Circulating Inhibin A and Inhibin B in Normal Menstrual Cycle during Breeding Seasons of Japanese Monkeys

In order to clarify the endocrinological profiles of inhibins during normal menstrual cycles in Japanese monkeys, plasma concentrations of inhibin A and inhibin B were measured by enzymelinked immunosorbent assay. In addition, circulating gonadotropins and steroid hormones were measured. Blood samples were taken from four Japanese monkeys showing normal menstrual cycles. Plasma inhibin A remained low during the early follicular phase but was high during the luteal phase. Plasma inhibin B was high in the early follicular phase, but fell during the late follicular phase, and remained low during the luteal phase. A significant inverse correlation was observed between plasma concentrations of inhibin B and FSH during the mid-follicular phase, but not between inhibin A and FSH. Plasma inhibin A showed a significant positive correlation with progesterone in the normal menstrual cycle. These results suggest that inhibin B during mid-follicular phase is mainly involved in the suppression of FSH secretion from the pituitary gland, and also that the main source of inhibin A during the luteal phase is corpora lutea in normal menstrual cycle of Japanese monkeys.