In vivo and in vitro evidence of basic fibroblast growth factor action in mouse mammary gland development

Basic fibroblast growth factor (bFGF) stimulated [3H]thymidine incorporation at all stages of development, although the magnitude of this effect was the greatest in cells derived from pregnant mice. Cells primed with insulin and bFGF synthesized more casein than cells not exposed to either hormone. bFGF inhibited casein synthesis and decreased the amounts of beta-casein and alpha-lactalbumin transcripts in cells from pregnant animals simultaneously incubated with insulin, hydrocortisone and prolactin. bFGF content in mammary gland increased with puberty and pregnancy, but decreased markedly in lactation; the number of bFGF receptors in epithelial cells changed in parallel. These data suggest that bFGF may have a physiological role both in stimulating growth and in inhibiting functional differentiation of normal mouse mammary epithelial cells.