Specific Binding of Iodinated Growth Hormone to Rat Liver in Vivo*

Abstract

The specific uptake by rat liver of human (hGH [growth hormone]) and bovine (bGH) GH labeled with 125I was studied by an in vivo procedure. A significant reduction of the uptake was observed when labeled hormones were injected together with different amounts of the corresponding native GH. This reduction was dose dependent, and the concentration of native hormone that prevents 50% of the liver uptake of the labeled hormone was close to 12 .mu.g/100 g BW [body wt]. In normal rats, only native hGH or bGH significantly decreased the liver uptake of [125I]iodo-bGH, while bovine PRL [prolactin] (oPRL) or heat-denatured bGH were inactive. The highest inhibition of the uptake of [125I]iodo-hGH by rat liver was obtained when this labeled hormone was injected either together with hGH or with bGH plus oPRL while partial displacement was observed with bGH or oPRL. hGH binds to both somatotropic and lactogenic sites in the liver of normal rats. In hypophysectomized animals, only the somatogenic binding sites could be detected.