Correlation Between Fluctuations of Testosterone Levels in Systemic Circulation and Sexual Behavior in Intact Female Japanese Monkeys in the Laboratory Condition

Abstract

Heterosexual interactions of pairs of Japanese monkeys were studied in connection with fluctuations of testosterone concentrations in blood plasma of females, using seven intact adult females and two males. Blood was collected from the females daily or with a few days interruption. Testosterone, estradiol-17b, and progesterone in blood plasma were determined by radioimmunoassay. The behavioral records were obtained through heterosexual pairing tests of 30 minutes duration. Testosterone levels in blood plasma considerably fluctuated in each female from day to day, and statistically significant change could not be detected during the normal menstrual cycle. Male approach to females increased simultaneously with the increment of plasma testosterone level in three out of seven females. In seven normal menstrual cycles both copulation with ejaculation in the early follicular phase of the menstrual cycle and male approach in the late follicular phase of the cycle were observed in significantly higher frequencies on days of high level of testosterone, as compared with them on days of low level of testosterone in respective phase. These results suggest that testosterone enhances some types of sexual behavior of the male partner, at least, in the existence of estradiol-17s in the late follicular phase of the menstrual cycle.