Lithium spectroscopic imaging of rat brain at therapeutic doses.

Since the discovery that lithium (Li) is efficacious for the treatment of manic depressive illness, the brain Li distribution of mammals treated with lithium has been of interest. However, the spatial relationship of lithium in the brain regions to its function remains largely unknown. Knowledge of Li distribution in the brain is necessary to localize its action in the brain. Both the therapeutic and neurotoxic side effects of Li are centered mainly in the central nervous system and hence there is considerable interest in understanding the extent of lithium penetration into the central nervous system. The mechanism by which neurotoxic side effects are generated is not known and may, in part, be related to the particular distribution of lithium in the brain. The regional specificity in lithium's brain distribution could underlie important steps on its action. Li levels in various brain regions for autopsied rats and humans have been reported. However, many results are conflicting due to ion redistribution at death or during sample preparation. A direct nondestructive measurement of Li levels in the brain where the drug exerts its effects is certainly desirable. Because magnetic resonance technique can be used to observe Li, it can be an appropriate method to monitor and map the distribution in the brain. The application of MR technology to rat brain regions has provided information on lithium distribution in a non-invasive manner. The earlier development work at lower field strengths provided brain lithium information at high dose of Li administration. Here we demonstrate the feasibility of quantitative spectroscopic imaging on rat brain under therapeutic doses.

Lithium distribution in red blood cells and plasma: NMR studies of rat blood.

To understand the interaction of lithium (Li+) with a coadministered drug in both the blood and the brain, we have treated rats with either Li+ alone or Li+ and a codrug. In this paper we address the important problem of quantitation of intra and extracellular Li+ ion contents in blood by the 7Li-NMR technique and the use of a shift reagent (SR). Although Li+ can be studied by atomic absorption techniques, these techniques involve tedious separation of intra- and extracellular components prior to chemical analysis. Magnetic resonance studies on rat blood, in the dose range of 0.5 to 10 meq/kg, indicate that the intracellular red blood cell Li+ predominates in the lower dose range of 0.5-1.0 meq/kg. As the lithium dose increases, a significantly larger amount of Li+ accumulates in the extracellular volume. Our studies on a number of animals at various doses of LiCl indicate that 7Li-NMR of blood samples provide a reliable, noninvasive quantification of red blood cell and plasma Li+ concentrations. The NMR method was further used to study the effect of coadministered drugs such as thioridazine on the intra- and extracellular Li+ concentration of RBCs.

NMR studies of intra- and extracellular red blood cell lithium by transverse relaxation measurements and shift reagents.

Lithium salts are used in the treatment and prophylaxis of bipolar or mood disorders. The mechanism of action by which the cation exerts its therapeutic influence is unknown. A knowledge of brain Li concentration, its distribution in the brain, and its properties in the cellular microenvironment may have a strong influence on the understanding of Li function. The differentiation of lithium in the intra and extracellular environments has been achieved in a noninvasive manner in red blood cell (RBC) model. The two distinct transverse relaxation (T2) components have been observed in the blood sample drawn from lithium treated rats. These results indicate two different environments for Li with a fast (T2f) and a slow (T2s) component in the RBC model corresponding fractions that contribute to each relaxation component. The results compare well with the intra- and extracellular RBC lithium measured using shift reagents. Our studies indicate that the T2 method has utility in estimating the intracellular Li in systems that exhibit similar T2 behavior. The studies performed at different Li doses in the rat model indicate that the method may have utility in following a wide range of intracellular Li.

Short-term intravenous milrinone for severe congestive heart failure: the good, bad, and not so good.

We evaluated the overall hemodynamic and clinical effects, beneficial and deleterious, of short-term intravenous milrinone in the management of severe congestive heart failure (CHF). Numerous hemodynamic measurements were obtained in 24 patients (mean age 65 yrs) with advanced, severe CHF (New York Heart Association class IV, ejection fraction 24 +/- 5%), including 3 with concomitant clinical sepsis. Hemodynamic data were recorded at baseline and after a bolus of intravenous milrinone 50 micrograms/kg and maintenance infusion based on creatinine clearance at 0.5, 3, 24 and 48 hours. Cardiac index increased and pulmonary capillary wedge pressure decreased significantly (p < 0.001; 2.07 +/- 0.36 to L/min/m2 and 20.6 +/- 4.0 to 13.5 +/- 2.8 mm Hg, respectively) in 24 patients 0.5 hour after initiation of therapy. These favorable hemodynamic responses, including significant decreases in systemic vascular resistance index and right atrial pressure, were sustained throughout the 48-hour study in 19 patients (79%). Severe hypotension occurred in three patients with superimposed sepsis as the result of exaggerated vasodilatation. One patient had recurrent ventricular tachycardia and another tolerance to milrinone. In two patients, excessive decline in preload and fall in cardiac index were reversed with volume expansion. Intravenous milrinone offered significant short-term hemodynamic benefits in most patients with severe CHF.

Septic cardiomyopathy as a cause of long QT syndrome.

A 63-year-old woman admitted with 2:1 infranodal atrioventricular block subsequently developed ventricular dysfunction incident to septic syndrome. Concomitant changes included an abnormally prolonged QTc interval (600 ms) and the occurrence of torsade de pointes. Restoration of a normal QTc interval and cessation of torsade de pointes was coincident with return of normal ventricular function and remission of sepsis. This report supports the view that sepsis-induced cardiomyopathy is another cause of the long QT syndrome.

Life-threatening hyponatremia due to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) in a patient with the miller fisher syndrome.

We report a life-threatening hyponatremia due to SIADH which developed suddenly in a patient with the Miller Fisher syndrome (a variant of Guillian Barré syndrome characterized by complete ophthalmoplegia, ataxia, and areflexia). A 55 year-old female was admitted with a clinical picture of the Miller Fisher syndrome. Cerebrospinal fluid was acellular with elevated proteins, and electromyographic changes were characteristic of polyneuropathy. On the third day of admission the patient was found to be mentally confused with a serum sodium of 108 mmol/L. Serum osmolality was 236 mosm/L and urine osmolality was 636 mosm/L. Urine sodium was 103 mmol/L. The serum sodium normalized after treatment with a single dose of intravenous furosemide, hypertonic saline infusion and fluid restriction. To our knowledge, this is the first description of SIADH developing in a patient with the Miller Fisher syndrome.

In vivo relaxation time measurements on a murine tumor model--prolongation of T1 after photodynamic therapy.

RIF tumors implanted on mice feet were investigated for changes in relaxation times (T1 and T2) after photodynamic therapy (PDT). Photodynamic therapy was performed using Photofrin II as the photosensitizer and laser light at 630 nm. A home-built proton solenoid coil in the balanced configuration was used to accommodate the tumors, and the relaxation times were measured before, immediately after, and up to several hours after therapy. Several control experiments were performed untreated tumors, tumors treated with Photofrin II alone, or tumors treated with laser light alone. Significant increases in T1s of water protons were observed after PDT treatment. In all experiments, 31P spectra were recorded before and after the therapy to study the tumor status and to confirm the onset of PDT. These studies show significant prolongation of T1s after the PDT treatment. The spin-spin relaxation measurements, on the other hand, did not show such prolongation in T2 values after PDT treatment.

In vivo 7Li NMR diffusion studies in rat brain.

Lithium (Li) is widely used for the treatment of several psychiatric disorders and is the drug of choice in the treatment of bipolar disorders. The mechanism of action of Li, however, is unknown. A knowledge of brain Li concentration, its distribution in the brain, and its properties in the cellular microenvironments may contribute significantly towards the understanding of its function. We recently demonstrated by in vivo 7Li NMR the distribution and pharmacokinetics of Li ion in rat brain. We have made diffusion measurements of Li in the head and brain regions of anesthetized rats using the localized STEAM (stimulated echo acquisition mode spectroscopy) technique suitably sensitized to diffusion. In this paper we demonstrate for the first time the feasibility of Li diffusion measurements in the mammalian brain model with the ultimate goal of performing such studies on humans under Li therapy.

Aminophylline induced atrial fibrillation.

Atrial fibrillation (AF) with a rapid ventricular response was induced by intravenous (i.v.) aminophylline during treatment for symptomatic pulmonary disease in three patients who had no evidence of underlying heart disease or previous cardiac arrhythmia. Serum theophylline concentration was therapeutic in two patients and toxic in the third. Previous reports of AF related to aminophylline have underscored its association with toxic serum theophylline concentration. Conversion to sinus rhythm occurred at a time interval (9-14 hours) appropriate to the serum decay of aminophylline, after its cessation. A shortened atrial refractory period and dispersed recovery of excitability consequent to aminophylline may engender multiple reentrant circuits and lead to AF. i.v. diltiazem was more effective than digoxin in the ventricular rate control of AF prior to conversion to sinus rhythm.

Comparison of the in vivo and in vitro nuclear magnetic resonance detection of trifluoromethyl penicillin V in rats.

Fluorine nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging were examined as noninvasive methods for characterizing antibiotic disposition and pharmacokinetics in vivo. For determination of their utility, a 19F surface coil was constructed and an m-(trifluoromethyl)-containing penicillin V analogue (LY242072; 1) was synthesized. Various concentrations of 1 were injected intravenously into anesthetized rats whose urethras were occluded. The animals were placed on the surface coil, which was tuned to 19F, and then into a 4.7-T, 33-cm bore instrument, in which in vivo measurements of 1 were made on urine excreted into the bladder. At sacrifice, the urine was collected, and antibiotic levels were determined in vitro by both HPLC and high-resolution NMR. The limit of detection of 1 by NMR was 0.7 mg/mL of urine. When compared with standard in vitro quantitative methods using current technology, quantitation by in vivo surface coil NMR is not precise. Magnetic resonance imaging was used to image the bladder at a 35-mm3 voxel resolution with datum collection times of approximately 1 h. The 19F surface coil was used successfully to spectroscopically locate xenobiotic fluorine in the rat thorax. 19F NMR may offer an opportunity for the noninvasive in vivo detection of the distribution of various classes of therapeutic compounds.

In vivo 7Li NMR imaging and localized spectroscopy of rat brain.

Lithium-7 in vivo NMR spectroscopy and imaging techniques have been developed at 4.7 T for rat head. The pharmacokinetics of lithium (Li) uptake in rat head has been measured using STEAM localized spectroscopy for the whole brain, which showed relatively rapid uptake of Li and a steady level of Li from about 5 to 20 h. Localized spectroscopy on brain sections revealed no differences in Li concentration among the front, middle, and rear of the brain. The spin-lattice relaxation time showed a single exponential decay for the head. The spin-spin relaxation time for head showed a biexponential behavior. Using a 1H-7Li double coil assembly, 7Li images were generated for rat head, as was the corresponding 1H image for anatomic localization. The 7Li image (7-mm slice thickness, 4-mm in-plane resolution) recorded after the last dose in a multiple ip dose protocol shows the Li distribution in the head and neck. Based on 7Li images, the Li level in muscle was about twice that in the brain. Variations of 7Li intensity level across the brain were typically small.

Proton nuclear magnetic resonance study of the solution distal histidine orientation in monomeric Chironomus thummi thummi cyanomet hemoglobins. Dynamic stability of the heme pocket as monitored by labile proton exchange.

The 1H nuclear magnetic resonance spectral characteristics of the cyano-Met form of Chironomus thummi thummi monomeric hemoglobins I, III and IV in 1H2O solvent are reported. A set of four exchangeable hyperfine-shifted resonances is found for each of the two heme-insertion isomers in the hyperfine-shifted region downfield of ten parts per million. An analysis of relaxation, exchange rates and nuclear Overhauser effects leads to assignments for all these resonances to histidine F8 and the side-chains of histidine E7 and arginine FG3. It is evident that in aqueous solution, the side-chain from histidine E7 does not occupy two orientations, as found for the solid state, rather the histidine E7 side-chain adopts a conformation similar to that of sperm whale myoglobin or hemoglobin A, oriented into the heme pocket and in contact with the bound ligand. Evidence is presented to show that the allosteric transition in the Chironomus thummi thummi hemoglobins arises from the "trans effect". An analysis of the exchange with bulk solvent of the assigned histidine E7 labile proton confirms that the group is completely buried within the heme pocket in a manner similar to that found for sperm whale cyano-Met myoglobin, and that the transient exposure to solvent is no more likely than in mammalian myoglobins with the "normal" distal histidine orientation. Finally, a comparison of solvent access to the heme pocket of the three monomeric C. thummi thummi hemoglobins, as measured from proton exchange rates of heme pocket protons, is made and correlated to binding studies with the diffusible small molecules such as O2.

In vivo NMR spectroscopy of lithium-7 in humans.

The pharmacokinetics of lithium uptake was measured by 7Li NMR spectroscopy at 24.83 MHz in vivo in the brain and muscle of a normal subject and a patient suffering from bipolar affective disorder, using a modified General Electric Signa clinical magnetic resonance imaging system. Comparison was made to standard phantoms to estimate Li concentrations. The levels of Li in brain and muscle were similar, were typically less than the level in serum, and generally tracked the level in serum. The Li level at steady state in the brain of a patient suffering from schizoaffective disorder was measured over a 7-month period. Substantial variation was seen, which showed some correlation with serum level. Serum level peaked about 2 h after a single 300-mg dose at steady state, and muscle level, immediately thereafter. Brain level peaked considerably later at 4 h. Localized in vivo 7Li NMR spectroscopy was demonstrated by acquisition of a 125-cm3 DRESS slice from the occipital region in less than 7 min.

Two-dimensional 1H-, 13C-, and 31P-nuclear magnetic resonance and molecular-mechanics investigation of D-fructose 2,6-bisphosphate.

Two-dimensional nuclear magnetic resonance studies have been carried out to assign unequivocally all the proton, carbon, and phosphorus resonances of D-fructofuranose 2,6-bisphosphate (1) and to verify its structure using a 400-MHz spectrometer. Several unexpected chemical-shift values and coupling constants were obtained. Molecular mechanics calculations (Sybyl) carried out to minimize the conformational energy of 1 yield phi C-1,P-2 = + 84, phi C-3,P-2 = - 155, and phi C-5,P-6 = + 175. Thus the unusual near-gauche orientations of C-1 and C-3 to P-2 in 1 can explain their small vicinal coupling constants (3JC-1,P-2 = 1.2, and 3JC-3,P-2 = 3.8 Hz), in contrast to the expected larger value seen for 3JC-5,P-6 namely, 6.9 Hz. Treatment of a sample of this compound with sodium borohydride did not affect its nuclear magnetic resonance spectrum, substantiating that O-2 is phosphorylated. Oxidation with sodium periodate yielded an intermediate which decomposed by a beta-elimination mechanism involving the 6-phosphate group. These data establish unequivocally the 1H, 13C, and 31P assignments and explain the observed anomalous shifts. Moreover they indicate that the activator of fructose 6-phosphate 1-kinase is the beta anomer of the 4T3 conformer of D-fructose 2,6-bisphosphate.

Solvent exchange of buried water and hydrogen exchange of peptide NH groups hydrogen bonded to buried waters in bovine pancreatic trypsin inhibitor.

Solvent exchange of 18O-labeled buried water in bovine pancreatic trypsin inhibitor (BPTI), trypsin, and trypsin-BPTI complex is measured by high-precision isotope ratio mass spectrometry. Buried water is labeled by equilibration of the protein in 18O-enriched water. Protein samples are then rapidly dialyzed against water of normal isotope composition by gel filtration and stored. The exchangeable 18O label eluting with the protein in 10-300 s is determined by an H2O-CO2 equilibration technique. Exchange of buried waters with solvent water is complete before 10-15 s in BPTI, trypsin, and BPTI-trypsin, as well as in lysozyme and carboxypeptidase measured as controls. When in-exchange dialysis and storage are carried out at pH greater than or equal to 2.5, trypsin-BPTI and trypsin, but not free BPTI, have the equivalent of one 18O atom that exchanges slowly (after 300 s and before several days). This oxygen is probably covalently bound to a specific site in trypsin. When in-exchange dialysis and storage are carried out at pH 1.1, the equivalent of three to seven 18O atoms per molecule is associated with the trypsin-BPTI complex, apparently due to nonspecific covalent 18O labeling of carboxyl groups at low pH. In addition to 18O exchange of buried waters, the hydrogen isotope exchange of buried NH groups H bonded to buried waters was also measured. Their base-catalyzed exchange rate constants are on the order of NH groups that in the crystal are exposed to solvent (static accessibility greater than 0) and hydrogen-bonded main chain O, and their pH min is similar to that for model compounds. The pH dependence of their exchange rate constants suggests that direct exchange with water may significantly contribute to their observed exchange rate.

N.M.R. of 'oriented' monosubstituted amides--cis and trans N-methyl formamide.

The n.m.r. spectrum of N-methyl formamide oriented in a lyotropic liquid crystal solvent shows the presence of the cis as well as the trans forms. Analysis of the spectra due to both the species has been carried out. Possible non-planar distortions at the nitrogen atom for the trans species have been computed using the derived dipolar couplings and the available structural data.