Characteristics of the action of prolactin on [3H]-thymidine incorporation into DNA in mammary gland explants from virgin mice.

The prolactin stimulation of the rate of [3H]-thymidine incorporation into DNA in mammary gland explants from virgin C3H mice was studied. The onset of this effect occurred between one and two days after adding prolactin to the culture medium. Prolactin effected an enhanced rate of [3H]-thymidine incorporation at all concentrations from 10 ng/ml to 10 micrograms/ml. The response is essentially an "all or none" phenomenon since the effect at 10 ng/ml was not different from that at 10 micrograms/ml. Hydrocortisone was not essential from the prolactin response, but it did significantly increase the basal rate of [3H]-thymidine incorporation. Both quinacrine (an inhibitor of phospholipase A2 activity) and indomethacin (an inhibitor of prostaglandin biosynthesis) abolished the action of prolactin on [3H]-thymidine incorporation into DNA.