Impact of Environmental Stress on the Expression of Insulin-Dependent Diabetes Mellitus

To investigate the influence of environmental factors on inherited tendencies, the impact of chronic environmental stress on the expression of a genetically determined autoimmune disease was explored in the bio-breeding (BB) rat, which is an animal model for human autoimmune insulin-dependent diabetes mellitus. Animals assigned at random to the experimental group received a triad of stressors designed to model chronic moderate stress over a 14-week period. Animals from 25 to 130 days of age were weighed and tested for glycosuria twice weekly. Weekly blood sampling was performed on all animals. Diabetes was diagnosed on the basis of weight loss, 2+ glycosuria, and blood glucose levels of 250+ mg/dl. We found that in the BB rat chronic stress significantly increased the incidence of the phenotypic expression of the gene for Type I diabetes. Eighty percent of the male stress and 70% of the female stress animals developed diabetes, compared with 50% in both control groups. Stressed males developed manifest diabetes at the same time as their matched controls, whereas stressed females had significantly delayed onset in relation to controls.