Somatomedin-C-Mediated Potentiation of Follicle-Stimulating Hormone-Induced Aromatase Activity of Cultured Rat Granulosa Cells*

Abstract

We have recently observed that nanomolar concentrations of exogenously added somatomedin-C (Sm-C) are capable of synergizing with FSH in the induction of cultured rat granulosa cell progesterone biosynthesis and LH receptors without altering granulosa cell survival or replication. To further characterize the cytodifferentiative properties of Sm-C, we have undertaken to investigate whether the acquisition of granulosa cell aromatase activity is also subject to modulation by this intraovarian peptide. Granulosa cells from immature hypophysectomized diethylstilbestrol-treated rats were initially cultured for up to 3 days in an androstenedione-free medium, during which time aromatase activity was induced by FSH in the absence or presence of Sm-C (treatment interval). At the conclusion of this period, the cells were washed and reincubated for an additional 8-h test interval, during which time aromatase activity was estimated. Basal aromatase activity, as assessed by the conversion of unlabeled androstenedione (10(-7) M) to radioimmunoassayable estrogen, was negligible, remaining unaffected by treatment with highly purified Sm-C (50 ng/ml) alone. However, concurrent treatment with Sm-C (50 ng/ml) produced a 7.0-fold increase in the FSH (100 ng/ml; NIH FSH S14)-stimulated accumulation of estrogen. Similarly, Sm-C produced a 6.1-fold increase in FSH-induced aromatase activity, as assessed by the stereospecific generation of tritiated water from [1 beta-3H]androstenedione substrate. Sm-C-potentiated aromatase activity was dose and time dependent, with an apparent median effective dose of 5.0 +/- 1.9 (+/- SE) ng/ml and a minimal time requirement of 24 h or less, but was independent of the FSH dose employed. Although bovine insulin and multiplication-stimulating activity, like Sm-C, proved capable of augmenting aromatase activity (albeit at a substantially reduced potency), little or no effect was observed for either porcine or rat relaxin, a distantly related member of the insulin-like growth factor family. Examination of the apparent kinetic parameters of the aromatase enzyme revealed that the Sm-C-mediated potentiation of aromatase activity was due to enhancement of the apparent maximal reaction velocity, but not substrate affinity (Km = 2.8 X 10(-8) M). Our findings indicate that nanomolar concentrations of exogenously added Sm-C synergize with FSH in the enhancement of the maximal reaction velocity, but not Km, of granulosa cell aromatase in a dose- and time-dependent fashion.(ABSTRACT TRUNCATED AT 400 WORDS)

Corticotrophin-releasing hormone inhibits insulin-like growth factor-I release from primary cultures of rat granulosa cells

“…Because of the well-known stimulatory role of IGF-I on oestrogen release and aromatase activity in granulosa cells (Adashi et al 1985a), we addressed the question whether CRH suppresses oestrogen release by interfering with the production of IGF-I from rat granulosa cells. The results of this study show that CRH is capable of inhibiting the production of IGF-I.…”

“…IGF-I, a basic member of this family, is produced by the granulosa cells of the developing follicle in the rat (Oliver et al 1989). In murine ovaries, besides a potent stimulatory effect on granulosa cell replication (Zhou et al 1991), IGF-I also exerts a stimulatory effect on the synthesis of proteoglycans (Adashi et al 1986) and on aromatase activity (Adashi et al 1985a). Moreover, it has a synergistic role with follicle-stimulating hormone (FSH) on steroidogenesis and luteinizing hormone receptor induction (Adashi et al 1985b,c), probably by stimulating FSH receptor gene expression in granulosa cells (Zhou et al 1997).…”

“…The antithetical effects of CRH and IGF-I (Adashi et al 1985a, Calogero et al 1996 at the ovarian level led us to hypothesise that the suppressive effects of CRH on oestrogen release from granulosa cells may be due to an inhibition of IGF-I production and/or a stimulation of IGFBP-3 production. To test this hypothesis, we studied the effects of CRH on IGF-I and IGFBP-3 release into the conditioned medium of primary cultures of rat granulosa cells.…”

IGFs and IGF-binding proteins in the regulation of human ovarian and endometrial function

“…This implies that IGF-I of thecal origin may facilitate LH action on androgen production. In contrast, IGF-I in the granulosa cells is capable of augmenting FSH-mediated estrogen synthesis (Adashi et al 1985a, Christman et al 1991; and after luteinization, in synergy with LH, stimulating progesterone synthesis (Adashi et al 1985b, Davoren et al 1985.…”

Nutritional management to optimize fertility of dairy cows in pasture-based systems

“…In many species including cattle, IGF-1 stimulates proliferation of ovarian granulosa cells (Gong et al, 1993;Hamilton et al, 1999) and acts synergistically with FSH to increase aromatase activity (Adashi et al, 1985). Indeed, IGF-1 is considered critical for follicular maturation due to its intrafollicular role in amplifying gonadotropin stimulus (Fortune et al, 2001).…”