Characteristics of the early effect of prolactin on lactose biosynthesis in mouse mammary gland explants.

These studies were carried out to characterize the early effect of prolactin (PRL) on lactose biosynthesis in cultured mammary gland explants derived from 12- to 14-day pregnant mice. The rate of lactose biosynthesis was assessed by the rate of radiolabeled glucose incorporation into lactose. For the rapid isolation of lactose, a new method which involves the use of thin-layer chromatography on cellulose-impregnated plastic sheets was employed. The onset of the PRL stimulation of [3H]glucose incorporation into lactose occurred 6-8 hr after exposing the explants to PRL. The response to PRL was essentially all or none with maximum responses occurring with PRL concentrations above 25 ng/ml. The lowest stimulatory concentration of PRL was 10 ng/ml. The action of PRL on lactose biosynthesis requires both ongoing RNA and protein synthesis since puromycin, cyclohexamide, and actinomycin D abolished the PRL effect.