One bovine mammary epithelial cell clone, designated PS-BME-Cl, and two bovine mammary epithelial cell lines, designated PS-BME-L6 and PS-BME-L7, were derived from mammary tissue of a pregnant (270 day) Holstein cow. The cells exhibit the distinctive morphologic characteristics of mammary epithelial cells and express the milk fat globule membrane protein, PAS-III. They form domes when cultured on plastic substrata and acinilike aggregates when cultured on a collagen matrix. These cells are capable of synthesizing and secreting alpha-lactalbumin and alpha-s1-casein when cultured on a collagen matrix in the presence of insulin, cortisol, and prolactin. The cells have a near-normal diploid number and do not grow in suspension culture. When transplanted to the cleared mammary fat pads of female athymic nude mice, the cells readily proliferate forming noninvasive palpable spherical cellular masses within 8 wk after inoculation. The cells may become a useful tool to study the regulation of ruminant mammary epithelial cell growth and differentiation.
Mammary tissue from five midpregnant heifers was transplanted subcutaneously into ovariectomired athymic mice (eight pieces/mouse). After a recovery period of 19 days, mice were injected daily for 5 days with buffer (50 mM NH,HC03, pH 7.8) as control, 17P-estradiol (1 wg) plus progesterone (1 mg). Concurrently with the buffer or steroid hormone injections, mice were injected with bovine placental lactogen (0, 5, or 25 fig), bovine prolactin (0, 3.4, or 17.2 Fg), or bovine growth hormone (0, 3.4, or 17.2 fig).All mice were injected with 2-bromo-or-ergocryptine (0.1 mg/day). Transplanted bovine mammary tissue was incubated for 4 hr in minimum essential medium containing 1 pCi/ml [3H]TdR. Two pieces were processed for autoradiography and the others were used for DNA assay and total [3H]TdR uptake. Bovine placental lactogen, prolactin, and growth hormone each increased [3H]TdR incorporation into DNA in a linear, doseresponse manner. Addition of ovarian steroids to bPL resulted in a significant increase over protein hormones alone. Autoradiographic analysis indicated that the observed differences in DNA synthesis were due to hormonal effects on epithelial, rather than stromal, DNA synthesis. These results provide the first evidence of a mammogenic role of bovine placental lactogen.
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