Leptin secretion from the epididymal fat pad is increased by the sexual maturation of the male rat

Although leptin has been implicated as an important factor in triggering the onset of puberty in females, much less is known about the role of this adipose tissue hormone in the sexual maturation of males. Previous work in the rat has suggested that the peripubertal rise in testosterone precedes an increase in leptin secretion, and it has been suggested that the testosterone rise induces the leptin increase. These studies examined some of the interactions between leptin secretion and the peripubertal testosterone rise in male rats. Serum leptin concentrations were significantly elevated in young adult male rats compared with immature rats. Cultured epididymal fat pads obtained from adult animals secreted significantly more leptin than did those obtained from immature rats. Castration of immature rats with or without testosterone replacement for 1 week did not result in a significant change in either the serum leptin concentrations or the ability of the epididymal fat pad to secrete leptin. Exposure of epididymal fat to 5 ng/mL of testosterone in vitro resulted in a significantly enhanced secretion of leptin into the media compared with plain media controls. These results confirmed that there is an increase in serum leptin concentrations with sexual maturation in the male rat. They also suggest that this increase is due to an enhanced ability of adipose tissue to secrete leptin. Within a normal physiologic range, testosterone may play a role in inducing this increased ability to secrete leptin.