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 hGH44-191 to bind both receptor classes. We found that hGH44-191 could not compete with [125I]hGH or [125I]bGH for bovine liver somatogenic binding sites. Additionally, hGH44-191 could not displace [125I]hGH from the somatogenic receptor sites when human liver microsomes were used as the receptor source. In contrast, hGH44-191 effectively competed with [125I]hGH for lactogenic receptor sites of lactating mammary gland microsomes and of bovine liver microsomes. In summary, hGH44-191 does not bind to somatogenic receptors but does not bind to lactogenic receptors. These data suggest that the biological actions of hGH44-191 could be mediated through lactogenic receptors.