Chorionic Somatomammotropin Hormone (CSH1) belongs to the Somatotropin/Prolactin family. It is located at the growth hormone locus on chromosome 17. It is produced by cells in the syncytiotrophoblast layer of the placenta only during pregnancy. Although CSH1 does not interact with GHR but only activates PRLR through zinc-induced dimerization. It is expressed mainly in the placenta and utilizes multiple transcription initiation sites. CSH1 plays an important role in stimulating lactation, growth control and metabolism.