Growth hormone-binding proteins of human serum: developmental patterns in normal man

The binding of GH by a low affinity binding protein (LA-BP) was measured from birth into adulthood and compared with binding of a high affinity binding protein (HA-BP) in human serum. Pooled serum samples for each year of age from birth to 16.5 yr were formed from 2500 separate samples and assayed for both binding proteins using a Sephadex chromatographic method. Individual samples in this age range and those from adults were assayed in a similar manner. Binding of [125I]GH was minimal by both binding proteins in cord blood (binding by LA-BP, 2.77 +/- 0.32%; binding by HA-BP, 2.58 +/- 0.35% mean +/- SEM). A 4-fold increase to maximal binding for LA-BP occurred by the age of 5 yr and remained relatively constant through adolescence, except for a transient decrease at puberty. From 16.5-20 yr of age, binding by LA-BP decreased to a level no greater than that seen at birth. Binding by the HA-BP, which increased 6- to 8-fold reached maximal binding between 23-25 yr of age. Binding by HA-BP did not decrease in adults between the ages of 20-30 yr. Whereas pregnancy increased LA-BP activity, GH binding by HA-BP was unaltered.