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BACKGROUND: Energy intake (EI) regulation is impaired in older adults, but it is not known if habitual physical activity affects accuracy of EI regulation in older compared with young adults. OBJECTIVE: We hypothesized that the ability to compensate for a high-energy yogurt preload beverage at a subsequent ad libitum meal (i.e. acute compensation) and over the course of the testing day (i.e. short-term compensation) would decrease with age, but the magnitude of the decline would be smaller in physically active compared with sedentary older adults. DESIGN: On two occasions, young active (n=15), young sedentary (n=14), older active (n=14) and older sedentary (n=11) subjects consumed either a high-energy yogurt preload beverage (YP: 500 ml, 1988 kJ, men; 375 ml, 1507 kJ, women), or no preload (NP), 30 min before an ad libitum test meal. EI at both ad libitum meals was measured, and total daily EI was determined on both testing days. Percent EI compensation for the YP was calculated for the test meal and testing day to determine acute and short-term compensation. RESULTS: Percent EI compensation at the test meal was significantly lower in the older compared with the young subjects (65+/-4 vs 81+/-4%, P=0.005). There was no effect of habitual physical activity level on acute compensation, and no age by physical activity level interaction (P=0.60). In contrast, short-term compensation was not different with age (87+/-5 vs 93+/-6%, older vs young, P=0.45), but was more accurate in active vs sedentary subjects (100+/-5 vs 79+/-6%, P=0.01). As with acute compensation, there was no age by physical activity interaction (P=0.39). CONCLUSION: Acute EI regulation is impaired in older adults, which is not attenuated by physical activity status. However, EI regulation over the course of a day is more accurate in active vs sedentary adults, which may facilitate long-term energy balance. Future work is needed to determine if higher energy expenditure in older active vs older sedentary adults improves long-term EI regulation.

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By enabling noninvasive measurements of tissue biochemistry, nuclear magnetic resonance spectroscopy (MRS) provides a unique means of characterizing tissues. Differences in equipment, techniques, and methodology between different laboratories cause major difficulties when comparing results, whether from measurements of tissue metabolism, or from the effects of different therapies. This is of concern in critically evaluating work from different laboratories and centres, causing potential difficulties in reproducing results, limiting the establishment of MRS as a standard method of diagnosis and of characterising disease and response to therapy in the laboratory and clinic. It also poses particular problems in establishing the multicentre clinical trials of MRS that are now required to provide adequate statistical power in confirming the encouraging preliminary clinical observations. These difficulties arise principally from imperfect localization of signal from selected regions of interest in the body, and from the subsequent analyses of the MRS spectra. Improvement is possible by establishing agreed procedures for test measurements and for data analysis, and by using appropriate test objects and test substances to establish the quality of measurements. A concerted research project on characterisation of biological tissues by NMR, principally concerned with MR imaging (MRI), was activated in 1984 by the European Economic Community as part of its third Medical and Health Research Programme, under the auspices of the Biomedical Engineering Concerted Actions' Committee (COMAC-BME). In 1988, this project was prolonged for 5 years, when the programme was expanded to encompass MRS.(ABSTRACT TRUNCATED AT 250 WORDS)

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The effects of infusion of amino acids alone or in combination with carbohydrate and lipid on triiodothyronine (T3) and reverse triiodothyronine (rT3) status, substrate availability and metabolism in surgically-stressed and clinically euthyroid patients were examined. The characteristic post-operative decline in T3 concentration was observed in all patient groups (p < 0.001) (8 patients in each group). However, infusion with amino acids alone retarded the decline in T3; the decrease was lower than those found in the controls and the mixed nutrition group and restoration of T3 values was incomplete, even by the sixth post-operative day. The pattern of increase in rT3 was similar in all 3 patient groups. However, the T3/rT3 ratio dropped to its lowest level on day 1 in the control group and the mixed infusion group (p < 0.001), with a complete restoration by the sixth post-operative day, whereas in the amino acids infused group the ratio was lowest on day 2 (p < 0.001) and was still significantly low by day 6 compared with the pre-operative value (p < 0.001). The findings, in the group infused with amino acids of a less prominent hyperglycaemia, with the significant slowing of T3 response and the significant correlation of rT3 with the plasma glucose, indicate a link between hyperglycaemia and the thyroid hormone response to surgical trauma. No correlations were found between thyroid hormone or urea concentrations, and the blood concentrations of free fatty acids, 3-hydroxybutyrate, or urea; or between thyroid hormone and the percentage of total urea nitrogen excretion. Results show that the changes in fat metabolism after operation are unlikely to be responsible for the changes in T3 and rT3. In conclusion, whereas the post-operative response of T3 concentration can be partially modified by the nutrition regimen employed, that of rT3 is largely related to surgical stress.

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The multi-parameter dependence of magnetic resonance (MR) images allows a unique flexibility of soft tissue contrast and gives access to peculiar sources of in vivo tissue characterization, mainly associated with magnetic relaxation properties. However, MR methodologies have not yet expressed their full potential in terms of tissue characterization for several reasons: a) problems of quality control and quantitation have generally not been addressed by centers using MRI equipment, nor in most of the published literature; and b) data scattering of quantitative measurements obtained from tissues in vitro and in vivo appear to be a major factor in inhibiting or limiting the clinical utility of MRI, for a possible in vivo characterization of pathological tissues. An international project, aimed at evaluating the clinical significance of tissue characterization by MR, was activated in 1984 by the Biomedical Engineering Advisory Committee of the European Communities (EC COMAC-BME) within the 3rd EC Medical and Health Research Programme (MHRP). The scientific achievements of this first project (Magn. Reson. Imaging, 6:171-222; 1988) represented the basis for launching and performing a second Concerted Action, in the frame of the 4th MHRP (1988-1992). Main areas of research of this second project were: a) development of standard methodologies for quantitative measurements of MR parameters and correlation with histo- and physiopathology; b) performance assessment and calibration of MR clinical equipment; c) harmonization of test procedures with other centers and industry; and d) pilot multi-center collections of data.(ABSTRACT TRUNCATED AT 250 WORDS)

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Based on an international "Interlaboratory Comparison of Protocol Trials for In Vitro Studies by NMR," the EEC COMAC-BME concerted action on "Identification and Characterization of Biological Tissue by NMR" started collection of a data bank for in vitro relaxation time data of normal and pathological tissues. Relaxation time measurements were performed in a frequency range from 10-90 MHz and in a temperature range from 3 to 40 degrees C; data analysis was done using single exponential fitting routines. Specimens were taken from different organs or tissues (n = 19) of various species (n = 5) and both sexes. More than 900 relaxation time data from 12 participating groups were collected. However, for quantitative analysis we concentrated on liver tissue (287 entries). Main results are the high reproducibility of data from different centers, allowing quantification of temperature dependence of T1 and T2, respectively, in fresh mouse (3.9 and 0.41 msec/degrees C), rat (2.1 and 0.24 msec/degrees C), and hamster (2.6 and 0.22 msec/degrees C) liver. Further, a highly significant species difference between mouse and rat liver, not depending on water content, has been established. We discuss results quantitatively as well as consequences for in vitro protocols and future multicenter data collection.

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NMR offers, in the complex proton relaxation properties of biological tissues, a unique and potentially powerful tool of tissue characterization. The difficulties encountered so far in comparing the results of in vitro and in vivo NMR studies carried out in different laboratories inhibit NMR methodologies from fully expressing their content of physiopathological information, as well as their potential for therapeutic monitoring. Moreover, obtaining accurate data on proton relaxation in vivo requires accurate location of the anatomical region under study. The acquisition of acceptable information about location and effects is dependent on the establishment of agreed procedures for tests, as well as on the use of appropriate test objects and test substances. A concerted research project entitled "Identification and Characterization of Biological Tissues by NMR" was activated in 1984 by the European Economic Community as part of the Third Medical Research Program, under the auspices of the Biomedical Engineering Concerted Action Committee. A series of papers is presented here which illustrates objectives and scientific programs of this project, the protocols adopted for multi-center comparison of in vitro and in vivo studies, and the results of validating trials, as well as problems of reference substances.

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Lipogenic rates (measured with 3H2O) in hepatocytes from fed or starved euthyroid rats were similar in magnitude to those measured in livers in vivo. Hepatic lipogenesis in vivo in fed triiodothyronine (T3)-treated rats was greater than in fed control rats, but rates in vitro were only 16% of those of control rats. It is concluded that hepatic lipogenesis in vivo in T3-treated rats utilizes precursors from extrahepatic tissues. Glycogen depletion of hepatocytes from fed control rats decreased lipogenesis, and rates were then similar to those in hepatocytes from fed T3-treated rats. Addition of lactate (2 mmol/l) and pyruvate (0.2 mmol/l) had little stimulatory effect on lipogenesis in hepatocytes from fed control rats, but increased lipogenesis in glycogen-depleted hepatocytes (by 86%), hepatocytes from starved rats (by 25%) and hepatocytes from T3-treated rats (by 60%). In the presence of lactate and pyruvate, 3-mercaptopicolinate (3-MPA) (an inhibitor of gluconeogenesis) did not affect lipogenesis in hepatocytes from fed control rats but substantially increased lipogenesis in hepatocytes from starved euthyroid rats or fed hyperthyroid rats. Thus, in hepatocytes from starved euthyroid rats or fed hyperthyroid rats gluconeogenesis competes with lipogenesis for available precursors (lactate and pyruvate). In contrast, in fed rats carbon flux is predominantly towards lipogenesis. Effects of 3-MPA in the presence of lactate and pyruvate were much less in glycogen-depleted cells from fed rats than in hepatocytes from starved or T3-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

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Spin-lattice relaxation rate (1/T1) was measured in the left (LV) and right (RV) ventricular cavities in four conscious normal humans and four anesthetized greyhound dogs breathing spontaneously. Inspired oxygen concentration (FIO2) was varied in five steps from 21 to 100%. In dogs, blood was sampled from indwelling catheters in the pulmonary artery and aorta for measurement of PO2. Saturation-recovery and inversion-recovery tomographic images of the ventricular cavities were obtained supine during quiet breathing using a whole-body NMR scanner operating at a static magnetic field strength of 0.15 Tesla. From FIO2 21 to 100%, 1/T1 of LV increased by 11.6% in humans and 9.6% in dogs. In dogs, 1/T1 increased by 2.8% per 100 mm Hg increase in aortic PO2 (r greater than 0.87). There was no correlation in dogs between 1/T1 in RV and pulmonary artery PO2. The LV/RV 1/T1 ratio in dogs increased by 4% per 100 mm Hg increase in the LV-RV PO2 difference, and by 8% in humans as FIO2 increased from 21 to 100%. A rise in dissolved oxygen concentration increases NMR spin-lattice relaxation rates of blood in vivo to a small but significant extent.

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The results of NMR examinations in 52 patients with histological or clinical diagnoses of cerebral tumor are reviewed. An increase in relaxation time was recognized in all tumors but problems were experienced in distinguishing the margin of tumors from surrounding edema. Mass effects were well demonstrated as a result of the high level of gray-white matter contrast available with inversion-recovery sequences and the use of coronal and sagittal imaging planes. In general repeated FID sequences were less sensitive in detecting tumors than inversion-recovery or spin-echo sequences. Periventricular edema was well demonstrated with spin-echo sequences and was of importance in recognizing acute or subacute hydrocephalus. Radiation therapy was associated with increased relaxation times particularly within white matter. Problems in the recognition of tumor recurrence following treatment are outlined. The opportunities and challenges that NMR imaging is now providing for physicists and radiologists are discussed.

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The two strands of the problem are the shapes and changes with time of cell survival curves on the one hand and the responses of cell constituents to radiation on the other. Evidence of correlations between results of studies of these two types of phenomena under the influence of a wide range of modifying agents is required to establish mechanisms. Recovery may be defined as referring to the whole cell, while repair should be regarded as a process carried out by one substance on another. The degrees of usefulness and possible deficiencies of a multi-hit/target model and a repair model for explaining cell survival curves and cell recovery are compared in a range of circumstances. A fully satisfactory model is not yet available.

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