Blood growth hormone-binding protein levels in premenopausal and postmenopausal women: Roles of body weight and estrogen levels

A substantial proportion of GH circulates bound to high affinity GH-binding protein (GHBP), which corresponds to the extracellular domain of the GH re ceptor. Current evidence indicates that nutritional status has an important role in regulating plasma GIIBP levels in humans. In the present study the relationship among plasma GHBP levels, body composition [by bioelectrical impedance analysis (BIA) and dual energy x-ray absorptiometry (DEXA)] and s erum estradiol (E-2) was evaluated in premenopausal (n = 92) and postmenopa usal (n = 118) healthy women with different body weight [three groups accor ding to body mass index (BMI): normal, 18.5-24.99; overweight, 25-29.99; ob ese, 30-39.99 kg/m(2)]. Plasma GHBP levels were measured by high pressure l iquid chromatography gel filtration. GH and insulin-like growth factor I le vels were determined by immunoradiometric assay and RIA, respectively. GHBP levels were significantly higher in premenopausal women with BMI above 25 kg/m(2) (overweight, 3.789 +/- 0.306 nmol/L; obese, 4.372 +/- 0.431 nmo l/L) than those observed in postmenopausal women (overweight, 1.425 +/- 0.0 9 nmol/L; obese, 1.506 +/- 0.177 nmol/L). No significant differences were f ound between normal weight premenopausal (1.741 +/- 0.104 nmol/L) and postm enopausal (1.524 +/- 0.202 nmol/L) women. In premenopausal women GHBP level s correlated positively with BMI (r = 0.675; P < 0.001), fat mass (FM; r = 0.782; P < 0.001; by BIA; r = 0.776; P < 0.001; by DEXA), truncal fat (TF; r = 0.682; P < 0.001), waist to hip circumference ratio (WHR; r = 0.551; P <less than> 0.001), and E-2 (r = 0.298; P < 0.05), whereas no significant c orrelation was found in postmenopausal women between GHBP levels and BMI, F M, TF, WHR, or E-2. In normal weight pre- and postmenopausal women GHBP lev els did not change between the ages of 20 and 69 yr. No statistically signi ficant correlation was found between GHBP and age for all groups studied. M oreover, in two distinct subgroups of pre- and postmenopausal women, aged 4 0-49 yr, the direct relationship between GHBP levels and all indexes of adi posity were only observed in premenopausal women [BMI: r = 0.836; Pt 0.001; FM: r = 0.745 (BIA) and r = 0.832 (DEXA); P < 0.001; TF: r = 0.782; P <les s than> 0.001; WHR: r = 0.551; P < 0.05], but not in postmenopausal women. In conclusion, the present data indicate a strong direct correlation betwee n GHBP and body fat in premenopausal, but not in postmenopausal women, wher eas they failed to detect a relationship between GHBP and age. Therefore, t hese results suggest that endogenous estrogen status may be an important de terminant of the changes in GHBP levels in women with different body weight s.