Effects of sex and age on serum GH binding protein levels in normal adults

OBJECTIVE: The effects of sex and age on serum growth hormone binding protein (GHBP) levels during adulthood were investigated. DESIGN: The levels of GHBP, insulin-like growth factor-I (IGF-I), and growth hormone (GH) were determined and analysed as a function of sex and age. PATIENTS: We studied 101 normal adults (45 men, aged 20-77 years; 56 women, aged 20-80 years). MEASUREMENTS: GHBP levels were determined using an Ultrogel AcA 44 minicolumn. RESULTS: During the second and third decade, GHBP levels were not different between men (22.8 +/- 1.1%) (mean +/- SE) and women (23.2 +/- 0.8%). After the age of 40 years, however, GHBP levels in men were significantly decreased (19.1 +/- 0.7%), and were lower than those in women (22.7 +/- 0.9%). IGF-I levels correlated positively with GHBP levels in men (r = 0.51, P less than 0.01) but not in women (r = 0.16, NS). CONCLUSIONS: These results indicate that both sex and age may have some effects on the GH-GH receptor-IGF-I axis.