The purpose of this study is to compare the changes of estradiol-17 B, progesterone and thyroxine and secondary sexual characteristics in pubescent female cynomolgus monkeys during pre-menarche and post-menarche periods. The results showed that the initiation of sexual swelling, sexual skin colour, growth and harddening of nipple in most monkeys were happened over 100 days prior to the onset of menarche. These changes were correlated with prominent rise in serum estradiol and thyroxine levels exceeded the levels found during 1-2 years of age. Serum E2 and P levels during pre- menarche were consistently lower than hormonal levels of adult cycling females but most monkeys instantly exhibited progesterone increment greater than 1,000 pg/ml for the first time during 2 weeks prior to the onset of menarche. These were followed by regularity of the menstrual cycle with increment of serum progesterone levels during the last 2 weeks of the cycle. Elevation of serum T, levels in mose monkeys were directly, correlated with the rise of progesterone levels (0.21 ≼ r ≼ 0.55, P 0.05)Unlike other Macaca species which exhibited breeding seasonality, maturation of the feedback regulation of hypothalamic-pituitary-gonadal axis in most female cynomolgus monkeys are capable to operate promptly and simultaneously with the onset of menarche.
