Insulin release and pancreatic insulin is reduced in young prediabetic BB rats

The pancreases of approximately 50 days old diabetes-prone BB/Hagedorn (BB/H) and of the genetically closely related, but non-diabetic BB w-subline (control BB) rats were perfused to determine the capacity of D-glucose to release insulin before the expected development of diabetes. The BB/H rats were from a colony with 82-84% incidence of insulin-dependent diabetes mellitus (IDDM) by 140 days of age. The total amount of insulin released from the BB/H rat pancreas during stimulation with 20 mmol/l D-glucose was reduced by nearly 50% (P < 0.01). The initial peak of insulin release was similar between the two groups of animals, whereas the amount of insulin released during the second peak accounted for the diminished release (P < 0.01). The extractable pancreatic insulin was 30% (P < 0.05) less in the BB/H rats. Total insulin release expressed relative to the pancreatic insulin content, was therefore not different between the two groups. It is concluded that about 20-40 days before the mean age of clinical onset of IDDM in BB/H rats, the capacity to release insulin in response to D-glucose is reduced along with a diminished pancreatic insulin content. This abnormality seems to be preceded only by islet cell surface antibodies but not by insulitis.