Factors affecting cataract formation and hyperglycemia in the degu (Octodon degus)
MetadataShow full item record
Hyperglycemia and cataract formation are of considerable interest because of their frequent association with diabetes mellitus in humans. Animal models are frequently studied to further the understanding of the cause and development of these conditions. The hystricomorph rodent, the degu (Octodon degus), is a potential diabetic model and was examined in this study. Three hypotheses implicated in the development of cataractous and hyperglycemic conditions in laboratory degus have been proposed. These involve the role of activity, diet and genotype in initiating hyperglycemia and cataract formation. Only the activity and diet hypotheses were directly tested in this study. A total of thirty-two weanling degus were tested over twenty-eight weeks in a randomized block experiment with two activity regimes and two diets and equal numbers of sexes. Sixteen animals were singly housed in cages without access to activity wheels and the remaining animals were housed in cages with attached wheels to provide a high activity treatment. One-half of the animals in each of the activity treatments (n=8) were provided a high caloric-carbohydrate diet made up of Lab BloxR and water ad libitum (Diet A), while the other half received a low caloric-carbohydrate diet consisting of hay and water ad libitum and carrots, lettuce and potatoes three times a week (Diet B). During the experiment, animals were weighed and examined for eye lens condition using direct opthalmoscopy weekly, and tested for blood glucose levels biweekly. Glucose tolerance tests were performed on weeks 20, 24 and 26. The results indicate that diet and activity had a significant effect on both growth and blood glucose levels of degus. The interaction of a high activity and low caloric diet resulted in animals with significantly lower weights; animals with low activity-high caloric diets were the only group with significantly higher mean blood glucose levels. Also, a positive correlation was found between weight and blood glucose, but the weights obtained during the twenty-eight weeks did not reach levels high enough to indicate classic hyperglycemia. Since the low activity-high caloric diet group showed some erratic abnormal glucose control, but relatively normal glucose tolerance curves, the possibility of the existence of a prediabetic condition in the de u was proposed. This implies a genetic predisposition which can lead to the manifestation of diabetes by addition of diabetogenic factors. The development of cataracts appears to have a strong genetic component. This was supported by the early appearance of cataracts in most members of the experimental group. This does not eliminate however, the possibility that factors such as hyperglycemia are involved in accelerating the manifestation of a cataract.