The major objectives of this proposal are to define the nature, extent, locus, and mechanism of age-related changes that occur in the human peripheral adrenergic nervous system. We postulate that age-related changes are limited to innervated beta-adrenoceptors. 1) What age-related changes occur in the adrenergic nervous system of humans? We postulate that the increased plasma norepinephrine concentration in the elderly is due, in part, to a defect in adrenergic neuronal uptake. We plan to quantify neuronal uptake of norepinephrine by determining the effect of desipramine on norepinephrine clearance. We also postulate that baroreceptor function is little changed with age. We plan to test baroreceptor function by determining the plasma norepinephrine response to pharmacologically induced changes in blood pressure. Since our previous data indicate that age-related changes in adrenergic function are limited to tissues that contain innervated beta-adrenoceptors, we will investigate the function of the innervated beta-adrenoceptor on human fat cells by determining catecholamine stimulated lipolysis in vivo and in vitro. cAMP accumulation in response to beta-adrenoceptor agonist, NaF, and forskolin will be determined in isolated human adipocytes. We plan to study the pharmacokinetics and pharmacodynamics of prazosin and the stereoisomers of propranolol in young and elderly healthy volunteers as a followup to our previous studies. 2) What is the locus and mechanisms of these changes? Recent reports suggest that endogenous adenosine may be responsible for reduced beta-adrenoceptor responses in elderly animals. We plan to test this possibility in humans by determining the effect of theophylline on the cardiac chronotropic response to beta-adrenoceptor stimulation. We will investigate the density of the beta-adrenoceptor on each subpopulation of mononuclear leukocyte in order to explain our previous observation that the elderly have a 2.5 fold increase in beta-adrenoceptor density on their mononuclear cell membranes. Cells will be separated by binding of each population subtype to immunomagnetic beads. We will characterize the human adipocyte beta-adrenoceptor subtype(s) by determining receptor density,, antagonist affinity, and coupling of the receptors to the catalytic subunit of adenylyl cyclase as assessed by the ratio of the agonist high and low affinity states. Iodinated pindolol will be used as the radioligand; agonists and antagonists for competition binding studies will be based on their specificity for the beta-adrenoceptor subtypes. We will determine whether age-related changes occur in post-receptor events in the human adipocyte by assessing protein phosphorylation in response to isoproterenol, forskolin, and dibutyryl cyclic AMP. Cellular ATP will be prelabelled with 32Pand phosphorylated peptides detected by autoradiographs of SDS-PAGE gels. These studies will be correlated with the functional studies.
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