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Hormone-induced Growth and Lactogenesis of Grafts of Bovine Mammary Gland Maintained in the Athymic "Nude" Mouse¹

Departments of Anatomy [C.W.W., M.J.M., J.V.D.] and Dairy Science [G.T.G., H.A.T.], Michigan State University, East Lansing, Michigan 48824

A midpregnant Jersey cow was sacrificed, and a portion of the mammary gland was excised and processed into 5- x 5- x 0.2-mm slices and grafted s.c. (dorsum) to 25 nine-week-old female athymic "nude" mice, ten slices/mouse. Thirty days after grafting, the 25 graft-bearing mice were divided into five groups of five mice each and treated once daily for ten days with the following hormonal combinations. Group 1, bovine growth hormone (GH) + bovine prolactin (PRL) + 17ß-estradiol + progesterone; Group 2, ovariectomized and GH + PRL; Group 3, 17ß-estradiol + progesterone; Group 4, 0.9% NaCl solution (controls); and Group 5, GH + PRL + 17ß-estradiol + progesterone. The mice of Group 5 were ovariectomized after hormone treatment and subsequently treated daily for seven days with GH + PRL + hydrocortisone (HC). Five grafts were excised from all mice of each group at the onset of hormone treatment; the remaining five grafts were excised at the termination of hormone treatment. The grafts obtained from the mice of Group 5 were analyzed for -lactalbumin by radioimmunoassay. The freshly excised grafts from the mice of Groups 1 to 4 were incubated for four hr in [³H]thymidine-enriched culture medium for DNA synthesis analysis. The mean number of [³H]thymidine-radiolabeled epithelial cells per unit area of epithelium (labeling index for DNA synthesis) in prehormone-treated grafts and post-hormone-treated grafts was, respectively: Group 1, 7.9 ± 2.0 (S. E.) and 37.9 ± 13.5; Group 2, 4.5 ± 1.8 and 18.8 ± 4.7; Group 3, 9.8 ± 2.6 and 20.8 ± 5.3; and Group 4, 9.3 ± 2.0 and 11.9 ± 3.4. All hormonal combinations significantly increased the labeling index above control values (p < 0.05 to 0.001). The hormonal combination of GH + PRL + 17ß-estradiol + progesterone was more effective (p < 0.05) than the combination of GH + PRL or 17ß-estradiol + progesterone. For Group 5, the mean -lactalbumin content (µg -lactalbumin per mg tissue) of prehormone-treated grafts and post-hormone-treated grafts was 0.2 and 52.7 (p < 0.001), respectively. Morphological viable duct and alveolar epithelium similar to that in the original biopsy was present in all of the grafts regardless of treatment. These results provide evidence that the athymic nude mouse can not only accept and maintain xenografts of bovine mammary gland tissues, but under the appropriate hormonal stimulus the epithelium in these grafts can be induced to grow and differentiate (lactate), simulating that which occurs in situ.

¹ Supported by Research Grant BC-220C from the American Cancer Society.

² To whom requests for reprints should be addressed.

Received 12/27/78. Accepted 3/ 1/79.