Magnetic resonance spectroscopy studies on changes in cerebral calcium and zinc and the energy state caused by excitotoxic amino acids

Under control conditions, superfused hippocampal slices exhibited a significantly higher phosphocreatine (PCr)/ATP ratio than cortical slices; the evidence suggests that this is due to lower concentrations of ATP, rather than higher concentrations of PCr. Glutamate caused relatively rapid decreases in PCr and ATP levels to approximately 45%, accompanied or immediately followed by an increased free intracellular calcium concentration ([Ca2+]i) and the release of Zn2+ in the cortex. In the hippocampus PCr and ATP decreased further to approximately 20% of control values, but the changes in [Ca2+]i and Zn2+ content were slower. This is in contrast to the effects of depolarisation, which produced the same rapid changes in the energy state and [Ca2+]i, with no detectable Zn2+, in both tissues. NMDA causes effects similar to those of glutamate in the cortex (decreases in the energy state, increased [Ca2+]i, and release of Zn2+). Pretreatment of the cortex for 1 h with the NMDA blocker MK-801 prevented all of the observed effects of NMDA. In contrast, pretreatment with MK-801 had no detectable effect on the increase in [Ca2+]i or the decreases in PCr and ATP caused by glutamate, although it prevented the release of zinc. The results are discussed in relation to the function of the NMDA subtype of glutamate receptor in excitotoxicity.

The effect of scanner sound in visual, motor, and auditory functional MRI

The potentially important effect of gradient switching sound on brain function during functional magnetic resonance imaging (fMRI) was studied by comparing experiments with low and high scanner sound levels. To provide a low sound level experiment, a sparse scanning method was used, characterized by long, 9 sec, periods of scanner silence interspersed with 1 sec echoplanar imaging (EPI) bursts. For the condition with high sound levels, extra EPI gradient modules were inserted in the 9 sec inter-image intervals. Visual, motor, or auditory stimuli were presented in the interval between imaging. It was found that with the addition of gradient sounds, auditory activation was significantly decreased while motor and visual activation were not significantly altered. Other general factors relating to fMRI were also examined, such as experimental duration and fatigue. For example, motion of the subjects during the experiments was found to be related to the time spent in the scanner, rather than to the ambient sound level.

SPARE: A robust method for magnetic resonance imaging in inhomogeneous fields

An imaging sequence based on a spin-echo train has been developed which is free from geometric distortions in the imaging plane due to main field inhomogeneity. Such inhomogeneities, and chemical shifts, cause only a displacement in the selected slice, which is minimized by the use of high gradient strengths and short radiofrequency pulses. Additionally, variations in the radiofrequency field strength cause variations in the image amplitude but cause no other artifacts. This allows the use of low-flip-angle refocusing pulses, reducing the power deposition to levels which are safe in vivo at high field strengths. The sequence was implemented on a Bruker whole-body 3T system. Example images from a perfluorocarbon phantom and a human head are presented.

Functional magnetic resonance imaging of single motor events reveals human presupplementary motor area

Conventional functional imaging paradigms use periods of repetitive task performance to generate sustained functional signal changes. We have developed a technique of imaging the small, transient signal changes that occur after single cognitive events. The technique uses echo-planar imaging at 3 T to generate functional images of the whole brain with a temporal resolution of 3 seconds. It uses a signal averaging technique to create time sweeps of functional activity. After a single cognitive event, widely distributed patterns of brain activation can be detected and their time course measured. This technique enables the individual cognitive tasks that constitute a paradigm to be analyzed separately and compared. We describe the application of this new technique to separate the cognitive elements in a simple "go/no-go" motor paradigm. Comparison of activation patterns during "go" and "no-go" responses reveals hierarchical subdivision of the medial premotor cortex into an anterior region (presupplementary motor area) involved in movement decision making and a posterior region (supplementary motor area proper) directly involved in motor execution.

The workup for bariatric surgery does not require a routine upper gastrointestinal series

BACKGROUND

Morbid obesity is a serious disease that afflicts over five million Americans, threatening their health with such co-morbidities as diabetes, arthritis, pulmonary failure and stroke. Surgery is the only effective therapy, providing long-term control of weight, diabetes, pulmonary failure, and hypertension for as long as 14 years. Because the operation presents a major expense, this study examined whether X-ray examination of the gut could be omitted safely as a cost-saving measure.

METHODS

The records of 814 consecutive morbidly obese patients who underwent gastric bypass were reviewed to determine: (1) whether these individuals had undergone an upper gastro-intestinal (GI) series, and (2) if these studies influenced therapy or caused cancellation or postponement of surgery.

RESULTS

Of the 814 patients, 657 (80.7%) underwent a preoperative GI radiography. Of these examinations, 393 (59.8%) were normal, with the following abnormalities in the remaining 264: hiatal hernia, 164; esophageal reflux, 39; Schatzki's ring, 18; small bowel diverticula, four; renal stones, four; malrotation, three; gall stones, two; pyloric ulcer, one; possible pelvic mass, one; calcified leiomyoma, one; and dysphagial lusoria, one. None of these findings resulted in cancellation or a delay in surgery.

CONCLUSIONS

The upper GI series can be safely omitted from the routine preoperative evaluation of patients undergoing gastric bypass. At a cost of $741.00 per examination, this change represents significant potential savings. Similar evaluations of other routine preoperative tests may well provide a better basis for the evaluation of these complex patients.

Who would have thought it? An operation proves to be the most effective therapy for adult-onset diabetes mellitus

OBJECTIVE

This report documents that the gastric bypass operation provides long-term control for obesity and diabetes.

SUMMARY BACKGROUND DATA

Obesity and diabetes, both notoriously resistant to medical therapy, continue to be two of our most common and serious diseases.

METHODS

Over the last 14 years, 608 morbidly obese patients underwent gastric bypass, an operation that restricts caloric intake by (1) reducing the functional stomach to approximately 30 mL, (2) delaying gastric emptying with a c. 0.8 to 1.0 cm gastric outlet, and (3) excluding foregut with a 40 to 60 cm Roux-en-Y gastrojejunostomy. Even though many of the patients were seriously ill, the operation was performed with a perioperative mortality and complication rate of 1.5% and 8.5%, respectively. Seventeen of the 608 patients (< 3%) were lost to follow-up.

RESULTS

Gastric bypass provides durable weight control. Weights fell from a preoperative mean of 304.4 lb (range, 198 to 615 lb) to 192.2 lb (range, 104 to 466) by 1 year and were maintained at 205.4 lb (range, 107 to 512 lb) at 5 years, 206.5 lb (130 to 388 lb) at 10 years, and 204.7 lb (158 to 270 lb) at 14 years. The operation provides long-term control of non-insulin-dependent diabetes mellitus (NIDDM). In those patients with adequate follow-up, 121 of 146 patients (82.9%) with NIDDM and 150 of 152 patients (98.7%) with glucose impairment maintained normal levels of plasma glucose, glycosylated hemoglobin, and insulin. These antidiabetic effects appear to be due primarily to a reduction in caloric intake, suggesting that insulin resistance is a secondary protective effect rather than the initial lesion. In addition to the control of weight and NIDDM, gastric bypass also corrected or alleviated a number of other comorbidities of obesity, including hypertension, sleep apnea, cardiopulmonary failure, arthritis, and infertility. Gastric bypass is now established as an effective and safe therapy for morbid obesity and its associated morbidities. No other therapy has produced such durable and complete control of diabetes mellitus.

Hypoxia stimulates glucose transport in insulin-resistant human skeletal muscle

Insulin and muscle contraction stimulate glucose transport into muscle cells by separate signaling pathways, and hypoxia has been shown to operate via the contraction signaling pathway. To elucidate the mechanism of insulin resistance in human skeletal muscle, strips of rectus abdominis muscle from lean (body mass index [BMI] < 25), obese (BMI > 30), and obese non-insulin-dependent diabetes mellitus (NIDDM) (BMI > 30) patients were incubated under basal and insulin-, hypoxia-, and hypoxia + insulin-stimulated conditions. Insulin significantly stimulated 2-deoxyglucose transport approximately twofold in muscle from lean (P < 0.05) patients, but not in muscle from obese or obese NIDDM patients. Furthermore, maximally insulin-stimulated transport rates in muscle from obese and diabetic patients were significantly lower than rates in muscle from lean patients (P < 0.05). Hypoxia significantly stimulated glucose transport in muscle from lean and obese patients. There were no significant differences in hypoxia-stimulated glucose transport rates among lean, obese, and obese NIDDM groups. Hypoxia + insulin significantly stimulated glucose transport in lean, obese, and diabetic muscle. The results of the present study suggest that the glucose transport effector system is intact in diabetic human muscle when stimulated by hypoxia.

Okadaic acid, vanadate, and phenylarsine oxide stimulate 2-deoxyglucose transport in insulin-resistant human skeletal muscle

In response to insulin, several proteins are phosphorylated on tyrosine and on serine/threonine residues. Decreased phosphorylation of signaling peptides by a defective insulin receptor kinase may be a cause of insulin resistance. Accordingly, inhibition of the appropriate phosphatases might increase the phosphorylation state of these signaling peptides and thereby elicit increased glucose transport. The purpose of this study was to examine the effect of the serine/threonine phosphatase inhibitor okadaic acid and the tyrosine phosphatase inhibitors phenylarsine oxide and vanadate on 2-deoxyglucose transport in insulin-resistant human skeletal muscle. All three phosphatase inhibitors stimulated 2-deoxyglucose transport in insulin-resistant skeletal muscle. These data suggest that these compounds have bypassed a defect in at least one of the signaling pathways leading to glucose transport. Furthermore, maximal transport rates induced by the simultaneous presence of insulin and phosphatase inhibitor in insulin-resistant muscle were equal to insulin-stimulated rates in lean control subjects. However, both vanadate alone and vanadate plus insulin stimulated 2-deoxyglucose transport significantly more in insulin-sensitive tissue than in insulin-resistant tissue. These results demonstrate that although vanadate is able to stimulate glucose transport in insulin-resistant muscle, it is not able to normalize transport to the same rate achieved in insulin-sensitive muscle.

Neither moderate hypoxia nor mild hypoglycaemia alone causes any significant increase in cerebral [Ca2+]i: only a combination of the two insults has this effect. A 31P and 19F NMR study

(1) The energy state and free intracellular calcium concentration ([Ca2+]i) of superfused cortical slices were measured in moderate hypoxia (approximately 65 microM O2), in mild hypoglycaemia (0.5 mM glucose), and in combinations of the two insults using 19F and 31P NMR spectroscopy. (2) Neither hypoxia nor hypoglycaemia alone caused any significant change in [Ca2+]i. Hypoxia caused a 40% fall in phosphocreatine (PCr) content but not in ATP level, and hypoglycaemia produced a slight fall in both (as expected from previous studies). These changes in the energy state recovered on return to control conditions. (3) A combined sequential insult (hypoxia, followed by hypoxia plus hypoglycaemia) produced a 100% increase in [Ca2+]i and a decrease in PCr level to approximately 25% of control. The reverse combined sequential insult (hypoglycaemia, followed by hypoglycaemia plus hypoxia) had the same effect. On return to control conditions there was some decrease in [Ca2+]i and a small increase in PCr content, but neither recovered to control levels. (4) Exposure of the tissue to the combined simultaneous insult (hypoxia plus hypoglycaemia) immediately after the control spectra had been recorded resulted in a fivefold increase in [Ca2+]i and a similar decrease in PCr level to 20-25% of control. There was little if any change of [Ca2+]i or PCr level on return to control conditions. (5) These results are discussed in terms of metabolic adaptation of some but not all of the cortical cells to the single type of insult, which renders the tissues less vulnerable to the combined insult.

Calcium measurements with a new high-affinity n.m.r. indicator in the isolated perfused heart

A new n.m.r. indicator, 1,2-bis-(2-[1-(hydroxycarbony)ethyl- (hydroxycarbonylmethyl)]amino-5-fluorophenoxy)ethane (DiMe-5FBAPTA), with a higher affinity for calcium (apparent Kd 46 nM, pH 7.2, 30 degrees C) than the parent 5FBAPTA chelator (Kd 537 nM, pH 7.1, 30 degrees C) has been used to measure the cardiac intracellular free Ca2+ ([Ca2+]i). DiMe-5FBAPTA was loaded into Langendorff-perfused ferret hearts maintained at 30 degrees C using the acetoxymethyl ester (AM) derivative. The intracellular concentration required to achieve an adequate signal-to-noise (S/N) ratio (> 10:1) for the n.m.r. spectra caused a similar reduction in developed pressure to that obtained using 5FBAPTA-AM. The DiMe-5FBAPTA was used to estimate [Ca2+]i in diastole, through the calcium transient and at rest in the presence of the slow calcium channel blocker diltiazem. At a pacing frequency of 1.0 Hz, end-diastolic [Ca2+]i was 198 +/- 30 nM (n = 9), and reducing the pacing frequency to 0.2 Hz lowered [Ca2+]i to 89 +/- 13 nM (n = 5). Perfusion with diltiazem (100 microM) for 60 min lowered [Ca2+]i to 10 +/- 1 nM (n = 4) in unpaced hearts and to 94 +/- 24 nM (n = 4) in hearts paced at 1.0 Hz. The [Ca2+]i transient measured with DiMe-5FBAPTA was sharper and delayed compared with the transient measured previously with 5FBAPTA. Co-loading the two indicators provided evidence that the indicator with the higher Kd had a dominant effect on the end-diastolic [Ca2+]i. The lower values for end-diastolic [Ca2+]i obtained with DiMe-5FBAPTA are consistent with fluorescent indicator measurements. These observations suggest that perturbations of [Ca2+]i caused by the new indicator are less than those induced by 5FBAPTA. DiMe-5FBAPTA therefore represents a useful step in the development of 19F-n.m.r. calcium indicators.

Leisure-time physical activity as a determinant of self-perceived fitness

This paper examined the extent to which a reliable measure of leisure-time physical activity is predictive of self-perceived fitness among 40 British university students (mean age = 20.6 yr.). Spearman's rank-order correlations indicated that self-perceived fitness, on an ordinal scale of 1 through 5, was positively correlated 0.48 with Total activity score and 0.54 with one of its subfractions, Very Hard activity. An additional association of 0.52 with an estimate of cardiorespiratory endurance capacity meant that 35.4% of the variation in self-perceived fitness was accounted for by leisure-time physical activity and fitness variables (R = 0.60). These findings provide support that notions of perceived fitness are not inaccurate and are influenced by the amount and types of leisure-time physical activity undertaken.

Resting and end-diastolic [Ca2+]i measurements in the Langendorff-perfused ferret heart loaded with a 19F NMR indicator

Intracellular free calcium concentration ([Ca2+]i) was measured in Langendorff-perfused ferret hearts (30 degrees C, pH 7.4) by loading paced hearts with the 19F NMR calcium indicator, the 5,5'-difluoro derivative of 1,2-bis(o-aminophenoxy)ethane-N, N,N',N'-tetraacetic acid (5FBAPTA), to an initial cytosolic concentration of approximately 120 microM. Increasing the pacing frequency raised the end-diastolic [Ca2+]i from 299 +/- 44 nM (mean +/- SEM) at 0.2 Hz to 522 +/- 54 nM at 1.0 Hz and 691 +/- 166 nM at 2.0 Hz. Raising [Ca]o from 1.8 to 7.0 mM at a pacing frequency of 1.0 Hz increased end-diastolic [Ca2+]i to 625 +/- 39 nM. In unpaced hearts perfused with diltiazem (100 microM), [Ca2+]i fell rapidly to a steady-state value of < 100 nM after 60 min. Raising [Ca]o from 1.8 to 7.0 mM had no detectable effect on resting [Ca2+]i. The time course of the [Ca2+]i transient was measured in hearts paced at 1.1 Hz and perfused with 1.8 mM [Ca]o. The peak [Ca2+]i was approximately 2 microM at approximately 150 msec after the pacing pulse, and peak developed LVP occurred at 550 msec compared with 280 msec in control hearts not loaded with 5FBAPTA. Comparisons with data obtained by other techniques, including fluorescent [Ca2+]i indicators, imply that although the end-diastolic [Ca2+]i values obtained with 5FBAPTA in beating hearts are elevated by the concentrations of intracellular 5FBAPTA required for signal detection, the changes in [Ca2+]i observed in response to experimental interventions are qualitatively consistent with previous data.

Glycerol 3-phosphate and lactate as indicators of the cerebral cytoplasmic redox state in severe and mild hypoxia respectively: a 13C- and 31P-n.m.r. study

The incorporation of 13C from [1-13C]glucose and [2-13C]acetate into selected intermediary metabolites in extracts prepared from incubated cerebral-cortex slices was monitored by using 13C-n.m.r. spectroscopy under conditions of mild and severe hypoxia. Mild hypoxia had little effect on labelling of tricarboxylic-acid-cycle-related amino acids [glutamate, glutamine and gamma-aminobutyrate (GABA)], although the pool sizes of glutamate and glutamine decreased. There were large increases in the labelling of lactate and of alanine, and an increase in the pool size of lactate. In severe hypoxia, the resonances of lactate and alanine remained high, whereas those of the other intermediates decreased greatly. The pool size of GABA increased. Calculation of percentage 13C enrichments and total label incorporated showed that lactate was not further affected by severe hypoxia, but the total label in alanine and its pool size were further increased. A new resonance appeared in the phosphomonoester region of the 13C-n.m.r. spectrum only in severe hypoxia. This was unambiguously assigned to glycerol 3-phosphate from a combination of 31P- and 13C-n.m.r. spectroscopy. The percentage 13C-enrichment was calculated from the 13C-n.m.r. spectrum, and the total label incorporated was measured by g.l.c./m.s. The results are discussed in terms of the ability of lactate dehydrogenase to maintain normal levels of NADH in mild hypoxia, but not in severe hypoxia. The pyruvate which accumulates under the latter condition is channelled into alanine, and the increased NADH is reflected by the increase in glycerol 3-phosphate. We conclude that glycerol 3-phosphate and alanine may provide novel means of monitoring severe hypoxia, whereas lactate is a reliable indicator only of mild hypoxia.

Neuronal-glial metabolism under depolarizing conditions. A 13C-n.m.r. study

Time courses of incorporation of 13C from 13C-labelled glucose and/or acetate into the individual carbon atoms of amino acids, citrate and lactate in depolarized cerebral tissues were monitored by using 13C-n.m.r. spectroscopy. There was no change in the maximum percentage of 13C enrichments of the amino acids on depolarization, but the maxima were reached more rapidly, indicating that rates of metabolism in both glycolysis and the tricarboxylic acid cycle were accelerated. Although labelling of lactate and of citrate approached the theoretical maximum of 50%, labelling of the amino acids was always below 20%, suggesting that there is a metabolic pool or compartment that is inaccessible to exogenous substrates. Under resting conditions labelling of citrate and of glutamine from [1-13C]glucose was not detected, whereas both were labelled from [2-13C]acetate, which is considered to reflect glial metabolism. In contrast, considerable labelling of these two metabolites from [1-13C]glucose was observed in depolarized tissues, suggesting that the increased metabolism may be due to increased consumption of glucose by glial cells. The labelling patterns on depolarization from [1-13C]glucose alone and from both precursors [( 1-13C]glucose plus [2-13C]acetate) were similar, which also indicates that the changes are due to increased consumption of glucose rather than acetate.

The design of practical selective pulses for magnetic resonance imaging and spectroscopy using SPINCALC

Recently, we introduced a new numerical approach to the design and optimization of NMR selective pulses, which we have christened "SPINCALC" (J. T. Ngo and P. G. Morris, Biochem. Soc. Trans. 14, 1271 (1986); J. T. Ngo and P. G. Morris, Magn. Reson. Med. 5, 217 (1987]. The first practical application of pulses generated by SPINCALC is demonstrated on a standard 0.5-T clinical MRI system. Results are shown for single phase pi pulses suitable both for selective inversion and for selective refocusing. The extension of SPINCALC to multidimensional pulses is illustrated by the design of a two-dimensional pi pulse.

19F nuclear magnetic resonance study of fluoropyrimidine metabolism in strains of Candida glabrata with specific defects in pyrimidine metabolism

Flucytosine (5-FC)-resistant strains were isolated from the haploid opportunistic pathogen Candida glabrata by UV-induced mutation and fluoropyrimidine selection. These strains were characterized biochemically, and the metabolism of fluorinated pyrimidines was studied by 19F nuclear magnetic resonance spectroscopy. No evidence was obtained from these studies for degradative metabolism of the fluorinated derivatives. In the parental susceptible strain of C. glabrata, 5-fluorouracil but not 5-FC was detected within the cells. 5-Fluorouracil was also present in the culture supernatant after incubation of the cells with 5-FC. The distribution of fluorinated derivatives within the 5-FC-resistant strains was consistent with their genotype. Two strains of C. glabrata which had only a partial loss of cytosine deaminase and UMP pyrophosphorylase activity had high levels of resistance to 5-FC. Both C. glabrata and Candida albicans were susceptible to 5-fluorouridine. This compound but not the anticancer drug 5-fluoro-2-deoxyuridine was shown to be transported into susceptible cells by a specific uridine permease.

Effects of N-methyl-D-aspartate on [Ca2+]i and the energy state in the brain by 19F- and 31P-nuclear magnetic resonance spectroscopy

The effects of N-methyl-D-aspartate (NMDA) on the free intracellular Ca2+ concentration [( Ca2+]i) and the energy state in superfused cerebral cortical slices have been studied using 19F- and 31P-nuclear magnetic resonance spectroscopy. [Ca2+]i was measured using the calcium indicator 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (5FBAPTA). NMDA (10 microM) in the absence of extracellular Mg2+ caused the expected rise in [Ca2+]i but produced an impairment of the energy state: the phosphocreatine (PCr) content was decreased by 42%, and the Pi/PCr ratio was increased by 55%. There was no detectable change in ATP or free intracellular Mg2+ concentration. Increasing the NMDA concentration in the superfusing medium to 100 or 400 microM caused no further increase in [Ca2+]i or further decrease in PCr content, but the Pi/PCr ratio continued to rise. The impairment of the energy state preceded the effect on [Ca2+]i, and these changes were irreversible on return to control conditions. Repeating the experiments in the presence of 1.2 mM extracellular Mg2+ resulted in similar changes in the energy state, with no change in [Ca2+]i. The possibilities that the effects were due to membrane depolarisation or to the presence of 5FBAPTA within the tissues were eliminated. The results suggest that low concentrations (10 microM) of NMDA produce an impaired energy state independent of the presence of extracellular Mg2+ and that the decreased energy state is not due to the changes in [Ca2+]i, which are seen only in the absence of extracellular Mg2+.

Use of 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (5FBAPTA) in the measurement of free intracellular calcium in the brain by 19F-nuclear magnetic resonance spectroscopy

We have applied the 19F-nuclear magnetic resonance (NMR) calcium indicator 1,2-bis(2-amino-5-fluoro-phenoxy)ethane-N,N,N',N'-tetraacetic acid (5FBAPTA) to the measurement of the free intracellular calcium concentration [( Ca2+]i) in superfused brain slices. A mean +/- SD control value of 380 +/- 71 nM (n = 18) was obtained at 37 degrees C using 2.4 mM extracellular Ca2+. Subcellular fractionation studies using [3H]5FBAPTA showed that after loading of its tetraacetoxymethyl ester, approximately 55% was de-esterified, with the other 45% remaining as the tetraester bound to membranes. Of the de-esterified 5FBAPTA, greater than 90% was in the cytosolic fractions, with less than 1% in the mitochondria or microsomes. The NMR-visible de-esterified 5FBAPTA slowly disappeared from the tissue with a t1/2 of 4 h. A time course after loading confirmed that the calculated [Ca2+]i was constant over a 5-h period, although the scatter of individual results was +/- 20%. The [Ca2+]i was increased by a high extracellular K+ concentration ([K+]e), by a low extracellular concentration of Na+, and by the calcium ionophore A23187. On recovery from high [K+]e, the [Ca2+]i "overshot" to values lower than the original control value. The [Ca2+]i was surpisingly resistant to changes in extracellular Ca2+ concentration.

The use of laboratory microcomputers to hold NMR data bases

Computer-based data bases are essential tools for NMR spectroscopists working with complex mixtures such as tissue extracts. Algorithms are described which are easily implemented on a small laboratory microcomputer and which can be used to make, edit, and query personalized laboratory data files. The data are stored in a series of small files accessed by pointers to overcome inherent redundancy in the information. Performance times are tabulated for a BBC Model B microcomputer working in the BASIC language and using 5.25-in. floppy discs as virtual memory.

Cerebral metabolism of acetate and glucose studied by 13C-n.m.r. spectroscopy. A technique for investigating metabolic compartmentation in the brain

The time courses of incorporation of 13C from 13C-labelled glucose or acetate into cerebral amino acids (glutamate, glutamine and 4-aminobutyrate) and lactate were monitored by using 13C-n.m.r. spectroscopy. When [1-13C]glucose was used as precursor the C-2 of 4-aminobutyrate was more highly labelled than the analogous C-4 of glutamate, whereas no label was observed in glutamine. A similar pattern was observed with [2-13C]glucose: the C-1 of 4-aminobutyrate was more highly labelled than the analogous C-5 of glutamate. Again, no labelling of glutamine was detected. In contrast, [2-13C]acetate labelled the C-4 of glutamine and the C-2 of 4-aminobutyrate more highly than the C-4 of glutamate; [1-13C]acetate also labelled the C-1 and C-5 positions of glutamine more than the analogous positions of glutamate. These results are consistent with earlier patterns reported from the use of 14C-labelled precursors that led to the concept of compartmentation of neuronal and glial metabolism and now provide the possibility of distinguishing differential effects of metabolic perturbations on the two pools simultaneously. An unexpected observation was that citrate is more highly labelled from acetate than from glucose.

Correlation of scrotal circumference and age in American Brahman bulls

Scrotal circumference (SC) measurements were taken of 921 American Brahman bulls located on two ranches in southcentral Texas. Measurements were taken at various seasons of the year over an 11-yr time span. Body condition scores, as reflected by fat cover, and a subjective estimate of overall nutritional status were 4 or better, based upon a 1 to 9 scoring system, with 5 representing an animal with an average amount of body fat. Associated body weights were not measured and semen evaluations were not performed. Ages were calculated from exact birthdates and rounded to the nearest whole month. Ages from 8 mo to more than 36 mo were reported. SC measurements ranged from 16.0 cm to 42.5 cm. The relationship of SC and age was positively correlated (r=0.74) (P<0.0001) and could be predicted using the equation y=0.525x + 18.702 where y=SC in centimeters and x=age in months. These data provide evidence that the relationship of scrotal circumference and age of American Brahman bulls is similar to that of other cattle breeds.

Ca2+ transient, Mg2+, and pH measurements in the cardiac cycle by 19F NMR

19F NMR indicators have been used to measure the free cytosolic cation concentrations ([Mn+]i, where M is the atomic symbol and n is the value of the charge) of Ca2+, H+, and Mg2+ in perfused ferret hearts. The [Ca2+]i transient, cytosolic pH (pHi), and [Mg2+]i have also been followed at 16 phases in the cardiac cycle in hearts paced at 1.25 Hz at 30 degrees C. The initial [Ca2+]i rose rapidly after a 50-ms delay, was maximal at greater than 1.5 microM after 150 ms, and declined thereafter to the initial concentration. In contrast, no significant changes in pHi (pH 7.03 +/- 0.08) or [Mg2+]i (1.2 +/- 0.1 mM) were detected in the cycle. A decrease in developed pressure when the [Ca2+]i indicator (but not the pHi or [Mg2+]i indicator) was loaded into hearts was substantially reversed by the addition of 50 microM ZnCl2 to the perfusion medium. The Zn2+ was taken up into the myoplasm and displaced Ca2+ bound to the indicator, a symmetrically substituted difluoro derivative of 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (5FBAPTA), as evidenced by the appearance of the Zn-5FBAPTA resonance. The decrease in developed pressure caused by 5FBAPTA, therefore, may be due to its Ca2+ buffering effect on the myoplasm. By coloading hearts with the [Ca2+]i and pHi indicators, simultaneous measurement of several [Mn+]i was demonstrated, which should provide a useful addition to the methods available to monitor cardiac function and pharmacology.

Kinetic analysis of the cerebral creatine kinase reaction under hypoxic and hypoglycaemic conditions in vitro. A 31P-n.m.r. study

1. The tissue concentration of phosphocreatine (PCr) and the pseudo-first-order rate constant of creatine kinase (kf) were monitored in superfused guinea-pig brain slices in vitro by using 31P-n.m.r. techniques. 2. Superfusion of slices in low oxygen partial pressure (pO2 approx. 16 kPa) decreased tissue PCr concentrations by 48% but ATP concentrations were unchanged. Regression analysis revealed a significant negative correlation between the PCr concentration in hypoxic tissue and the increase in the rate constant, kf. Nevertheless the forward flux through the enzyme (Jf = kf.[PCr]) declined under these conditions. 3. Lowering the glucose concentration to 0.2 or 0.1 mM decreased PCr concentrations by 29% and 48% respectively; here ATP concentrations as well as PCr concentrations also decreased. Only in the presence of the lower glucose concentration (0.1 mM) was kf increased. However, unlike the situation in hypoxic tissue, Jf was maintained at control rates. 4. In spectra obtained in the presence of low oxygen or low glucose concentrations, a resonance attributable to tissue inorganic phosphate became dectectable. This observation is discussed in terms of known changes in tissue phosphate concentrations and possible alterations in cytoplasmic pH.

Measurement of free intracellular calcium in the brain by 19F-nuclear magnetic resonance spectroscopy

We report the first measurement of the free intracellular calcium level in an actively metabolising intact cerebral tissue preparation. To this end, we applied the recently developed 19F-nuclear magnetic resonance calcium chelator, 5,5'-F2-1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (5FBAPTA), in superfused cerebral cortical slices to give values for the intracellular Ca2+ concentration of 350 and 480 nM, at external calcium concentrations of 1.2 and 2.4 mM, respectively. Under both conditions, the intracellular Ca2+ concentration was increased by depolarisation using a high external K+ concentration. Interleaved 31P spectra showed that the presence of the 5FBAPTA had a deleterious effect on the metabolic state of the tissue with an external Ca2+ concentration of 1.2 mM, but normal viability was maintained using 2.4 mM.

General solution to the NMR excitation problem for noninteracting spins

The design of an NMR excitation scheme, whether selective or nonselective, is essentially the simultaneous inversion of an array of Bloch equations driven by magnetic fields which differ according to well-defined constraints. We find that if relaxation effects are negligible, nearly exact inversion of the Bloch equations is straightforward when performed in a special time-varying frame of reference. Repeated inversions of the Bloch equations for small perturbations provide the basis for arbitrarily large, optimal adjustments of the magnetization response to an applied time-varying magnetic field. Choice of the target response to be sought at each iteration is not trivial if overall adjustments of more than one-half rotation are required. We present the analysis both formally and in geometric terms and show how it leads to a general algorithm for the optimization of NMR excitation schemes. The unprecedented efficiency of the algorithm and its ability to generate novel pulses from distant starting approximations are demonstrated in the optimization of slice-selective pi pulses for inversion and refocusing, and a prefocused slice-selective pi/2 pulse. Other applications are discussed, including use of the algorithm to compensate for instrumental imperfections such as radiofrequency inhomogeneity.

Nuclear magnetic resonance as a tool to study brain metabolism

Nuclei which are most appropriate for nuclear magnetic resonance (NMR) spectroscopy in biological systems include, in decreasing sensitivity, 1H, 19F, 23Na, 31P, 13C and 15N. Proton NMR has achieved remarkable prominence in imaging of the brain, and though clinical 1H spectroscopy is still in its infancy, current developments indicate that it will provide interesting information on brain metabolism. The naturally abundant form of phosphorus (31P) has proved particularly useful in studies on energy metabolism in metabolically perturbed states in the brain in vivo and in vitro. Dynamic studies on turnover rates of ATP and creatine phosphate can be performed using saturation transfer techniques. The use of 13C to follow intermediary metabolism shows great potential, even though it is a relatively insensitive nucleus and has only 1% natural abundance. 19F is a highly sensitive and naturally abundant nucleus. When covalently attached to various chelators, it provides a most sensitive method for accurate measurement of many cations of biological importance, by virtue of the chemical shift of the 19F on binding of the cation to the chelator.

Design of an indicator of intracellular free Na+ concentration using 19F-NMR

The development is described of an Na+ chelator with appropriate properties for an indicator of intracellular free Na+ concentration ([Na+]i). The new indicator, FCryp-1, is a tribenzo derivative of the parent (2:2:1) cryptand structure, incorporating the same F-substituted dibenzo 19F-NMR reporter group as the free [Ca2+] indicator, 5FBAPTA (Smith, G.A., Hesketh, T.R., Metcalfe, J.C., Feeney, J. and Morris, P.G. (1983) Proc. Natl. Acad. Sci., USA 80, 7178-7182). FCryp-1 has appropriate affinity for Na+ (KNa = 10(1.3) M-1) and selectivity over other intracellular cations (KK; KCa; K Mg less than 10(-1) M(-1)) for a [Na]i indicator. There is an 19F-NMR chemical shift of 2.00 ppm between free FCryp-1 and the Na-FCryp-1 complex which provides a direct read out of free [Na+]. FCryp-1 carries four carboxylate groups to confer aqueous solubility which can be esterified with acetoxymethyl groups to render the indicator membrane permeant. Experiments on pig lymphocytes loaded with FCryp-1 gave an indicated [Na+]i of 13.8 +/- 1.8 mM (n = 4). The FCryp-1 structure can also be readily modified to provide fluorescent [Na+]i indicators.

Metabolic consequences of increasing intracellular calcium and force production in perfused ferret hearts

31P nuclear magnetic resonance was used to measure the relative concentrations of phosphorus-containing metabolites in Langendorff-perfused ferret hearts. Intracellular concentrations of inorganic phosphate ([Pi]i), phosphocreatine [( PCr]i), ATP ([ATP]i) and [H+] (pHi) were determined. Exposure of the heart to strophanthidin (10-40 microM) produced an increase in developed pressure over 5-10 min. In the presence of strophanthidin, [ATP]i was unchanged, [PCr]i showed a small fall, [Pi]i showed a small rise and there was a small acidosis. Exposure of the heart to a solution in which all the Na had been replaced by K (0 Na(K) solution) produced an increase of resting pressure which then decayed. During this contracture [PCr]i fell transiently and [Pi]i rose transiently with approximately the same time course as the contracture. However, [ATP]i remained constant throughout. The exposure to the 0 Na(K) solution also produced an intracellular acidosis. The changes in [PCr]i and [Pi]i and the intracellular acidosis were all increased during perfusion with 0 Na(K) if the heart had previously been exposed to strophanthidin. The efflux of lactate from the heart was increased during the exposure to the 0 Na(K) solution. The magnitude of this increase was enhanced by prior exposure to strophanthidin. The increase of intracellular lactate (calculated from this efflux) was sufficient to account for the observed intracellular acidification. An increase of lactate efflux could also be measured when an isolated papillary muscle was exposed to the 0 Na(K) solution. The intracellular acidification produced by Na removal was substantially decreased after prevention of glycolysis either by substrate depletion or by the application of iodoacetate. Elevation of the extracellular calcium concentration ([Ca2+]o) produced a large increase of developed pressure which was accompanied by a small transient increase of [Pi]i, a decrease of [PCr]i and a small intracellular acidosis. There was also an increase of lactate efflux. After exposure to strophanthidin the same increase of [Ca2+]o decreased developed pressure. The associated rise in [Pi]i and fall in [PCr]i were increased but there was no significant acidosis under these conditions. In addition to other explanations (Allen, Eisner, Pirolo & Smith, 1985a), it is likely that the fall of force is partly accounted for by the rise of [Pi]i.

The molecular structure of a rapidly formed oligomeric adenosine tetraphosphate derivative from rat heart

The inability to account for large systematic variations with time in soluble adenine nucleotides in perfused rat hearts [Bates, Perrett & Mowbray (1978) Biochem. J. 176, 485-493; Mowbray, Bates & Perrett (1981) FEBS Lett. 131, 55-59; Mowbray, Perrett & Bates (1984) Int. J. Biochem. 16, 889-894] led us to show that the soluble nucleotides are in rapid equilibrium with some hitherto unrecognized trichloroacetic acid/methanol-precipitable highly phosphorylated heteropolymeric form [Mowbray, Hutchinson, Tibbs & Morris (1984) Biochem. J. 223, 627-632]. Selective digestion coupled to chromatographic analysis together with m.s. and 31P-n.m.r. spectrometry have now been used to show that the likely structure for a purified oligomer that is in specific-radioactivity equilibrium with tissue ATP is 3-phospho-[glyceroyl-gamma-triphosphoroyl-5'-adenosine-3'-3- phospho]4 glyceroyl-gamma-triphosphoroyl-5'-adenosine.

Hindlimb hyperesthesia associated with rabies in two horses

Rabies was diagnosed in 2 adult Quarter Horses with hindlimb hyperesthesia and progressive weakness. Microscopic examination of the cord and brain of the first horse revealed nonsuppurative meningomyelitis and ganglioneuritis in the cord extending cranially to the 6th cervical segment. Fluorescent antibody test results of both horses were positive for rabies in hindlimb peripheral nerve specimens, but negative in sections of the upper lip. Salivary gland, cerebrum, cerebellum, hippocampus, musculocutaneous nerve, cornea, and optic nerve specimens were tested for rabies by fluorescent antibody technique to determine viral distribution in the body of the second horse.

Phosphorylation status of liver by 31P-n.m.r. spectroscopy, and its implications for metabolic control. A comparison of 31P-n.m.r. spectroscopy (in vivo and in vitro) with chemical and enzymic determinations of ATP, ADP and Pi

An investigation into the measurement of Pi and ADP in rat liver in vivo and in freeze-clamped extracts by 31P-n.m.r. spectroscopy was carried out. The concentration of Pi estimated in vivo is less than 25% [1 mM (mumol/ml of cell water)] of the value obtained from freeze-clamped liver (4 mM), whereas ADP in vivo is undetectable (1.4 mM in vitro). At 5 min after infusion of 750 mg of fructose/kg, the Pi content of liver extracts fell to 1.3 mM, whereas Pi is undetectable in vivo under these conditions [Griffiths, Stevens, Gadian, Iles & Porteous (1980) Biochem. Soc. Trans. 8, 641]. The results indicate that the lower Pi and ADP concentrations found in vivo may be due to compartmentation or binding rather than to degradation of labile organic phosphates during extraction. The results are discussed with reference to previous measurements of liver phosphates and investigations of compartmentation in the liver, as are some of the possible consequences for metabolic control in the liver of low ADP and Pi concentrations.

31P-saturation-transfer nuclear-magnetic-resonance measurements of phosphocreatine turnover in guinea-pig brain slices

The technique of 31P saturation-transfer n.m.r. was used to determine the forward and the reverse rate constants of creatine phosphotransferase in superfused guinea-pig cerebral tissues in vitro. The calculated forward rate constant of 0.22 +/- 0.03s-1 compared well with a previously reported value for rat brain in vivo [Shoubridge, Briggs & Radda (1982) FEBS Lett. 140, 288-292]. The reverse rate constant was found to be 0.55 +/- 0.10s-1. 3. By using concentrations of ATP and phosphocreatine estimated previously for this superfused preparation [Cox, Morris, Feeney & Bachelard (1983) Biochem. J. 212, 365-370], forward and reverse flux rates were calculated to be 0.68 and 0.72 mumol X s-1 X g-1 respectively. The concordance of forward and reverse fluxes contrasts with the situation observed in vitro in other tissues, and suggests that the creatine phosphotransferase reaction is at equilibrium under the conditions used here. 4. Lowering the concentration of glucose in the superfusing medium from 10mM to 0.5mM had no significant effect on phosphocreatine concentration or on the forward (ATP-generating) flux through creatine phosphotransferase. The results indicate that a normal phosphocreatine content in the presence of lowered glucose availability is reflected by an unchanged turnover rate.

A nuclear magnetic resonance study of metabolism in the ferret heart during hypoxia and inhibition of glycolysis

31P nuclear magnetic resonance was used to measure the relative concentrations of phosphorus-containing metabolites in Langendorff-perfused ferret hearts. Intracellular concentrations of inorganic phosphate ([Pi]i), phosphocreatine ([PCr]i), ATP ([ATP]i) and H+ (pHi) were monitored under control conditions and while oxidative phosphorylation and/or glycolysis were prevented. Mechanical performance was assessed by recording the pressure developed in a balloon placed in the left ventricle. Oxidative phosphorylation was prevented either by replacement of O2 with N2 or by addition of cyanide. When the rate of oxidative phosphorylation was reduced by either method, developed pressure fell to a stable level of about 35% of control after 5 min. The pHi (control value 6.98) first increased to a peak of 7.07 after 2 min but then decreased to give a stable acidosis (pH 6.85). [PCr]i decreased rapidly to about 15% of the control value after 5 min whereas [ATP]i declined very slowly, reaching about 90% of the control value after 10 min. Reduction in the rate of glycolysis was achieved either (i) by removal of external glucose and depletion of glycogen stores by a long (1-2 h) period of stimulation or (ii) by removal of glucose and application of 2-deoxyglucose (1 mM) for 30-60 min. These procedures had only a small effect on pressure development, [ATP]i, [PCr]i and pHi. Measurements of lactate production showed that these procedures reduced the rate of glycolysis by a factor of about 10. When oxidative phosphorylation was prevented during periods when the rate of glycolysis was reduced, developed pressure fell to less than 5% of control after 5 min and there was a subsequent increase in resting pressure (hypoxic contracture). pHi (control value 7.03) first increased to a peak of 7.12 and then declined to about pH 7.00, but there was no subsequent acidosis. [PCr]i fell rapidly to about 10% of control after about 5 min while [ATP]i declined to about half of its control value over 10 min. It is concluded that (i) when oxidative phosphorylation alone is prevented, the changes in pHi can account for a substantial part of the changes in developed pressure. The increase in [Pi]i probably also contributes to the decline of developed pressure. (ii) When oxidative phosphorylation was prevented under conditions in which the rate of glycolysis was also reduced, the more pronounced decline in developed pressure which occurs within 5 min cannot be accounted for by pHi changes and is probably not explained by the rise in [Pi]i or by the moderate fall of [ATP]i.(ABSTRACT TRUNCATED AT 400 WORDS)

High-time-resolution 31P NMR studies of the perfused ferret heart

A cell is described that has enabled isolated Langendorff-perfused ferret hearts to be studied in a Bruker WM200 widebore superconducting nuclear magnetic resonance (NMR) spectrometer. Left ventricular pressure was monitored with a latex balloon catheter, and the hearts were paced with a stimulator triggered from the spectrometer's central computer, enabling gated studies to be performed. Suitable radiofrequency filtering for the pacing leads is described. Phosphorus (31P) NMR was used to determine internal pH and the concentration of phosphorylated metabolites under resting conditions. The perfusion rate is shown to affect the phosphocreatine/ATP ratio at low flow rates, but the removal of phosphate from the perfusate is shown not to affect metabolite levels or the internal pH. The time resolution of the method is assessed and its potential for monitoring transient effects illustrated by studies of the effects of acetylcholine and cyanide-induced anoxia. The cardiac gated 31P NMR experiment is discussed and four spectra, corresponding to mid- and end systole and mid- and end diastolic are presented. No effects of cycling of high-energy phosphates are evident in these results.

The discovery of a rapidly metabolized polymeric tetraphosphate derivative of adenosine in perfused rat heart

The predicted presence in perfused rat hearts of a rapidly metabolized but hitherto unrecognized form of adenosine phosphate has been confirmed by specific radioactive labelling. The properties of the purified compound suggest that it is a heteropolymer of a small organic acid, phosphate and purine nucleoside in the proportions 1:4:1.

Serum ferritin as a measure of stored iron in horses

Occasionally, horses are given large amounts of iron to improve performance. Although iron deficiency could limit erythrocyte production and other functions related to nonhematological tissues, it probably only occurs in blood loss. We have developed an enzyme immunoassay for ferritin in equine sera and evaluated its relationship to iron stored in liver and spleen. Serum ferritin correlated significantly (P less than 0.0001) with the concentration of nonheme iron in the liver and spleen. It increased following iron therapy and decreased after phlebotomy. We conclude that serum ferritin provides a good index of hepatic and splenic iron and can be used to evaluate iron storage in horses.

Intracellular calcium measurements by 19F NMR of fluorine-labeled chelators

Symmetrically substituted difluoro derivatives of 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (nFBAPTA) show large 19F NMR chemical shifts on chelating divalent cations. The complexes of Ca2+ with 4FBAPTA and 5FBAPTA show fast and slow exchange behavior, respectively, and the chemical shift or the areas of the resonances from the free and complexed forms can be used to determine the free Ca2+ concentration. The measurement of the free Ca2+ concentration by either ligand is unaffected by free Mg2+ concentrations less than 10 mM, by pH 6-8, or by contaminating divalent ions of high affinity (Zn2+, Fe2+, Mn2+). The tetraacetoxymethyl ester derivative of 5FBAPTA was used to load mouse thymocytes with 5FBAPTA to intracellular concentrations of 1 mM, and the 19F spectrum indicated a free intracellular Ca2+ concentration [( Ca]i) of 250 nM. The [Ca]i was increased to 350 nM by addition of succinylated concanavalin A at mitogenic concentrations, and the addition of A23187 saturated the intracellular chelator with Ca2+ from the external medium. The method provides a measurement of [Ca]i and other divalent cation concentrations with direct identification of the ionic species chelated.

31P-n.m.r. studies on cerebral energy metabolism under conditions of hypoglycaemia and hypoxia in vitro

A system has been developed for performing 31P-n.m.r. studies on cerebral tissues superfused in vitro, and gives results comparable with those reported from studies in vivo. Under optimal superfusion conditions [10 mM-glucose and O2/CO2 (19:1)] the tissue concentrations of phosphocreatine and ATP were calculated to be approx. 3.1 and 1.3 mumol/g respectively. When the glucose of the superfusing medium was lowered to 0.5 mM, slightly decreased sugar phosphate peaks were observed, but there was no detectable change in [ATP] or [phosphocreatine]. At 0.2 mM-glucose, significantly decreased concentrations of phosphocreatine and ATP were observed. Substitution of pyruvate plus malate for glucose did not decrease levels of phosphocreatine and ATP. When the superfusing medium was gassed with air/CO2 (19:1; 'mild hypoxia'), there was an appreciable fall in sugar phosphates and phosphocreatine with no detectable effect on ATP. In the presence of N2/CO2 (19:1; 'severe hypoxia', since O2 was not completely excluded), concentrations of phosphocreatine fell considerably, but with little effect on ATP. The results demonstrate the feasibility of studying cerebral energy metabolism in vitro using the non-invasive 31P-n.m.r. technique and are discussed in relation to the sensitivity of cerebral tissues to metabolic insults in vitro and in vivo.

A 31P-nmr study of the intact liver fluke Fasciola hepatica

31P-NMR techniques offer a useful method of studying changes in the metabolism of intact parasitic worms. The liver flukes, Fasciola hepatica, provide good quality 31P high resolution NMR spectra for at least 6 h under anaerobic conditions. The levels of ATP remain constant throughout this period. There is no signal for phosphocreatine or phosphoarginine. In contrast to the findings in mammalian tissues, there is a distinct peak for the terminal phosphate of ADP. A number of signals are observed in the phosphodiester region of the spectrum the largest of which is identified as L-alpha-glycerophosphoryl choline. Serotonin (5-hydroxytryptamine) causes an appreciable increase in the levels of sugar phosphates when the flukes are incubated in the absence of glucose. The addition of glucose also causes a marked increase in the signals for the hexose phosphate.

Detection of glycogen in a glycogen storage disease by 13C nuclear magnetic resonance

The livers of gsd/gsd rats homozygous for the glycogen storage disease phosphorylase b kinase deficiency were observed by 13C NMR using a surface coil. Clear signals were detected from glycogen. The concentration of glycogen as determined by NMR was approximately 3-times that found in normal strains agreeing well with chemical determinations. Starvation did not significantly reduce the glycogen content of the livers with glycogen storage disease whereas it reduced the signal below detectability in normal rats. Difference spectra of starved normal rats from fed gsd/gsd rats gave spectra similar in appearance to that of purified glycogen. Glycogen both in vivo and in vitro is fully visible using 13C NMR.

The effects of NMR exposure on living organisms. I. A microbial assay

Various bacterial strains have been exposed to a homogeneous magnetic field of 1 Tesla and to the conditions found in an NMR imaging experiment of the type used in a recent abdominal scan (Mansfield et al., 1978). No mutagenic or lethal effects were observed. The activity of the bacterial enzyme beta-galactosidase was also found to be independent of the applied magnetic field.