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

The transition from regular ovarian cyclicity to menopause is associated wi th a rise in the circulating concentrations of follicle stimulating hormone (FSH), despite the maintenance of serum oestradiol concentrations during t he perimenopause. The aim of this study was to compare the pattern of secre tion of dimeric inhibins, activin A, gonadotrophins and steroids in regular ly cycling women of 40-50 years with normal and raised early follicular pha se serum FSH concentrations and young women (25-33 years) during the menstr ual cycle. Blood samples were taken prospectively almost daily throughout t he menstrual cycle. Women recruited were classified into three groups: (i) older women with normal FSH [(ON-FSH), day 3 FSH <8 mIU/ mi, n = 10]; (ii) older women with raised FSH [(R-FSH), day 3 FSH >8mIU/ml, n = 6] and (iii) young normal FSH (YN-FSH) women, age 25-32 years (n = 6), Cyclic patterns o f 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 price r to the luteinizing hormone (LH) surge and in the mid-luteal phase and low er concentrations of inhibin B in the early follicular phase compared with the ON-FSH group. Serum concentrations of activin A, progesterone and oestr adiol were similar in all three groups. It is concluded from this study tha t 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 fo llicular phase. However, lower circulating concentrations of inhibin A in t he luteal phase of the R-FSH group may also contribute to the rise in early follicular phase FSH concentrations during the menstrual cycle, although f urther studies with larger numbers are required to confirm this observation .