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Biomedical subjects

E C Johnson

Publications and source records attributed to E C Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1985

Noninvasive Doppler determination of cardiac output during submaximal and peak exercise.

We compared pulsed Doppler (PD) measurements of stroke volume (SV) and cardiac output (CO) as a function of work load with previously reported values that were obtained by standard invasive methods. Suprasternal notch measurements of Doppler-shifted frequency (delta f) were obtained from the ascending aorta and SV calculated with the Doppler equation and an independent measurement of aortic diameter. Motion artifacts were minimized with the aid of a restraining table cycle ergometer. Signal aliasing was accommodated with manual summation of delta f waveforms. A total of 207 determinations were made in 10 sitting subjects exercising to exhaustion. Linear regression analysis of CO vs. work load was significant (P less than 0.001). The correlation coefficient (r = 0.95) and standard error of estimate value (1.21 1/min) were similar to values from the literature. Absolute values of CO and SV underestimated the literature values across all work loads. Technical reproducibility was assessed by comparing with paired t tests the differences between 65 duplicate serial measurements of CO and SV at rest and exercise. No significant differences (P less than 0.001) were found. We concluded that PD-determined SV and CO are reproducible and correlate linearly with work load in a manner consistent with reported invasive techniques. Thus the PD method appears suitable for use during submaximal and peak exercise.

Adult↗
PubMed1981

Effect of iron, vitamin B-6 and picolinic acid on zinc absorption in the rat.

True daily zinc absorption was determined in rats fed a high iron diet (220 ppm Fe; 16.5 ppm Zn), and adequate iron diet (30 ppm Fe) and a high iron diet with varying levels of pyridoxine-HCl (2-40 ppm). Zinc absorption in rats fed the high iron diet was significantly less than in rats fed the adequate iron diet. Zinc absorption in rats fed the high iron diet supplemented with picolinic acid (200 ppm) was markedly increased and did not differ from that in rats fed the adequate iron diet. True, daily zinc absorption increased as the level of dietary vitamin B-6 was increased. Zinc absorption was the least in rats fed 2 ppm vitamin B-6 and was greatest in rats fed 40 ppm vitamin B-6. The concentration of picolinic acid in the pancreas increased as the level of dietary vitamin B-6 was increased. Zinc absorption was significantly elevated in rats fed the high iron diet that contained either 4 or 10 ppm vitamin B-6 and 200 ppm picolinic acid. The turnover rate of 65Zn was determined in rats fed an adequate iron, marginal zinc diet (8.5 ppm Zn) with varying levels of vitamin B-6. The turnover of 65Zn was greatest in rats fed 2 ppm vitamin B-6 and least in rats fed 40 ppm vitamin B-6 or 2 ppm vitamin B-6 + 200 ppm picolinic acid. The results suggest that high levels of dietary iron inhibit zinc absorption via competition for binding with endogenous picolinic acid. The results provide further evidence to support the hypothesis that picolinic acid facilitates absorption of dietary zinc.

Absorption↗
PubMed1980

Zinc concentration of liver and kidneys from rat pups nursing dams fed supplemented zinc dipicolinate or zinc acetate.

The zinc concentration of liver and kidneys was determined in rat pups nursing dams given 10 micrograms Zn/ml as either zinc dipicolinate or zinc acetate in water solution during the last week of gestation and for 5 days of lactation. Dams were fed a casein-based diet that contained 8.5 micrograms Zn/g and 2.0 micrograms pyridoxine-HCl/g during this period. The zinc concentrations of both liver and kidneys from the 5-day-old pups nursing dams fed the zinc dipicolinate solution were significantly greater than the zinc concentrations of these tissues from pups nursing dams given a solution of zinc acetate. The results demonstrate that a greater quantity of dietary zinc is transferred from the intestine of the lactating female rat to the pups when zinc is fed in the form of zinc dipicolinate.

Acetates↗
PubMed1980

Zinc absorption in rats fed a low-protein diet and a low-protein diet supplemented with tryptophan or picolinic acid.

Zinc absorption was examined in rats fed a basal diet with 5% vitamin-free casein, in rats fed the 5% casein-based diet supplemented with tryptophan and in rats fed the 5% casein-based diet supplemented with picolinic acid. True, total daily zinc absorption was determined by an isotope dilution technique after the rats had been injected intramuscularly with carrier-free 65Zn. The zinc concentration of the kidneys from the rats fed the 5% casein diet was significantly less than that of the kidneys from rats fed the same diet supplemented with either tryptophan or picolinic acid. The specific activity of Zn in the kidneys from the rats fed the low-protein diet was significantly greater than that of the kidneys from rats fed the diet supplemented with either tryptophan or picolinic acid. The specific activity of Zn in the feces from rats fed the low-protein diet was significantly less than the specific activity of the feces from rats fed either supplemental tryptophan or supplemental picolinic acid. True, total daily zinc absorption in rats fed the low-protein diet was significantly less than the total daily zinc absorption in rats fed either supplemental tryptophan or supplemental picolinic acid. Since tryptophan is a metabolic precursor of picolinic acid, the results support the hypothesis that endogenous and exogenous picolinic acid facilitates zinc absorption.

Absorption↗
PubMed1979

Erythrocyte glucose metabolism in Duchenne muscular dystrophy.

We compared glucose metabolism by erythrocytes from patients with Duchenne muscular dystrophy and by erythrocytes from control individuals. There was a significant decrease in the rate of lactate production at pH 7.2 in the dystrophic group. When the pH of the incubation medium was changed to 8.0, we found that the increase in the rate of lactate production for the dystrophic group was significantly larger. We measured the concentrations of key glycolytic metabolites and adenine nucleotides and determined the values of the energy charge during these incubations. We also determined the concentrations of polyol pathway intermediates, the activities of the oxidative portion of the pentose phosphate pathway and the activities and kinetics of phosphofructokinase from both cell groups. There were no significant differences between groups for any of these variables.

Adenine Nucleotides↗
PubMed1979

Zinc absorption in the rat determined by radioisotope dilution.

Zinc absorption in rats was examined by use of an isotope dilution technique. Young rats and mature rats fed varying levels of dietary zinc were injected intramuscularly with 65Zn. Nine days later, a zinc balance study was begun and continued for 5 days. The rats were then decapitated and the intestines and kidneys were removed and analyzed for zinc and 65Zn content. The feces were analyzed for zinc and 65Zn content and the specific activities of the intestines and kidneys were used to compute the contribution of endogenous zinc to total daily zinc excretion and thus calculate the true daily absorption of zinc. The zinc concentration of the intestines and kidneys did not differ significantly among groups but the specific radioactivity in these organs decreased as dietary zinc intake increased. Endogenous zinc excretion was greatest in mature rats and young rats fed the highest level of dietary zinc. Mature rats actually absorbed as much or more zinc than young rats fed the same dietary level of zinc. The results demonstrate that zinc homeostasis in rats is maintained by zinc secretion from the intestine rather than by regulation of zinc absorption.

Aging↗
PubMed1975

Scanning electron microscopy of the luminal epithelium of the mouse uterus.

Four methods of manipulating mouse uterine tissue during fixation, preparatory to examination of the luminal epithelium by scanning electron microscopy (S.E.M.), are described and the results assessed. The appearance of the epithelium varies according to the technique used, the choice of method depending on the type of information required from the S.E.M. study. Surface topography is preserved in a condition most closely resembling that of fresh tissue by opening the uterus and fixing the tissue flat. Critical examination of cellular and subcellular surface detail, however, depends on adequate spreading of the epithelial layer during fixation by distension of the uterine lumen under positive pressure. The method of tissue manipulation has a more profound effect on the appearance of the sample than any of the dehydration techniques which follow. For routine S.E.M. examinations at medium magnifications (smaller than X10,000), specimens which were air dried from alcohol, acetone or ether, or freeze dried, gave satisfactory results. Air drying from amyl acetate, and CO2 critical-point drying gave superior results at higher magnifications (greater than X10,000) with better preservation of individual microvilli.

Air↗
PubMed1971

Characterization of growth stimulants in corn steep for lactic streptococci.

The production of acid in milk cultures of lactic streptococci was stimulated by the addition of corn steep liquor. Separation by ion-exchange and paper chromatography indicated the presence of four major stimulatory components in the corn steep. Some variation was noted in the response of the lactic streptococci to the individual stimulatory components. The four components were further purified by paper and column chromatography. One of the four stimulatory components stained positively on chromatograms with ninhydrin. The remaining stimulatory components were detectable only by bioautography. All four components were unstable to acid hydrolysis and absorbed ultraviolet light between 230 and 275 nm in aqueous solution. The stimulatory components did not contain pentoses, suggesting that they were not nucleotides or nucleosides; however, they might be purine or pyrimidine bases.

Absorption↗