Differential regulation of serum growth hormone (GH)-binding protein during continuous infusion versus daily injection of recombinant human GH in GH-deficient children.

Serum GH-binding protein (GHBP) was evaluated in 2 randomly divided groups of prepubertal children presenting with idiopathic GH deficiency and receiving recombinant human GH, either continuously by sc infusion (group 1) or as 1 daily sc injection (group 2). After the first 6 months, group 1 switched from continuous infusion to daily injections for the following 6 months. There was no significant difference in clinical data, GH values, or GHBP levels between the 2 groups before treatment. During the first 6 months, GHBP levels increased in all except 1 of the 8 children in group 1 from 8.6% to 16.9% after 3 months and 22.5% after 6 months. The increment factor ranged from 1.1-7.9, with wide individual variations. In group 2, the mean variation in GHBP was from 8.3-8.2% after 3 months and 10.7% after 6 months. Only 2 of the 10 children in this group showed a significant increase in GHBP levels. During the second period, group 1 maintained their GHBP levels, whereas the 2 children in group 2 tended to a continued increase in their GHBP levels. There was no correlation with the increase in growth velocity, as children in both groups grew equally well, but higher insulin-like growth factor-I levels were found in group 1, although the difference between the two groups was not significant. These data show that GH can increase GHBP levels and that there is a differential effect depending on the mode of GH administration, although the reason for and the role of such regulation remains to be explained.