Archive for the ‘Hormonal Regulation’ Category


Our findings indicate that the inductive nature of steroidogenesis in LTC is in fact a reflection of its StAR, rather than P450scc, gene expression. Nevertheless, even after stimulation, theca-derived luteal cells contained lower StAR mRNA levels (and progesterone production) than granulosa-derived luteal cells. buy cheap antibiotics

The orphan nuclear receptor SF-1 was initially shown to be an essential regulator of the cytochrome P450 steroid hydroxylases and was subsequently linked to various genes expressed throughout the hypothalamic-pituitary-steroidogenic organ axis. Analyses of the human and mouse StAR gene promotors revealed sequence elements that bind SF-1, thus implicating SF-1 in the expression of StAR gene as well. Whether SF-1 expression is hormonally regulated is still an open question.

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  • DISCUSSION(5)

    Numerous reports have shown that granulosa-derived large luteal cells exhibit unique functional characteristics as compared with other steroidogenic cell types or even with theca-derived small luteal cells. In vivo, large luteal cells, which constitute only a minority of luteal cells, contribute the major portion of total progesterone output from the CL. Previously, we and others have shown that this is partially due to high P450scc mRNA levels and a stable protein content, which is maintained in the absence of cAMP-inducing agents. Data presented in this study further expand our understanding of the steroidogenesis in large luteal cells. birth control yasmin

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  • However, in LTC this synergism was also apparent in P450scc gene expression and in progesterone production; therefore, it is reasonable to assume that it occurs at an early step(s) of their signaling pathways. Potentiation of forskolin-activated adenylyl cyclase by insulin/IGF-I may account for such a phenomenon. No such synergism could be detected in LGC, in which the stimulation of P450scc was cAMP-dependent and that of StAR was insulin-dependent. Different mechanisms may, therefore, operate to control the expression of these genes in the two respective luteal cell types. In this regard, it is worth noting that the expression of the LH receptor also differed between the two luteal cell types. The existence of cell-type specific, cis-acting factors might explain such observations. buy flovent inhaler

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  • DISCUSSION(3)

    In the present study, the cells induced to luteinized were mature granulosa cells derived from preovulatory follicles. Such cells had already acquired the ability to produce low levels of progesterone and to express StAR gene, in contrast to the immature granulosa cells of medium follicles. Therefore, it may be suggested that the initial induction of StAR mRNA (in immature cells) is regulated by different mechanisms from those that control its continuous transcription (in mature cells). buy yasmin online

    StAR is believed to play a key role in the acute regulation of steroidogenesis; this acute stimulation might be regulated by changes in message stability or translation of mRNA or by posttranslational modification of this protein (e.g., phosphorylation ). The observations presented here address the longer-term regulation of StAR, which may be particularly relevant to the process of luteinization. Indeed, during luteal development there is a gradual up-regulation in StAR mRNA as well as P450scc levels, which reach a plateau at mid-luteal phase (Days 8 and 12 for pigs and cows, respectively).

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  • Since the discovery of StAR a few years ago, it has been argued that cAMP (being a mediator of tropic hormones) was sufficient for the induction of StAR mRNA. For instance, incubation of transformed Leydig cells or human granulosa and theca-lutein cells with cAMP analogues dramatically elevated StAR mRNA. These results seem to conflict with the present findings for bovine luteal cells, demonstrating that forskolin alone (in both cell types) only marginally affected the induction of StAR. However, in these previous studies, cells were cultured in the presence of 15% serum, which may contain considerable amounts of several growth factors including IGF-I; therefore, the necessity for IGF-I in StAR gene expression cannot be ruled out. buy ventolin inhalers

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  • DISCUSSION(1)

    SF-1, StAR, and P450scc mRNA levels, and progesterone production were documented during differentiation/luteinization of bovine theca and granulosa cells. Major differences were observed in this study between the two luteal cell types, in their hormonal regulation of steroidogenesis as well as in the regulation of P450scc and StAR gene expression within each cell type. Our findings demonstrated for the first time that insulin/IGF-I are sufficient to induce considerable levels of StAR mRNA in bovine granulosa-derived luteal cells. This might represent a special, perhaps unique control of StAR expression in these cell types. buy cipro

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  • Maintenance of P450scc and StAR mRNA Levels in Luteal Cells

    We next examined the roles of forskolin and insulin in the maintenance of P450scc and StAR mRNA expression in luteal cells that had already acquired high steroidogenic capacity (i.e., cells cultured in the presence of 10 ^M forskolin and 2 ^g/ml insulin). On Day 8 of culture, forskolin, insulin, or both were withdrawn from the media, and incubation was continued for an additional 24 h (Fig. 5). In LTC, the removal of forskolin caused a significant reduction in both StAR and P450scc mRNA levels (45% and 70%, respectively, p < 0.01), and a small, nonsignificant decrease in the expression of both genes was evident in cells incubated for 24 h without insulin (Fig. 5). In contrast, in LGC, insulin appeared to play a major role in maintaining StAR mRNA levels; its withdrawal reduced StAR mRNA levels by 50% (p < 0.01). As observed for LTC, P450scc mRNA levels were significantly reduced in LGC (by 30%, p <0.05) as a result of the removal of forskolin. flovent inhaler

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  • RESULTS(3)

    However, the independent actions of forskolin (up-regulating P450scc) and insulin (up-regulating StAR) were combined in their effect on progesterone production by LGC (Fig. 2f). In this cell type, insulin and forskolin each significantly (p < 0.01) elevated progesterone synthesis. However, while 10 of forskolin alone was necessary to exert a significant effect, progesterone could be stimulated to its maximal levels by 1/100 of this concentration in the presence of insulin. buy birth control online

    The expression of SF-1 in luteal cells is demonstrated in Figure 3. SF-1 protein content did not vary with luteal cell type or in the presence of either forskolin or insulin (Fig. 3a). Similarly, SF-1 mRNA levels were not altered by the hormonal treatment in either LTC or LGC (Fig. 3b). The induction of StAR mRNA was clearly visible in LTC incubated with forskolin plus insulin.

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