Norepinephrine triggers medullar epinephrine depletion during normoglycemia

Our experiments did show that chronic 12 hours administration of norepinephrine (NE) to rats by means of subcutaneously implantable retard tablets, led to a highly significant epinephrine (E) depletion of the adrenal medulla during normoglycemia. The expected rise of free plasma NE at 6 and 12 hours was accompanied by increased free plasma E values at 12 hours. At this very time point the liver contents of glycogen and free intracellular glucose showed their most pronounced decrease. Since at 12 hours both liver glycogen and medullar E values were at their lowest, a second experiment was performed to examine a possible causal relationship. In order to curb the breakdown of liver glycogen, rats were force fed with 50% glucose solution 9 hours after NE tablet implantation. Glucose feeding not only caused a much less pronounced liver glycogen fall at 12 hours, but, at the same time also prevented E depletion of the adrenal medulla. These observations suggested that rapid fall of liver glycogen and/or liver intracellular free glucose might be the trigger for medullar E depletion, even before hypoglycemia.