Stimulation of nitric oxide-cyclic guanosine monophosphate pathway in bovine ovarian theca cells by tumor necrosis factor α (TNFα). Is this pathway implicated in the TNFα-induced inhibition of luteinizing hormone- stimulated prorenin production?

Abstract

Gonadal function is known to be controlled by many factors, including locally acting cytokines like tumor necrosis factor (TNEα). One of the ways this cytokine acts is via the nitric oxide (NO)-cGMP pathway. Since we have shown that in the ovary theca cells are a target of TNFα's action, it was of interest to determine whether TNFα stimulates the NO-cGMP pathway in these cells and whether such a mechanism can be implicated in the observed TNFα- mediated inhibition of LH-stimulated prorenin synthesis and secretion. Treatment of isolated theca cells with TNFα resulted in a dose- and time- dependent increase in cGMP production. This increase was not detectable until 6 h after the addition of TNFα and was totally abolished by the protein synthesis inhibitor cycloheximide. Addition of either t-N(G)-nitroarginine methyl ester (L-NAME), an inhibitor of all three NO synthase (NOS) isoforms, or 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a specific inhibitor of the inducible isoform of the enzyme, likewise reversed the action of TNFα on cGMP formation. Finally, addition of 1H-[1,2,4]oxadiazolo [4,3-a] quinoxalin 1-one (ODQ), an inhibitor of NO-sensitive soluble guanylate cyclase, resulted in a concentration-dependent reduction of TNFα-stimulated cGMP formation. In contrast, the TNFα-mediated inhibition of LH-stimulated prorenin secretion was not affected by either L-NAME, AMT, or ODQ. Also the addition of stimulators of soluble guanylate cyclase, sodium nitroprusside, and S-nitroso-N-acetylpenicillamine, or 8 bromo-cGMP had no effect on the action of LH on theca cells. We conclude that although TNFα is able to stimulate cGMP formation in theca cells by inducing the expression of inducible NOS, the mechanism underlying the TNFα-mediated inhibition of LH- stimulated prorenin production is independent of its ability to induce cGMP formation.