Heterogeneous cardiac sympathetic innervation in heart failure after myocardial infarction of rats

We examined cardiac neuronal function and beta-receptor with a dual-tracer method of [I-131]metaiodobenzylguanidine (MIBG) and [I-125]iodocyanopindolo l (ICYP) in rat heart failure after myocardial infarction (MI). In rats wit h MI, left ventricular (LV) systolic function decreased, and LV dimension a nd right ventricular (RV) mass increased gradually. MIBG accumulations of t he noninfarcted LV (remote region) and RV decreased by 15% at 1 wk compared with sham-operated rats, and these accumulations were restored by 71% and 56%, respectively, at 24 wk compared with age-matched sham rats despite sus tained depletion of myocardial norepinephrine contents in these regions. IC YP accumulation of the remote region and of the RV did not decrease at any stages. Myocardial MIBG distribution was heterogeneous at 1 wk when it was lower in the peri-infarcted region than in the remote region, associated wi th reduced ICYP accumulation in the peri-infarcted region. The heterogeneou s distribution of both isotopes disappeared at 12 wk. Thus cardiac sympathe tic neuronal alteration was coupled with downregulation of beta-receptors i n rat heart failure after MI. The abnormal adrenergic signaling occurred he terogeneously in terms of ventricular distribution and time course after MI .