Subclinical diabetes mellitus in the BB rat

The spontaneously diabetic BB Wistar rat is a well recognized animal model for the study of insulin-dependent diabetes mellitus (IDDM). Previously we have noted hyperglycemia and insulitis in BB rats without clinical diabetes. 121 rats were studied prospectively. 43 (36%) were normal and 64 (52%) developed IDDM suspected by the presence of glycosuria and acute weight loss, and confirmed with pancreatic histology. In the remaining 14 (12%) animals, pancreatic histology was also abnormal, varying from mild insulitis only to moderate insulitis and beta-cell degranulation. Since these rats gained weight normally, had no glycosuria, or hyperglycemia they were designated as having subclinical diabetes. At death, their plasma-insulin concentrations and the amount of extracted pancreatic insulin was intermediate between that of the normal and diabetic group (p less than 0.001). We have identified a group of rats with pancreatic features of diabetes but no clinical expression. Further investigation of this syndrome may reveal clinical, immunological or histological features which protect these animals from the development of overt disease.