Attenuation of ischemic liver injury by prostaglandin E<inf>1</inf> analogue, misoprostol, and prostaglandin I<inf>2</inf> analogue, OP-41483

Background: Prostaglandin has been reported to have protective effects against liver injury. Use of this agent in clinical settings, however, is limited because of drugrelated side effects. This study investigated whether misoprostol, prostaglandin E1 analogue, and OP-41483, prostaglandin I2 analogue, which have fewer adverse effects with a longer half-life, attenuate ischemic liver damage. Study Design: Thirty beagle dogs underwent 2 hours of hepatic vascular exclusion using venovenous bypass. Misoprostol was administered intravenously for 30 minutes before ischemia and for 3 hours after reperfusion. OP-41483 was administered intraportally for 30 minutes before ischemia (2 μg/kg/min) and for 3 hours after reperfusion (0.5 μg/kg/min). Animals were divided into five groups: untreated control group (n = 10); high-dose misoprostol (total 100 μg/kg) group (MP-H, n = 5); middle-dose misoprostol (50 μg/kg) group (MP-M, n = 5); low-dose misoprostol (25 μg/kg) group (MP-L, n = 5); and OP-41483 group (OP, n = 5). Animal survival, hepatic tissue blood flow (HTBF), liver function, and histology were analyzed. Results: Two-week animal survival rates were 30% in control, 60% in MP-H, 100% in MP-M, 80% in MP-L, and 100% in OP. The treatments with prostaglandin analogues improved HTBF, and attenuated liver enzyme release, adenine nucleotrides degradation, and histologic abnormalities. In contrast to the MP-H animals that exhibited unstable cardiovascular systems, the MP- M, MP-L, and OP animals experienced only transient hypotension. Conclusions: These results indicate that misoprostol and OP-41483 prevent ischemic liver damage, although careful dose adjustment of misoprostol is required to obtain the best protection with minimal side effects

Low-lying excitations and magnetization process of coupled tetrahedral systems

We investigate low-lying singlet and triplet excitations and the magnetization process of quasi-1D spin systems composed of tetrahedral spin clusters. For a class of such models, we found various exact low-lying excitations; some of them are responsible for the first-order transition between two different ground states formed by local singlets. Moreover, we find that there are two different kinds of magnetization plateaus which are separated by a first-order transition.Comment: To appear in Phys.Rev.B (Issue 01 August 2002). A short comment is adde

Magnetization plateaus in antiferromagnetic-(ferromagnetic)_{n} polymerized S=1/2 XXZ chains

The plateau-non-plateau transition in the antiferromagnetic-(ferromagnetic)$_{n}$ polymerized $S=1/2$ XXZ chains under the magnetic field is investigated. The universality class of this transition belongs to the Brezinskii-Kosterlitz-Thouless (BKT) type. The critical points are determined by level spectroscopy analysis of the numerical diagonalization data for $4 \leq p \leq 13$ where $p(\equiv n+1)$ is the size of a unit cell. It is found that the critical strength of ferromagnetic coupling decreases with $p$ for small $p$ but increases for larger enough $p$. It is also found that the plateau for large $p$ is wide enough for moderate values of exchange coupling so that it should be easily observed experimentally. This is in contrast to the plateaus for $p = 3$ chains which are narrow for a wide range of exchange coupling even away from the critical point

Magnetization plateaus in weakly coupled dimer spin system

I study a spin system consisting of strongly coupled dimers which are in turn weakly coupled in a plane by zigzag interactions. The model can be viewed as the strong-coupling limit of a two-dimensional zigzag chain structure typical, e.g., for the $(ac)$-planes of KCuCl_3. It is shown that the magnetization curve in this model has plateaus at 1/3 and 2/3 of the saturation magnetization, and an additional plateau at 1/2 can appear in a certain range of the model parameters; the critical fields are calculated perturbatively. It is argued that for the three-dimensional lattice structure of the KCuCl_3 family the plateaus at 1/4 and 3/4 of the saturation can be favored in a similar way, which might be relevant to the recent experiments on NH_4CuCl_3 by Shiramura et al., J. Phys. Soc. Jpn. {\bf 67}, 1548 (1998).Comment: serious changes in Sect. II,III, final version to appear in PR

Attenuation of ischemic liver injury by monoclonal anti-endothelin antibody, awETN40

Background: Enhanced production of endothelin-1 (ET1), vasoconstrictive 21 amino acids produced by endothelial cells during ischemia and after reperfusion of the liver, is known to cause sinusoidal constriction and microcirculatory disturbances, which lead to severe tissue damage. Using a 2- hour hepatic vascular exclusion model in dogs, we tested our hypothesis that neutralization of ET-1 by monoclonal anti-ET-1 and anti-ET-2 antibody (AwETN40) abates vascular dysfunction and ameliorates ischemia/reperfusion injury of the liver. Study Design: After skeletonization, the liver was made totally ischemic by cross-clamping the portal vein, the hepatic artery, and the vena cava (above and below the liver). Venovenous bypass was used to decompress splanchnic and inferior systemic congestion. AwETN40, 5 mg/kg, was administered intravenously 10 minutes before ischemia (treatment group, n = 5). Nontreated animals were used as controls (control group, n = 10). Animal survival, hepatic tissue blood flow, liver function tests; total bile acid, high-energy phosphate, ET-1 levels, and liver histopathology were studied. Results: Treatment with AwETN40 improved 2-week animal survival from 30% to 100%. Hepatic tissue blood flow after reperfusion was significantly higher in the treatment group. The treatment significantly attenuated liver enzyme release, total bile acid, and changes in adenine nucleotides. Immunoreactive ET-1 levels in the hepatic venous blood of the control group showed a significant increase and remained high for up to 24 hours after reperfusion. Histopathologic alterations were significantly lessened in the treatment group. Conclusions: These results indicate that ET-1 is involved in ischemia/reperfusion injury of the liver, which can be ameliorated by the monoclonal anti-ET-1 and antiET-2 antibody AwETN40

Magnetization plateaus as insulator-superfluid transitions in quantum spin systems

We study the magnetization process in two-dimensional S=1/2 spin systems, to discuss the appearance of a plateau structure. The following three cases are considered: (1) the Heisenberg antiferromagnet and multiple-spin exchange model on the triangular lattice, (2) Shastry-Sutherland type lattice, [which is a possible model for SrCu2(BO3)2,] (3) 1/5-depleted lattice (for CaV4O9). We find in these systems that magnetization plateaus can appear owing to a transition from superfluid to a Mott insulator of magnetic excitations. The plateau states have CDW order of the excitations. The magnetizations of the plateaus depend on components of the magnetic excitations, range of the repulsive interaction, and the geometry of the lattice.Comment: 5 pages, RevTeX, 7 figures, note and reference adde

Magnetization Plateaus in a Solvable 3-Leg Spin Ladder

We present a solvable ladder model which displays magnetization plateaus at fractional values of the total magnetization. Plateau signatures are also shown to exist along special lines. The model has isotropic Heisenberg interactions with additional many-body terms. The phase diagram can be calculated exactly for all values of the rung coupling and the magnetic field. We also derive the anomalous behaviour of the susceptibility near the plateau boundaries. There is good agreement with the phase diagram obtained recently for the pure Heisenberg ladders by numerical and perturbative techniques.Comment: 4 pages, revtex, 3 postscript figures, small changes to the text and references update

A Strong-Coupling Approach to the Magnetization Process of Polymerized Quantum Spin Chains

Polymerized quantum spin chains (i.e. spin chains with a periodic modulation of the coupling constants) exhibit plateaux in their magnetization curves when subjected to homogeneous external magnetic fields. We argue that the strong-coupling limit yields a simple but general explanation for the appearance of plateaux as well as of the associated quantization condition on the magnetization. We then proceed to explicitly compute series for the plateau boundaries of trimerized and quadrumerized spin-1/2 chains. The picture is completed by a discussion how the universality classes associated to the transitions at the boundaries of magnetization plateaux arise in many cases from a first order strong-coupling effective Hamiltonian.Comment: 5 pages REVTeX, three PostScript figures included using psfig.st