Leptin is an adipose-tissue secreted
hormone, that acts to decrease caloric intake and to increase energy expenditure. Some of the
leptin effects on the energy balance are known to be mediated by the hypothalamo-pituitary-adrenal (HPA) axis, but the role of this
cytokine in the regulation of the growth and steroidogenic capacity of adrenal cortex is still controversial. Therefore, the present study was designed to explore the long-term effects of native
leptin[1-147] and its biologically active fragment
leptin[116-130] (6 daily
subcutaneous injection of 20 nmol/kg) on the rat HPA axis.
Leptin[1-147] and
leptin[116-130] caused a significant adrenal
atrophy, which was mainly due to the decrease in the volume of zona fasciculata (ZF) and in the number of its parenchymal cells. Both leptins provoked a marked drop in the plasma concentrations of
ACTH and
corticosterone, the main
hormone produced by ZF cells. The effects of
leptin[116-130] were more intense than those of
leptin[1-147].
Leptin[1-147], but not its fragment, evoked a clear-cut rise in the plasma concentration of
aldosterone. Collectively, these findings indicate that prolonged
leptin administration, by inhibiting pituitary
ACTH release, exerts a potent suppressive action on the growth and
glucocorticoid secretory capacity of the adrenal cortex in the rat. The mechanism(s) underlying the
aldosterone secretagogue action of native
leptin remain(s) to be investigated.