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Biomedical subjects

R W Welch

Publications and source records attributed to R W Welch.

At least 19 recordsLinked to original sources
PubMed1995

Accumulation of vitamin C (ascorbate) and its oxidized metabolite dehydroascorbic acid occurs by separate mechanisms.

It is unknown whether ascorbate alone (vitamin C), its oxidized metabolite dehydroascorbic acid alone, or both species are transported into human cells. This problem was addressed using specific assays for each compound, freshly synthesized pure dehydroascorbic acid, the specially synthesized analog 6-chloroascorbate, and a new assay for 6-chloroascorbate. Ascorbate and dehydroascorbic acid were transported and accumulated distinctly; neither competed with the other. Ascorbate was accumulated as ascorbate by sodium-dependent carrier-mediated active transport. Dehydroascorbic acid transport and accumulation as ascorbate was at least 10-fold faster than ascorbate transport and was sodium-independent. Once transported, dehydroascorbic acid was immediately reduced intracellularly to ascorbate. The analog 6-chloroascorbate had no effect on dehydroascorbic acid transport but was a competitive inhibitor of ascorbate transport. The Ki for 6-chloroascorbate (2.9-4.4 microM) was similar to the Km for ascorbate transport (9.8-12.6 microM). 6-Chloroascorbate was itself transported and accumulated in fibroblasts by a sodium-dependent transporter. These data provide new information that ascorbate and dehydroascorbic acid are transported into human neutrophils and fibroblasts by two distinct mechanisms and that the compound available for intracellular utilization is ascorbate.

Ascorbic Acid↗
PubMed1995

Determination of optimal vitamin C requirements in humans.

Although the recommended dietary allowance provides an estimate for vitamin C ingestion in humans, optimal vitamin C requirements are unknown. We define optimal vitamin C requirements operationally based on the following: dose-function relations, availability in the food supply, steady state concentrations in plasma and tissues achieved at each dose of vitamin C, urinary excretion, bioavailability, toxicity, and epidemiologic observations. Optimal vitamin C requirements can be estimated when information is available for at least some of these criteria.

Ascorbic Acid↗
PubMed1991

Cloning of an NADH-dependent butanol dehydrogenase gene from Clostridium acetobutylicum.

The acetone-butanol fermentation of C. acetobutylicum is characterized by the unique shift from acid to solvent production. The mechanism of the solventogenic switch involves the induction of several enzymes, including NADH-dependent butanol dehydrogenase (BDH) at the onset of solventogenesis. This enzyme is responsible for the final conversion of butyraldehyde to butanol, and is distinct from the NADPH-dependent alcohol dehydrogenase (ADH) also present in the organism. To characterize the genetic control of this gene, we have cloned and expressed it in E. coli. A lambda EMBL3 phage library of C. acetobutylicum DNA was screened via plaque hybridization using a [32P]-radiolabeled, 32-fold degenerate, 62-mer oligonucleotide probe. The probe was designed by reverse translation of the NH2-terminal amino acid sequence of purified BDH II. Southern blot experiments indicate that the phage insert was of clostridial origin and had no homology with the previously cloned NADPH-dependent ADH. Subcloning of DNA from purified positive plaques has localized the gene to a 3.5-kb EcoRI fragment from which the enzyme is well expressed. The sequence of the 25 NH2-terminal amino acids for the cloned enzyme purified from E. coli was determined and found to be identical to that for the clostridial NADH-dependent BDH II. Maxicell analysis of [35S]-radiolabeled plasmid-encoded proteins identified a species encoded by the clostridial insert with the expected Mr of 42 kD.

Alcohol Oxidoreductases↗
PubMed1991

Ascorbic acid accumulation in human skin fibroblasts.

The transport and accumulation of ascorbic acid in normal human skin fibroblasts in culture was investigated by using high-performance liquid chromatographic separation and coulometric electrochemical detection. Results measured as picomole ascorbic acid per microgram cell protein were expressed in molar amounts after determining the volume of skin fibroblasts. Confluent fibroblasts contained undetectable amounts of ascorbic acid. On incubation with micromole per liter amounts of ascorbic acid in the medium, cells showed increasing uptake of ascorbic acid with time, accumulating a 15-fold excess in 3.5 h. Kinetic experiments suggested two transport mechanisms, a high-affinity and a low-affinity transport activity. Both transport activities were temperature sensitive and accumulated ascorbic acid against a concentration gradient.

Ascorbic Acid↗
PubMed1991

Ascorbic acid and in situ kinetics: a new approach to vitamin requirements.

Ascorbic acid requirements are based on preventing the deficiency disease scurvy and on urinary excretion of vitamin C. We proposed the first quantitative approach to determining optimal requirements for ascorbic acid and other vitamins, called in situ kinetics. In situ kinetics biochemically is based on the application of Michaelis-Menten reaction kinetics to ascorbic acid-dependent reactions in situ. Clinically in situ kinetics is based on determining vitamin availability to tissues so that cell-specific reactions can occur. The biochemical concepts of in situ kinetics are verified for the first time through studying ascorbic acid regulation of norepinephrine biosynthesis. The principles of in situ kinetics can now be applied to humans and human cells and for determining optimal requirements for ascorbic acid and for other vitamins.

Ascorbic Acid↗
PubMed1991

Molecular cloning of an alcohol (butanol) dehydrogenase gene cluster from Clostridium acetobutylicum ATCC 824.

In Clostridium acetobutylicum, conversion of butyraldehyde to butanol is enzymatically achieved by butanol dehydrogenase (BDH). A C. acetobutylicum gene that encodes this protein was identified by using an oligonucleotide designed on the basis of the N-terminal amino acid sequence of purified C. acetobutylicum NADH-dependent BDH. Enzyme assays of cell extracts of Escherichia coli harboring the clostridial gene demonstrated 15-fold-higher NADH-dependent BDH activity than untransformed E. coli, as well as an additional NADPH-dependent BDH activity. Kinetic, sequence, and isoelectric focusing analyses suggest that the cloned clostridial DNA contains two or more distinct C. acetobutylicum enzymes with BDH activity.

Alcohol Dehydrogenase↗
PubMed1991

The gastrointestinal management of patients undergoing heart transplantation.

Between March 1985 and December 1989, 86 patients underwent heart (80) or heart-lung (6) transplantation. Thirty-seven (43%) developed one or more significant gastrointestinal problems. Dyspepsia and gallbladder disease were common, but easily managed. Cytomegalovirus disease occurred in 25 patients (29%) and required aggressive investigation and early therapy with ganciclovir; all patients so treated responded satisfactorily. Features of acute peritonitis were seen in 6 patients and required exploratory laparotomy in 4. Non-Hodgkin's lymphoma of the stomach in one patient has regressed following a combination of reduction in immunosuppressive therapy and a course of chemotherapy. The development of hepatitis or severe liver dysfunction of unknown cause has been associated with significant morbidity and mortality. Since this study was undertaken, the incidence of gastrointestinal complications has been greatly reduced by modifications to our immunosuppressive and anti-infection prophylactic drug protocols. Nevertheless, such complications still occur and it is important that the gastroenterologist should understand the need for urgent and intensive investigation and therapy.

Female↗
PubMed1990

Separation of micro-organisms from meat and their rapid enumeration using a membrane filtration-epifluorescent microscopy technique.

A new method of separating bacteria from beef mince has been developed, in which an alkaline protease, Alcalase 0.6 L, was used to degrade the meat proteins, leaving micro-organisms in suspension. The organisms were then counted, using a membrane filtration-epifluorescent microscopy technique. A correlation coefficient of 0.97 was obtained between this method and the standard plate count, indicating its suitability for use in quality control.

Acridine Orange↗
PubMed1989

Purification and characterization of the NADH-dependent butanol dehydrogenase from Clostridium acetobutylicum (ATCC 824).

Two butanol dehydrogenases with different cofactor requirements and different pH ranges have been detected in Clostridium acetobutylicum ATCC 824. The NADH-dependent butanol dehydrogenase (NADH-BDH) was purified to near homogeneity and characterized. One striking feature of the enzyme is that Zn2+ was needed to obtain a significant recovery during purification. The enzyme was a dimer composed of two subunits with subunit molecular mass of 42 kDa and a native molecular mass of 82 +/- 2 kDa. The kinetics were studied in the direction of the reduction of butyraldehyde. Inhibition studies with S-NADH and butanol indicate that the NADH-BDH follows an ordered bibi mechanism with kinetic constants of 4.86 s-1, 0.18 mM, and 16 mM for Kcat, KNADH, and Kbutyraldehyde, respectively. Activity in the reverse direction was 50-fold lower than that in the forward direction. The NADH-BDH had higher activity with longer chained aldehydes and was inhibited by metabolites containing an adenine moiety.

Alcohol Oxidoreductases↗
PubMed1982

A computer-assisted technique for 24-hour esophageal monitoring.

Modern computer design offers the opportunity to rapidly and objectively analyze the large quantity of data obtained during prolonged intraesophageal monitoring. The purpose of this study is: (1) to describe a rapid automated technique for acquisition and analysis of esophageal parameters, using a microcomputer; and (2) to compare computerized versus manual analysis of physiograph recordings. Ten normal subjects underwent 24-hr computerized monitoring of intraesophageal function, including: (1) pH recording at 5 and 10 cm above the lower esophageal sphincter (LES); (2) pharyngeal contraction; (3) esophageal contraction at 5 and 10 cm; (4) posteriorly directed LES pressures; and (5) gastric pressure. Segments from several studies were chosen for comparison of physiograph data with that obtained by computer. No significant differences were found except for the number of esophageal contractile events. This difference stems from a problem of shifting baseline related to subject position. Thus, the computer can be used for analysis of large quantities of data obtained from prolonged esophageal monitoring.

Computers↗
PubMed1982

Influence of respiration on recordings of lower esophageal sphincter pressure in humans.

Respiratory-related fluctuations in lower esophageal sphincter pressure recording were examined by evaluating both axial respiratory motion and inspiratory compression of the high pressure zone in 20 volunteers. High-pressure zone length measurements were made by motorized slow and rapid pull-through techniques. Further studies were done using the hand withdrawn station pull-through technique with simultaneous quantitation of inspiratory depth. During quiet respiration, there was 0.6 +/- 0.2 cm axial motion in the abdominal portion and 0.4 +/- 0.1 cm movement in the thoracic portion of the high-pressure zone. A hypothetical waveform was constructed based upon this calculated axial motion. There was good agreement between hypothetical and actual pressure profiles except for the distal segment of the high-pressure zone where deep inspiration increased peak pressures to levels 2-3 times those of quiet respiration. It is concluded, therefore, that both axial motion and inspiratory compression contribute to the high-pressure zone waveform.

Adult↗
PubMed1981

Differential effect of atropine on rightward and leftward lower esophageal sphincter pressure.

To establish whether radially determined lower esophageal sphincter pressure responds symmetrically or asymmetrically to anticholinergic medication, we compared the rightward and leftward pressure responses to intravenous atropine injection. In 12 normal adult volunteers, the decrease in highest leftward lower esophageal sphincter pressure with atropine was more marked (40% decrease) than rightward (20% decrease). The result of this differential response to atropine was to reduce right-left pressure asymmetry. Mean highest leftward pressure fell 15-30 min postinjection from 35 to 21 mmHg and mean highest rightward pressure fell from 22 to 18 mmHg. Studies of the pharmacologic effect of drugs on the human lower esophageal sphincter may give variable results depending on sampling orientation within the sphincter. These radial differences should be considered in interpreting the effect of drugs on the human lower esophageal sphincter.

Adult↗
PubMed1980

Lower esophageal sphincter pressure in histologic esophagitis.

The fasting lower esophageal sphincter pressure of 18 normal volunteers was compared to 22 patients with symptoms and objective evidence of gastroesophageal reflux. Lower esophageal sphincter pressure was measured by rapid pull-through using an 8-lumen radially perfused catheter that sampled pressure every45 degrees around the circumference of the sphincter. The 22 reflux patients were subdivided for analysis into two groups, those with an acute inflammatory infiltrate on biopsy and those without inflammation. Those patients without inflammatory esophagitis had normal sphincter pressures. Those with a definite inflammatory infiltrate had pressures significantly less than normal. The least reliable separation between normals and those with inflammatory esophagitis occurred in the anterior orientations. We conclude that while basal lower esophageal sphincter pressure measurement may identify patients with reflux and inflammatory esophagitis, it is of no help in identifying those patients with reflux unassociated with inflammation. Decreased basal fasting LESP does not appear to be the most important primary determinant of gastroesophageal reflux.

Adult↗
PubMed1979

Manometry of the normal upper esophageal sphincter and its alterations in laryngectomy.

Rapid pull-through pressure profiles of the normal human upper esophageal sphincter (UES) were simultaneously studied with a conventional three-orifice Honeywell solid-state probe, an eight lumen radially perfused (RP) probe, and a circumferentially sensitive (CS) probe designed to measure UES pressure (UESP) without regard to probe orientation. Pressure curves were digitized and analyzed by computer. The Honeywell probe recorded significantly lower peak pressures than the other two methods, and had wide intrasubject pressure variations (average coefficient of variation, 53%). In contrast, UESP measured with the CS probe was constant for each subject (mean peak UESP, 121 mm Hg; average coefficient of variation, 15%). Anteroposterior RP probe UESP were identical to CS probe pressures. Thus, peak perfused anteroposterior UESP correlates with circumferentially measured sphincter squeeze.Computer programs were written that allowed RP probe pressures to be mapped in three dimensions. Normal three-dimensional maps were characterized by anteroposterior accentuation of peak pressures and also by consistent axial asymmetry with anterior peak pressures occurring 0.8+/-0.2 cm closer to the pharynx. After defining the normal two- and three-dimensional UESP configuration, patients who had undergone laryngectomy were studied. Peak pressures measured with the RP probe decreased to congruent with50 mm Hg and radial pressure asymmetry vanished. Like normals, CS probe pressures corresponded to peak RP probe pressures. UES length did not change significantly. Three-dimensional mapping showed that axial asymmetry also vanished. It therefore appears that the anatomic alterations produced by laryngectomy abolishes UESP asymmetry.

Adult↗
PubMed1979

Symptomatic duodenal duplication cyst in an adult demonstrated by endoscopic retrograde cholangiopancreatography. Case report and literature review.

A patient with a symptomatic duodenal duplication cyst demonstrated by endoscopic retrograde cholangiopancreatography (ERCP) is presented. This lesion usually does not communicate with duodenal lumen but should be added to the list of cystic duodenal lesions demonstrable by ERCP. ERCP preoperatively is helpful to the surgeon in isolating adjacent duct structures but cyst wall histology is mandatory for correct anatomic diagnosis as this lesion has often been confused with Type III choledochal cysts.

Adult↗