Effects of atrial natriuretic peptide on rat ovarian granulosa cell steroidogenesis in vitro

The localization and biological effects of atrial natriuretic peptide (ANP) are not limited to cardiac tissue but extend to a number of extra-atrial tissues and organs, including the ovary. The objective of the present study was to determine the effects of ANP on granulosa cell steroidogenesis. Hence, the direct effects of ANP on the production of progesterone, 20 alpha-hydroxpregn-4-en-3-one (20 alpha-OH-P), and estrogen by undifferentiated and differentiated rat ovarian granulosa cells were examined in vitro.

Undifferentiated granulosa cells obtained from the ovaries of diethylstilbestrol-primed, immature rats were treated with increasing doses (10(-12) to 10(-6) M) of rANP for 48 h.

ANP evoked a two- and threefold increase in progesterone and 20 alpha-OH-P production relative to untreated controls, respectively. Increasing doses of ANP in combination with porcine FSH (125 ng/well) resulted in a biphasic response in progesterone production above FSH-treated controls. Specifically, a maximal inhibition of 35% in progesterone production was achieved at 10(-9) M ANP, followed by a stimulation to levels comparable with FSH-stimulated controls at higher doses examined. Increasing doses of ANP evoked a twofold increase in FSH-stimulated 20 alpha-OH-P production over respective controls. Following pretreatment of granulosa cells with FSH for 48 h to evoke differentiation, ANP caused a significant dose-dependent inhibition in basal progesterone production that resulted in a 76% suppression at the highest dose examined. In contrast, ANP evoked a 2.8-fold increase in 20 alpha-OH-P production when compared with controls. Finally, in FSH-stimulated differentiated granulosa cells, ANP evoked a threefold increase in progesterone production and a 65% inhibition in 20 alpha-OH-P production. ANP exerted no significant effects on estrogen production by either undifferentiated or differentiated granulosa cells in the presence or absence of FSH.

These data demonstrate that ANP can modulate directly progestin steroidogenesis in both undifferentiated and differentiated rat ovarian granulosa cells in vitro and, therefore, may play an important role in granulosa cell differentiation and follicular maturation.