The ontogeny of serum GH binding protein in man: a possible indicator of hepatic GH receptor development

Experiments in rabbits suggest that a serum GH binding protein (GH-BP) probably is derived largely from hepatic membrane bound GH receptors. Human serum contains a specific GH binding protein which can be easily measured by incubation with [125I] hGH and separation of [125I] hGH-BP complexes from free [125I] hGH by gel filtration through an Ultrogel AcA 44 minicolumn. In each assay GH-BP activity of a reference (normal young adult) serum is similarly run and the results are expressed as a percentage of the activity of the unknown serum divided by the GH-BP activity of the reference serum after correction for the expected inhibition of GH binding resulting from the GH content of the unknown serum. The mean relative specific GH binding protein (RSGH-BP) of cord serum from 11 premature infants was only 3.2 +/- 1.4% (SE) and of cord serum from 17 full term infants was 14.9 +/- 2.5%. During the first two decades of life there was a progressive rise of RSGH-BP with considerable individual variation. The mean serum RSGH-BP of 13 such subjects was 54.5 +/- 6.2%. More uniform RSGH-BP results were obtained in serum from 15 young adults, 91.7 +/- 7.4%. Lower RSGH-BP 77.2 +/- 5.4% was found in serum from 12 healthy older adults (age 60 to 70 years). The low levels of RSGH-BP in fetal serum are consistent with the reported low concentrations of GH receptors in sheep and rat fetal liver membranes. We suggest the measurement of GH-BP activity provides a simple, noninvasive measure of the ontogeny of GH receptors of human beings.