A longitudinal study of leptin during development in the male rhesus monkey: The effect of body composition and season on circulating leptin levels

The objective of this study was to examine longitudinal changes in serum le ptin concentrations during development and to correlate those changes with sexual development in male rhesus monkeys housed under natural environmenta l conditions. Blood samples were drawn from 8 control animals approximately every other month from 10 to 30 mo of age and thereafter monthly through 8 0 mo of age. Leptin levels declined through the juvenile period until the o nset of puberty and were negatively correlated with body weight. Seven of t he eight animals became sexually mature during the breeding season of their fourth year of life. Puberty was delayed in the other animal until the sub sequent breeding season. There were no significant fluctuations in leptin l evels prior to or in association with the pubertal rise in LH and testoster one (T) secretion. During the peripubertal period, levels of leptin varied between 2 and 3 ng/ml. The animal that exhibited delayed puberty had the lo west body weight and highest leptin levels during this period. With the ach ievement of sexual maturity, leptin levels varied seasonally, with peak lev els in the late winter (Jan-Mar) and a nadir in the late summer (Aug-Sept). A late winter rise in leptin was also evident in most of the animals durin g Years 2 and 3, but not during Year 4. In the fall of Years 5 and 6, the s easonal rise in leptin concentrations lagged 3-4 mo behind the seasonal inc rease in LH and T. In the fall of Year 5, but not thereafter, leptin levels were positively related to percent body fat and negatively correlated with lean body mass. The data do not support the hypothesis that increasing lep tin concentrations trigger the onset of puberty in the male rhesus monkey. During the juvenile period and after sexual maturation, but not during the peripubertal period, leptin secretion varied with season in the animals; bu t the environmental factors that cue or drive this rhythm remain to be dete rmined.