The concept of transfer function for organ performance (work output vs. biochemical input) is developed for skeletal and cardiac muscle under steady-state exercise conditions. For metabolic control by the ADP concentration, the transfer function approximates a Michaelis-Menten hyperbola. Variation of the work identifies metabolic operating points on the transfer function corresponding to ADP concentrations or to a ratio of inorganic phosphate to phosphocreatine that can be determined by phosphorus nuclear magnetic resonance. This operating point is characterized by the fraction (V/VJ) of maximal activity of oxidative metabolism in the steady state. This quantity appears to be useful in predicting the degree to which metabolic homeostasis is effective; poorly controlled metabolic states can readily be identified and are used in the diagnosis and therapy of metabolic disease in the organs of neonates and adults.Analytical biochemistry has great strengths in measuring the more stable components of cell bioenergetics, particularly ATP [as buffered by creatine kinase equilibrium in skeletal tissue, brain, and heart (1, 2)]. However, the more labile and indeed interesting components, phosphocreatine (PCr) and inorganic phosphate (Pi) are measured with significantly less accuracy for two reasons: (i) the breakdown of PCr during extraction in the interval between cessation of metabolism and assay and (ii) even more serious, the difficulty in distinguishing, by usual analytical techniques, the bound and free forms and the contents of different intracellular compartments (3).Phosphorus NMR (P NMR) is selectively sensitive to the unbound form of cell metabolites and affords a wholly noninvasive approach to the study of metabolic control in the cytoplasmic compartment of cells and tissues (4, 5). P NMR can be used to obtain the relative concentrations of PCr, Pi, and ATP with rapidity and with significant atcuracy (± 10% in a 1-min scan). These concentration ratios are of great usefulness and importance in the study of metabolic control in animal models, neonates, and adults. Additional information is available when the absolute values of tissue concentrations of PCr and Pi are calculated from the value of ATP, and also creatine, as determined by analytical biochemistry [or prospectively by proton NMR (6, 7)]. When ADP plays its usual role as a regulatory metabolite, its concentration is maintained too low to be directly determined by NMR but can be calculated from the PCr/P1 value with appropriate assumptions. Under these conditions, NMR becomes a very useful tool because the principal elements of energy metabolism are determined and thermodynamic values may be estimated. As we shall discuss here, rates of oxidative metabolism relative to their maximal rates for the particular tissue conditions may be determined with significant accuracy particularly when P NMR data are used to include the effect of pH. We shall show how P NMR can be used, particularly in tissues stressed with hypoxia, for the prediction of stabili...

Continuous (CW) and pulsed light were used for the noninvasive measurement of hemoglobin oxygenation in tissues. A dual wavelength method of continuous illumination spectroscopy used 760 nm (deoxyhemoglobin peak) and 800 nm (an oxyhemoglobin-deoxyhemoglobin isosbestic point) to measure the kinetics and extent of oxyhemoglobin deoxygenation in brains during mild ischemia/hypoxia. Absorption and scattering were modeled in an artificial milk/yeast blood system, which gave an exponential relationship between absorption and optical path length to a depth of 7 cm. Time-resolved spectroscopy (10-ps resolution) afforded a display of the times and distances of arrival of photons emitted by the cat brain in response to a 10-ps input pulse. The emitted photons rose to a peak in a fraction of a nanosecond and declined exponentially over a few nanoseconds. The half-time of exponential decay corresponds to photon migration over a distance of 4 cm. Exponential light emission continued for several more nanoseconds when the brain was encased by the skull, which plays a key role in prolonging light emission. The exponential decline of light intensity has a value [exp( -pL)], where L is the path length determined from the time/distance scale and ,u is the characteristic of the migration of light in the brain. The factor ,u is increased by increasing absorption, and 1z' = EC where E and C are the Beer-Lambert parameters of extinction coeffilcient (E) and concentration (C). Thus, deoxyhemoglobin can be quantified in brain tissues.The utility of optical methods in studying metabolism and oxidative processes in cells and tissues was significantly enhanced in the early 1950s when a time-sharing dualwavelength system was developed for the quantitation of small changes in absorption in a highly scattering medium such as cell suspensions or muscle tissues in the visible and near-infrared (NIR) regions (1,2). Fluorescence signals from mitochondrial NADH complemented the absorption method for studies of the surface of heart, brain, and skeletal tissue (3,4). NIR spectroscopy was used to detect the redox state of the copper component of cytochrome oxidase in mitochondria (2) and yeast cells (5), and Jobsis-VanderVliet and coworkers (6-8) pioneered the study of NIR absorption in tissues by transillumination. More recently, algorithms have been developed by vanderZee and Delpy (9) to compensate for the interference from hemoglobin and myoglobin with cytochrome copper, as the latter may constitute as little as 10% of the total signal at 830 nm (see also ref. 10).This paper compares the use of continuous (CW) and pulsed light. The CW method has been applied to both animal and model systems to determine: (i) the attenuation characteristic of the light in models containing localized deoxyhemoglobin (Hb) and (ii) the ability to observe hypoxia in the brains of human subjects.II However, CW systems fail to quantify concentrations because they do not measure the optical path.The pulsed-light system time-resolves the emergence of light pulses ...

Fluorescence polarization immunoassay (FPIA) is a homogeneous (without separation) competitive immunoassay method based on the increase in fluorescence polarization (FP) of fluorescent-labeled small antigens when bound by specific antibody. The minimum detectable quantity of FPIAs with fluorescein label (about 0.1 ng analyte) is comparable with chromatography and ELISA methods, although this may be limited by sample matrix interference. Because of its simplicity and speed, FPIA is readily automated and therefore suitable for high-throughput screening (HTS) in a variety of application areas. Systems that involve binding of ligands to receptor proteins are also susceptible to analysis by analogous FP methods employing fluorescent-labeled ligand and HTS applications have been developed, notably for use in candidate drug screening.

Introduction Over the past half century, evidence has been accumulating on the emergence of obstructive sleep apnea (OSA), the most prevalent sleep-disordered breathing, as a major risk factor for cardiovascular disease. A significant body of research has been focused on elucidating the complex interplay between OSA and cardiovascular risk factors, including dyslipidemia, obesity, hypertension, and diabetes mellitus that portend increased morbidity and mortality in susceptible individuals. Conclusion Although a clear causal relationship of OSA and dyslipidemia is yet to be demonstrated, there is increasing evidence that chronic intermittent hypoxia, a major component of OSA, is independently associated and possibly the root cause of the dyslipidemia via the generation of stearoyl-coenzyme A desaturase-1 and reactive oxygen species, peroxidation of lipids, and sympathetic system dysfunction. The aim of this review is to highlight the relationship between OSA and dyslipidemia in the development of atherosclerosis and present the pathophysiologic mechanisms linking its association to clinical disease. Issues relating to epidemiology, confounding factors, significant gaps in research and future directions are also discussed.

The occurrence of peroxidative damage, as distinguished from anaerobic damage, to brain fatty acids and phospholipids was characterized in vitro. Fez+ and ascorbic acid were used to stimulate peroxidation in cortical homogenates from rat brain incubated with or without oxygen. Lipid peroxidation was established in samples incubated with oxygen by increased diene conjugation, accumulation of thiobarbituric acid-reactive material (TBAR), and of lipid-soluble fluorescent products. No peroxidation occurred in samples incubated in the absence of oxygen (100% N2). Lipid peroxidation was charac-Abbreviations used: MDA, Malondialdehyde; TBAR, thiobarbituric acid-reactive. Scand. 105, 524-526. Wills E. D. (1964) The effect of inorganic iron on the thiobarbituric acid method for the determination of lipid peroxides. Biochim. Biophys. Acta 84, 475-477. Physiof. -350.15, 132-145.