Implications of multiple phenotypes observed in prolactin receptor knockout mice

The development of a mouse line deficient in the PRL receptor (PRLR) would be an ideal means to better understand the multiple functions of prolactin. We were worried initially that removal of the PRLR from the mouse genome might be lethal and were surprised to find this not to be the case. We identified numerous deficiencies in PRLR knockout (KO) animals. Female homozygous mice are completely infertile and lack normal mammary development, while hemizogotes are unable to lactate following their first pregnancy. PRLR KO males and females have markedly elevated (30- to 100-fold) serum prolactin levels and in some instances pituitary hyperplasia is present. Maternal behavior is severely affected in both hemizygous and heterozygous animals. Bone formation is reduced in young animals and adults (males and females). Recently, we noticed that older KO animals show a slight reduction in body weight which appears to be due to reduced abdominal fat deposition.