Bimodal influence of plasma estradiol on relation between insulin-like growth factor-I (IGF-I) and estradiol in women.
OBJECTIVE: To compare the influence of low and normal endogenous estradiol concentration on circulating hGH, IGF-I and IGFBP-3 levels as well as on mutual correlations of these parameters.
PATIENTS: 45 women (age 30.7 ± 9.0 years, BMI 25.7 ± 8.0) divided into group A - 15 hypoestrogenic women and group B - 30 normoestrogenic controls. Neither of the women was menopausal nor hyperprolactinemic.
METHODS: Blood sample was taken at the standard conditions prior to the initiation of hormonal supplementation therapy in group A and at the day 3-5 of menstrual cycle in group B. Serum hGH, IGF-I, IGFBP-3, insulin, testosterone, sex hormone binding globulin (SHBG) dihydroepiandrosterone sulphate (DHEAS) and LH as well as prolactin (PRL), FSH and estradiol levels were measured by standard RIA kits.
RESULTS: Mean IGF-1, LH, FSH, testosterone and estradiol and PRL plasma levels were lower in group A compared to group B. There were no significant differences in mean SHBG, insulin and DHEAS levels. There were also no differences in mean: age, body mass, BMI as well as percentage of each BMI range between groups. Regardless the estradiol level the IGF-I/age link was found in both groups. A IGF-I/IGFBP-3 relation was found in both groups. IGF-I/estradiol link was seen only in group A. In group B hGH/SHBG link was found, in group A this relation was indirect. A link between hGH and testosterone levels was found only in group B. SHBG was related in group B to IGFBP-3, testosterone and to DHEAS. Insulin/IGFBP-3 link was seen in group B. The stepwise multiple regression revealed DHEAS and LH as predictors of IGF-I level in group A, while in group B none of the parameters predicted IGF-I level. The results of the same analysis in case of hGH are as follows: in group A hGH level was predicted by estradiol and SHBG. In group B none of factors predicted hGH levels.
CONCLUSION: Estradiol plasma level is correlated to circulating IGF-I, albeit the relation seems to be biphasic....