title: Influence of aging and tyrosine hydroxylase inhibition on tissue levels of norepinephrine during stress.
abstract: The effect of aging was evaluated on norepinephrine content of the heart (ventricles) and spleen of 3- and 24-month-old F344 and Sprague-Dawley rats utilizing a sensitive radioenzymatic assay. To assess sympathetic nervous system activity, the decline in organ norepinephrine content was compared in young and old F344 rats 6 hours after blockade of norepinephrine synthesis with alpha-methyl-p-tyrosine, a tyrosine hydroxylase inhibitor. Three conditions were studied: (a) normal, (b) brief starvation (54 hours), and (c) cold exposure (6 hours, 4 degrees C). There was no significant age-related difference in steady state organ norepinephrine concentration. Based on the response to alpha-methyl-p-tyrosine, aging did not affect the rate of heart and spleen norepinephrine synthesis and, therefore, sympathetic nervous system impulse activity during normal or cold stress conditions. Starvation, however, did not suppress sympathetic nervous system activity to the heart in old animals, as it did in the young rats.
mesh_terms: D000375:Aging; D000818:Animals; D001835:Body Weight; D003080:Cold Temperature; D008297:Male; D008781:Methyltyrosines / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D009929:Organ Size; D051381:Rats; D011916:Rats, Inbred F344; D011919:Rats, Inbred Strains; D013154:Spleen / Q000378:metabolism; D013217:Starvation / Q000378:metabolism; D013312:Stress, Physiological / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors*; D019805:alpha-Methyltyrosine
chemical_list: D008781:Methyltyrosines; D019805:alpha-Methyltyrosine; D014446:Tyrosine 3-Monooxygenase; D009638:Norepinephrine