Glucoregulatory response to moderate exercise in long-term islet cell autografted dogs

The glucoregulatory response to moderate treadmill exercise (approximately 60% maximum heart rate; 60 min at 100 m/min, 12% grade) was examined in six controls and six pancreatectomized dogs that had been normoglycemic and insulin independent for more than 1 year since autograft of isolated islets of Langerhans (Tx). There were no significant intergroup differences in plasma glucose levels during exercise, but return to baseline after exercise was delayed in Tx (p less than 0.05). In Tx, the initially suppressed insulin levels rose above baseline from 30 to 60 min. Within Tx, exercise-induced levels of plasma glucagon and epinephrine were more variable than control and strongly correlated (r = 0.81, p less than 0.001), perhaps indicating that the A cells within the grafted islets were regulated by circulating beta-adrenergic agonists. We conclude that the isolated islets were removed from direct central control. In Tx dogs, the variable counterregulatory responses and the diminished recovery of plasma glucose after exercise indicate reliance on alternative glucoregulatory mechanisms.