TIME-COURSE OF THE DEFECTIVE ALPHA-CELL RESPONSE TO HYPOGLYCEMIA IN DIABETIC BB RATS

Although it is understood that patients with insulin-dependent diabete s mellitus (IDDM) lose the ability to release glucagon during a hypogl ycemic challenge, the relationship of this defect to the disease onset and loss of beta-cell function is not well defined. To address this i ssue, we measured the counterregulatory response in three groups of BB /wor rats during sequential 90-minute euglycemic (7 mmol/L) and hypogl ycemic (3 mmol/L) insulin cramps (180 pmol/kg . min). Group 1 (n = 8) consisted of nondiabetic BE rats (aged 84 +/- 3 days), and groups 2 an d 3 were rats studied 1 day (n = 7) or 7 days (n = 6) after diabetes o nset. Plasma glucagon concentrations were similar in all groups during euglycemia (244 +/- 47 ng/L for nondiabetic. 308 +/- 38 for 1 day of diabetes, and 277 +/- 30 for 7 days of diabetes). Moreover, after I da y of diabetes, the increase in plasma glucagon during hypoglycemia was similar to that seen in controls (to 581 +/- 94 and 650 +/- 118 ng/L, respectively) even though insulin production by the pancreas was virt ually absent. However, after 7 days of diabetes, plasma glucagon only increased to 339 +/- 59 ng/L during hypoglycemia (P = nonsignificant v basal), despite normal pancreatic glucagon content (11.5 +/- 1.2 v 10 .8 +/- 0.6 mu g/g in nondiabetic controls). In conclusion, the hypogly cemia-associated defect in glucagon release occurs early in the course of diabetes in BE rats and is not associated with decreased baseline plasma or pancreatic glucagon levels. This impairment, although not im mediately linked to the decrease in pancreatic insulin content, occurs soon afterward, implying that the two events are related. Copyright ( C) 1996 by W.B. Saunders Company