Transforming growth factor-alpha (TGF alpha) and epidermal growth factor receptor (EGF-R) mRNAs were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) in the normal and neoplastic mammary glands of four strains of mice with different mammary tumor potentials (from highest to lowest potential): SHN, GR/A, SLN and C3H/He. At 2 months of age, when the mammary glands of these strains consisted mostly of normal tissue, the samples examined showed the positive expressions of both TGF alpha and EGF-R mRNAs in all strains (4-6 mice per group), except for EGF-R mRNA in the SLN mice, expressed in only 2 of 4 samples associated with no end-bud formation in the mammary glands. At 10 months, all of the samples from all four strains had a positive expression of TGF alpha mRNA. The EGF-R mRNA expression paralleled the degree of the formation of preneoplastic hyperplastic alveolar nodules (HAN) in all strains. These findings indicate that TGF alpha and EGF-R participate in the growth of the mammary glands, and that EGF-R especially contributes to the formation of end-buds at younger ages and to that of preneoplastic HAN at later ages. All of the samples of mammary tumors from four strains had positive expressions of both TGF alpha and EGF-R mRNAs.

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 mug / 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 alpha (TGFalpha) mRNA and epidermal growth factor receptor (EGFR) mRNA in the mammary gland was increased by danazol. However, TGFalpha 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 TGFalpha on mammary gland is rather suppressed by PRL, while mammary gland growth needs the participation of PRL; in other words, PRL is dominant to TGFalpha on the mammary gland growth. OVX resulted in a significant decrease of TGFalpha 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.

Abstract. To understand the relationship between transforming growth factor α (TGFα) and mammary gland involution, changes in the growth of normal and preneoplastic mammary glands, the expression of TGFα and epidermal growth factor receptor (EGFR) mRNAs in the mammary gland, and serum prolactin (PRL) level were examined in 3-month-old virgin SHN mice 4 to 108 days after ovariectomy (OVX). The formation of normal end-buds and preneoplastic hyperplastic alveolar nodules was significantly reduced after 9 days of OVX, associated with the decreased serum PRL level. Both TGFα and EGFR mRNA expression in the mammary glands declined 18 days after OVX. Thereafter, TGFα mRNA tended to increase, while EGFR mRNA continued to decrease. These observations suggest that the decline of both estrogen and PRL play major roles in the mammary gland involution after OVX, and that the decline of EGFR, through which TGFα manifests its effects, play a secondary role in this process. Key words: EGFR, Mammary gland, Mouse, Ovariectomy, TGFα.(J. Reprod. Dev. 44: [371][372][373][374][375] 1998) TGFα and EGFR mRNAs in the mammary gland and the growth of normal and preneoplastic mammary gland in OVX mice. We also examined the changes in serum prolactin (PRL) levels in these mice, since PRL is one of the key hormones necessary for mammary gland growth and secretion of PRL is largely controlled by ovarian estrogen [15]. Materials and Methods Animals and treatmentsAnimals used were virgin SHN/Mei mice maintained in our laboratory by strict brother × sister mating [16]. At 3 months of age, they were divided into two groups; the first group underwent a sham operation and served as the control. The ransforming growth factor α (TGFα) is a polypeptide which has been suggested to play

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 mug / 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 alpha (TGFalpha) mRNA and epidermal growth factor receptor (EGFR) mRNA in the mammary gland was increased by danazol. However, TGFalpha 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 TGFalpha on mammary gland is rather suppressed by PRL, while mammary gland growth needs the participation of PRL; in other words, PRL is dominant to TGFalpha on the mammary gland growth. OVX resulted in a significant decrease of TGFalpha 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.