Effect of ischemia and reperfusion of pig skin flaps on epidermal glycogen metabolism.

Pedicled skin flaps in the pig have been used to investigate the effects of 3-h ischemia and reperfusion on the epidermal metabolism of glycogen and glucose. Epidermal glycogen content fell steadily at a rate of about 1.2 mumol of glucose-equivalents per g wet weight per h whereas the rate of glucose consumption declined from 1.8 mumol per g wet weight during the first hour to about 0.25 mumol per g wet weight in the third hour. During ischemia the proportion of glycogen synthase in the I form increased progressively from an initial value of about 8% to about 70%, but the proportion of phosphorylase in the a form decreased only in the third hour of ischemia. The concentration of ATP decreased and ADP and AMP increased but the total pool of epidermal adenine nucleotides was not depleted. On reperfusion, these changes were reversed and normal epidermal concentrations of glucose and adenine nucleotides were restored within 30 min and remained stable thereafter. The resynthesis of glycogen proceeded at a steady rate of about 1 mumol per h per g wet weight and the phosphorylation state of both glycogen synthase and phosphorylase approached normal values after 3 h. It is concluded that epidermal glycogenolysis in ischemia is, at least in part, a consequence of activation of phosphorylase b by AMP, and that glycogen resynthesis on reperfusion is promoted by the ischemic activation of glycogen synthase.