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Biomedical subjects

M C Hall

Publications and source records attributed to M C Hall.

13 recordsLinked to original sources
PubMed1992

Mechanism of ammonium transport by intestinal segments following urinary diversion: evidence for ionized NH4+ transport via K(+)-pathways.

Using a previously reported in vivo intestinal perfusion model in the rat, we have shown that net total ammonium absorption accounts for the majority of the acid load resulting from urinary intestinal diversion. In the present study, by varying perfusate pH and therefore NH3 concentrations, we demonstrated that the net flux of total ammonium did not correlate with non-ionized NH3 concentrations (r = .039). This indicates that the basic mechanism of total ammonium flux is via ionized NH4+ movement. To more precisely define the transport processes involved, we manipulated this system with the following chemical and pharmacologic probes of electrolyte transport: amiloride (0.5 mM/l.), furosemide (1 mM/l.), 2,4,6-triaminopyrimidine (TAP) (15 mM/l.), methylprednisolone (3 mg./100 gm./B.W.) S.Q. x 3 days followed by perfusion, and barium (Ba2+) (15 mM/l.). Net solute flux was not significantly altered by the mucosal addition of amiloride or TAP. Methylprednisolone treated rats exhibited significantly diminished Na+ secretion (p less than .01) and increased Cl- absorption (p less than .05) without affecting net total ammonium flux providing evidence for the inducibility of Na+ conductance channels and against significant NH4+ movement via this pathway. The mucosal addition of furosemide resulted in significantly decreased net absorption of both total ammonium (p less than .001) and K+ (p less than .05). The addition of Ba2+ resulted in a three-fold reduction of ammonium absorption (p less than .001) and a greater than ten-fold reduction in K+ absorption (p less than .001). The observation of significant inhibition of ammonium absorption by furosemide and barium suggests that K+ transport pathways play a significant role in the intestinal transport of NH4+.

Acidosis↗
PubMed1992

Mechanism of ammonium transport: inhibition by potassium and barium.

Elucidating the precise mechanism of intestinal ammonium transport is critical to the understanding of the acidosis associated with intestinal urinary diversion. Unfortunately, it is incompletely understood and controversial. Recently, we have shown that furosemide and Ba2+ significantly inhibit ammonium absorption in the ileum. On the basis of this and other data, we have suggested that ionized ammonium absorption occurs via K(+)-transport pathways. The present study examines intestinal ammonium absorption and its inhibition by K+ and Ba2+ utilizing a simplified in vivo system in rat distal ileum. Ammonium absorption demonstrates a tendency towards saturation at initial concentrations between 0 and 300 mM/l. Above 300 mM/l. there was a marked increase in ammonium absorption suggesting a possible biological effect of high NH4+ concentrations on the intestinal segment. Potassium inhibits ammonium absorption. K+ (50 mM/l.) significantly inhibited ammonium at an initial concentration of 100 mM/l. (p less than 0.05) and K+ (100 mM/l.) inhibited ammonium absorption at both 50 and 100 mM/l. (p less than 0.05 and p less than 0.01 respectively). Potassium inhibition of ammonium absorption was lost at concentrations above 200 mM/l. suggesting that K+ inhibition occurs via a competitive mechanism. Ba2+ (25 mM/l.) was shown to be a potent inhibitor of ammonium absorption. This significant inhibition persisted at high initial ammonium concentrations suggesting a complex, noncompetitive mechanism of inhibition. In conclusion, this study provides important data further suggesting that ammonium transport in the intestine occurs via K+ transport pathways, and suggests that the traditionally held mechanism of nonionic ammonium diffusion needs reevaluation.

Animals↗
PubMed1992

Long-term metabolic effects of urinary diversion: a comparison of myelomeningocele patients managed by clean intermittent catheterization and urinary diversion.

We previously reported that chronic urinary diversion through intestinal segments may have adverse effects on bone and mineral metabolism. This study examined the long-term health of patients managed by urinary diversion (94% by ileal conduit) for neuropathic bladders secondary to myelomeningocele defects and compared them to a control population of myelomeningocele patients managed by intermittent catheterization. Of the patients 93 were studied by personal interview, chart review, morphometric analysis, serum studies and dual-photon bone density determination. Average followup was 23 +/- 6 years in the urinary diversion group and 17 +/- 5 years in the intermittent catheterization group. Fractures occurred in 40% of the patients in both groups. Patients with a urinary diversion had an increased need for surgery to correct spinal curvature (57% versus 40%) and a significantly increased incidence of complications resulting from orthopedic procedures (17% versus 3%, p less than or equal to 0.05). There was also an adverse effect on renal function. The urinary diversion group had an increased incidence of radiographic renal deterioration (57% versus 8%, p less than 0.001), nephrolithiasis (43% versus 2%, p less than 0.001), pyelonephritis (60% versus 21%, p less than 0.001) and intermittent metabolic acidosis (20% versus 5%, p = 0.05). Surgery was required in 37% for stomal complications and in 17% for ureterointestinal stricture. Linear growth was adversely affected by urinary diversion. Patients with urinary diversion had decreased lengths for all morphometric parameters and a greater percentage of them were at or below the 10th percentile standards. Serum electrolytes, liver function studies, vitamin D3 and parahormone showed no differences in the 2 groups. No patient had a significant metabolic acidosis at the time of study. Bone densities were significantly diminished in both groups and not significantly different. This study strongly suggests that urinary diversion through intestinal segments is associated with adverse effects on bone health.

Bone Density↗
PubMed1992

A pleiotropic, posttherapy, enoxacin-resistant mutant of Pseudomonas aeruginosa.

An enoxacin-resistant Pseudomonas aeruginosa mutant (G49) isolated during patient therapy was characterized in detail. The G49 mutant was cross resistant to several classes of antibiotics including quinolones, beta-lactams, chloramphenicol, and tetracycline, but not imipenem or aminoglycosides. Compared with its paired pretherapy isolate G48, this mutant had several alterations in outer membrane proteins including a complete loss of the major porin protein OprF and a substantially altered lipopolysaccharide profile. Revertants were selected at a frequency of approximately 1% after enrichment for OprF+ cells on low-salt proteose peptone no. 2 medium. Ninety-seven of these OprF+ revertants were as susceptible to carbenicillin and norfloxacin as the pretherapy isolate. One of these revertants was characterized in more detail and shown to be indistinguishable in all properties from the pretherapy isolate. It is proposed that the multiple-antibiotic-resistance (Mar) phenotype of this mutant resulted from a single pleiotropic mutation.

Anti-Bacterial Agents↗
PubMed1991

Phenotypic characterization of quinolone-resistant mutants of Enterobacteriaceae selected from wild type, gyrA type and multiply-resistant (marA) type strains.

The NCTC type strains of Escherichia coli, Enterobacter cloacae, Serratia marcescens and Klebsiella pneumoniae were exposed to 3, 5 and 10 x MIC of nalidixic acid, enoxacin, ciprofloxacin, PD 117596 and PD 127391. From each strain a mutant with a high MIC of quinolones alone (gyrA) and a mutant with intermediate resistance to quinolones, some beta-lactams, chloramphenicol and tetracycline (multiply resistant, m-r) were selected on agar containing antibiotics. The gyrA mutants required a higher concentration of quinolone to inhibit DNA synthesis by 50% but quinolone uptake kinetics and outer membrane profile were the same as the wild type. The m-r mutants had similar DNA synthesis IC50 as the wild type, decreased quinolone uptake kinetics and had decreased expression of an OMP of approximately 40 kD. The gyrA and m-r mutants were then exposed to 3, 5 and 10 x MIC of the same quinolones and new mutants (F2) selected. The F2 mutants from the gyrA mutants displayed a further increase in quinolone MIC; the F2 mutants from the m-r mutants had several phenotypes: high quinolone MICs with cross resistance to other agents, high quinolone resistance alone, or intermediate quinolone resistance alone. Most F2 mutants had MICs above the recommended breakpoint concentrations for quinolones. The F2 mutants often had altered biochemical profiles (API 20E), however, only in the case of E. cloacae did this affect speciation with the strains being identified as Rhanella aquatalis.

Anti-Infective Agents↗
PubMed1991

Metabolic consequences of urinary diversion through intestinal segments.

The use of intestinal segments in the reconstruction of the urinary tract for a variety of malignant and nonmalignant conditions is generally accepted. Metabolic derangements may result any time urine is in contact with the intestinal mucosa. Numerous studies concerning the pathophysiology of this syndrome have demonstrated that it is in large part secondary to reabsorption of urinary acid as ammonium and, to a lesser degree, to bicarbonate secretion into the urine. The syndrome of metabolic acidosis resulting from urinary diversion has been most common after ureterosigmoidostomy, often in the setting of renal insufficiency secondary to pyelonephritis and obstruction. It became a lesser clinical problem with the popularization and frequent use of conduit urinary diversions. At present, with a greater emphasis on the construction of large-capacity continent urinary diversions, there is an increased likelihood of metabolic derangements, especially in the setting of renal insufficiency. Furthermore, although the reported incidence of clinically problematic metabolic derangements is low with the newer modes of continent urinary diversion, it is impossible to assess the significance of a mild or asymptomatic acidosis, which may occur even in the setting of normal serum electrolytes. Only with close long-term follow-up can the significance of this change be determined.

Acidosis↗
PubMed1990

Mechanism of action of lomefloxacin.

The inhibition of supercoiling activity of reconstituted Escherichia coli DNA gyrase by lomefloxacin, ciprofloxacin, and norfloxacin was determined. The concentrations of quinolones needed to inhibit DNA synthesis in Escherichia coli, Enterobacter cloacae, Serratia marcescens, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus were also measured. The kinetics of uptake of [14C]lomefloxacin and unlabeled lomefloxacin into whole cells of E. coli KL-16 and S. aureus NCTC 8532 and the induction of RecA in E. coli GC2241 were assayed. All strains had wild-type susceptibilities to quinolones. The concentration of quinolones needed to inhibit DNA synthesis by 50% correlated with the MIC for members of the family Enterobacteriaceae and P. aeruginosa. The concentration of quinolones needed to inhibit DNA synthesis by 50% for late-logarithmic-phase S. aureus also correlated with the MIC, unlike the data from early-logarithmic-phase cultures. E. coli and S. aureus showed a similar pattern of uptake kinetics of [14C]lomefloxacin and unlabeled lomefloxacin, indicating that the difference in the susceptibilities of the two species is probably due to different target site affinities. Essentially, lomefloxacin was less active than ciprofloxacin and ofloxacin and had activity similar to those of norfloxacin and enoxacin.

Anti-Infective Agents↗
PubMed1989

Validity of bioelectric impedance for body composition assessment in children.

Whole-body bioelectrical impedance analysis (BIA) was evaluated for its reliability and accuracy in estimating body composition in children. The hypothesis that the index, body height2 divided by resistance (RI), can accurately predict fat-free body mass (FFB) and percent fat (%FAT) in children was tested on 94 caucasian children 10-14 yr old. Criterion variables were FFB and %FAT estimated using multicomponent equations developed for children. BIA measurements (resistance and reactance) were found to be reliable. Prediction accuracy (standard error of the estimate, SEE) for FFB from RI alone was 2.6 kg and for %FAT from RI and body weight was 4.2%. For RI, anthropometric variables and reactance, the SEE improved to 1.9 kg FFB. For RI and anthropometric variables, the SEE was 3.3% FAT. For anthropometric variables alone, the SEE's were 2.1 kg FFB and 3.2% FAT. Adult FFB and %FAT prediction equations cross-validated with this sample resulted in SEE's similar to those for adult samples. We conclude that RI together with anthropometry is a reliable and an acceptably accurate method of estimating FFB mass and %FAT in children.

Adipose Tissue↗
PubMed1977

Eustachian tube blockage and Meniere's disease.

On the basis of our clinical experience, it has been noted that an unusually large proportion of patients with Meniere's disease have intermittent eustachian tube blockage. A review of the tympanograms of 81 patients with Meniere's disease, representing 107 ears, showed that 25 (30.9%) of the patients and 35 (32.7%) of the ears had abnormal negative middle ear pressure. The maximum compliance peak was in at a pressure point in excess of --100 mm H2O. Further investigation of these patients has led us to conclude that intermittent eustachian tube blockage frequently accompanies Meniere's disease, yet it is not necessarily the cause of the symptomatic disorder.

Adult↗
PubMed1976

Cardiac monitoring during exercise tests in the horse. 2. Heart rate responses to exercise.

Data on resting heart rates, pre-exercise heart rates, the anticipatory rises before exercise, the influence of speed of work and recovery heart rates have been presented. Some observations on differences in the heart rate response on slow and fast working days are also recorded. In conformity with other workers, a linear relationship between heart rate and working speed within the range of 400-800 metre/min was observed. When the speed of work was between 400-800 metre/min, horses with resting ECG's classed as abnormal had significantly higher heart rates than those regarded as normal. It was also observed that the abnormal animals showed lower heart rates than a small number classed as borderline. The significance of these findings is discussed and the need for further work indicated.

Animals↗
PubMed1976

Cardiac monitoring during exercise tests in the horse. 3. Changes in the electrocardiogram during and after exercise.

Changes that occur in the equine ECG during and after exercise have been described and compared with resting ECG's obtained from the same horses. When the speed of work equals or is greater than "three-quarter pace" (i.e. "even time" or 200 metres in 15 seconds) the high heart rates developed cause the loss of ECG waveforms that are readily discernible at rest. Although differences in the waveforms between horses with normal and abnormal resting ECG's have been observed, the more definitive useful information is the fact that abnormal horses showed significantly higher heart rates than normal horses at a particular speed of work. When this occurs in combination with a resting ECG classified as borderline or abnormal and the exercise ECG shows positive, low amplitude, broad rounded T waves or transient bursts of sine-waves suggestive of ventricular flutter, racing performance is likely to be impaired. Although more work needs to be done and improvements in technology are necessary, the exercise ECG has potential for improving understanding of physical fitness and the significance of resting cardiac abnormalities.

Animals↗
PubMedDate not supplied

Pamihall stain.

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Cytodiagnosis↗