Liver glycogen metabolism in endotoxin shock. II. Endotoxin administration increases glycogen phosphorylase...

The effects of E. coli endotoxin administration on hepatic glycogen phosphorylase activities in dogs were investigated. Hepatic glycogen phosphorylase activities in both control and endotoxic dogs were inactivated spontaneously by preincubation of enzyme preparations at 25 degrees C. Total glycogen phosphorylase activity was not significantly altered during preincubation. The activity of glycogen phosphorylase a was increased by 83 and 80% at 1 and 2 hr postendotoxin, respectively, without preincubation; and by 203 and 133% at 1 and 2 hr postendotoxin, respectively, after 30 min preincubation. Without preincubation, the glycogen phosphorylase percentage a activity was increased from the control value of 37 to 58% at 1 hr postendotoxin and to 53% at 2 hr postendotoxin. After 30 min preincubation, the glycogen phosphorylase percentage a activity was increased from the control value of 10 to 28% at 1 hr postendotoxin and to 20% at 2 hr postendotoxin. The time required for half maximum inactivation of percentage a activity was 16.5, 33, and 24 min for control, 1 and 2 hr postendotoxin, respectively. Although the Vmax and Km for glucose-1-P for total glycogen phosphorylase were not affected by endotoxin administration, the Vmax for glucose-1-P for glycogen phosphorylase a was increased by 57.3 and 42.7% at 1 and 2 hr postendotoxin, respectively, with no change in the Km values. Glucose inhibited glycogen phosphorylase a activity both in control and endotoxin-injected dogs, but the I50 value was increased by 35% in endotoxin-injected (2 hr) dogs. AMP activated glycogen phosphorylase b activity both in control and endotoxin-injected dogs with no change in A0.5 values between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)