Gonadotropin responses to estrogen-positive and -negative feedback are identical in African-American and Caucasian women

Abstract

Context: Gonadotropin levels are similar in African-American women (AAW) and Caucasian women (CW), despite higher preovulatory estradiol (E2) levels in AAW, suggesting that AAW may be less sensitive to E2 feedback than CW.

Objective: The aim of the study was to determine whether responsivity to estrogen feedback differs in AAW and CW.

Design and setting: Subjects were studied in the early follicular phase using a 5-d, graded E2 and progesterone infusion.

Subjects: Healthy, normal-cycling AAW (n = 10) and CW (n = 13) aged 23-30 yr participated in the study.

Main outcome measures: Blood samples were collected every 4 h and assayed for LH, FSH, E2, and progesterone.

Results: There was no difference in E2-negative feedback on LH (nadir, 3.8 ± 0.4 vs. 5.4 ± 0.9 IU/liter; time of nadir, 33.2 ± 3.3 vs. 32.3 ± 2.7 h) or FSH (nadir, 3.1 ± 0.4 vs. 3.1 ± 0.3 IU/liter; time of nadir, 48.8 ± 2.7 vs. 50.5 ± 3.1 h) in AAW compared to CW. The two groups also demonstrated similar positive feedback responses of E2 on LH (peak, 80.3 ± 13.3 vs. 73.1 ± 11.6 IU/liter; time of peak, 80.4 ± 4.3 vs. 86.5 ± 3.1 h) and FSH (peak, 13.4 ± 1.4 vs. 10.2 ± 1.0 IU/liter; time of peak, 82.2 ± 4.0 vs. 97.2 ± 4.9 h).

Conclusions: LH and FSH feedback responses to a controlled steroid infusion do not differ between AAW and CW, indicating that AAW do not have diminished hypothalamic-pituitary responsivity to E2. These studies support the concept of a threshold effect of E2 in generating LH-positive feedback, suggest pituitary insensitivity to differences in E2 of the magnitude observed in prior studies, and account for similarities in gonadotropins despite E2 differences in AAW compared with CW.

Trial registration: ClinicalTrials.gov NCT00455962.

Figures

Fig. 1.

Mean ± sem for AAW (filled symbols) and CW (open symbols) for LH (middle panel) and FSH (bottom panel) during a graded steroid infusion demonstrate the negative- and positive-feedback effects of E2. In the top panel, the horizontal bars demonstrate the sex steroid infusion rates. LH and FSH levels are expressed in international units per liter (IU/liter) as equivalents of the 2nd IPRP 80/552 for LH and the 2nd IPRP 78/549 for FSH.