Age and Autonomic Balance. ∗

Conclusion

When rats of varying age groups (21, 45, 75, 100, and more than 200 days) are exposed to five successive periods of anoxia (each lasting 25 minutes at 280 mm Hg.) the blood sugar curve shows a definite dependence on the age of the animal. Hyperglycemia is greatest and sustained in very young animals (21 and 45 days). In rats of 75 and 100 days the hyperglycemic phase is greatest initially and diminishes gradually as the experiment progresses. Finally, in adult animals the initial hyperglycemic phase is definitely lessened. At the end of the test period the blood sugar is either about normal or definitely hypoglycemic as an indication that the vago-insulin system has come into prominence. This shift in the balance is, however, not due to an alteration in the activity of the vago-insulin system, but is a result of a diminished excitability of the sympathetico-adrenal system as age increases since the hypoglycemic effect of anoxia on the vago-insulin system as shown by experiments on adreno-demedullated rats is not influenced by the age of the animals.