The biochemistry of folic acid and vitamin B 12 .
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Acetates↗
Biomedical subjects
M M Lubran
Publications and source records attributed to M M Lubran.
Measurement of salicylsalicylic acid and salicylic acid in plasma by high pressure liquid chromatography.
Salicylsalicylic acid (SS) and salicylic acid (SA) both appear in plasma after the oral ingestion of the former. They can be estimated in the presence of each other after extraction into dichloromethane using high pressure liquid chromatography. SS is unstable in plasma, being converted to SA in vitro. Conversion can be prevented by using ethylene diaminetetraacetic (EDTA) as an anticoagulant and carrying out the extraction in the cold. An aliquot of the extract is dried and dissolved in methanol. Weak solutions of SS in methanol are unstable at room temperature. Methanolysis can be prevented by the addition of dilute hydrochloric acid. By adding phenylbutazone to the plasma as an internal standard, variations in extraction and sample application are nullified. Quality control is achieved by concurrent extraction of two different plasma standards containing SS and SA in known amounts. About 40 ng of SS and SA can be detected; reproducibility at 200 ng and above is better than 6.5 percent.
Chromatography, High Pressure Liquid↗
Lead toxicity and heme biosynthesis.
Lead intoxication results in a disturbance of heme biosynthesis, its degree depending on the severity and duration of exposure to lead. A mild secondary, sideroblastic anemia is common; basophilic stippling may occur, especially in severe lead poisoning. Increased excretion in the urine of delta-aminolevulinic acid and coproporphyrin III may occur; porphobilinogen excretion is not usually increased. Delta-aminolevulinate dehydratase, coproporphyrin oxidase, and ferrochelatase activities are reduced; delta-aminolevulinate synthetase activity is increased. Erythrocyte protoporphyrin (FEP and ZPP) is increased. Recent knowledge of the heme biosynthetic enzymes is reviewed and the significance of FEP and ZPP discussed. A brief history is given of the relationship of lead toxicity to the porphyrins.
5-Aminolevulinate Synthetase↗
Comparison ot two methods of measurements of the same substance: an evaluation of some statistical procedures.
Linear regression analysis and calculation of the correlation coefficient are usually used to compare the results of two methods of measurement of the same substance. The limitations of these procedures are illustrated with numerical examples, in which X (the independent variable contains random errors of measurement. Formulas are given for estimating a linear functional relationship in this case. An alternative procedure, not involving linear regression, is described in which means and variances of replicate measurements by each method are compared at various concentrations over the analytical range. The appropriate statistical tests are discussed.
Regression Analysis↗
Effect of vitamin B-6 on plasma and red blood cell magnesium levels in premenopausal women.
The effect of 100 mg of vitamin B6 twice a day on plasma and red blood cell (RBC) magnesium was evaluated in nine premenopausal subjects during the period of one month. According to reported normal ranges for plasma and RBC magnesium (1.7 to 2.3 and 4.7 to 7.0, mg per dl, respectively), three subjects had low plasma magnesium, and all subjects had low RBC magnesium during the control period. Following vitamin B6 administration, the mean plasma and RBC magnesium levels were significantly elevated, with a doubling of RBC levels after four weeks of therapy. These results support the postulate that vitamin B6 plays a fundamental role in the active transport of minerals across cell membranes.
Administration, Oral↗
Renal function in the elderly.
Renal size and volume decrease with age, accompanied by intrarenal vascular changes. The number of glomeruli decreases and the mass of the juxtamedullary nephrons falls. The result is a decrease in the filtration area of the glomerular basement membrane and decreased permeability. The glomerular filtration rate (GFR) is reduced with aging. The GFR is approximated by the endogenous creatinine clearance, which falls in parallel with the inulin clearance (the true measure of GFR) and is always greater because of tubular excretion of creatinine. Analytical methods for serum and urine creatinine overestimate its concentration and suffer, to varying degrees, from interferences, making the normal range method dependent. A further uncertainty arises from the use of a correction to standard surface area. Serum creatinine concentration is an insensitive indicator of renal function in the elderly. Deduction of creatinine clearance from serum creatinine concentration, weight and age using one of many formulae gives only approximate values, usually too high, and is unsuitable for debilitated and seriously ill patients. Tubular function, in general, is decreased in the elderly. The ability of the kidney to concentrate urine maximally after water deprivation decreases with age, as does the ability to excrete a water and salt load, particularly during the night. Nocturnal polyuria is common in the elderly. The aged kidney can maintain acid-base balance under normal conditions, but not when subjected to an acid load.
Aged↗
Quality control of gamma counters. I. Experimental evaluation of sources of error.
Errors of counting rate as large as 2 percent may occur through variations in instrumental parameters during the measurement of I-125 activity using a gamma counter. Much larger errors result from failure to maintain constant sample geometry; in particular, the slope of calibration curves depends on sample volume.
Quality Control↗