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

Objective: To evaluate the sensitivity of I-123-labeled metaiodobenzylguani dine (I-123-MIBG) scintigraphy in detecting diabetic autonomic nervous syst em disorders. Materials and Methods: Thirty-one-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of spontaneous non-insulin-dependent d iabetes mellitus, were maintained for 8 weeks with or without 30% sucrose s olution 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 I-123-MIBG scintigraphy was performed with a gamma camera equ ipped with a pinhole collimator for animals. Plasma and cardiac tissue cath ecolamine levels were also determined. Results: Plasma glucose levels of OLETF rats with and without sucrose loadi ng (554 +/- 106 and 141 +/- 1.5 mg/dl respectively) were significantly high er than those of LETO rats (116 +/- 3.7 mg/dl). Norepinephrine concentratio ns in heart and plasma tended to be lower in diabetic rats. The washout rat e of I-123-MIBG in diabetic rats was significantly higher than the rate in control rats. Cardiac uptake of I-123-MIBG, calculated as % dose/g of tissu e, was significantly lower in diabetic rats than in control rats. Conclusion: These results suggest that myocardial I-123-MIBG scintigraphy i s suitable for assessing cardiac sympathetic activity noninvasively in diab etic states, even in the early stages.