Stimulation of Casein Synthesis and Histological Development of Mammary Gland by Human Placental Lactogenin Vitro

Abstract

The placental protein "human placental lactogen" (HPL) and ovine pituitary prolactin were compared by studying their respective abilities to stimulate casein and DNA synthesis and to induce histological changes in mouse mammary gland explants maintained for 48 hr. in organ culture. HPL was found to synergize with and require hydrocortisone (F) in the presence of insulin (I) to cause histological development of the alveoli. The degree of development was indistinguishable from that produced by pituitary prolactin combined with I and F. Like prolactin, HPL stimulated the biosynthesis of P32-labeled casein in the presence of I and F and had little effect on casein synthesis in the absence of F. This stimulation involved augmentation of all the casein components. The minimal effective concentration of HPL was 8 x 109 M. The maximal stimulation of HPL was about 90% of that produced by prolactin. These biological effects of HPL on mammary tissue suggest that HPL plays an important role in mammary gland development during pregnancy.