EFFECTS OF HYPOTHYROIDISM OR HYPERTHYRODISM ON GROWTH HORMONE-BINDING PROTEIN

OBJECTIVE Growth hormone (GH) receptors are influenced by the thyroidal state of experimental animals. It has been suggested that GH-binding protein (BP) might serve as an indirect measure of the GH receptors. The present study was undertaken to investigate the growth hormone binding protein in patients with hypo or hyperthyroidism. PATIENTS Patients included 42 adults with untreated hyperthyroidism (FT4 > 25 pmol/l; TSH < 0.15 mU/l) and 29 adults and three children with untreated hypothyroidism (FT4 < 10 pmol/l; TSH > 15 mU/l). MEASUREMENTS Growth hormone binding protein was measured by a binding assay with dextran-coated charcoal separation. The specific binding of I-125-human GH (1 ng) obtained with 50-mu-l serum was expressed as a percentage of the total c.p.m. RESULTS Growth hormone binding protein specific binding in hypothyroid adults and children was significantly lower than in their respective controls in both adults and children (P < 0.001). In patients with FT4 levels > 40 pmol/l, the mean (+/- SEM) growth hormone specific binding (12.89 +/- 0.59%) was higher than in controls (P < 0.05). However, in 15 hyperthyroid patients with levels of FT4 of 25-40 pmol/l, the mean growth hormone binding protein specific binding (11.22 +/- 0.76%) was not different from that in normal human subjects. The affinity constants (K(a)) obtained by Scatchard analysis for the hypothyroid and hyperthyroid patients' sera were not significantly different from that for normal human sera. Binding capacity for the hypothyroid sera was significantly lower (P < 0.02), while that of hyperthyroid sera was increased (P < 0.001). CONCLUSIONS Growth hormone binding protein correlates positively with the thyroid status. It can be indirectly deduced that this reflects a similar relationship with the human GH receptor.