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Activin Modulates Differential Effects of Estradiol on Synthesis and Secretion: RESULTS

FSH and LH Release from Pituitary Cells after Estradiol Treatment

Estradiol reduced secretion of FSH in a dose-dependent manner (P < 0.001; Fig. 1A). In the presence of 0.01 and 1.0 nM estradiol, FSH concentrations were suppressed by 37% and 54%, respectively, of mean basal release in control cultures. In contrast, secretion of LH was significantly enhanced by estradiol (P < 0.001; Fig. 1B). In the presence of 0.01 and 1.0 nM estradiol, LH concentrations were increased to 237% and 267%, respectively, of mean basal release in control cultures.

FSH and LH Release from Pituitary Cells after Treatment with Anti-Activin

Anti-activin reduced mean secretion of FSH by 51% (P < 0.01) but did not influence secretion of LH (Fig. 2).

Changes in Amounts of mRNA

As revealed by RT-PCR analysis, levels of mRNA for FSHp in pituitary cells were reduced up to 70% (P < 0.001) following treatment with estradiol compared with untreated controls (Fig. 3). Similar results were obtained by slot-blot analysis (data not shown).

Treatment with estradiol reduced the amount of mRNA for activin (3B (Fig. 4). The reduction in activin (3B expression was dose-dependent, with a decrease of 27% ± 4.9% (P < 0.02) and 46% ± 3.9% (P < 0.002), observed in response to 0.01 nM and 1.0 nM estradiol, respectively. There was no significant change in the amounts of mRNA for follistatin in response to treatment with estradiol (Fig. 5).
Fig1Activin Modulates Differential
FIG. 1. Secretion of FSH (A) or LH (B) from ovine pituitary cells after 24 h of treatment with estradiol (0.01 nM and 1.0 nM). Each treatment represents the mean of 12 replicates for each of five animals. Data are expressed as mean ± SEM. * P < 0.01, ** P < 0.001 compared to control.

Fig2Activin Modulates Differential
FIG. 2. Amounts of LH and FSH secreted by ovine pituitary cells after 24 h of treatment with monoclonal antibody to activin B (25 ^g/ml). Each treatment represents the mean of 5 replicates for each of three animals. Data are expressed as mean ± SEM. * P < 0.01 compared to control.

Fig3Activin Modulates Differential
FIG. 3. Relative expression of FSHp subunit in ovine pituitary cells after treatment with estradiol (0.01 and 1.0 nM). Data are expressed as the ratio of FSHp/p-actin obtained in the same amplification reaction and converted to percent of control. Each group represents the mean ± SEM of five animals. * P < 0.001.

Fig4Activin Modulates Differential
FIG. 4. Relative expression of activin pB in ovine pituitary cells after treatment with estradiol (0.01 nM and 1.0 nM). Data are expressed as the ratio of activin pB/p-actin obtained in the same amplification reaction and converted to percent of control. Each group represents the mean ± SEM of five animals. * P < 0.02, ** P < 0.002.

Fig5Activin Modulates Differential
FIG.5. Relative expression of follistatin in ovine pituitary cells after treatment with estradiol (0.01 nM and 1.0 nM). Data are expressed as the ratio of follistatin/p-actin obtained in the same amplification reaction and converted to percent of control. Each group represents the mean ± SEM of five animals.