Somatotropic axis and body weight in pre-menopausal and post-menopausal women: evidence for a neuroendocrine derangement, in absence of changes of insulin-like growth factor binding protein concentrations

The altered function of the somatotropic axis observed in perimenopause may underlie the changes in body weight and fat distribution. The aim of the present study was to evaluate, in pre-menopausal and post-menopausal women with body mass index (BMI) > or = or <25, the basal plasma levels of growth hormone (GH), insulin-like growth factor (IGF)-I and -II, IGF binding protein (IGFBP)-1 and -3, and the response of GH and IGFBP-1 and -3 to GH releasing hormone (GHRH) and GHRH plus arginine tests. GH and IGF-I basal concentrations were significantly higher in pre-menopausal than in post-menopausal women, while IGF-II, IGFBP-1 and IGFBP-3 concentrations did not vary significantly. IGFBP-1, but not IGFBP-3, concentrations were higher in lean than in obese patients. Insulin concentrations were significantly higher in obese patients, while no differences were observed between pre-menopausal and post-menopausal women. In all subjects, GH concentrations increased significantly during GHRH test; pre-menopausal and lean women showed a higher response compared to post-menopausal and obese women. The GHRH plus arginine test stimulated GH response in all women, irrespective of age and BMI. IGFBP-1 and -3 concentrations did not vary in response to GHRH or GHRH plus arginine tests. The somatotropic axis undergoes modifications in post-menopausal women, apparently not involving IGFBP-1 and -3. Arginine infusion restores the response of GH to GHRH, in both post-menopausal and obese subjects. A somatostatinergic hyperactivity at the climateric period may underlie the changes both in body weight and somatotropic axis.