Paramagnetic manganese (Mn) ions (Mn(2+)) are taken up into cardiomyocytes where they are retained for hours. Mn content and relaxation parameters, T(1) and T(2), were measured in right plus left ventricular myocardium excised from isolated perfused rat hearts. In the experiments 5 min wash-in of MnCl(2) were followed by 15 min wash-out to remove extracellular (ec) Mn(2+) MnCl(2), 25 and 100 micro M, elevated tissue Mn content to six and 12 times the level of control (0 micro M MnCl(2)). Variations in perfusate calcium (Ca(2+)) during wash-in of MnCl(2) and experiments including nifedipine showed that myocardial slow Ca(2+) channels are the main pathway for Mn(2+) uptake and that Mn(2+) acts as a pure Ca(2+) competitor and a preferred substrate for slow Ca(2+) channel entry. Inversion recovery analysis at 20 MHz revealed two components for longitudinal relaxation: a short T(1 - 1) and a longer T(1 - 2). Approximate values for control and Mn-treated hearts were in the range 600-125 ms for T(1 - 1) and 2200-750 ms for T(1 - 2). The population fractions were about 59 and 41% for the short and the long component, respectively. The intracellular (ic) R(1 - 1) and R(2 - 1) correlated best with tissue Mn content. Applying two-site exchange analyses on the obtained T(1) data yielded results in parallel to, but also differing from, results reported with an ec contrast agent. The calculated lifetime of ic water (tau(ic)) of about 10 s is compatible with a slow water exchange in the present excised cardiac tissue. The longitudinal relaxivity of Mn ions in ic water [60 (s mM)(-1)] was about one order of magnitude higher than that of MnCl(2) in water in vitro [6.9 (s mM)(-1)], indicating that ic Mn-protein binding is an important potentiating factor in relaxation enhancement.

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The efficacy of manganese ions (Mn 2؉ ) as intracellular (ic) contrast agents was assessed in rat myocardium. T 1 and T 2 and Mn content were measured in ventricular tissue excised from isolated perfused hearts in which a 5-min wash-in with 0, 30, 100, 300, or 1000 M of Mn dipyridoxyl diphosphate (MnDPDP) was followed by a 15-min wash-out to remove extracellular (ec) Mn 2؉ . An inversion recovery (IR) analysis at 20 MHz revealed two T 1 components: an ic and short T 1-1 (650 -251 ms), and an ec and longer T 1-2 (2712-1042 ms). Intensities were about 68% and 32%, respectively. Tissue Mn content correlated particularly well with ic R 1-1. A two-site water-exchange analysis of T 1 data documented slow water exchange with ic and ec lifetimes of 11.3 s and 7.5 s, respectively, and no differences between apparent and intrinsic relaxation parameters. Ic relaxivity induced by Mn 2؉ ions in ic water was as high as 56 (s mM) - Key words: manganese; MnDPDP; heart; T 1 relaxation; R 1 relaxivity Recent studies (1-3) have shown that divalent manganese ions (Mn 2ϩ ) are promising intracellular (ic) contrast agents, and that Mn 2ϩ -releasing contrast media may be used for cardiac MRI in ischemic heart disease (4). The key factors in the potential success of these agents are that Mn-based MRI (MnMRI) utilizes physiological pathways, and Mn 2ϩ ions are tightly bound to both extracellular (ec) and ic proteins. Thus, cardiac cell uptake of Mn 2ϩ occurs in competition with the calcium ion (Ca 2ϩ ) (5), and Mn-MRI may mirror slow Ca 2ϩ channel function (2). Competition with Ca 2ϩ for cell efflux is less effective, since it may lead to cell Mn 2ϩ retention for hours, as well as to the possibility of delayed MRI. After uptake, Mn 2ϩ ions exert paramagnetic properties inside cardiac cells, and, as we recently demonstrated (3), proton relaxation is greatly enhanced compared to Mn 2ϩ ions in vitro-most probably due to extensive binding to slowly tumbling macromolecules (6). These unique endogenous properties of Mn 2ϩ ions may be exploited in both basic research and future clinical diagnostic techniques.The development of MnMRI has been hampered by the notion that Mn 2ϩ ions are cardiotoxic (7,8), since they may inhibit Ca 2ϩ channels in the cardiac cell membrane. However, recent studies have shown that the fear of cardiotoxicity in this case is largely unfounded (9 -11). Thus, while Mn 2ϩ entry in cardiomyocytes undoubtedly occurs via Ca 2ϩ channels (2,5,9,12), an inhibition of Ca 2ϩ influx that initiates cardiac contraction will not occur before ec [Mn 2ϩ ] exceeds ϳ25 M (1,3). However, extensive plasma protein binding ensures that only a very few M of Mn 2ϩ may exist in the free form in the blood pool or the interstitial space (13,14).We recently studied ic proton relaxation in rat myocardium with MnCl 2 present in the perfusate of isolated rat hearts (3). Relaxography performed after wash-in plus wash-out experiments revealed slow water exchange in the excised nonperfused cardiac tissue. Biexponential T 1 behavior dominated, and reve...

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Lipid oxidation includes a complex set of chemical reactions; and no single analytical method is available to give a satisfactory description of lipid oxidation status. High-resolution NMR spectroscopy techniques were tested to establish possible correlations with traditional analytical methods and to study lipid oxidation products. Ethyl esters of all-cis 4,7,10,13,16,19-docosahexaenoic acid (DHA) (22:6n-3), with and without added α-tocopherol, were oxidized in the dark at 25°C in an air-circulating oven. Correlations were found between primary oxidation products (PV and conjugated dienes) and the appearance of peaks in the 8.0-10.5 ppm chemical shift region of the 1 H NMR spectra. Multivariate data analysis (partial least squares; principal component regression) and the study of specific regions of the spectra obtained made it possible to easily separate samples of esters with and without α-tocopherol based on the oxidation products formed. Based on knowledge about lipid oxidation products formed in marine lipids, selected oxidation products have been studied in the 1 H NMR spectra with the aim of finding detection limits and their chemical shift values.