AJP - Endocrinology and Metabolism, Vol 273, Issue 3 E549-E556, Copyright © 1997 by American Physiological Society
Growth hormone-binding protein enhances growth hormone activity in vivo
D. Turyn, F. P. Dominici, A. I. Sotelo and A. Bartke
Instituto de Quimica y Fisicoquimica Biologica (Universidad de Buenos Aires-CONICET), Facultad de Farmacia y Bioquimica, Argentina.
The decay curve of labeled growth hormone (GH) in the plasma followed a
three-compartment model and could be described by the equation:
concentration = Ae-alpha t + Be-beta t + Ce-gamma t, where A, B, and C are
y-intercepts and alpha, beta, and gamma are compartments. When 125I-labeled
ovine prolactin (oPRL) was injected, the decay curve could be described by
the equation: concentration = Ae-alpha t + Ce-gamma t. Formation of
125I-labeled bovine-GH-binding protein (GHBP) complexes with somatogenic
characteristics was demonstrated in the serum of both normal and GH
transgenic mice. In contrast, 125I-oPRL was unable to form complexes of
this type in any of the mice studied. Receptor-mediated liver uptake was
found to be faster for PRL than for GH (5-6 min vs. 15-20 min). Liver
uptake of radioactivity was significantly lower for PRL than for GH [liver
to blood ratio (L/B) of 1.7 +/- 0.3 at 6 min vs. L/B of 3.7 +/- 0.6 at 20
min, respectively]. The presence of binding proteins for GH substantially
reduces the clearance of this hormone and consequently increases the liver
uptake of GH (mediated by GH receptors). This suggests that GHBPs act to
increase the biological activity of GH in vivo.
