Creatine

About: Creatine is a research topic. Over the lifetime, 7075 publications have been published within this topic receiving 220853 citations. The topic is also known as: Kreatin & (α-methylguanido)acetic acid.

Creatine and Creatinine Metabolism

Abstract: The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis an...

Effect of Ischemia on Known Substrates and Cofactors of the Glycolytic Pathway in Brain

Abstract: This is a record of the concentrations of the nonenzyme components of the Embden-Meyerhof system in mouse brain measured at brief intervals after the production of complete ischemia by decapitation. All of the 18 recognized active components were looked for. Of these, 1,3-diphosphoglycerate did not reach levels measurable by the procedures used. Additional substances determined were glycogen, phosphocreatine, creatine, adenosine 5’-phosphate, cu-glycerophosphate, and triphosphopyridinenucleotide and its reduced form. The pyridine nucleotide values are only provisional. Considerable attention is devoted to methodology, since there are numerous possibilities for serious errors in preparation of samples as well as in the analyses for individual substrates. The substances measured account for all the known significant sources of energy available to the brain after its blood supply is cut off. Therefore it is possible to calculate the metabolic rate during the brief period of survival, as well as the time sequence according to which the brain taps its reserve sources of energy. Ischemia resulted in increases in glycolytic rates of at least 4to 7-fold in different experimental groups of mice. The coincident changes in substrate concentrations show which steps were facilitated to make this increase in flux take place, i.e. which steps control glycolysis in brain. These steps are the phosphorylations of glucose and fructose 6-phosphate, and the phosphorolysis of glycogen. There is no evidence that facilitation occurs at any other step in the glycolytic pathway.

Elevation of creatine in resting and exercised muscle of normal subjects by creatine supplementation

Abstract: 1. The present study was undertaken to test whether creatine given as a supplement to normal subjects was absorbed, and if continued resulted in an increase in the total creatine pool in muscle. An additional effect of exercise upon uptake into muscle was also investigated. 2. Low doses (1g of creatine monohydrate or less in water) produced only a modest rise in the plasma creatine concentration, whereas 5g resulted in a mean peak after 1h of 795 (SD 104) mumol/l in three subjects weighing 76-87 kg. Repeated dosing with 5g every 2h sustained the plasma concentration at around 1000 mumol/l. A single 5g dose corresponds to the creatine content of 1.1 kg of fresh, uncooked steak. 3. Supplementation with 5g of creatine monohydrate, four or six times a day for 2 or more days resulted in a significant increase in the total creatine content of the quadriceps femoris muscle measured in 17 subjects. This was greatest in subjects with a low initial total creatine content and the effect was to raise the content in these subjects closer to the upper limit of the normal range. In some the increase was as much as 50%. 4. Uptake into muscle was greatest during the first 2 days of supplementation accounting for 32% of the dose administered in three subjects receiving 6 x 5g of creatine monohydrate/day. In these subjects renal excretion was 40, 61 and 68% of the creatine dose over the first 3 days. Approximately 20% or more of the creatine taken up was measured as phosphocreatine. No changes were apparent in the muscle ATP content.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycogen, glycolytic intermediates and high-energy phosphates determined in biopsy samples of musculus quadriceps femoris of man at rest. Methods and variance of values.

Abstract: Methods are described for the determination of glycogen, glycolytic intermediates, and high-energy phosphates in muscle biopsy samples. Initial freezedrying of samples and extraction of metabolites with relatively weak acid are preferred. Normal values in muscle are similar to those found by other workers. Variation in muscle content of ATP, ATP + ADP + AMP, phosphorylcreatine (PC), creatine (Cr), PC + Cr, and glycogen, between legs, between sites on the same muscle, or as a result of error introduced during analysis, was small compared with the between-individuals variance. The importance of the different sources of variance on taking a biopsy is discussed.

Measurement of muscle mass in humans: validity of the 24-hour urinary creatinine method.

Abstract: Measuring muscle mass is an important component of the nutritional assessment examination and a suggested index of this body space is the 24-h urinary excretion of creatinine. The method originated from studies in a variety of animal species in whom early workers found a parallelism between total body creatine and urinary excretion of creatinine. Assuming that nearly all creatine was within muscle tissue, that muscle creatine content remained constant and that creatinine was excreted at a uniform rate, an obvious "corollary" was that urinary creatinine was proportional to muscle mass. The so-called "creatinine equivalence" (kg muscle mass/g urinary creatinine) ranged experimentally from 17 to 22. One of the limiting factors in firmly establishing this constant and its associated variability was (and is) the lack of another totally acceptable noninvasive technique of measuring muscle mass to which the creatinine method could (or would) be compared. An improved understanding of creatine metabolism and a variety of clinical studies in recent years has tended to support the general validity of this approach. However, specific conditions have also been established in which the method becomes either inaccurate or invalid. While creatinine excretion may serve as a useful approximation of muscle mass in carefully selected subjects, there remains a need for accurate and practical indices of muscle mass for use in the individuals in whom the method cannot be reliably applied.