Higher Steady-state Concentrations Research Articles

On the mechanism of the benzophenone‐sensitized photolysis of 2,3‐diazabicyclo[2.2.1]hept‐2‐ene in the laser jet: Evidence for intermolecular triplet diradical reactions

AbstractThe benzophenone‐sensitized laser jet photolysis of 2,3‐diazabicyclo[2.2.1]hept‐2‐ene (1) affords, besides the previously reported cyclopentene and housane (2), also cyclopentane, cyclopentadiene, and the dimers bicyclopent‐2‐en‐1‐yl (7), 3‐cyclopentylcyclopent‐1‐ene (8), and 1,1'‐bicyclopentyl (9). As a model reaction, the pyrolysis of dimer 8 at 600°C/20 Torr leads to the other dimers 7 and 9 together with cyclopentadiene, cyclopentene, and traces of cyclopentane. Control experiments showed that H abstraction by the cyclopentane‐1,3‐diyldiracidal (3) from cyclohexene (as model substrate for cyclopentene) and addition to housane (2) with formation of diradical 6 are unlikely pathways. Instead, the product data available can be best explained in terms of an intermolecular disproportionation of two diradicals 3 to give the cyclopent‐2‐en‐1‐yl (4) and cyclopentyl (5) radical pair, which is subsequently converted to the observed products by in‐cage and out‐of‐cage coupling and H transfer reactions. Such intermolecular diradical chemistry becomes feasible due to the high steady‐state concentrations (ca, micromolar) generated in the laser jet. Two‐photon processes take place, but are of subordinate importance.

Reactive nitrogen intermediates, antinuclear antibodies and copper-thionein in serum of patients with rheumatic diseases.

Sera from 354 patients with various inflammatory and autoimmune rheumatic diseases were screened for the presence of reactive nitrogen intermediates, antinuclear antibodies and the anti-oxidase copper-thionein (Cu-thionein), and compared to sera from healthy donors and patients with non-rheumatic diseases including AIDS, various internal as well as neurological diseases and carcinoma of different organs. When compared to healthy individuals, the levels of nitric oxides in sera from patients with autoimmune rheumatic diseases were elevated by 240-600% (P < 0.01). The status of reactive nitrogen intermediates (NOx, RNI) in sera from donors with inflammatory rheumatic diseases was increased by 170-540%, but was also significantly enhanced in sera of patients with non-rheumatic diseases, indicating a general inflammatory mechanism that is predominantly triggered by inducible nitric oxide (NO) syntheses of phagocytes. All rheumatic sera were dramatically depleted of the anti-oxidase Cu-thionein (P < 0.001), a powerful consumer of hydroxyl radicals and singlet oxygen and an efficient superoxide dismutase. The NOx levels were positively correlated with the serum titers of antinuclear antibodies (r = 0.77) and negatively correlated with Cu-thionein levels (r = 0.94), reflecting a high steady-state concentration of free radicals generated during inflammatory and autoimmune rheumatic diseases.

Human Plasma all-trans-, 13-cis- and 13-cis-4-Oxoretinoic Acid Profiles during Subchronic Vitamin A Supplementation: Comparison to Retinol and Retinyl Ester Plasma Levels

Plasma concentrations of retinyl esters, retinol, retinol-binding protein and the polar retinol metabolites all-trans-retinoic acid, 13-cis-retinoic acid, all-trans-4-oxoretinoic acid and 13-cis-4-oxoretinoic acid were measured for six male volunteers who received 0.46 mg retinyl palmitate per kilogram body weight as oily drops (equivalent to 0.25 mg retinol per kilogram body weight) once daily over a 20-d period. Retinol and retinol-binding protein levels remained virtually constant throughout the study. Following absorption of vitamin A, retinyl esters as well as all-trans-retinoic acid and 13-cis-retinoic acid were transiently increased in plasma. 13-cis-4-Oxoretinoic acid increased gradually to a steady state level present on d 10 or 20. All-trans-4-oxoretinoic acid was not detected in plasma of the volunteers, with the exception of one on d 10 of the study. Plasma pharmacokinetic profiles of retinyl esters and polar metabolites of retinol displayed great interindividual differences (peak concentrations, time to peak, area-under-the-concentration-time curve values) among the volunteers. Because of the relatively high and consistent steady state concentrations of plasma 13-cis-4-oxoretinoic acid, we suggest that this compound be further investigated as a biochemical marker of vitamin A uptake in humans.

Determination of absolute rate constants for radical polymerization of diisopropyl fumarate based on a quantitative scavenge of propagating radical

During polymerization of diisopropyl fumarate (DiPF), the propagating poly(DiPF) radical was scavenged quantitatively by a stable free radical, because of its long-lived nature and high steady-state concentration. By addition of a known amount of 1,3,5-triphenylverdazyl to the polymerization mixture, the concentration of poly(DiPF) radical was determined to be 10 −5−10 −4 mol dm −3, which allowed the evaluation of the propagation rate constant ( k p) from the overall rate of polymerization: k p = 0.31 ± 0.07 dm 3 mol −1 s −1 at 30°C. The lifetime of the polymer radical was too long for a rotating sector experiment. The rate constant for bimolecular termination of the radical ( k t) was calculated from the decay of poly(DiPF) radical followed by the scavenger method: k t = 0.84 dm 3 mol −1 s −1. These rate constants, which are exceptionally small, are accounted for by the steric factor of the ester alkyl group accumulated along the polymer chain and extremely slow diffusion of the polymer radical. Because the termination rate determined is too slow to interpret the molecular weight of the polymer formed, primary radical termination is to be considered as an additional termination process in the actual polymerization.

Concentrations of Volatile Organic Compounds at a Building with Health and Comfort Complaints

For four separate periods over a 1-yr span, the concentrations of volatile organic compounds (VOCs) have been measured at a facility with a history of occupant complaints. The reported symptoms were characteristic of "sick building syndrome." This study was initiated to determine if VOC levels were higher than those measured in "complaint-free" buildings and, if so, to identify sources and other factors that might contribute to the elevated concentrations. VOCs were collected with passive samplers, using a sampling interval that lasted from 3 to 4 weeks. Following collection, the samplers were extracted, and the compounds in the extract were separated and identified using standard gas chromatographic-mass spectrometric procedures. Over 40 different organic compounds with concentrations in excess of 1 microgram/m3 were identified; several species had values greater than 100 micrograms/m3. For each of the first three sampling periods, the total concentration of VOCs detected using this methodology was in excess of 3 mg/m3. Sources of the identified compounds included cleaning products, floor wax, latex paints, and reentrained motor vehicle exhaust. However, the dominant source was the hydraulic system for the buildings' elevators. Compounds were volatilizing from the hydraulic fluid used in this system. Neither the elevator shafts nor the mechanical room housing the fluid reservoirs were vented to the outside. The problem was compounded by the relatively small amount of outside air used for ventilation at this facility (less than 6 L/sec [12 cfm]/occupant or about 1/4 air change/hr). At such low ventilation rates, compounds with strong sources can achieve high steady-state concentrations within the facility. Recommendations have been made to reduce the VOC levels at this site. Although implementing the recommendations will be costly, even a slight improvement in employee productivity will offset these costs.

The correlation of vinblastine pharmacokinetics to toxicity in testicular cancer patients.

The clinical pharmacokinetics of vinblastine administered by continuous 5-day infusion (3 mg/m2/day) was studied in 12 patients with primary testicular cancer. Serum vinblastine concentrations were determined by radioimmunoassay on serum collected over a 10-day period. Steady-state vinblastine concentrations were achieved within 60 to 108 hours (median, 72 hours). Vinblastine pharmacokinetics were analyzed and correlated to hematologic and nonhematologic toxicity. Hematologic toxicity was severe (granulocytopenia of less than 500/microL) in all patients; however, no correlation of vinblastine pharmacokinetics to duration of granulocytopenia or nadir was noted. Nonhematologic toxicity, however, showed a direct correlation to steady-state vinblastine concentrations. Two distinct groups of patients were identified by a toxicity score evaluating nonhematologic toxicity: as low (group A) or high (group B). The toxicity score was calculated for each patient based on accumulated toxicity during the course of treatment. The mean toxicity score for all patients was 7.11 and for groups (A and B) it was 4.0 and 9.6, respectively (P = .02). Steady-state vinblastine concentration for each patient was compared with toxicity where the mean steady-state vinblastine concentration was 7.3 ng/mL for all patients, and 5.8 ng/mL and 8.5 ng/mL for groups A and B, respectively (P = .01). These steady-state vinblastine concentrations correlated directly with the mean toxicity scores revealing that patients with high steady-state vinblastine concentrations demonstrated more nonhematologic toxicity. Application of these data to pharmacokinetically directed studies are warranted to investigate this relationship and designate dosages of vinblastine to avoid excessive toxicity.

Compliance during tricyclic antidepressant therapy: pharmacokinetic and analytical issues.

Information on steady-state concentrations of parent tricyclic antidepressants (TCAs) and their major metabolites in plasma is useful in ascertaining compliance, for possible pharmacokinetic changes during longer treatment, and for prospective individualized dosing procedures. Adequate response can be maintained when there are relatively small fluctuations in drug concentration from visit to visit, but large fluctuations increase the liklihood of relapses during the acute-treatment phase and recurrences afterwards. Changes in the individualized in dosage regimens complicate measurement of concentrations in plasma at steady state. Longitudinal examinations of concentration/dosage (L/D) values in our three-year imipramine (IMI) maintenance study reveal that patients having large intra-individual fluctuations can be classified as noncompliers, likely to have recurrences. The time course and magnitude of L/D values reflect higher accumulation of both components, IMI and desipramine (DMI), in plasma. Evidently, dose-dependent kinetics lead to higher steady-state concentrations in plasma than previously observed with similar dosages in shorter-term treatment. With amitriptyline (AMI), in a 12-month study, the mean total concentrations of both AMI and nortriptyline (NT) progressively increased, by 22% and 33%, respectively. The pharmacokinetic linearity of AMI and (or) NT, i.e., (L/D)high/(L/D)low, is maintained over much wider dosage and age range than with IMI or DMI. We advocate concurrent use of the L/D method and co-administration of riboflavin for identification of noncompliers. We describe our current experience with various analytical procedures in this regard, concluding that high-performance liquid-chromatographic methods, with appropriate selection among ultraviolet, enhanced fluorescence, and electrochemical detectors for each TCA under specified therapeutic conditions, are most suitable and versatile, having superior analytical parameters. A suitable alternative procedure is gas-chromatography (N/P mode). Although immunoassays (EMIT, radiochemical) are most convenient for toxicological screens, their significant cross reactivities with several phenothiazines and the detection limits, requiring higher concentrations for EMIT, restrict their usage during research and (or) clinical monitoring.

A spin probe study of the water associated with a steady-state level of phosphoenzyme of the Ca-ATPase

The electron spin resonance spectrum of a water-soluble nitroxide free radical TEMPOL has been measured in concentrated suspensions of sarcoplasmic reticulum vesicles. Spectra observed in the presence of a high steady-state concentration of phosphoenzyme, formed from inorganic phosphate in the presence of Mg 2+, have been compared with those observed in the absence of phosphoenzyme. Quite large and reproducible differences in the two spectra were observed. Below 0 ° C the bulk water froze, and TEMPOL accumulated into a residual liquid phase of high microscopic viscosity, and of polarity slightly less than water. When lipids were extracted from the vesicles, dispersed in water and frozen, the residual signal from TEMPOL showed that it was in an environment of polarity similar to ethanol. It is proposed that the water which did not freeze at 0 ° C was contained in the hydrophobic cleft of the ATPase containing the active site. Like water in small hydrophobic pores of synthetic polymers, it consisted of large strongly-bonded clusters, and had high viscosity, low entropy and profoundly changed solvent properties.

Subcellular distribution of ependymins in goldfish brain measured by radioimmunoassay.

Goldfish CNS was fractionated by differential and density gradient centrifugation. The fractions obtained were characterized by marker enzymes typical of various subcellular organelles. They were further analyzed by radioimmunoassay for their contents of ependymins, two CNS glycoproteins known to participate in biochemical reactions after learning events. Ependymins were shown to be major constituents of the soluble cytoplasm (5.6% of the total protein content). The nuclear fraction was virtually devoid of ependymins (0.6% of protein). Small amounts were observed in the crude synaptosomal and microsomal fractions (1.0 and 3.5%, respectively). The highest steady-state concentration of ependymins, however, was measured in the brain extracellular fluid (15.6% of the protein), including the CSF. The specificity of the distribution was examined by intracerebroventricular injection of 125I-labeled ependymins as exogenous marker substances. No indication of an artificial redistribution of the radiolabel during homogenization and fractionation was obtained. The exogenous analogues of ependymins were, however, incorporated in vivo into organelles recovered in the nuclear and crude synaptosomal fractions. Our results suggest that ependymins may interact with synaptic membranes from the extracellular fluid, although so far no evidence for a specific receptor-type binding site could be obtained in vitro.

Regional distribution of ependymins in goldfish brain measured by radioimmunoassay

Ependymins are goldfish glycoproteins known to participate in biochemical reactions of memory consolidation after an operant vestibulomotor training-task. The distribution of these proteins was analysed by means of a highly sensitive and specific radioimmunoassay. Ependymins were shown to be characteristic constituents of the nervous system, but they were virtually absent from all other tissues investigated. They were widely distributed over many brain regions and particularly enriched in mesencephalic structures. In the optic tectum, the tegmentum and in the vagal lobes ependymins constituted 3.2, 2.8 and 3.5%, respectively, of the total protein content. The highest steady-state concentration of ependymins (15.4% of protein) was measured, however, in the brain extracellular fluid including the cerebrospinal fluid. Lactate dehydrogenase activity was monitored to demonstrate that only negligible amounts of cytoplasmic constituents were released during the collection of extracellular proteins. Ependymin concentrations were lower in those brain areas which contain few cell bodies, but many glial and fibrous elements. The specific distribution of the intrinsic ependymins was compared with that of intracerebroventricularly injected [(125)I]-labeled ependymin. This exogenous marker substance was quickly incorporated and then cleared rapidly from the central nervous system with a half-life of 2 h. Our quantitative analysis of the distribution of ependymins reveals that they are specific major constituents of the goldfish nervous system. Their fast turnover, their wide distribution over many brain regions, with some enrichment in mesencephalic structures, and especially their very high concentration in the extracellular brain fluid suggest that ependymins may act on neuronal membranes from the extracellular fluid.

Mechanism of toxicity of nitro compounds used in the chemotherapy of trichomoniasis.

The mechanism of the trichomonicidal activity of metronidazole and other 5-nitroimidazoles appears to depend on the ferredoxin-mediated reduction of their nitro group, with generation of a reactive metabolite or metabolites which interact with DNA leading to a subsequent inhibition of nucleic acid and protein synthesis. Redox cycling of these compounds under aerobic conditions appears to be a detoxification reaction by inhibiting net reduction of the drugs, thereby inhibiting their uptake. On the other hand, redox cycling of nitrofurans or other compounds with more positive reduction potential results in formation of high steady-state concentrations of oxygen-derived metabolites that might be of toxicological significance. It seems likely that reduced metabolites of nitroimidazoles (perhaps through covalent binding to tissue macromolecules and/or thiols depletion) are also involved in the nitroimidazoles' toxic effects to animal tissues and in their mutagenic and carcinogenic action.

Pharmacology of propranolol in patients with cirrhosis and portal hypertension.

Ten patients with cirrhosis and protal hypertension received an initial 20 mg oral test dose of propranolol and subsequently 160 mg of a slow release preparation, orally, each day for seven days. Protein binding, serial plasma propranolol concentrations and effects on heart rate were studied. Protein binding was slightly reduced (mean 85%, range 78.9-88.1%) compared with four normals (mean 87.9%). In patients with severe liver disease (serum albumin less than 30 g/l) propranolol remained detectable in plasma 24 hours after the single 20 mg dose and high steady state concentrations (mean 266.5 ng/ml, range 84-406) were observed during regular dosing. At steady state there was a significant correlation between log total plasma propranolol concentrations and the percentage fall in heart rate (r = 0.659, p less than 0.05). We suggest that in patients with severe liver chronic disease (serum albumin less than 30 g/l), propranolol therapy should be initiated in hospital. The starting dose should be low (20 mg of the conventional formulation tds or 80 mg of the slow release preparation daily) and that regular monitoring of the heart rate should be carried out.

Migration of Radionuclides in Fissured Rock: Analytical Solutions for the Case of Constant Source Strength

An analytical solution is derived for the problem of radionuclide migration in fissured rock, where the rock blocks are modelled as spheres. The solution differs from a previous one mainly in the inlet boundary condition. In the present paper the case of constant source strength is treated instead of a decaying step release. The solution developed here is considerably more complex. Processes that are accounted for are advection and longitudinal dispersion in the fissures, external and internal diffusion into spherical rock blocks, sorption onto the fissure surfaces, and sorption within the matrix and radioactive decay. The solution is obtained in the form of an infinite single integral depending in general on six dimensionless parameters. The steady state solution includes five dimensionless quantities. A comparison with previously published results for a system of parallel fractures is made. It is shown that if the area‐to‐volume ratio of the slabs and the spherical rock blocks is the same, identical breakthrough curves are produced for short and long contact times. In the intermediate range the solution with spherical rock blocks will give earlier breakthrough and higher steady state concentrations. It is shown that the analytical solution for parallel fractures, previously given as an infinite double integral, may be derived as an infinite single integral. The numerical evaluation is thereby considerably simplified. Examples demonstrate the impact of hydrodynamic dispersion and water transport time on radionuclide transport in situations considered to be realistic repository conditions.

Distinct reduction of nitrofurans and metronidazole to free radical metabolites by Tritrichomonas foetus hydrogenosomal and cytosolic enzymes.

Anaerobic Tritrichomonas foetus hydrogenosomes supplemented with pyruvate and CoA effectively reduce nitrofurans and metronidazole to their respective anion free radicals. Addition of purified ferredoxins from Clostridium pasteurianum or Spinacia oleracea to these preparations causes a great stimulation of metronidazole reduction, but does not affect nitrofuran reduction. A similar stimulatory effect of ferredoxin on metronidazole reduction, but not on nitrofuran reduction, is observed in incubations containing purified NADPH:ferredoxin oxidoreductase from S. oleracea. NADH is less effective than pyruvate as a reducing cofactor for metronidazole and nitrofuran reduction by the hydrogenosomes, and these activities are not modified by the addition of ferredoxins. In contrast to the results observed with hydrogenosomes, the T. foetus soluble fraction supplemented with NADH or NADPH is able to reduce nitrofurans, but not metronidazole. Under aerobic conditions, the anion free radical metabolites generated from metronidazole and nitrofurans are oxidized, resulting in catalytic superoxide anion formation as detected by spin-trapping experiments. Oxygen consumption and H2O2 formation by T. foetus hydrogenosomes and NADPH:ferredoxin oxidoreductase are also stimulated by nitrofurans and high concentrations of metronidazole. Addition of ferredoxin enhances metronidazole-stimulated, but not nitrofuran-stimulated, oxygen consumption and H2O2 formation in both systems. These results support the role of air oxidation as a detoxification reaction of the metronidazole anion radical and the involvement of ferredoxin in its formation. On the other hand, redox cycling of nitrofurans with formation of high steady state concentrations of oxygen-derived radicals might be of toxicological significance.

Clinical Pharmacology of Calcium Antagonists

Although diltiazem, nifedipine, and verapamil exhibit great diversity in chemical structure, they exhibit common pharmacokinetic properties. They are all highly cleared drugs and thus subject to a significant hepatic first-pass metabolism. Therefore, their bioavailability is low despite their almost complete absorption following oral administration. In addition, the bioavailability of these drugs is subject to inter- and intraindividual variations even in healthy subjects. In patients with liver disease, bioavailability increases substantially due to intra- and extrahepatic shunting. During multiple dosing, the oral clearance decreases and bioavailability increases, thus leading to higher steady-state concentrations than those predicted from single-dose studies. The interpretation of pharmacodynamic data in relation to plasma drug concentrations should consider the following points: presence of hysteresis effect and pharmacodynamic models employed for the analysis of the concentration-effect relationship (log-linear versus Emax model). The route of administration can influence the concentration-effect relationship due to the formation of active metabolites and/or stereoselective first-pass metabolism. The available pharmacokinetic data for the three calcium antagonists are discussed with special emphasis on their contribution to pharmacodynamic effects.

Electron spin resonance-spin stabilization in enzymatic systems: Detection of semiquinones produced during peroxidatic oxidation of catechols and catecholamines

The electron spin resonance-spin stabilization technique has been applied in an enzymatic system. This technique, which generates radicals in high steady-state concentration under static conditions, involves the use of limited quantities of enzyme and substrate while allowing facile spectral interpretation. In this work o -semiquinone intermediates produced during peroxidase-catalyzed oxidation of catechols and catecholamines have been detected as their metal complexes with Zn 2+. No significant effect on the peroxidase activity was found for the concentrations of Zn 2+ ions employed.

Accumulation of histone repeat transcripts in the sea urchin egg pronucleus

RNA transcripts complementary to a genomic histone repeat are found in high concentration in sea urchin egg pronuclei. In situ hybridizations with the recombinant plasmid pCO2 indicate that the nuclear concentration is at least 25 to 50 fold higher than that in the cytoplasm. If nuclear transcripts are predominantly histone mRNAs, they comprise about 12% of the histone mRNA in eggs, or about 0.36 pg. After fertilization these molecules persist through pronuclear fusion but disappear from nuclei by mid 2-cell stage. A similar high nuclear concentration is not observed for polyadenylated mRNAs or for two individual abundant maternal mRNAs. The high steady-state concentration of nuclear histone repeat transcripts suggests that they have an unusually long lifetime in pronuclei of unfertilized sea urchin eggs.

Aspects of quantitative secondary ion mass spectrometry

The present state of quantitative secondary ion mass spectrometry (SIMS) is analysed critically. Because of the strong gain in sensitivity obtained by loading the instantaneous sample surface with either oxygen or cesium, chemically enhanced secondary ion emission is discussed almost exclusively. The implications brought about by a fixed experimental geometry and by the mass dependence of instrumental factors are discussed in some detail. Normal beam incidence is to be prefered because of the high steady state concentration of oxygen attainable. Positive secondary ion yields of elements emitted from a common matrix under conditions of complete saturation with oxygen are proportional to exp(− βE i), where E i is the respective ionization potential and β a parameter of unknown origin. Interpretation of β in terms of equilibrium thermodynamics (i.e. β −1 = kT) is shown to be unjustified and misleading. Enhanced positive ion emission in the presence of oxygen is likely to result from disintegration of metal oxygen complexes occurring at the final stage of sputter emission (bond breaking model). Similar processes may determine negative ion emission in the presence of cesium. However, a simple relation between negative ion yields and electron affinity does not seem to exist. Presently, the most accurate quantitative analyses are obtained by the use of experimentally determined relative sensitivity factors.

Light-induced EPR signal I and signal II in wheat etioplasts greened under intermittent light without or with subsequent continuous light

The behaviour of light-induced electron paramagnetic resonance (EPR) Signal I and Signal II in wheat plastids lacking O 2 evolving capacity due to development under intermittent light (IL plastids) is compared with that of plastids whose water-splitting system has been photoactivated by a brief subsequent continuous light (ICL plastids). EPR spectra in the absence or presence of DCMU as well as the observations of rise kinetics over a long time course clearly reveal that in ICL plastids Signal I (identified with P 700 +) is the result of competing processes that oxidize P 700 on the one hand and reduce it on the other. In IL plastids the high Signal I level indicates a high steady-state concentration of oxidized P 700 due to the absence of normal electron flow from Photosystem II (PS II). The three kinetic components (dark, slow-decaying and fast-decaying) of Signal II are observed both in IL and ICL plastids. Signal II is not chemically induced as Signal I by ferricyanide. Protease eliminates Signal II but leaves Signal I intact. Only the fast Signal II is abolished by DCMU and electron donors to PS II. It is assumed to reflect the oxidation state of a component functioning on the PS II oxidizing side.

Adriamycin: Effect on mammalian cardiac cells in culture I. Cell population and energy metabolism

The use of adriamycin, an effective cancer chemotherapeutic agent, may be precluded because of cardiotoxic side effects of unknown etiology. Mammalian cardiac cells in culture were used as a model system in the study of the mechanisms involved. Adriamycin treatment inhibited cell growth and cytochemical staining demonstrated that the cell population was enriched in myocardial cells following the drug treatment. The fast-dividing non-myocardial cells were particularly susceptible to adriamycin. The latter might be a contributing factor in the cardiomyopathy but the cessation of the rhythmic contractions characteristic of myocardial cells in culture remains to be elucidated. The analysis of acid soluble cells extracts showed a 30% decrease in intracellular concentrations of ATP and phosphorylcreatine. The addition of creatine to adriamycin treated cells resulted in a several-fold increase in the steady state concentration of phosphorylcreatine. Therefore, the regulation of energy production and the potential to maintain a high steady state concentration of phosphorylcreatine were not impaired.