We have examined the ability of co-cultured mouse mammary fat pad (MFP) to modulate the response of mouse mammary epithelial cells to a number of mitogens in vitro. In a series of 4 experiments, COMMA-1D cells were cultured with or without epithelium-free MFP obtained from the abdominal mammary glands of 23-day old virgin, female BALB/c mice. Final cell number was quantified as total DNA after 7 days. The main effect of MFP was significant in all experiments, MFP alone inducing a 6.1 to 8.2-fold increase in cell number relative to basal medium (BM) controls (P<0.001). Furthermore, this stimulatory effect of MFP synergised (P<0.02) with the mitogenic effect of 10% foetal calf serum (FCS). Examination of the response to several mammogenic hormones indicated that insulin (10 ug/ml) alone did not increase cell number (P>0.05), and interacted with the effect of MFP (P<0.001). There was no effect of prolactin (2.5 ug/ml) either alone or with MFP, whereas hydrocortisone (2.5 ug/ml) attenuated the response to MFP (P<0.001). In the absence of MFP, insulin-like growth factor-I (IGF-I; 75 ng/ml) did not increase cell number (P>0.05), whilst epidermal growth factor (EGF; 25 ng/ml) significantly increased cell number 3.7-fold. Both of these growth factors markedly interacted with the effect of MFP (P<0.001). When cultured with the combination of these growth factors and MFP, the final cell number was 29.2 times that of BM alone (25.14 ± 0.84 vs 0.86 ± 0.12 ug DNA/well). There was no effect of prostaglandin E2 (PGE2; 0.5 ug/ml) or indomethacin (5 mg/ml), an inhibitor of prostaglandin synthesis, in the absence or presence of MFP. These findings demonstrate that a diffusible factor(s) from the MFP interacts with several regulators of mammary growth to markedly stimulate epithelial proliferation in vitro. Such a factor appears distinct from a number of classical mitogens, and may be involved in the regulation of mammary development in vivo.
Proceedings of the New Zealand Society of Animal Production, Volume 54, , 121-124, 1994
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