Biochemical Basis of Heart Function. V. Effect of Starvation on Storage, Transport, and Synthesis of Cardiac Norepinephrine in Rats

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Abstract
Starvation of rats was observed to increase the concentration of endogenous norepinephrine in both normal and adrenalectomized animals. Refeeding the starved animals restored the cardiac level of norepinephrine toward the control value. The proportion of norepinephrine decreased in the granular fraction and increased in the soluble fraction of the heart in fasted rats. Although the plasma level of norepinephrine in starved rats was higher than the control, no appreciable difference in the abilities of the hearts from these animals to accumulate 3H-norepinephrine was observed. The uptake of 14C-tyrosine by the hearts of starved animals was comparable to that by the control rats; however, the rate of synthesis of 14C-catecholamines in the hearts of starved rats was significantly decreased. Tyramine treatment was found to lower the cardiac norepinephrine content in the starved rats to the same extent as in the control. On the other hand, exposure of the rats to cold reduced the cardiac norepinephrine to a lesser degree in the starved animals in comparison to the control. It is suggested that starvation may decrease the proportion of norepinephrine which is available for release from the storage granules and thus reduces the influence of sympathetic activity in the heart.

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