Human Growth Hormone Deletion Mutant (hGH44-191) Binds with High Affinity to Lactogenic Receptors but Not to Somatogenic Receptors

The carboxyl-terminal hGH fragment, hGH44–191, displays diabetogenic activity. To understand whether this biological activity is mediated through somatogenic or lactogenic receptors, we investigated the ability of hGH44–191to bind both receptor classes. We found that hGH44–191could not compete with [125I]hGH or [125I]bGH for bovine liver somatogenic binding sites. Additionally, hGH44–191could not displace [125I]hGH from the somatogenic receptor sites when human liver microsomes were used as the receptor source. In contrast, hGH44–191effectively competed with [125I]hGH for lactogenic receptor sites of lactating mammary gland microsomes and of bovine liver microsomes. In summary, hGH44–191does not bind to somatogenic receptors but does not bind to lactogenic receptors. These data suggest that the biological actions of hGH44–191could be mediated through lactogenic receptors.