Binding Sites for Pituitary Growth Hormone and Prolactin in the Liver and Mammary Gland of the Pregnant Rabbit

Abstract

The use of 125I-labelled growth hormone (GH) and prolactin to study ‘receptor’ in membrane preparations from rabbit liver and mammary gland is described. Different methods for preparing labelled hormone have been compared, and receptors in a crude microsomal fraction, purified plasma membranes and after solubilization with Triton-X-100 have been studied. The importance of species specificity in the source of hormones is considered. The ability of receptors from rabbit mammary gland to bind various GHs and prolactins accords well with a role for these receptors as mediators of the actions of lactogenic hormones. Binding of GHs and prolactins to liver ‘receptors’, on the other hand, bears little relationship to the grovrth-promoting activity of these various hormones. In an attempt to investigate further the differences between mammary-gland and liver receptors for human GH, the ability of a series of monoclonal antibodies to human GH to inhibit binding has been investigated. It was found that some of these antibodies inhibited receptor binding v/hereas others had little effect, and that the results were similar whether the receptors were obtained from mammary gland or liver.