Abstract
The present study was conducted to reveal the developmental changes in plasma IGF-1 concentrations in male and female Japanese macaques by a long-term longitudinal method from 3 to 6 years of age. The sexual maturation and reproductive seasonality in both genders were determined by plasma profiles of gonadal steroids, such as testosterone and progesterone. Since Japanese macaques have been known to have a rather unique characteristic of clear seasonality in reproduction, the present study introduced a time series analysis to extract two factors -seasonal and age changes- from the changes in plasma hormonal levels. Plasma IGF-1 concentrations showed seasonal and age-development changes in males. Plasma IGF-1 levels were high in summer and low in spring. Age-dependent changes would be superimposed on the seasonal change, because the IGF-1 levels of 4- and 5-year-old males were nearly twice as high as those of 3-year-old males in every corresponding season. Females, on the other hand, did not have clear age-dependent changes in the plasma IGF-1 level. The time series analysis suggests a close functional relationship between IGF-1 and testosterone secretion in regulating skeletal growth and seasonal changes in body weight.
