Effects of extrinsically elevated plasma norepinephrine concentration on myocardial 123I-MIBG kinetics in rats.
Rapid 123I-metaiodobenzylguanidine (MIBG) washout and high plasma norepinephrine (NE) levels are frequently observed in patients with congestive heart failure, and high plasma NE levels are not necessarily induced by increased cardiac NE spillover. The purpose of this study was to assess the effect of extrinsically elevated plasma NE levels on myocardial MIBG kinetics.


METHODS
MIBG was injected into the femoral vein in 47 adult male Wister rats. In the first study, normal saline solution or NE (0.3, 1.0 and 3.0 microg/kg/min) was administered to each group of 6 or 7 rats continuously from 30 min before to 30 min after MIBG injection. In the second study, NE was administered at 3.0 microg/kg/min to each group of 7 rats continuously from 30 min before to 2 h after or from 30 to 60 min after MIBG injection, and NE was not administered to a control group of 7 rats. For 2 or 4 h after MIBG injection, scintigrams were acquired using a gamma camera with a pinhole collimator, after which myocardial MIBG uptake (percentage injected dose normalized for the difference in rat weight per tissue weight) was determined in isolated heart with a gamma counter.


RESULTS
In the first study, the MIBG washout rate from the heart was significantly increased during high-dose NE infusion (1.0 and 3.0 microg/kg/min) compared with that during saline infusion, whereas the washout rate was not increased during low-dose NE infusion. In the second study, the MIBG washout rate from the heart during NE infusion was significantly increased compared with that of the control but was not increased during discontinuation of NE infusion.


CONCLUSIONS
Extrinsically induced high levels of plasma NE may accelerate MIBG washout from the heart.
Shouda
S
S
Department of Medicine III, Hamamatsu University School of Medicine, Japan.
Kurata
C
C
Mikami
T
T
Wakabayashi
Y
Y
D019797:3-Iodobenzylguanidine / Q000493:pharmacokinetics*; D000818:Animals; D001794:Blood Pressure; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics*; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000097:blood* / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
D007457:Iodine Radioisotopes; D019797:3-Iodobenzylguanidine; D009638:Norepinephrine