Dietary restriction modulates the norepinephrine content and uptake of the heart and cardiac synaptosomes

The present study was designed to examine the effects of long-term dietary restriction on cardiac sympathetic nerves and neurotransmitter. The food intake of male, 6-week-old Fischer 344 rats was reduced to 60% of the intake of control rats fed ad libitum. The body and heart weights of rats diet restricted for 4.5 months were less than those of the ad libitum fed animals, while the heart weight to body weight ratios were higher. The norepinephrine (NE) content of hearts from restricted rats (1073 ± 84 ng/g wet wt) was higher than controls (774 ± 38 ng/g wet wt), although the total amount of NE per heart was unchanged. Similarly, the cardiac synaptosomal P₂ fraction from restricted rats possessed a higher NE content (24.1 ± 2.4 ng/mg protein) than the P₂ fraction of ad libitum fed controls (13.7 ± 1.3 ng/mg protein). The desmethylimipramine-sensitive norepinephrine uptake of the P₂ fraction from restricted rats was significantly higher than that of control rats (9.44 ± 1.33 vs 4.75 ± 0.35 ng/mg protein/hr). The NE uptakes of the two groups were similar when uptake was normalized to endogenous NE levels. These results demonstrate that long-term dietary restriction affects cardiac sympathetic nerve endings and suggest that part of the beneficial action of life-long dietary restriction on the age-related decline in cardiovascular regulation may be related to changes in cardiac sympathetic nerves.