Effect of enzyme and enzyme inhibitors on specific binding of hGH to human peripheral lymphocytes

A recently described method to investigate growth hormone (GH) receptors on circulating human blood cells has been used to study the effect of a trypsin preparation and antitrypsin moieties on hormone binding to lymphocytes. Trypsinization with one defined dose of trypsin (10 ng/ml) led to a considerable decrease both of specific binding and of binding affinity (affinity constant after 60 min trypsinization 0.5 X 10(9) vs 1.5 X 10(9) M-1 in untreated control cells). Exposure of peripheral blood lymphocytes (PBL) to antitrypsin activities was followed by a steady increase of affinity and specific binding (affinity constant: with 10 KIU anti-trypsin 1.9 X 10(9) M-1, with 100 KIU 2.4 X 10(9) M-1, with 1000 KIU 3.6 X 10(9) M-1). This antitrypsin effect exceeds the binding values expected after blocking trypsin activities in the incubation medium. In a subset of experiments somatomedin-B (SM-B) was used as the antitrypsin moiety and was shown to increase specific GH binding to PBL in a similar manner as did antitrypsin (with 1000 ng SM-B affinity constant (Ka) 12.0 X 10(9) M-1, specific binding 9.7% of total radioactivity). It is concluded that enzymatic factors and their inhibitors including partially GH dependent moieties like SM-B modulate specific GH binding to human peripheral lymphocytes in vitro.