One of the best examples of adaptation to cardiovascular perturbations at the molecular level is the induction of tyrosine hydroxylase (TH) in adrenal glands and sympathetic ganglia in response to reserpine-induced hypotension. It has been shown that aging is associated with alterations in TH, the rate limiting enzymatic step in catecholamine (CA) synthesis. However, the role of TH gene expression in the age-related decline in cardiovascular homeostatic mechanisms remains to be elucidated. In the research described in this proposal, the hypothesis will be tested that aging animals are impaired in the ability to induce TH in response to reserpine because of alterations in mechanisms regulating TH gene expression. The specific objectives of this project are the following: 1. The induction of TH expression in vivo by reserpine will be compared in the adrenal glands of rats 4-30 months of age: Alterations in the TH protein will be measured with a specific antibody and correlated with the kinetics of TH activity and TH mRNA levels. The time course of induction of TH and TH mRNA will be compared in rats of different ages and correlated with rates of TH mRNA transcription. Translatability of TH mRNA will be correlated with alterations in TH protein and activity. Age-related alterations in pre-and post-synaptic parameters of neurotransmitters that regulate TH induction will also be correlated with age-related alterations in induction of TH and TH mRNA. 2. The induction of TH gene expression in vitro will be compared in cultured adrenal medullas isolated from different aged rats; the induction of TH and TH mRNA by dexamethasone and nicotinic receptor agonist will be compared. The time course and magnitude of induction of TH activity, TH protein levels and TH mRNA will be compared with rates of TH protein synthesis in situ. TH mRNA transcription will be measured and compared with time course and magnitude of induction of TH mRNA and TH activity. 3. The effects of dietary restriction on age-associated alterations in adrenal TH gene expression will be assessed. In the past several years, life-long caloric restriction, a treatment that increases the life-span of mammals, has become a tool to distinguish time-dependent effects from biological aging. Therefore, dietary restriction will be used to determine if age-related differences in modulation of TH gene expression by reserpine in vivo and in culture is integral to the aging process.
