Compensatory capabilities of islets of BB Wor rats exposed to sustained hyperglycemia

To determine if discordance for autoimmune diabetes in genetically homogeneous animals might reflect differences in the compensatory capacity of their β cells, the glycemic responses of diabetes-prone BBWor rats during a high rate infusion of 50% glucose were compared with normal and with 40% pancreatectomized Wistar rats similarly infused. In all three groups, the initially severe hyperglycemia declined after the first 48 hours to below the target level of 300 mg/dL despite an increasing rate of glucose infusion. The glycemic profile did not differ from controls and was lower than that of the partially depancreatized rats. Five of 20 hyperglycemic BBWor rats became diabetic during the 12-day infusion of 50% glucose; there was no difference between their glucose profiles and those of the 15 prediabetic BBWor rats that remained nondiabetic throughout the period of hyperglycemic infusion. The latter group of BBWor rats, many of which would ultimately have become diabetic, exhibited a 2.4-fold increase in the volume density of their β cells, compared with a 2.1-fold increase in the Wistar controls. This clinical and morphologic evidence of β-cell compensation in diabetes-prone rats, even in on the verge of overt diabetes, excludes the possibility that subnormal compensation by β cells contributes to diabetes in the BBWor rat.