Gestational profile and affinity cross-linking of the mouse serum growth hormone-binding protein

The modulation of the serum concentration of mouse GH-binding protein during gestation was characterized. A rapid increase in the concentration of the binding protein began on day 9 of pregnancy and peaked by day 15. The increase in the serum GH-binding protein concentration was preceded several days by an increase in the hepatic GH receptor concentration. The serum GH-binding protein was recognized by antibodies produced against the hepatic GH receptor, and its mol wt (major form mol wt, approximately 41,800) was similar to that of low mol wt forms of the hepatic GH receptor, demonstrating the similarity of the serum GH-binding protein and the hepatic GH receptor. The apparent affinity of the serum GH-binding protein for mGH in untreated serum samples from 17-day pregnant mice was 6.9 X 10(7) M-1. However, when the serum was treated to remove endogenous GH, the apparent affinity increased to 1.5 X 10(8) M-1. Likewise, the binding capacity of the GH-binding protein in serum differed in treated (60.1 nM) and untreated serum (101.2 nM).