A novel "Cleaved Prolactin" in the rat pituitary: Part II in vivo mammary mitogenic activity of its N-terminal 16K moiety

Abstract

Preparative sodium dodecyl sulphate polyacrylamide gel electrophoresis of fresh rat pituitary extract or culture medium, under reducing conditions, was used to separate intact prolactin from the 16K and 8K moieties of cleaved prolactin. Regions of the gel containing the intact prolactin and 16K bands were excised from unstained gels and injected subcutaneously into adult virgin female rats as a single inoculum. The 16K polypeptide significantly increased the rate of DNA synthesis and cell division in the mammary epithelial cells. Gel bands containing intact prolactin were ineffective. In separate experiments, the injection of NIH rat prolactin B-1 in saline, given in physiological doses, also failed to increase the rate of mammary cell division.