Regional in vivo and in vitro characterization of autonomic innervation in cardiomyopathic human heart.

BACKGROUND: In contrast to healthy volunteers, regional differences of cardiac autonomic innervation have been described through the use of C11-hydroxyephedrine positron emission tomography (HED-PET) in the left ventricles of patients with dilated cardiomyopathy. The goal of the present study was to correlate HED-PET images with biochemical analysis of tissue samples. METHODS AND RESULTS: To assess the significance of altered HED uptake, we used HED-PET to examine eight patients with dilated cardiomyopathy before heart transplantation. After explantation, we measured the density and affinity of uptake1 (3H-mazindol binding) and tissue norepinephrine content as markers of presynaptic function, and we determined beta-receptor density and affinity (3H-CGP 12177 binding) in the corresponding areas of the same patients. The density of uptake1 and norepinephrine content showed marked regional variation, with highest values in the anterior septal wall and lowest in inferoapical and apical areas. Both parameters were closely correlated (r=.65, P=.05). Similarly, uptake1 density or norepinephrine content and HED retention (PET) showed clear correlations (r=.63 and .60, respectively). Uptake1 affinities did not vary significantly and were not correlated to the other parameters. Beta-Adrenergic receptor density showed some, albeit less pronounced, regional variation and was weakly correlated to uptake1 density and local HED retention (r=.38 and .31, respectively). CONCLUSIONS: Uptake1 density and tissue norepinephrine content showed marked regional variation in cardiomyopathic left ventricles. HED-PET is significantly correlated to the density but not the affinity of uptake1 sites in the human heart, suggesting either loss of neurons or downregulation of uptake1 in dilated cardiomyopathy. HED-PET is a valuable marker for alterations of the presynaptic sympathoadrenergic system in humans.

Upregulation of cardiac uptake 1 carrier in ischemic and nonischemic rat heart.

Neuronal uptake1 constitutes the main elimination process of cardiac norepinephrine under normoxic conditions. Uptake1 may be subject to changes during myocardial ischemia. We therefore studied the regulation of the uptake1 carrier in isolated perfused rat hearts, comparing ischemic and nonischemic conditions. Radioligand binding with [3H]mazindol was used to determine carrier densities and affinities, whereas cardiac clearance of[3H]norepinephrine served as a measure of the transport capacity of the uptake1 carrier. When exocytotic norepinephrine release was induced in nonischemic rat hearts by electrical field stimulations, we observed an increase in the cardiac density of uptake1 carriers (Bmax) to 210 +/- 5 fmol/mg protein (versus 134 +/- 3 fmol/mg in control hearts). Simultaneously, the cardiac clearance of [3H]norepinephrine increased to 41 +/- 4% versus 30 +/- 4% in control hearts. Both carrier density and norepinephrine clearance returned to baseline values within a period of 40 minutes after stimulation. Carrier affinities (Kd values) did not differ between the groups. Stop-flow ischemia induced a substantial overflow of norepinephrine by itself. Additionally, carrier density was increased to 144% after 40 minutes of stop-flow ischemia (P < .005 versus control hearts). When ischemia was followed by 20 minutes of reperfusion, the Bmax of the uptake1 carrier remained significantly elevated. With a further extension of the reperfusion period to 40 minutes, however, carrier density declined to baseline values. Kd values were not influenced by any of these interventions. Clearance of [3H]norepinephrine was suppressed (to 5 +/- 2%) in the first minutes of reperfusion, which may reflect the inverse transport direction of the norepinephrine carrier known to occur in ischemia. After 20 minutes of reperfusion, clearance increased to 39 +/- 5% (P < .005 versus control hearts) and then fell to 29 +/- 5% after 40 minutes of reperfusion (NS). These results demonstrate that after both electrical field stimulation and myocardial ischemia, the density of uptake1 carrier proteins temporarily increases, which may result in an increased transport capacity for norepinephrine.