Norepinephrine content in cardiovascular tissues from the aged Fischer 344 rat.

The major aim of the present study was to examine cardiovascular tissues and to determine if norepinephrine (NE) stores declined in aged (22-30 months old) male Fischer 344 (F344) rats. NE content was measured by HPLC in the whole heart, ventricle, atria, caudal artery, renal arteries, portal vein and kidney. The release of [3H]NE from the caudal artery of adult and aged rats was assessed as a functional index of sympathetic innervation. Renal alpha 2-adrenergic binding sites were also determined using 2.0 nM [3H]rauwolscine. In general, total NE content per organ was not altered in aged rats. The exception was the ventricle of aged rats which exhibited a 25% decrease in NE content. In contrast, NE content per gram of tissue weight was significantly decreased in the whole heart, atria, ventricle, kidney and caudal artery of aged rats when compared to that of adults (6-8 months old). Neither basal nor potassium-stimulated NE release was altered in the caudal artery of aged rats. Presynaptic regulation of NE release by taurine and alpha 2-adrenoceptors was also not affected by age. Renal alpha 2-adrenergic binding sites were decreased 23% in aged rats. Tissue growth that occurs as a function of aging does not appear to receive a concomitant increase in sympathetic growth as indexed by NE content. The findings of the present study would lead to the conclusion that with the exception of the ventricle, sympathetic nerve terminals of the aged male F344 rat are relatively intact.