Effects of ovariectomy and prolactin on mammary gland expressions of transforming growth factor α and epidermal growth factor receptor mRNAs in mice

Beginning 15 days after ovariectomy (OVX), a high mammary tumor strain of SHN virgin mice at 3 months of age received subcutaneous injections of danazol (0.5 μg / 0.1 ml olive oil, once a day), perphenazine (0.05 mg / 0.1 ml saline, twice a day) or ovine prolactin (oPRL: 0.25 mg / 0.05 ml buffer, twice a day) for 3 days to modulate their circulating PRL levels. The serum PRL level was significantly decreased by danazol and increased by perphenazine compared to the intact and OVX-control groups. The expression of both transforming growth factor α (TGFα) mRNA and epidermal growth factor receptor (EGFR) mRNA in the mammary gland was increased by danazol. However, TGFα mRNA expression was decreased by perphenazine. Meanwhile, mammary end-bud formation was inhibited in danazol-treated group. All findings suggest that the manifestation of the effect of TGFα on mammary gland is rather suppressed by PRL, while mammary gland growth needs the participation of PRL; in other words, PRL is dominant to TGFα on the mammary gland growth. OVX resulted in a significant decrease of TGFα mRNA expression in the mammary gland despite of little alteration in serum PRL, confirming the previous observations. The similar trend was observed in ICR mice; however, the response to hormonal modulation is generally less susceptible than SHN mice.