Temporal relation between leptin and various indices of sexual maturation in the male rat

Recent studies in humans and rhesus monkeys have suggested the possibility that the adipose tissue hormone leptin has a stimulatory and/or permissive effect on the onset of puberty in the male. We evaluated this hypothesis by measuring leptin in groups of male rats between the ages of 26 days and 96 days. A statistically significant positive correlation was present between serum leptin and age, body weight, prostate, seminal vesicle, and testes w eight (both absolute and as a function of body weight). A statistically sig nificant negative correlation was present between leptin and serum FSH and alpha-inhibin. There was not a statistically significant correlation betwee n leptin and testosterone or LH. There was a statistically significant incr ease in the serum leptin concentrations at day 47. This rise was coincident with the peripubertal growth spurt in the secondary sexual organs and the peripubertal testosterone rise but occurred after the prepubertal rise in t esticular weight, the appearance of elongating spermatids in the testes, an d the start of the decline in FSH. In animals in which the peripubertal tes tosterone rise was delayed by the administration of EDS, serum leptin showe d statistically significant differences from control. These data do not sup port the hypothesis that leptin provides a trigger for the onset of puberty in the male rat. They do suggest that leptin may be involved in the second ary sexual organ growth spurt and are consistent with the hypothesis that t estosterone stimulates leptin synthesis during puberty.