Some characteristics of the normal menstrual cycle of the bonnet monkey (M. radiata)

Abstract

Sixty-two menstrual cycles were observed in five bonnet monkeys over a period of 12 months. The menstrual cycles ranged in length from 22 to 35 days, although cycles of from 26 to 29 days were most frequent. Menstrual flow occurred for two to seven days, the flow lasting for three to four days in the majority (82%) of the cycles. Serum estradiol-17β (E₂) and progesterone (P) were measured by radioimmunoassay in two consecutive cycles in each monkey and correlated with changes in the quantity of cervical mucus secretion and spinnbarkeit. The day of the estradiol peak was considered as day 0. The E₂ levels began to rise one to three days before the peak, returning to baseline levels within two days and thereafter remained at low levels. The serum P rose 2 days after the E₂ peak, and maximum level was attained at 10 to 12 days after the E₂ peak. The quantity of cervical mucus increased proportionately with estrogen. However, the quantity remained at maximum levels even after the decline of the serum E₂ level. Similar trends were observed with the spinnbarkeit.