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Biomedical subjects

A Mitchell

Publications and source records attributed to A Mitchell.

At least 253 records · Page 14Linked to original sources

Enzymes of intermediary carbohydrate metabolism in Ureaplasma urealyticum and Mycoplasma mycoides subsp. mycoides.

Cell extracts of Ureaplasma urealyticum and Mycoplasma mycoides were examined for enzymes of intermediary carbohydrate metabolism using a sensitive radiochemical assay procedure. For M. mycoides, the enzyme activities detected were supporting evidence for the existence of a glycolytic pathway giving lactate anaerobically and acetate aerobically. U. urealyticum also had activities of many glycolytic enzymes. Enzymes of the pentose phosphate pathway occurred in both M. mycoides and U. urealyticum. Their presence allowed the proposal of a sequence for the synthesis from glycolytic pathway intermediates of ribose 5-phosphate, and hence phosphoribosyl diphosphate, for the synthesis of nucleotides. Pathways for the further metabolism of deoxyribose 1-phosphate and ribose 1-phosphate produced from nucleoside phosphorylase reactions operated in extracts from both organisms.

Carbohydrate Metabolism↗

Interrelation between donor and recipient heart rates during exercise after heterotopic cardiac transplantation.

The interrelation between the rates of the innervated recipient heart and the denervated donor heart at rest, on standing, and during the different phases of maximal exercise was studied in nine patients 1-6 months after heterotopic cardiac transplantation. The resting heart rate was significantly higher in the donor heart compared with the recipient heart. Eight of the nine recipient hearts and none of the donor hearts showed an increase in heart rate on standing up. All patients were exercised using a Bruce protocol until fatigued. The increase in heart rate during the first three minutes of exercise was lower in the donor hearts (10.7(6) beats/min) than in the recipient hearts (30(4.8) beats/min) but the peak heart rates were almost identical (donor hearts 152.7(2.9) and recipient hearts 152(2.8) beats/min). Five of the nine donor hearts and none of the recipient hearts showed a significant increase in heart rate after cessation of exercise. Three minutes after exercise heart rate had decreased by only 0.2(5.7) beats/min in the donor hearts compared with 33.6(6) beats/min in the recipient hearts. In spite of these differences in response between the donor hearts and recipient hearts, there were significant correlations between the two heart rates in the same patient at rest, after the first three minutes of exercise, at peak exercise, and during recovery.

Adult↗

Individuality and hubris in mythology: the struggle to be human.

Mankind's social and psychological evolution require changing attitudes and behavior to maintain a harmony with the world, society, and his own self. Loss of immediacy with the world, power over it, and the increasing capacity for individuality pose special problems for the accomplishment of such harmony. How this is recognized, understood, and dealt with is a task undertaken through psychoanalysis, myth, philosophy, and literature. Various examples are given to show that the constancy of the basic truths about the nature of being human leads to a resonance among the diverse approaches and across the span of millennia and cultures.

Humans↗

Uptake and utilization of deoxynucleoside 5'-monophosphates by Mycoplasma mycoides subsp. mycoides.

Mycoplasma mycoides subsp. mycoides has been shown to possess an unusual capacity for the uptake and utilization of exogenous deoxyribonucleoside 5'-monophosphates intact without prior dephosphorylation. In this study, it was found that once inside the cell, deoxyribonucleoside 5'-monophosphates were rapidly phosphorylated to the triphosphate level and incorporated into DNA. Catabolism of deoxyribonucleoside 5'-monophosphates was also observed. Competition studies indicated that a single uptake system with a higher affinity for deoxyribonucleotides mediates the uptake of nucleoside 5'-monophosphates.

Biological Transport↗

The roles of self-esteem and self-consciousness in the Wortman-Brehm model of reactance and learned helplessness.

The present experiments were designed to study the conditions under which failure would enhance or inhibit subsequent task performance. Based on the theory of Wortman and Brehm (1975), it was expected that small amounts of failure would produce reactance (manifested by improved performance at a subsequent task), whereas large amounts would lead to learned helplessness (i.e., impaired later performance). It was further expected that individual differences in self-esteem and private self-consciousness would serve as moderator variables for the above effects. In Experiment 1, subjects were exposed to either a small amount of failure or no failure before working on an anagrams task. As predicted, subjects high in self-consciousness, who have shown greater reactance arousal in attitude change studies, performed better on the anagrams task than subjects low in self-consciousness in the small-failure condition, but not in the no-failure condition. Further analyses revealed that this Self-Consciousness X Small Failure interaction was attributable to the performance data of the low, but not the high self-esteem subjects. Experiment 2 was designed to replicate and extend these results. Subjects were pretreated with either a small amount of failure, an extended amount of failure, or no failure before working on the anagrams task. A significant Self-Esteem X Helplessness Training interaction emerged. Relative to the no-failure condition, in which the two self-esteem groups did not differ, low self-esteem participants (low SEs) performed marginally better than did high self-esteem individuals (high SEs) in the small-failure condition but significantly worse than high SEs in the extended-failure condition. The effect of private self-consciousness was considerably weaker in this study, possibly because the sample included few low SEs (who are especially influenced by self-focused attention) who were also relatively low in self-consciousness. Questionnaire data from Experiment 2 were consistent with the notion that enhanced performance reflected reactance, whereas impaired performance signified helplessness.

Arousal↗

Effects of retrograde luminal perfusion of the canine jejunum on intestinal absorption and myoelectrical activity.

The effects of retrograde luminal perfusion of a 75 cm jejunal segment on absorption, transit time and myoelectrical activity were studied in four dogs. Retrograde perfusion increased jejunal absorption of water (0.016-0.021 ml cm intestinal length-1 min-1. P less than 0.001) together with sodium (1.15-1.82 mumol cm-1 min-1; P less than 0.001) and glucose (1.98-2.27 mumol cm-1 min-1; P less than 0.01). Mean jejunal transit time was prolonged (9.2-13.9 min; P less than 0.001) and jejunal spike activity was reduced compared with antegrade perfusion (14.5-4% of slow wave frequency; P less than 0.01). These results suggest that the reversal of small bowel segments in the treatment of the short bowel syndrome can result in an increase in absorption from the reversed segment itself in addition to any effect from delayed transit in the proximal bowel.

Action Potentials↗

Pathways of pyrimidine deoxyribonucleotide biosynthesis in Mycoplasma mycoides subsp. mycoides.

By measuring the specific activity of deoxyribonucleotides isolated from DNA after the incorporation of 14C-labeled precursors with and without competition from other nucleotide precursors, we defined the major pathways of pyrimidine deoxyribonucleotide synthesis in Mycoplasma mycoides subsp. mycoides. Uracil, guanine, and thymine are required for the synthesis of nucleotides. Cytidine competed effectively with uracil to provide all of the deoxycytidine nucleotide, as well as most of the deoxyribose-1-phosphate, for the synthesis of thymidylate from thymine via thymidine phosphorylase. Each of dUMP, dCMP, and dTMP competed with cytidine for incorporation into DNA thymidylate. Appreciable incorporation of exogenous deoxyribonucleoside 5'-monophosphates into DNA without prior dephosphorylation was observed. Dephosphorylation also occurred since the added deoxyribonucleotide provided phosphate for the synthesis of the other nucleotides in DNA in competition with the 32Pi in the growth medium. Hydroxyurea inhibited cell growth and decreased the intracellular level of dATP, consistent with the action of a ribonucleoside diphosphate reductase with regulatory properties similar to those of the Escherichia coli enzyme.

Base Composition↗

Enzymes of pyrimidine deoxyribonucleotide metabolism in Mycoplasma mycoides subsp. mycoides.

Cell-free extracts of Mycoplasma mycoides subsp. mycoides were assayed for enzymes associated with the salvage synthesis of pyrimidine deoxyribonucleotides. They possessed kinases for deoxycytidine, (d)CMP, thymidine (deoxyuridine), dTMP, and nucleoside diphosphates; dCTPase and dUTPase; dCMP deaminase; thymidine (deoxyuridine) phosphorylase; and dUMP (dTMP) phosphatase. The existence of these enzymic activities together with ribonucleoside diphosphate reductase explains the capacity of cytidine to provide M. mycoides with deoxyribose for the synthesis of thymidine nucleotides from thymine.

DCMP Deaminase↗

Surgery of the spleen.

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Anemia, Hemolytic, Congenital↗

A scintigraphic method for the assessment of intraluminal volume and motility of isolated intestinal segments.

The isolated in vivo intestinal segment is a popular experimental preparation for the investigation of intestinal function, but its value has been limited because no method has been available for measuring changes in intraluminal volume under experimental conditions. We report a scintigraphic technique for measuring intraluminal volume and assessing intestinal motility. Between 30 and 180 ml, the volume of a 75-cm segment of canine jejunum, perfused with Tc-99m-labeled tin colloid, was found to be proportional to the recorded count rate. This method has been used to monitor the effects of the hormone vasopressin on intestinal function.

Animals↗

Trends in management of acute cholecystitis.

A retrospective review has been carried out of the management of acute cholecystitis in one hospital from 1974 to 1978. The policies and outcome are compared with those of the same centre during 1953-62. In the intervening period there has been a move towards early cholecystectomy. Overall mortality has fallen from 7.7% to 1.6%. The results of early surgery are comparable with those of delayed operations. The data also compare favourably with those of controlled clinical trials and support the adoption of early cholecystectomy for acute cholecystitis in routine practice. The saving of resources, however, may not be as great as is suggested by the results of clinical trials.

Acute Disease↗