STIMULATION OF THE SYNTHESIS OF MACROMOLECULES BY OVARIAN HORMONES DURING EARLY DEVELOPMENT OF THE MOUSE MAMMARY GLAND

Abstract

SUMMARY The influence of oestradiol and progesterone on nucleic acids and protein synthesis during early development of 3- to 4-week-old C3H mouse mammary gland in vivo was studied. The hormones were administered daily by subcutaneous injections for 6–9 days. Uptake of tritium-labelled appropriate nucleoside and amino acid precursors, as determined by radio-chemical and autoradiographic methods, was used as a measure of cellular biosynthesis. Administration of the steroid hormones induces a pronounced increase of RNA, protein, and DNA synthesis in the mammary parenchyma of both intact and ovariectomized mice. Increased RNA and protein synthesis were detectable after two injections of the hormones, the maximal level was reached after the 6th injection. Hormone-induced DNA synthesis rose sharply reaching a peak after four treatments. The stimulatory effect of the steroids on DNA synthesis was more pronounced on the end-bud cells up to the 4th injection but in the duct cells [3H]thymidine uptake continued to rise progressively even after the 6th injection. Autoradiographs showed that the hormones also cause a twofold increase in the silver grain count per nucleus indicating an accelerated uptake rate of the DNA precursor. In end-bud cells mitotic activity, used as a measure of cellular proliferative activity, rose to a sharp peak after four injections of the hormones but in duct cells it continued to rise even after the 6th injection. The significance of these results with respect to further lobulo-alveolar development of the mammary parenchyma is discussed.