RESUMO
Nitric oxide (NO) synthase (NOS) expression was analyzed in rat adrenal zona fasciculata. Both neuronal NOS and endothelial NOS mRNAs were detected by RT-PCR, immunohistochemistry, and immunoblot analysis. The biochemical characterization of adrenal zona fasciculata NOS enzymatic activity confirmed the presence of a constitutive isoform. In a cell line derived from mouse adrenal cortex, only endothelial NOS expression was detected by both RT-PCR and immunoblot analysis. Nitrate plus nitrite levels in Y1 cell incubation medium were increased in the presence of L-arginine and the calcium ionophore A23187, but not D-arginine, indicating enzymatic activity. Moreover, a low, but significant, conversion of Larginine to L-citrulline, abolished by the NOS inhibitor, N(G)-nitro-L-arginine, was detected in Y1 cells. The effect of L-arginine on pregnenolone production was examined. L-Arginine decreased both basal and ACTH-stimulated pregnenolone production in Y1 cells. The inhibitory effect of L-arginine could be attributed to endogenously generated NO, because it was blocked by N(G)-nitro-L-arginine, and it was mimicked by the addition of a NO donor, diethylenetriamine-NO. An inhibitory effect of NO on pregnenolone production from 22Rhydroxycholesterol and on steroidogenic acute regulatory protein expression was also determined. Taken together, these results suggest that at least part of the adrenal NO could derive from steroidogenic cells and modulate their function.