Dual-tracer autoradiography with thallium-201 and iodine-125-metaiodobenzylguanidine in experimental myocardial infarction of rat.
Dual-isotope scintigraphic studies with 201Tl and radioiodinated metaiodobenzylguanidine (MIBG) suggest that acute myocardial infarction causes extensive regional myocardial denervation beyond the infarcted area. We therefore investigated the histopathological and biochemical significance of the discrepancy between 201Tl and 125I-MIBG distribution determined by dual-tracer autoradiography in experimental myocardial infarction.


METHODS
Left coronary arteries of 12 male Wistar rats were ligated for 30 min followed by reperfusion. Dual-tracer autoradiography of infarcted heart sections was performed with 201Tl and [125I]MIBG 4 hr or 2 days after coronary reperfusion, followed by immunohistochemical staining with myoglobin monoclonal antibody to determine the area of myocardial infarction. Ultrastructural alterations and myocardial norepinephrine (NE) content in the region determined by dual-tracer autoradiography and myglobin immunostaining were studied.


RESULTS
Thirty-minute coronary ligation with 4-hr reperfusion produced myocardial infarction associated with discrepant region in the peri-infarcted myocardium characterized by decreased [125I]MIBG uptake and normal 201Tl distribution (discrepant region), as determined by dual-tracer autoradiography. In the discrepant region, which disappeared after 2 days, the nerve terminals showed loss of granular cores, with normal structures between normal myocytes. The mean myocardial NE level in the discrepant region was significantly lower than that in the nonischemic region (255.2 +/- 85.9 versus 549.5 +/- 82.5 ng/mg).


CONCLUSIONS
The uptake discrepancy of 201Tl and [125I]MIBG observed in the infarcted heart represents a transient functional denervation of the regional cardiac sympathetic nerve terminals in the noninfarcted myocardium.
Iwasaki
T
T
Second Department of Internal Medicine, Gunma University, School of Medicine, Japan.
Suzuki
T
T
Tateno
M
M
Sasaki
Y
Y
Oshima
S
S
Imai
S
S
D019797:3-Iodobenzylguanidine; D000818:Animals; D001345:Autoradiography / Q000379:methods; D003287:Contrast Media; D006321:Heart / Q000000981:diagnostic imaging / Q000294:innervation; D007124:Immunoenzyme Techniques; D007457:Iodine Radioisotopes; D007462:Iodobenzenes; D008297:Male; D008854:Microscopy, Electron; D009203:Myocardial Infarction / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D009206:Myocardium / Q000737:chemistry / Q000648:ultrastructure; D009211:Myoglobin / Q000032:analysis; D009638:Norepinephrine / Q000032:analysis; D011877:Radionuclide Imaging; D051381:Rats; D017208:Rats, Wistar; D013794:Thallium Radioisotopes; D013997:Time Factors
D003287:Contrast Media; D007457:Iodine Radioisotopes; D007462:Iodobenzenes; D009211:Myoglobin; D013794:Thallium Radioisotopes; D019797:3-Iodobenzylguanidine; D009638:Norepinephrine