a mouse pituitary tumour cell line (AtT20/D16)

To elucidate whether anterior pituitary cells express the nitric oxide (NO) synthase gene, we studied the synthesis of NO and the expression of NO synthase (NOS) mRNA by a mouse pituitary tumour cell line (AtT20/D16). Interleukin-1 beta (IL-1 beta) stimulated production of NO2-/NO3-(NOx) in a time-dependent manner and both NOx and cyclic GMP formation were stimulated in a dose-dependent manner by IL-1 beta. IL-1 beta-induced NOx production and intracellular cyclic GMP formation were similarly blocked by an NO synthase inhibitor, NG-monomethyl-L-arginine (LNMMA), whose effect was reversed by L-arginine, but not by D-arginine. Dexamethasone inhibited IL-1 beta-induced NOx production in a dose-dependent manner. A calmodulin inhibitor (W-7) showed no effect on IL-1 beta-induced NOx production, whereas cycloheximide and the actinomycin D completely inhibited NOx production. Northern blot analysis using cDNA for mouse macrophage-inducible NOS as a probe revealed the expression of inducible NOS mRNA in the cells only after exposure to IL-1 beta. Although IL-1 beta stimulated ACTH release from tumour cells, LNMMA failed to affect ACTH release stimulated by IL-1 beta. These results demonstrate for the first time that a pituitary tumour cell line (AtT20/D16) possesses cytokine-inducible and Ca2+/calmodulin-independent NOS, although NO may not be involved in ACTH release.