Serum concentrations of dimeric inhibins, activin A, gonadotrophins and ovarian steroids during the menstrual cycle in older women

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Abstract
The transition from regular ovarian cyclicity to menopause is associated with a rise in the circulating concentrations of follicle stimulating hormone (FSH), despite the maintenance of serum oestradiol concentrations during the perimenopause. The aim of this study was to compare the pattern of secretion of dimeric inhibins, activin A, gonadotrophins and steroids in regularly cycling women of 40–50 years with normal and raised early follicular phase serum FSH concentrations and young women (25–33 years) during the menstrual cycle. Blood samples were taken prospectively almost daily throughout the menstrual cycle. Women recruited were classified into three groups: (i) older women with normal FSH [(ON-FSH), day 3 FSH 8 mIU/ml, n = 6] and (iii) young normal FSH (YN-FSH) women, age 25–32 years (n = 6). Cyclic patterns of serum inhibins and activin A were similar in the ON-FSH and YN-FSH groups. The R-FSH group had significantly lower concentrations of inhibin A prior to the luteinizing hormone (LH) surge and in the mid-luteal phase and lower concentrations of inhibin B in the early follicular phase compared with the ON-FSH group. Serum concentrations of activin A, progesterone and oestradiol were similar in all three groups. It is concluded from this study that the rise in early follicular phase serum FSH in older women is associated with a decrease in circulating concentrations of inhibin B in the early follicular phase. However, lower circulating concentrations of inhibin A in the luteal phase of the R-FSH group may also contribute to the rise in early follicular phase FSH concentrations during the menstrual cycle, although further studies with larger numbers are required to confirm this observation.
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