Glycogen accumulated in the brain following insults is not degraded during a subsequent period of ischemia

The primary objective of this study was to attempt to induce excessive intraglial acidosis during ischemia by subjecting rats to an initial insult which leads to postinsult accumulation of glycogen, presumed to accumulate primarily in astrocytes. The initial insults were 15 min of transient forebrain ischemia, 30 min of hypoglycemic coma, and intraperitonial injection of methionine-sulphoximine (MSG). In the first two of these insults, glycogen content in neocortex increased to 6-7 mM . kg(-1) after 6 h of recovery, and in MSO-treated animals even higher values were measured 24 h after administration (similar to 12 mM . kg(-1)). In spite of this glycogen loading, the amount of lactate formed during a subsequent ischemic insult (of 5-30 min duration) did not exceed values usually obtained during complete ischemia in animals with normal glycogen contents (tissue lactate contents of similar to 15 mM . kg(-1)). This was because appreciable amounts of glycogen (3-7 mM . kg(-1)) remained undegraded even after 30 min of ischemia. The undigested part largely reflected the extra amount of glycogen accumulated after the initial insults. It is discussed whether this part is unavailable to degradation by phosphorylase.