Ray L. Nunnally

The use of the chemical shift of the phosphomonoester P-31 magnetic resonance peak for the determination of intracellular pH in the brains of neonates

The use of the chemical shift of the phosphomonoester P-31 magnetic resonance peak for the determination of intracellular pH has been assessed for piglet and neonatal human brain in vivo. The chemical shift difference between resonance peaks corresponding to phosphoethanolamine and inorganic phosphate, compared with phosphocreatine, was determined for piglets and human neonates. Using in vitro pH titration data to calculate intracellular pH, it was found that pH values from the phosphoethanolamine peak (pH 6.84 to 6.80) were lower than pH estimates from the inorganic phosphate peak (pH 7.22 to 6.99). This difference suggests that phosphoethanolamine and inorganic phosphate may exist in different intracellular environments. Results are presented to demonstrate that the phosphomonoester peak may also be used to measure changes in intracellular pH associated with brain ischemia.

Alterations in Cerebral Blood Flow and Phosphorylated Metabolites in Piglets during and after Partial Ischemia

ABSTRACT: Ventilated piglets were studied before, during (15 min), and after (90 min) hemorrhagic hypotension to correlate a 60% reduction in cerebral blood flow with cerebral energy state using radiolabeled microspheres (n = 12) and in vivo 31P nuclear magnetic resonance spectroscopy (n = 11). Cerebral blood flow (ml · min−1 · 100 g−1) decreased during hypotension (98 ± 28 to 41 ± 28, p < 0.05), increased at 5 min postreperfusion (131 ± 53, p < 0.05), and returned to control values by 90 min postreperfusion. Cerebral O2 uptake was reduced during partial ischemia, remained depressed 5 min postreperfusion, and increased to within 20% of control values at 90 min postreperfusion. Relative to control, hypotension was associated with decreased (p < 0.05) phosphocreatine (62 ± 11%), phosphocreatine/inorganic phosphate ratio (41 ± 10%), and nucleoside triphosphate (82 ± 12%) while inorganic phosphate increased (155 ± 32%, p < 0.05). During ischemia intracellular pH dropped from 7.06 ± 0.07 to 6.59 ± 0.31 (p < 0.05) and the cerebral arteriovenous difference of glucose increased. Phosphorylated metabolites returned to within 10% of control 15 min after blood reinfusion and remained constant thereafter. Based on calculations of ATP synthesis and utilization rates during control and hypotension, we speculate that the rate of energy utilization of the brain during ischemia is reduced 18–49% relative to the control utilization rate.

Intracellular pH, Lactate, and Energy Metabolism in Neonatal Brain During Partial Ischemia Measured In Vivo by 31P and 1H Nuclear Magnetic Resonance Spectroscopy

Abstract: Sequential 31P and 1H nuclear magnetic resonance spectra were measured for neonatal piglets (n = 7) to determine the relationship between brain intracellular pH (pHi), lactate, and phosphorylated energy metabolites during partial ischemia. Simultaneous determinations of arterial and cerebral venous blood gases, pH, O2 content, and plasma concentrations of glucose and lactate were also made. Ischemia, induced by bilateral carotid artery ligation plus hemorrhagic hypotension for 35 min, resulted in variable reductions in ATP, phosphocreatine, and increases in Pi, H+, and lactate relative to control levels. In four piglets, whose arterial blood glucose rose above control, brain lactate exceeded 20 μmol g−1 with corresponding decreases in pHi of >0.7 units compared to control levels. The extents of brain acidosis and lactosis showed a strong linear correlation with each other (r= 0.94). Maximal changes in brain lactate, pHi, and ATP at the end of ischemia showed significant positive linear correlations with the control levels of arterial blood glucose, but did not correlate with arterial glucose or arterial cerebral‐venous glucose difference values during ischemia. The relationship between pHi and buffer base deficit was comparable to results reported for adult animals up to 20 μmol ml−1. However, in contrast to models proposed for adult brain, the continued linear relationship between pH and higher buffer base levels is most consistent with a theoretical model that assumes the presence of weak acid buffers with pKa values from 6.7 to 5.2.

Evaluations of magnetic resonance imaging parameters with simple phantoms.

Imaging parameters associated with a clinical magnetic resonance imaging (MRI) system, evaluated with the use of simple and inexpensive phantoms, are described in evaluation of a clinical MRI system. Images, obtained with a Diasonics 0.35-T MRI system using an elliptical whole-body radio frequency coil, are presented which demonstrate geometric distortion, inaccuracy of image dimensions, and artifacts. Measurements of reproducibility and uniformity of both signal intensity and spin-lattice relaxation times are presented for uniform phantoms. Replicate measurements are analyzed by two-way analyses of variance to determine the significance of variations as a function of position and slice. Apparent T1s are not significantly different among the slices for the images analyzed, but there is a significant effect due to position in the field. Direct measurement of the radio frequency field for the center slice follows a pattern which is similar. Spin-lattice relaxation times are compared among two-point calculations and nonlinear four-point calculations, and the effects of pooling data are found to increase the precision of T1 measurements.

Hypotonia of Rickets: A Sequential Study by P-31 Magnetic Resonance Spectroscopy

ABSTRACT: To address the role of high-energy phosphorus compounds in the hypotonia of vitamin D-dependent rickets, nuclear magnetic resonance spectra were obtained sequentially from resting gastrocnemius muscle of a 10-month-old infant with rachitic hypotonia during supplementation with vitamin D, calcium, and phosphorus. During the initial weeks of treatment, the hypotonia resolved before evidence of epiphyseal mineralization. Over the early treatment period, the muscle phosphocreatine/β-adenosine triphosphate [PCr/β-ATP] ratio increased from 2.7–2.8 [wk 1–2] to 3.9–4.5 [wk 7–9]. The PCr/β-ATP ratio for 6-month-old normal infant gastrocnemius and adult forearm were 4.0 and 5.7, respectively. Muscle strength appeared to recover concomitantly with an increase in retained muscle phosphorus and high-energy phosphate compounds, and with relative increase in the muscle phosphocreatine to ATP ratio. The synchrony of clinical recovery may relate to the recovery kinetics of these metabolic changes.

IN VIVO TIME COURSE OF MUSCLE PHOSPHOCREATINE, PHOSPHORUS, AND ADENOSINE TRIPHOSPHATE DURING TREATMEN OF RICKETS

To assess potential skeletal muscle changes of high energy phosphate compounds and inorganic phosphate (P) in early childhood rickets, a non-invasive but direct estimate of the relative concentrations in gastrocnemius muscle of P, phosphocreatine (PCr), & adenosine triphosphate (ATP) was measured by magnetic resonance spectroscopy (MRS) in an infant, age 10 months. He had generalized weakness and low serum P (3.5mg/dl) and Ca (6.7mg/ dl). Therapy was begun with vitamin D & dietary P & Ca, and weekly 31-P MRS spectra were obtained in an Oxford 30 cm, 1.9T magnet. Initially, PCr was approximately 50% reduced compared to that in gastrocnemius of a normal 6-month infant. Tissue P, PCr & ATP gradually normalized, preceding return of serum P & Ca to normal. Data below are serum (Ser) values, & tissue peak heights (mm) and peak height ratio:Functional muscle tone & strength gradually improved in concordance with MRS spectral return to a normal pattern. High energy phosphate depletion may explain the hypotonia of rickets. MRS may uniquely allow definition of individual muscle phosphorus components over time.

In Vivo Phosphorus-31 Nuclear Magnetic Resonance (NMR) Spectroscopy Of Cardiac Metabolism: Initial Observations Of Hypoxia And Adrenergic Stimulation

High resolution 31P nuclear magnetic resonance (NMR) spectroscopy has been applied to the direct, noninvasive examination of phosphorylated substrate metabolism in the myocardium of live rabbits. By the combination of field profiling gradients and a surface, or flat, NMR coil placed directly over the region of the thorax which contains the heart, spatially localized NMR measurements of metabolic function in live animals can be obtained. This technique, termed topical magnetic resonance or TMR, has been used to follow the effects of several physiological conditions on the tissue pH and levels of key, energy-rich phosphorylated compounds in the hearts of live, anesthetized rabbits. Changes in tissue content of adenosine triphosphate (ATP), creatine phosphate (CP), and inorganic phosphate (Pi) and the NMR line widths of these species have been observed in animals given appropriate doses of adriamycin for a five day period. These preliminary data demonstrate the potential of spectroscopic NMR techniques in the evaluation of disease states in organs and tissues within the body and the ability to monitor both toxic and therapeutic effects of drugs.