Exercise training reverses the age-related decline in tyrosine hydroxylase expression in rat hypothalamus

Tyrosine hydroxylase (TH) is the rate-limiting enzymatic step in the catecholamine biosynthesis pathway. Some studies have demonstrated that aging is associated with a decrease in TH activity and TH mRNA in rat hypothalamus. We previously demonstrated that exercise training can decrease TH gene expression in the adrenal medulla of young but not senescent rats. This study was designed to examine the effects of endurance training on the TH expression in hypothalamus with aging. To this end, we assessed TH mRNA, TH immunoreactivity, and TH activity with or without exercise training. Young and old F-344 female rats were trained by treadmill running for 8 weeks. All parameters examined were significantly lower in hypothalamus of old (25-month) compared with young (5-month) control animals (p < .05). Exercise training significantly elevated TH mRNA (n = 5-7 in each group), TH immunoreactivity (n = 5-8 in each group), and TH activity (n = 12-13 young groups and n = 6 old groups) in the hypothalamus of old animals (p < .05), but there was no significant change in any of these parameters in young animals following training. These data indicate that endurance training can reverse the age-related decline in catecholamine biosynthesis in the hypothalamus.