The effects of estradiol treatment, which stimulates cell division in rat uterine epithelial cells, on the in vivo expression of heparinbinding epidermal growth factor (HB-EGF), cyclin D1, and cyclin B1 messenger RNA (mRNA) in these cells have been examined using ribonuclease protection assays. Estradiol gave rise to significant increases in steady state levels of HB-EGF 2 and 24 h after treatment. Cyclin D1 mRNA levels were elevated 8 and 10 h after estradiol administration, corresponding to

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... e G1 phase of the mitotic cycle, and cyclin B1 mRNA was only expressed 16 -24 h after estradiol treatment, which corresponds to the G2 and M phases of the rat uterine epithelial cell cycle. Estradiol-stimulated increases in HB-