To demonstrate the expression of soluble guanylyl cyclase (sGC) alpha and beta subunits in rat granulosa cells and determine the effects sGC activation on levels of cyclic GMP (cGMP), E 2 , and cAMP. Basic research study. University research laboratory. Estrogen-treated immature Sprague-Dawley female rats from which primary cell culture of granulosa cells was obtained. Functionally immature rat granulosa cells were incubated for 48 hours with media alone, FSH, or FSH plus YC-1, a specific activator of sGC. Expression of sGC alpha and beta subunits was determined by immunoblot analysis. Media concentrations of E 2 , cAMP, and cGMP were measured by radioimmunoassays. Immunoblot analysis of granulosa cells revealed the expression of sGC alpha and beta subunits. While cGMP accumulation was low in cells incubated with media alone or with FSH, cotreatment with FSH plus YC-1 increased cGMP levels approximately five-fold. Incubation of cells with FSH stimulated E 2 production in a dose-dependent manner. However, cotreatment of cells with FSH plus YC-1 significantly decreased E 2 concentrations at all doses of FSH tested. Similarly, while FSH increased cAMP accumulation from granulosa cells, cotreatment with YC-1 markedly inhibited FSH-stimulated cAMP levels. These findings demonstrate the expression of sGC subunits in rat granulosa cells and indicate that activation of sGC increases cGMP levels, which are associated with inhibition of FSH-stimulated E 2 production and cAMP accumulation.