LACK OF MITOTIC EFFECTS OF INSULIN DURING SYNTHESIS OF CASEIN INDUCED BY PROLACTIN IN PSEUDOPREGNANT RABBIT MAMMARY GLAND ORGAN CULTURES

Abstract

The effects of insulin and prolactin on DNA and casein synthesis were studied in explants from pseudopregnant rabbits to compare the mammogenic and lactogenic effects of these hormones at various O2 concentrations. Casein synthesis occurred in the rabbit mammary tissue at the time of explantation, day 12 of pseudopregnancy, but at a very low level. After 48 h, insulin alone did not increase casein synthesis. Casein synthesis was significantly (P < 0.05) increased when prolactin alone or insulin + prolactin were present in culture media for 48 h. Hydroxyurea, which specifically inhibited DNA synthesis, did not affect casein synthesis in response to insulin + prolactin at 57% O2. Since the effect of insulin on DNA synthesis can be shown only at 1 high O2 concentration, the role of this hormone as the primary stimulus to mitogenesis in the pseudopregnant rabbit mammary gland seems unlikely.