Prolactin receptor signal transduction pathways and actions determined in prolactin receptor knockout mice

Prolactin-receptor-deficient mice are a good model in which to study the va rious actions of prolactin. Female homozygous knockout mice are completely infertile and show a lack of mammary development, while hemizogotes are una ble to lactate following their first pregnancy. Male and female homozygotes have markedly elevated serum prolactin levels, and in some instances pitui tary hyperplasia is present. Maternal behaviour is severely affected in bot h hemizygous and homozygous animals. Bone formation is reduced in young ani mals and in adults (males and females). Finally, older males and females sh ow a slight reduction in body weight, which seems to be due to reduced abdo minal fat deposition in the knockout animals.