Aging and fasting regulation of leptin and hypothalamic neuropeptide Y gene expression

To investigate the role of aging on the fasting-induced suppression of leptin gene expression and increase in hypothalamic neuropeptide Y (NPY) gene expression, we fasted or fed ad libitum male F-344xBN rats aged 3, 24, and 31 mo for 2 days. We examined leptin mRNA levels in retroperitoneal, inguinal, and epididymal white adipose tissue (WAT); serum leptin levels; and NPY mRNA levels in the hypothalamus. We found that leptin mRNA levels were increased from 3 to 24 mo and leveled off between 24 and 31 mo in both retroperitoneal WAT and inguinal WAT but were unchanged with age in epididymal WAT. Serum leptin levels increased with age, whereas hypothalamic NPY mRNA levels did not change with age. Fasting suppressed leptin gene expression in all three WATs and serum leptin. Moreover, this suppression of serum leptin and of leptin message in retroperitoneal WAT was less in aged rats. Conversely, fasting increased hypothalamic NPY message, again to a lesser extent in aged rats. In both fed (ad libitum) and fasted rats, there was a strong correlation between serum leptin and hypothalamic NPY mRNA levels in the young but not in either of the two aged groups. These data suggest that aged F-344xBN rats are leptin resistant and that the fasting regulation of serum leptin, leptin mRNA, and hypothalamic NPY mRNA is impaired in aged rats.