Circadian rhythm of corticosterone in diabetic rats

We proposed that the circadian rhythm of corticosterone in diabetic rats would have a different pattern than that in non-diabetic control rats. To test this hypothesis, 20 male Sprague-Dawley rats were given ad libitum access to a stock diet and housed individually in a light and temperature controlled room. Ten rats were made diabetic by two subcutaneous injections of streptozotocin. Ten rats which were not injected served as controls. Thirteen days after induction of the diabetes, tail blood samples were taken every 4 h for 24 h. Plasma corticosterone levels were significantly higher in diabetic rats than in control rats at 3 time points during the light cycle; however, concentrations were similar during the dark cycle. We speculate that diabetes may cause alterations in the steroid feedback mechanism to the hypothalamus and/or pituitary, resulting in an abnormal circadian rhythm of plasma corticosterone.