Offset-Dependent Partial Saturation in Binomial Solvent Suppression Sequences

Hsu, Alex C.; Gregory, Carl D.

doi:10.1006/jmre.1997.1324

Cited by 5 publications

(3 citation statements)

References 17 publications

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“…Two additional peaks are used to account for exercise‐induced alterations in the baseline due to broadening of the lipid peak in the 1.3 ppm region, for a total of six peaks included in the fitting. For short TR/ T 1 , the appropriate excitation profile and exact offset‐dependent partial saturation factors (14) were used to obtain corrected peak areas. 1 H T 1 s of metabolites were measured using progressive saturation with the JRE sequence, using the exact offset‐dependence of partial saturation (14).…”

Section: Methodsmentioning

confidence: 99%

“…For short TR/ T 1 , the appropriate excitation profile and exact offset‐dependent partial saturation factors (14) were used to obtain corrected peak areas. 1 H T 1 s of metabolites were measured using progressive saturation with the JRE sequence, using the exact offset‐dependence of partial saturation (14). Repetition times were in the order 10.3, 5.3, 2.3, 1.3, 0.8, 0.5, 0.4 sec, with TE fixed at 1 msec.…”

Section: Methodsmentioning

confidence: 99%

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Accuracy of1H and31P MRS analyses of lactate in skeletal muscle

Hsu

Dawson

2000

Magn. Reson. Med.

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As the end product of anaerobic metabolism and a source of H+, lactic acid is important in metabolism and pH regulation. Several methods have been introduced to calculate changes in the lactate anion (Lac–) concentration in exercising skeletal muscle from information derived from the 31P spectrum. Alternatively, Lac–may be observed directly with 1H MRS. Both 1H and 31P spectroscopy have potential problems, which could prevent accurate determination of [Lac–]. It is demonstrated that quantitatively accurate 1H MRS measurements of changes in [Lac–] due to exercise are possible in isolated muscle. In general, calculation by 31P MRS overestimates Lac–production. An analysis is presented of possible sources of errors in the 1H and 31P MRS methods. Magn Reson Med 44:418–426, 2000. © 2000 Wiley‐Liss, Inc.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Accuracy of1H and31P MRS analyses of lactate in skeletal muscle

Hsu

Dawson

2000

Magn. Reson. Med.

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“…For 1 H partial saturation corrections, T 1 's of 0.45, 0.64, and 0.62 sec were used for Cr, downfield Lac − peak, and upfield Lac − peak (9), respectively. The sin 3 excitation profile and exact partial saturation corrections were used (14). Lactate was quantified using 30 mmol/kg (45 mM) total creatine as an internal standard (13).…”

Section: Methodsmentioning

confidence: 99%

Muscle glycogenolysis is not activated by changes in cytosolic P‐metabolites: A ³¹P and ¹H MRS demonstration

Hsu¹,

Dawson²

2003

Magnetic Resonance in Med

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Skeletal muscle contraction and glycogenolysis are closely coupled. The standard explanation for this coupling, as taught in modern biochemistry textbooks, is that the metabolic products of contraction (ADP, AMP, P i ) feed back to activate glycogenolytic enzymes, thus providing for resynthesis of ATP. However, both in vivo 31 P MRS analyses and chemical analyses of muscle extracts have provided results that are contrary to this theory, at least in its simplest form. The MRS studies suffer from ambiguous assumptions. More importantly, in 31 P MRS studies the dependent and independent variables are often confounded because the glycogenolytic rate is calculated from the same data which are used to calculate the other metabolic variables. The analysis of biopsies has been necessarily quite limited, and suffers from a different set of experimental artifacts. Thus, the problem of contraction-glycogenolysis-coupling was reassessed using a quantitatively accurate 1 H MRS method. It is confirmed that glycogenolysis and contractions are closely coupled during repetitive exercise, while glycogenolysis and P-metabolite concentrations are not. A simple metabolic feedback system cannot explain contraction-glycogenolysis-coupling.Magn Despite its fundamental importance in all prokaryotic and eukaryotic life, the in vivo regulation of glycolysis is still not fully understood. In standard textbook descriptions, glycolysis is activated by a feedback mechanism at phosphofructokinase (PFK) by metabolites such as ADP and P i , direct products of the actomyosin-ATPase, and AMP, which is in equilibrium with ADP through adenylate kinase (1). By this simple feedback mechanism, glycolysis is activated whenever the direct and indirect products of ATP hydrolysis are increased. However, during the past 20 years it has been shown that, as calculated from changes in the 31 P MRS spectrum of intact ex vivo and in vivo animal and human muscle, glycolysis is closely coupled to contractions and not to metabolite levels (2-6).Similar results have been obtained using muscle biopsies and extracts (7,8).Close coupling of glycolysis or glycogenolysis to contraction is referred to as contraction-glycolysis-coupling or contraction-glycogenolysis-coupling (CGC). In this article, glycogenolysis refers to the degradation of glycogen to lactate. In the absence of oxygen, CGC is characterized by a partial metabolic recovery from contraction, followed by metabolic stasis during anaerobic rest, i.e., very low glycogenolytic rate with little to no net change in metabolite concentrations. During and closely following contraction the glycogenolytic rate is increased by orders of magnitude over the resting rate and then it falls to near zero without restoring P-metabolites to their precontractile values. In other words, glycogenolysis and contractions are coupled temporally. Glycogenolysis and contractions are also coupled quantitatively, since the amount of lactate (Lac -) produced is proportional to the magnitude of mechanical activity.The methods previously us...

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