Evaluation of the cardiac autonomic nervous system in spontaneously non-insulin-dependent diabetic rats by super(123)I-metaiodobenzylguanidine imaging

Objective: To evaluate the sensitivity of super(123)I-labeled metaiodobenzylguanidine ( super(123)I-MIBG) scintigraphy in detecting diabetic autonomic nervous system disorders. Materials and Methods: Thirty-one-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of spontaneous non-insulin-dependent diabetes mellitus, were maintained for 8 weeks with or without 30% sucrose solution as a drinking water (n = 3 each). Long-Evans Tokushima Otsuka (LETO) rats (n = 3), served as controls. Plasma glucose and insulin levels were measured, and super(123)I-MIBG scintigraphy was performed with a gamma camera equipped with a pinhole collimator for animals. Plasma and cardiac tissue cathecolamine levels were also determined. Results: Plasma glucose levels of OLETF rats with and without sucrose loading (554 c 106 and 141 c 1.5 mg/dl respectively) were significantly higher than those of LETO rats (116 c 3.7 mg/dl). Norepinephrine concentrations in heart and plasma tended to be lower in diabetic rats. The washout rate of super(123)I-MIBG in diabetic rats was significantly higher than the rate in control rats. Cardiac uptake of super(123)I-MIBG, calculated as % dose/g of tissue, was significantly lower in diabetic rats than in control rats. Conclusion: These results suggest that myocardial super(123)I-MIBG scintigraphy is suitable for assessing cardiac sympathetic activity noninvasively in diabetic states, even in the early stages.