Adenosine 3',5'-Monophosphate, Luteinizing Hormone Receptor, and Progesterone during Granulosa Cell Differentiation: Effects of Estradiol and Follicle- Stimulating Hormone*

Abstract

The present studies were designed to relate granulosa cell differentiation to changes in gonadotropin stimulation of cAMP accumulation in vivo and in vitro. Accordingly, immature hypophysectomized female rats treated with vehicle, estradiol, or estradiol followed by FSH were injected iv with either hFSH (0.25–100 μg) or hCG (0.31–5 IU). In addition, granulosa cells were isolated first and then incubated with increasing concentrations of hFSH (0.002–2 μg/300 μl) or hCG (0.005–5 IU/300 μl). Estradiol priming of hypophysectomized rats enhanced FSH-dependent cAMP accumulation in vivo and in vitro in the absence of any change in the number of FSHbinding sites. This suggests that estradiol may modify the FSHresponsive adenylate cyclase system. In contrast, hCG stimulation of cAMP accumulation in granulosa cells required an increase in LH-binding sites, and therefore, was observed only in granulosa cells isolated from estradiol- and FSH-primed hypophysectomized rats. Specific granulosa cell responses to gonadotropins at different stages of development were associated with different intracellular concentrations of cAMP. Thus, doses of FSH which stimulated granulosa cells of estradiol-primed hypophysectomized rats to accumulate cAMP were related to doses of FSH which induce granulosa cell LH receptor but do not stimulate progesterone production. In contrast, doses of hFSH (0.25–0.5 μg) and hCG (0.31–1.25 IU) which did not stimulate appreciable cAMP accumulation in vivo in granulosa cells of estradiol- and FSH-primed rats did promote 65-fold increases in serum progesterone concentrations within 90 min. Further, luteinization in these rats occurred only in response to doses of hFSH (10–100 μg) or hCG (5–50 IU) which caused maximal cAMP accumulation at 30 min. These studies indicate that there are at least two mechanisms for increasing granulosa cell responsiveness to gonadotropins. Estradiol treatment of hypophysectomized rats increases FSH stimulation of granulosa cell cAMP accumulation and LH receptors without detectable changes in FSH receptor. Conversely, an increase in LH responsiveness, both LH stimulation of cAMP accumulation and luteinization, only occurs in association with the induction of LH receptors in estradiol- and FSH-primed hypophysectomized rats.