Genetically inbred cardiomyopathic hamsters were examined to investigate the mechanism of reduced myocardial accumulation of metaiodobenzylguanidine (MIBG) in the cardiomyopathic heart. METHODS Bio 14.6 Syrian hamsters (hypertrophic stage: n = 15, early heart failure stage: n = 17) and control F1b strain golden hamsters (n = 36) were injected with 296 kBq of [125I] MIBG and killed 30 min or 4 hr later. Thirty-three of these hamsters were pretreated with 10 mg/kg of desipramine to determine non-neuronal MIBG accumulation. To evaluate the nonexocytotic MIBG release from nerve endings, desipramine was administered to four Bio 14.6 hamsters 15 min after [125I]MIBG injection. To determine the role of the activated renin-angiotensin system (RAS) in MIBG washout from sympathetic nerve terminals in cardiomyopathy at early heart failure stage, 10 mg/kg/day cilazapril, an angiotensin-converting enzyme inhibitor, was given orally to 7 controls and 16 cardiomyopathic hamsters for 16 wk. RESULTS In the absence of desipramine pretreatment, left ventricular [125I]MIBG accumulation 4 hr after injection was 0.376% +/- 0.015 %kg dose/g (mean +/- s.e.m.) in the hypertrophic hamsters (versus 0.418 +/- 0.019 in controls of the same age; ns), and 0.195 +/- 0.025 in early heart failure hamsters. Treatment with cilazapril partially restored MIBG accumulation in the Bio 14.6 hamsters but did not affect the controls. CONCLUSIONS Decreased [125I]MIBG accumulation in cardiomyopathic hamsters during the early heart failure stage is caused by neuronal release which is partially modulated by the activated RAS.