Effect of kinase C inhibitor, gossypol, on the actions of prolactin in cultured mouse mammary tissues.

Gossypol, a drug which has been shown to be an inhibitor of kinase C activity in mouse mammary tissues, is shown to abolish several of the actions of prolactin in cultured mouse mammary gland explants. The prolactin effects that are abolished include its stimulatory effects on ornithine decarboxylase activity, the rate of [3H]uridine incorporation into RNA, the rate of [3H]leucine incorporation into a casein-rich phosphoprotein fraction, and the rate of [14C]acetate incorporation into lipids. Since the inhibitory concentrations of gossypol employed in these studies correspond well with the gossypol concentrations required to inhibit kinase C activity, we conclude that ongoing kinase C activity is essential for prolactin to express its differentiative actions in mammary tissues.