Synthesis of highly crystalline and monodisperse maghemite nanocrystallites without a size-selection process

The synthesis of highly crystalline and monodisperse gamma-Fe(2)O(3) nanocrystallites is reported. High-temperature (300 degrees C) aging of iron-oleic acid metal complex, which was prepared by the thermal decomposition of iron pentacarbonyl in the presence of oleic acid at 100 degrees C, was found to generate monodisperse iron nanoparticles. The resulting iron nanoparticles were transformed to monodisperse gamma-Fe(2)O(3) nanocrystallites by controlled oxidation by using trimethylamine oxide as a mild oxidant. Particle size can be varied from 4 to 16 nm by controlling the experimental parameters. Transmission electron microscopic images of the particles showed 2-dimensional and 3-dimensional assembly of particles, demonstrating the uniformity of these nanoparticles. Electron diffraction, X-ray diffraction, and high-resolution transmission electron microscopic (TEM) images of the nanoparticles showed the highly crystalline nature of the gamma-Fe(2)O(3) structures. Monodisperse gamma-Fe(2)O(3) nanocrystallites with a particle size of 13 nm also can be generated from the direct oxidation of iron pentacarbonyl in the presence of oleic acid with trimethylamine oxide as an oxidant.

A phase I vaccine trial with peptides reflecting ras oncogene mutations of solid tumors

Mutations in the ras genes occur in 20% of all human cancers. These genes, in turn, produce mutated proteins that are unique to cancer cells, rendering them distinguishable from normal cells by the immune system. Thus, mutated Ras proteins may form potential targets for immune therapy. We conducted a phase I/pilot clinical trial in patients with advanced cancers to test the toxicity and the ability to induce an immune response by vaccination with 13-mer mutated Ras peptides reflecting codon 12 mutations. These peptides corresponded to each of the patient's own tumor Ras mutation. Patients were vaccinated monthly x3 subcutaneously with the specific Ras peptide along with Detox adjuvant (RiBi ImmunoChem Research, Inc., Hamilton, MT, U.S.A.) at one of five different peptide dose levels (100, 500, 1,000, 1,500, and 5,000 micrograms). Three out of 10 evaluable patients generated a mutant Ras specific CD4+ and/or CD8+ T-cell immune response. The CD8+ cytotoxic cells specific for Gly to Val mutation at codon 12 were capable of lysing an HLA-A2-matched tumor cell line carrying the corresponding mutant but not the wild-type ras gene. The treatment has been well tolerated with no evidence of serious acute or delayed systemic side effects on any of the five dose levels. We demonstrated that we can generate in cancer patients specific T-lymphocyte responses that detect single amino acid differences in Ras oncoproteins. Neither the immune responses nor the minor side effects seen were found to be dose dependent. This approach may provide a unique opportunity for generating a tumor-directed therapy. Also, in vitro stimulation of these cells with the corresponding peptide generated specific T-cell lines that could be used for adoptive immune therapy.

Myoglobin desaturation with exercise intensity in human gastrocnemius muscle

The present study evaluated whether intracellular partial pressure of O(2) (PO(2)) modulates the muscle O(2) uptake (VO(2)) as exercise intensity increased. Indirect calorimetry followed VO(2), whereas nuclear magnetic resonance (NMR) monitored the high-energy phosphate levels, intracellular pH, and intracellular PO(2) in the gastrocnemius muscle of four untrained subjects at rest, during plantar flexion exercise with a constant load at a repetition rate of 0.75, 0.92, and 1.17 Hz, and during postexercise recovery. VO(2) increased linearly with exercise intensity and peaked at 1.17 Hz (15. 1 +/- 0.37 watts), when the subjects could maintain the exercise for only 3 min. VO(2) reached a peak value of 13.0 +/- 1.59 ml O(2). min(-1). 100 ml leg volume(-1). The (31)P spectra indicated that phosphocreatine decreased to 32% of its resting value, whereas intracellular pH decreased linearly with power output, reaching 6.86. Muscle ATP concentration, however, remained constant throughout the exercise protocol. The (1)H NMR deoxymyoglobin signal, reflecting the cellular PO(2), decreased in proportion to increments in power output and VO(2). At the highest exercise intensity and peak VO(2), myoglobin was approximately 50% desaturated. These findings, taken together, suggest that the O(2) gradient from hemoglobin to the mitochondria can modulate the O(2) flux to meet the increased VO(2) in exercising muscle, but declining cellular PO(2) during enhanced mitochondrial respiration suggests that O(2) availability is not limiting VO(2) during exercise.

Interference between two indistinguishable electrons from independent sources

Very much like the ubiquitous quantum interference of a single particle with itself, quantum interference of two independent, but indistinguishable, particles is also possible. For a single particle, the interference is between the amplitudes of the particle's wavefunctions, whereas the interference between two particles is a direct result of quantum exchange statistics. Such interference is observed only in the joint probability of finding the particles in two separated detectors, after they were injected from two spatially separated and independent sources. Experimental realizations of two-particle interferometers have been proposed; in these proposals it was shown that such correlations are a direct signature of quantum entanglement between the spatial degrees of freedom of the two particles ('orbital entanglement'), even though they do not interact with each other. In optics, experiments using indistinguishable pairs of photons encountered difficulties in generating pairs of independent photons and synchronizing their arrival times; thus they have concentrated on detecting bunching of photons (bosons) by coincidence measurements. Similar experiments with electrons are rather scarce. Cross-correlation measurements between partitioned currents, emanating from one source, yielded similar information to that obtained from auto-correlation (shot noise) measurements. The proposal of ref. 3 is an electronic analogue to the historical Hanbury Brown and Twiss experiment with classical light. It is based on the electronic Mach-Zehnder interferometer that uses edge channels in the quantum Hall effect regime. Here we implement such an interferometer. We partitioned two independent and mutually incoherent electron beams into two trajectories, so that the combined four trajectories enclosed an Aharonov-Bohm flux. Although individual currents and their fluctuations (shot noise measured by auto-correlation) were found to be independent of the Aharonov-Bohm flux, the cross-correlation between current fluctuations at two opposite points across the device exhibited strong Aharonov-Bohm oscillations, suggesting orbital entanglement between the two electron beams.

Ripe fruit of Solanum nigrum L. inhibits cell growth and induces apoptosis in MCF-7 cells

Solanum nigrum L. (SNL) has been traditionally used as a herbal plant, whose fruit is believed to have anti-tumor properties, although the mechanism for the activity remains to be elucidated. In this study, we prepared an ethanol extract from ripe fruits of SNL and investigated the mechanism involved in its growth-inhibitory effect on MCF-7 human breast cancer cells. Results from proliferation assay using tritium uptake showed that the proliferative capacity of MCF-7 cells was strongly suppressed in the presence of SNL ethanol extract. This was further confirmed through MTT assay and trypan blue exclusion experiments, which showed a very close correlation between the SNL extract concentration and the surviving cell numbers. The SNL extract-mediated suppression of cell growth was verified to be apoptotic, based on the appearance of DNA laddering, increase in DNA fragmentation, and low fluorescence intensity in nuclei after propidium iodide staining of the cells. Furthermore, the SNL extract was revealed to be a potential scavenger of hydroxyl radicals and DPPH radicals rather than superoxide anions. Collectively, our findings suggest that SNL fruit extract could be used as an anti-oxidant and cancer chemo-preventive material.

Comparative analysis of NMR and NIRS measurements of intracellular PO2 in human skeletal muscle

1H NMR has detected both the deoxygenated proximal histidyl NdeltaH signals of myoglobin (deoxyMb) and deoxygenated Hb (deoxyHb) from human gastrocnemius muscle. Exercising the muscle or pressure cuffing the leg to reduce blood flow elicits the appearance of the deoxyMb signal, which increases in intensity as cellular PO2 decreases. The deoxyMb signal is detected with a 45-s time resolution and reaches a steady-state level within 5 min of pressure cuffing. Its desaturation kinetics match those observed in the near-infrared spectroscopy (NIRS) experiments, implying that the NIRS signals are actually monitoring Mb desaturation. That interpretation is consistent with the signal intensity and desaturation of the deoxyHb proximal histidyl NdeltaH signal from the beta-subunit at 73 parts per million. The experimental results establish the feasibility and methodology to observe the deoxyMb and Hb signals in skeletal muscle, help clarify the origin of the NIRS signal, and set a stage for continuing study of O2 regulation in skeletal muscle.

Myoglobin and hemoglobin rotational diffusion in the cell

The detection of the 1H NMR signal of myoglobin (Mb) in tissue opens an opportunity to examine its cellular diffusion property, which is central to its purported role in facilitating oxygen transport. In perfused myocardium the field-dependent transverse relaxation analysis of the deoxy Mb proximal histidyl NdeltaH indicates that the Mb rotational correlation time in the cell is only approximately 1.4 times longer than it is in solution. Such a mobility is consistent with the theory that Mb facilitates oxygen diffusion from the sarcoplasm to the mitochondria. The microviscosities of the erythrocyte and myocyte environment are different. The hemoglobin (Hb) rotational correlation time is 2.2 longer in the cell than in solution. Because both the overlapping Hb and Mb signals are visible in vivo, a relaxation-based NMR strategy has been developed to discriminate between them.

Generation of stable CD4+ and CD8+ T cell lines from patients immunized with ras oncogene-derived peptides reflecting codon 12 mutations

Previous studies have identified and characterized both murine in vivo and human in vitro T cell responses reflecting specific mutations in the ras proto-oncogenes at codon 12, 13, or 61. In an attempt to determine whether peptide epitopes reflecting point mutations in the ras oncogenes are immunogenic in humans for the production of CD4+ and/or CD8+ T cell responses, a phase I clinical trial was initiated in metastatic carcinoma patients whose primary tumors harbor mutations in the K-ras proto-oncogenes at codon 12. The peptides used here as immunogens, which were administered in Detox adjuvant, spanned the ras sequence 5-17 and reflected the amino acid substitution of glycine (Gly) at position 12 to aspartic acid (Asp), cysteine (Cys), or valine (Val). Three of eight evaluable patients have demonstrated peptide-specific cell-mediated immunity, as determined by the production of T cell lines resulting from the vaccination. First, an antigen (Ag)-specific, major histocompatibility complex (MHC) class II (DP)-restricted CD4+ T cell line was established in vitro from postvaccination lymphocytes of a non-small cell lung carcinoma patient whose primary tumor contained a Cys12 mutation when cultured on the immunizing peptide. Moreover, CD4+ proliferation was inducible against the corresponding mutant K-ras protein, suggesting productive T cell receptor recognition of exogenously processed Ag. Second, an Ag-specific, MHC class I (HLA-A2)-restricted CD8+ cytotoxic T lymphocyte (CTL) line was established in vitro from postvaccination lymphocytes of a colon carcinoma patient whose primary tumor contained an Asp12 mutation. To that end, a 10-mer peptide, nested within the 13-mer immunizing peptide, was identified [i.e., ras5-14(Asp12)], which was shown to bind to HLA-A2 and display specific functional capacity for expansion of the in vivo primed CD8+ CTL precursors. Third, both Ag-specific, MHC class II (DQ)-restricted CD4+ and MHC class I-restricted (HLA-A2) CD8+ T cell lines were generated from a single patient with duodenal carcinoma whose primary tumor contained a Val12 mutation when cultured on the immunizing 13-mer peptide or a nested 10-mer peptide [i.e., ras5-14(Val12)], respectively. Evidence is thus provided that vaccination with mutant ras oncogene peptides in adjuvant may induce specific anti-ras cellular immune responses, with no detectable cross-reactivity toward normal proto-ras sequences. Moreover, we have identified for the first time human HLA-A2-restricted, CD8+ CTL epitopes reflecting specific point mutations in the K-ras oncogenes at codon 12 which, in concert with the activation of the CD4+ T cell response, may have important implications for both active and passive immunotherapies in selected cancer patients.

Metabolic fluctuation during a muscle contraction cycle

Gated 31P-nuclear magnetic resonance followed the metabolic fluctuation in rat gastrocnemius muscle during a contraction cycle. Within 16 ms after stimulation, the phosphocreatine (PCr) level drops 11.3% from its reference state. The PCr minimum corresponds closely to the time of maximum force contraction. Pi increases stoichiometrically, while ATP remains constant. During a twitch, PCr hydrolysis produces 3.1 mumol ATP/g tissue, which is substantially higher than the reported 0.3 mumol ATP.twitch-1.g tissue-1 derived from steady-state experiments. The results reveal that a substantial energy fluctuation accompanies a muscle twitch.

Human immunodeficiency virus causes mononuclear phagocyte dysfunction

There is compelling clinical evidence for dysfunction of the mononuclear phagocyte system in patients with AIDS, which is believed due in part to loss of T-cell cooperativity. The direct consequences of human immunodeficiency virus infection on macrophage function are unknown. To address this question we infected normal human macrophages in vitro with a monocytotropic strain of human immunodeficiency virus and performed assays to quantify their extra- and intracellular killing ability. Human immunodeficiency virus-infected macrophages were significantly less effective than control cells in mediating antibody-dependent cell-mediated cytotoxicity against leukemic cell targets and intracellular killing of Candida pseudotropicalis. The functional defects were profound, related temporarily to active virus production by the macrophages, and could not be overcome by granulocyte-macrophage colony-stimulating factor. Treatment of macrophages with 3'-azido-3'-deoxythymidine (AZT) 6 days after infection caused a marked decrease in virus production and prevented development of the intracellular killing functional defect. The results suggest that early antiviral therapy may be useful in preventing or mitigating some virus-induced mononuclear phagocyte dysfunction.

Differential in vivo regulation of mRNA encoding the norepinephrine transporter and tyrosine hydroxylase in rat adrenal medulla and locus ceruleus

To investigate the regulation of norepinephrine transporter mRNA in vivo, we analyzed the effects of reserpine on its expression in the rat adrenal medulla and locus ceruleus. First, PCR was used to clone a 0.5-kb rat cDNA fragment that exhibits 87% nucleotide identity to the corresponding human norepinephrine transporter cDNA sequence. In situ, the cDNA hybridizes specifically within norepinephrine-secreting cells, but in neither dopamine nor serotonin neurons, suggesting strongly it is a partial rat norepinephrine transporter cDNA. Reserpine, 10 mg/kg administered 24 h premortem, decreased steady-state levels of norepinephrine transporter mRNA in the adrenal medulla by approximately 65% and in the locus ceruleus by approximately 25%, as determined by quantitative in situ hybridization. Northern analysis confirmed the results of the in situ hybridization analysis in the adrenal medulla but did not detect the smaller changes observed in the locus ceruleus. Both analyses showed that reserpine increased tyrosine hydroxylase expression in the adrenal medulla and locus ceruleus. These results suggest that noradrenergic neurons and adrenal chromaffin cells can coordinate opposing changes in systems mediating catecholamine uptake and synthesis, to compensate for catecholamine depletion.

Cyclin D1 overexpression and prognosis in colorectal adenocarcinoma

Recently, it has been reported that cyclin D1 plays a major role in oncogenesis in various cancers; however, there have been few studies on the association of cyclin D1 overexpression and prognosis of patients with malignant tumors. We evaluated the prognostic significance of cyclin D1 overexpression in colorectal adenocarcinoma. One hundred twenty-three specimens resected from patients with colorectal adenocarcinomas were investigated by staining with a monoclonal antibody against cyclin D1. As a result, both overall survival and disease-free survival were significantly poorer in the patients with tumors strongly positive for cyclin D1 than in those with cyclin-D1-negative or weakly positive tumors. The 5-year survival rate of the patients with tumors strongly positive for cyclin D1 was 53.3%, while the 5-year survival rates of patients with cyclin-D1-negative and weakly positive tumors were 96.2 and 78.8%, respectively. Moreover, multivariate analysis indicated that cyclin D1 overexpression is an independent predictor of disease recurrence in our patients. In conclusion, cyclin D1 overexpression may be useful as a predictor of disease recurrence in colorectal adenocarcinoma.

Systemic Treatment with Tetra-O-Methyl Nordihydroguaiaretic Acid Suppresses the Growth of Human Xenograft Tumors

PURPOSE

We have previously shown that the transcriptional inhibitor tetra-O-methyl nordihydroguaiaretic acid (M4N) induces growth arrest in tumor cells and exhibits tumoricidal activity when injected intratumorally into tumor cell explants in mice. The experiments reported here were designed to determine whether M(4)N can be given systemically and inhibit the growth of five different human xenograft tumors.

EXPERIMENTAL DESIGN

Nude (nu/nu) mice bearing xenografts of each of five human tumor types (i.e., hepatocellular carcinoma, Hep 3B; prostate carcinoma, LNCaP; colorectal carcinoma, HT-29; breast carcinoma, MCF7; and erythroleukemia, K-562) were treated with M4N given i.v. or i.p. in a Cremophor EL-based solvent system or orally in a corn oil based diet. Tumors from the treated animals were measured weekly and analyzed for the expression of the Cdc2 and survivin genes, both previously shown to be down-regulated by M4N.

RESULTS

Systemic M4N treatment suppressed the in vivo growth of xenografts in each of the five human tumor types. Four of the five tumor models were particularly sensitive to M4N with tumor growth inhibitions (T/C values) of < or = 42%, whereas the fifth, HT-29, responded to a lesser extent (48.3%). Growth arrest and apoptosis in both the xenograft tumors and in the tumor cells grown in culture were accompanied by reductions in both Cdc2 and tumor-specific survivin gene expression. Pharmacokinetic analysis following oral and i.v. administration to ICR mice indicated an absolute bioavailability for oral M4N of approximately 88%. Minimal drug-related toxicity was observed.

CONCLUSION

These preclinical studies establish that when given systemically, M4N can safely and effectively inhibit the growth of human tumors in nude mice.

Automatic Detection of Cow's Oestrus in Audio Surveillance System

Early detection of anomalies is an important issue in the management of group-housed livestock. In particular, failure to detect oestrus in a timely and accurate way can become a limiting factor in achieving efficient reproductive performance. Although a rich variety of methods has been introduced for the detection of oestrus, a more accurate and practical method is still required. In this paper, we propose an efficient data mining solution for the detection of oestrus, using the sound data of Korean native cows (Bos taurus coreanea). In this method, we extracted the mel frequency cepstrum coefficients from sound data with a feature dimension reduction, and use the support vector data description as an early anomaly detector. Our experimental results show that this method can be used to detect oestrus both economically (even a cheap microphone) and accurately (over 94% accuracy), either as a standalone solution or to complement known methods.

Air pollution and daily mortality in Seoul and Ulsan, Korea

The relationship between air pollution and daily mortality for the period 1991-1995 was examined in two Korean cities, Seoul and Ulsan. The observed concentrations of sulfur dioxide (SO2; mean = 28.7 ppb), ozone (O3; mean = 29.2 ppb), and total suspended particulates (TSP; mean = 82.3 microg/m3) during the study period were at levels below Korea's current ambient air quality standards. Daily death counts were regressed separately in the two cities, using Poisson regression on SO2, O3, and/or TSP controlling for variability in the weather and seasons. When considered singly in Poisson regression models controlling for seasonal variations and weather conditions, the nonaccidental mortality associated with a 50-ppb increment in a 3-day moving average of SO2 concentrations, including the concurrent day and the preceding 2 days, was 1.078 [95% confidence interval (CI), 1.057-1.099] for Seoul and 1.051 (CI, 0.991-1.115) for Ulsan. The rate ratio was 1.051 (CI, 1.031-1.072) in Seoul and 0.999 (CI, 0. 961-1.039) in Ulsan per 100 microg/m3 for TSP, and 1.015 (CI, 1. 005-1.025) in Seoul and 1.020 (0.889-1.170) in Ulsan per 50 ppb for 1-hr maximum O3. When TSP was considered simultaneously with other pollutants, the TSP association was no longer significant. We observed independent pollution effects on daily mortality even after using various approaches to control for either weather or seasonal variables in the regression model. This study demonstrated increased mortality associated with air pollution at both SO2 and O3 levels below the current World Health Organization recommendations.

Eighteen-month Clinical Study of Universal Adhesives in Noncarious Cervical Lesions

OBJECTIVE

To evaluate the clinical performance of Scotchbond Universal (3M Oral Care) and Prime & Bond Elect (Dentsply Sirona) in the restoration of noncarious cervical lesions (NCCLs).

METHODS AND MATERIALS

This was a randomized controlled clinical trial involving 63 subjects. Two hundred and three NCCLs were restored using Scotchbond Universal and Prime & Bond Elect using both an etch-and-rinse and a self-etch technique. Lesions were notch-shaped NCCLs, and the restorations were placed without any mechanical retention. Restorations were finished immediately after placement and scored with regard to retention, marginal discoloration, marginal adaptation, and secondary caries. Similar assessment of the restorations was performed 18 months after placement. Logistic regression was performed for each outcome separately with a compound symmetric variance-covariance structure assumed to consider a correlation of restorations within subjects. All analyses were conducted using SAS version 9.4 (SAS Inc).

RESULTS

One hundred and fifty-eight teeth (77.8% of the restorations placed) in 46 subjects (73% of subjects enrolled) were available for the 18-month follow-up. A statistically significant difference was reached only for the comparison Scotchbond Universal/self-etch (SU_SE) and Prime & Bond Elect/etch-and-rinse (PBE_E&R) groups ( p=0.01), where a restoration with SU_SE was 66% less likely to maintain a score of Alpha for marginal discoloration than a restoration performed with PBE_E&R.

CONCLUSIONS

Scotchbond Universal and Prime & Bond Elect presented acceptable clinical performance after 18 months of clinical service. However, Scotchbond Universal, when applied with a self-etch approach, did demonstrate a relatively high level of marginal discoloration when compared to the other groups.

Hypoglossal nerve stimulation affects the pressure-volume behavior of the upper airway

To determine the effects of electrical hypoglossal nerve and submental stimulation on upper airway collapsibility, we examined the pressure-volume (P-V) relationships during bilateral supramaximal stimulation of the distal cut hypoglossal nerve ends over a range of frequencies from zero to 100 Hz in the sealed upper airway of 10 anesthetized supine dogs. Animals were artificially ventilated with 50% O2 and maintained under relative hyperoxia and hypocapnia during the study to eliminate the ventilatory drive output. Sealed upper airway pressures were obtained during random injections of different volumes of air from zero to 50 ml with and without hypoglossal nerve stimulation, and the upper airway P-V curves were obtained. The characteristics of the P-V curves were as follows: (1) the upper airway compliance defined as the slope of the regression of P-V curves fell from 4.07 +/- 0.33 ml/cm H2O without stimulation to 3.02 +/- 0.30 ml/cm H2O with stimulation at 50 Hz and plateaued at frequencies greater than 50 Hz, and (2) the volume at a given pressure during stimulation was larger than that without stimulation. The effects of submental stimulation on upper airway collapsibility were similar to those of hypoglossal nerve stimulation. These results suggest that the increase of upper airway muscle tone by hypoglossal nerve or submental stimulation stiffens the upper airway and that increases in muscle tone expand the upper airway.

H-NMR characterization of the human myocardium myoglobin and erythrocyte hemoglobin signals

The 1H-NMR signal of deoxy Mb provides a unique opportunity to measure tissue oxygenation in vivo. To utilize the technique for human application, however, requires a specific spectral characterization of both human Mb and erythrocyte Hb. We report that the proximal histidyl-NH signal of human deoxy Mb resonates at 80.3 ppm at 25 degrees C and maintains a 3.9 ppm separation with the corresponding Hb A signal throughout the physiological temperature range. In the particular case of the human thenar muscle, the deoxy Mb signal is clearly detectable without any interference from Hb.

Engineering topological states in atom-based semiconductor quantum dots

The realization of controllable fermionic quantum systems via quantum simulation is instrumental for exploring many of the most intriguing effects in condensed-matter physics1-3. Semiconductor quantum dots are particularly promising for quantum simulation as they can be engineered to achieve strong quantum correlations. However, although simulation of the Fermi-Hubbard model4 and Nagaoka ferromagnetism5 have been reported before, the simplest one-dimensional model of strongly correlated topological matter, the many-body Su-Schrieffer-Heeger (SSH) model6-11, has so far remained elusive-mostly owing to the challenge of precisely engineering long-range interactions between electrons to reproduce the chosen Hamiltonian. Here we show that for precision-placed atoms in silicon with strong Coulomb confinement, we can engineer a minimum of six all-epitaxial in-plane gates to tune the energy levels across a linear array of ten quantum dots to realize both the trivial and the topological phases of the many-body SSH model. The strong on-site energies (about 25 millielectronvolts) and the ability to engineer gates with subnanometre precision in a unique staggered design allow us to tune the ratio between intercell and intracell electron transport to observe clear signatures of a topological phase with two conductance peaks at quarter-filling, compared with the ten conductance peaks of the trivial phase. The demonstration of the SSH model in a fermionic system isomorphic to qubits showcases our highly controllable quantum system and its usefulness for future simulations of strongly interacting electrons.

Oxygen supply and oxidative phosphorylation limitation in rat myocardium in situ

The 1H-NMR signal of the proximal histidyl-N(delta)H of deoxymyoglobin is detectable in the in situ rat myocardium and can reflect the intracellular PO2. Under basal normoxic conditions, the cellular PO2 is sufficient to saturate myoglobin (Mb). No proximal histidyl signal of Mb is detectable. On ligation of the left anterior descending coronary artery, the Mb signal at 78 parts/million (ppm) appears, along with a peak shoulder assigned to the corresponding signal of Hb. During dopamine infusion up to 80 microg. kg(-1) x min(-1), both the heart rate-pressure product (RPP) and myocardial oxygen consumption (MVO2) increase by about a factor of 2. Coronary flow increases by 84%, and O2 extraction (arteriovenous O2 difference) rises by 31%. Despite the increased respiration and work, no deoxymyoglobin signal is detected, implying that the intracellular O2 level still saturates MbO2, well above the PO2 at 50% saturation of Mb. The phosphocreatine (PCr) level decreases, however, during dopamine stimulation, and the ratio of the change in P(i) over PCr (DeltaP(i)/PCr) increases by 0.19. Infusion of either pyruvate, as the primary substrate, or dichloroacetate, a pyruvate dehydrogenase activator, abolishes the change in DeltaP(i)/PCr. Intracellular O2 supply does not limit MVO2, and the role of ADP in regulating respiration in rat myocardium in vivo remains an open question.