Evidence of Insulin Resistance in Healthy Miniature Schnauzers with Idiopathic Hypertriglyceridemia
Miniature Schnauzers have been reported to have a high prevalence of idiopathic hypertriglyceridemia, which has been suspected to be familial in this breed. In humans, familial forms of hypertriglyceridemia have been associated with insulin resistance. The effects of familial hypertriglyceridemia on insulin function have not yet been studied in dogs. Thus, the aim of this study was to determine whether idiopathic hypertriglyceridemia in Miniature Schnauzers is associated with insulin resistance as determined by the homeostasis model assessment (HOMA).
Blood samples from 18 healthy Miniature Schnauzers with idiopathic hypertriglyceridemia and 23 healthy Miniature Schnauzers with normal serum triglyceride concentrations were used in this study. Samples were collected after food had been withheld for at least 12 hours. All dogs were free of clinical signs of any disease for at least 3 months prior to blood collection, had no history of a chronic disease, and were not receiving any medications that are known to affect lipid metabolism. The effect of lipemia was evaluated by comparison of each parameter before and after centrifugation of lipemic serum samples. Mean age and body weight were calculated and compared between groups. Serum insulin and glucose concentrations were measured and the HOMA index (HOMA index = fasting insulin (mU/L) X fasting glucose (mmol/L)/22.5) was calculated, and medians were compared between groups using a Mann-Whitney U test. Proportions of dogs with serum insulin concentrations above the reference range were compared between groups using a Fisher's exact test, and odds ratios (OR) with 95% confidence intervals (CI) were calculated. Non-esterified fatty acid (NEFA) concentrations, which might be increased in patients with insulin resistance, were also measured in 14 control and 12 hypertriglyceridemic dogs.
The effect of lipemia on insulin concentrations was not significant (p=0.16). There was no significant age (p=0.14) or body weight (p=0.078) difference between the 2 groups. Median serum insulin concentration was significantly higher in hypertriglyceridemic Miniature Schnauzers (28.4 mU/L) than in controls (12.2 mU/L; p<0.001). Also, the proportion of dogs with serum insulin concentrations above the reference range was significantly higher in hypertriglyceridemic Miniature Schnauzers (44.4%) than in controls (13.0%; p=0.036; OR=5.3; 95% CI=1.2-24.6). The median HOMA index score was significantly higher in hypertriglyceridemic Miniature Schnauzers (5.9) than in controls (2.9; p=0.003). There was no significant difference in mean serum concentrations of NEFA between hypertriglyceridemic dogs and controls (p=0.528).
The results of the present study suggest that idiopathic hypertriglyceridemia in Miniature Schnauzers is associated with insulin resistance. Further studies are in progress to determine the prevalence and significance of insulin resistance in hypertriglyceridemic Miniature Schnauzers.