Control of estradiol secretion in reproductive ageing

Abstract

Background: Estradiol (E2) concentration is preserved in older reproductive-aged women despite a decrease in follicle number and androstenedione (AD) levels. We hypothesized that increased aromatase activity accounts for E2 preservation in older women. Methods: Older (36-46 years; n = 11) and younger (21-35 years; n = 10) women with 25- to 35-day menstrual cycles participated in a parallel design study. Daily blood samples were drawn starting at menses, and recombinant human FSH (rhFSH), 150 IU, was administered when the dominant follicle's diameter was ≥16 mm. FSH, LH, E2, estrone (E1), AD and the AD/E1 ratio were compared. Results: E2 and E1 concentrations and the E1/E2 ratio were similar across the follicular phase in older compared with younger women, whereas AD and the AD/E1 ratio were lower. Older women had higher FSH concentrations in the early follicular phase and fewer small follicles. RhFSH-stimulated changes in E1 were similar between older and younger subjects despite the smaller number of follicles. Conclusions: These findings suggest that E2 secretion is maintained by increased aromatase function in older compared with younger reproductive-aged women, whereas there is no apparent difference in 17β-hydroxysteroid dehydrogenase activity. The increased aromatase is probably driven by increased FSH in the early follicular phase and compensates for the decreased follicle number in older reproductive-aged women. © 2006 Oxford University Press.