A new mutation (db3J) at the diabetes locus in strain 129/J mice. I. Physiological and histological characterization.

A spontaneous recessive mutation appearing in strain 129/J mice at the diabetes (db) locus on Chromosome 4 has been characterized. The new allele, designated db3J, produced hyperphagia and severe obesity. Mutants weighed in excess of 70 g by 6 months of age, compared to 22-28 g for lean littermates. Although the disease was similar to the mild hyperglycaemia-severe obesity syndrome exhibited by db gene presentation on the C57BL/6J inbred background, the syndrome in 129/J mice reduced lifespan, with mutants exhibiting sudden weight loss, hypoglycaemia, and a 67% mortality between 6 and 14 months of age. Mutant males, but not females, were transiently hyperglycaemic between 2 to 4 months of age, attaining a maximum mean blood sugar of 196 +/- 27 (SEM) mg/dl. Thereafter glucose levels declined to normoglycaemic values (80-100 mg/dl), and with increasing age, mutants of both sexes became hypoglycaemic (60 mg/dl at 9 months). Mutants of both sexes were extremely hyperinsulinaemic at the earlier ages, with mean plasma insulin at months 5 reflecting 30-fold elevations above normal for males and 18-fold for females. These levels diminished with age, the decline being more marked in males. Plasma glucagon levels were 3-fold elevated in the younger mutants of both sexes (86 pg/ml versus 28 pg/ml in normal mice), mean levels increasing to almost 5-fold above mean control vaues in the older age group (198 pg/ml versus 41 pg/ml in normal mice). Histopathological findings were limited to pancreas. Increasing necrosis of the exocrine, but not endocrine, pancreas was noted in aging mutants. Aldehyde fushsin staining of the mutant pancreas revealed hyperplastic islets filled with heavily granulated B-cells. B-cell hyperplasia was accompanied by a 30-fold increase over controls in pancreatic insulin content in the 8 month old mutants, whereas pancreatic glucagon content was only doubled. Morphometric analysis showed less than a 2-fold increase in the mean number of A-cells per islet. Thus, an interesting feature of expression of the diabetes gene in the 129/J strain is the persisting hyperglucagonaemia in the face of moderating hyperinsulinaemia.