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Comparison of the handling of norepinephrine in the myocardium of adult and old rats.

The handling of norepinephrine was compared in the myocardium of adult and old rats. Endogenous norepinephrine levels were significantly lower in the hearts of old animals. Following intravenous injection of 3H-norepinephrine [3H-NE] the initial uptake was slightly higher in the old animals; subsequently, however, there was a more pronounced and prolonged fall in 3H-NE specific activity in the myocardium of the old rats. The increased turnover rate was associated with normal catecholamine synthesis. Studies of the subcellular distribution of 3H-NE showed an inability of the myocardium from ageing rats to retain norepinephrine in the storage granules with subsequent loss of the soluble fraction.