TURNOVER OF CATECHOLAMINES IN ACTIVE AND HIBERNATING GROUND SQUIRRELS

¹ Departments of Pharmacology and Anatomy, Harvard Medical School, Boston, Massachusetts

The turnover of endogenously labeled norepinephrine and epinephrine was studied in different tissues of active and hibernating ground squirrels. The animals were injected with dl-3,4-dihydroxy-phenylalanine-H³ to label the catecholamine stores and the rate of fall of specific activity of endogenously labeled norepinephrine and epinephrine was taken as an index of the turnover of these amines in different organs. In the active state the turnover rate of catecholamines was highest in the brown adipose tissue where the specific activity of norepinephrine and epinephrine fell by 97% in 24 hr. It was lowest in the adrenal medulla where the fall of specific activity was 45%/24 hr. In the heart and brain the rate of fall of specific activity of catecholamines was similar: 90% in 24 hr. In hibernating ground squirrels the turnover rates of norepinephrine and epinephrine were greatly diminished in all organs studied, indicating a considerably reduced sympathetic activity. The highest turnover rate in this state was observed again in the brown adipose tissue, where the specific activity of norepinephrine and epinephrine fell by 32% in 24 hr. The turnover of norepinephrine and epinephrine in the brain stopped completely from the very beginning of hibernation when the temperature of the animal was still in the normal range, suggesting that the lack of function of central adrenergic neurons might in some way initiate hibernation, rather than simply be a consequence of it.

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