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Biomedical subjects

S Churchill

Publications and source records attributed to S Churchill.

18 recordsLinked to original sources
PubMed2001

Pulmonary edema associated with hyperbaric oxygen therapy.

We report three cases of pulmonary edema associated with hyperbaric oxygen therapy, including one fatality. All three patients had cardiac disease and reduced left ventricular (LV) ejection fractions (EFs). Two patients had diabetes, and one patient had severe aortic stenosis. Hyperbaric oxygen therapy may contribute to pulmonary edema by increasing LV afterload, increasing LV filling pressures, increasing oxidative myocardial stress, decreasing LV compliance by oxygen radical-mediated reduction in nitric oxide, altering cardiac output between the right and left hearts, inducing bradycardia with concomitant LV dysfunction, increasing pulmonary capillary permeability, or by causing pulmonary oxygen toxicity. We advise caution in the use of hyperbaric oxygen therapy in patients with heart failure or in patients with reduced cardiac EFs.

Aged↗
PubMed2000

Minority recruitment in clinical trials: a conference at Tuskegee, researchers and the community.

PURPOSE: This article describes the planning, implementation, and evaluation of a 2-day conference designed to examine the factors related to the participation of African Americans in cancer clinical trials. METHODS: Pre-conference formative evaluations (e.g., focus group discussions and key informant interviews with community leaders and health providers) were conducted in several rural and urban counties in the state of Alabama to determine African Americans' perceptions of participation in clinical research. The findings from these evaluations were used to develop a conference format and agenda. The 2-day conference included: (i) a pretest of African Americans' perceptions of cancer research, participation factors, and communication and recruitment issues; (ii) individual presentations high-lighting community leaders, church leaders, and researchers' perspectives regarding minority participation in research; (iii) working group discussions regarding the barriers and solutions to minority participation in research; and (iv) a posttest evaluation to measure changes in African Americans' perceptions of research. RESULTS: Several recruitment barriers and solutions were identified and reported by the working groups. Comparisons of the pretest and posttest measures showed significant (p > .05) and favorable shifts in the areas of perceptions of cancer research, participation factors, communication issues, and recruitment issues. Participation in the conference reflected a positive change in attitudes on these measures. However, the theme, "barriers that contributed to nonparticipation," did not show any significant changes during the two testing periods. The most critical lesson that resulted from this conference was the need for researchers and community members to have open dialogue about participation in research. CONCLUSIONS: This conference demonstrated that progress can be made when all parties are at the "table" and can be heard. In this model, community members proved to be valuable resources in providing researchers with information that was vital to the success of recruitment and retention studies and trials.

Black or African American↗
PubMed2000

Performance of the Baxter Flo-Gard 6201 volumetric infusion pump for monoplace chamber applications.

For non-hyperbaric purposes, the Baxter Flo-Gard 6201 volumetric pump is capable of infusing multiple types of fluids at rates of 1-1,999 ml x h(-1). We designed a study to determine flow accuracy of this pump at variable rates, fluid viscosities, and volumes over a range of chamber pressures. For hyperbaric use, the pump pressure sensor was adjusted. Sodium chloride solution 0.9% (NS), enteral formula, and packed red blood cells (PRBC) were infused at varying rates from 86.1 to 304 kPa (0.85 to 3.0 atm abs). For NS, measured compared to set flow rates ranged from 12.5% to -7.5% at settings of 1 and 5 ml x h(-1) from 86.1 to 304 kPa (0.85 to 3.0 atm abs) pressures, respectively. For NS infusions at a set rate of 100 ml x h(-1), the measured flow was identical to the set rate at all pressures. At flow settings of 1,999 ml x h(-1), the measured flow varied from the set flow by +/-4.9% Enteral infusion at 100 ml x h(-1) showed approximately a 3% increase in the measured vs. set flow rate. PRBC measured flow rates ranged from -0.4 to 6% of the set rate. During chamber compression and decompression, with set flow rates from 1 to 10 ml x h(-1), the measured flow was considerably less than expected during compression and more than expected during decompression. In conclusion, the Baxter Flo-Gard 6201 infusion pump demonstrated acceptable performance for infusing saline, enteral formula, and PRBC at low and high infusion rates into the pressurized monoplace hyperbaric chamber up to 304 kPa (3 atm abs), with the exception of low rates during compression and decompression.

Atmosphere Exposure Chambers↗
PubMed1996

Purification and characterization of a (R)-3-hydroxybutyrate dehydrogenase deletion mutant. Evidence for C-terminal involvement in enzyme activation by lecithin.

(R)-3-Hydroxybutyrate dehydrogenase (BDH; EC 1.1.1.30) is a lipid-requiring enzyme with a specific requirement of phosphatidylcholine for optimal function. The purified enzyme, devoid of lipid, can be reactivated with soluble lecithin or by insertion into phospholipid vesicles containing lecithin. In order to obtain insight into the mechanism of lipid activation, a C-terminal deletion mutant was constructed which contained 18 amino acids less than BDH. The purified deletion mutant had low, but detectable catalytic activity in the absence of phospholipid. However, the addition of either soluble lecithin or phospholipid vesicles containing lecithin had no effect on enzymatic function. Further experiments were conducted to determine if the deletion mutant had also lost its ability to bind to phospholipid vesicles and natural membranes. Our findings indicate that the mutant enzyme binds to both liposomes and rat liver microsomes. These results suggest that the binding of BDH to the phosphatidylcholine head group is independent of its interaction with the apolar core of the phospholipid bilayer.

Animals↗
PubMed1992

Primary structure of rat liver D-beta-hydroxybutyrate dehydrogenase from cDNA and protein analyses: a short-chain alcohol dehydrogenase.

The amino acid sequence of D-beta-hydroxybutyrate dehydrogenase (BDH), a phosphatidyl-choline-dependent enzyme, has been determined for the enzyme from rat liver by a combination of nucleotide sequencing of cDNA clones and amino acid sequencing of the purified protein. This represents the first report of the primary structure of this enzyme. The largest clone contained 1435 base pairs and encoded the entire amino acid sequence of mature BDH and the leader peptide of precursor BDH. Hybridization of poly(A+) rat liver mRNA revealed two bands with estimated sizes of 3.2 and 1.7 kb. A computer-based comparison of the amino acid sequence of BDH with other reported sequences reveals a homology with the superfamily of short-chain alcohol dehydrogenases, which are distinct from the classical zinc-dependent alcohol dehydrogenases. This protein family, initially discerned from Drosophila alcohol dehydrogenase and bacterial ribitol dehydrogenase, is now known to include at least 20 enzymes catalyzing oxidations of distinct substrates.

Alcohol Dehydrogenase↗
PubMed1992

Effects of repeated gestation and lactation on milk n-6 fatty acid composition in rats fed on a diet rich in 18:2n-6 or 18:3n-6.

The present study examined the effect of repeated gestation and lactation on the levels of long-chain n-6 polyunsaturated fatty acids in rat milk fat, and examined whether such levels might be modulated by supplementing the diet of the lactating dams with either (g/kg) 50 safflower oil (SFO; containing 800 g 18:2n-6/kg), or 50 evening primrose oil (EPO; containing 720 g 18:2n-6 and 90 g 18:3n-6/kg). The milk was collected at three different times (days 1, 8 and 15) in each given lactation period from female Sprague-Dawley rats which were successively bred for four pregnancies and lactations. Results showed that dietary fat and breeding frequency had no significant effects on milk triacylglycerol content, but they modified the pattern of milk fatty acids in both triacylglycerol and phospholipid fractions. After three or four successive breedings rats fed on EPO produced milk containing less saturated but more monounsaturated and polyunsaturated fatty acids compared with those fed on SFO. During the course of lactation the levels of n-6 metabolites, e.g. 18:3n-6, 20:3n-6 and 20:4n-6, in milk fat declined progressively. However, they were consistently higher in the EPO group than in the SFO group. These findings suggest that the levels of long-chain n-6 metabolites in the milk fat may be increased through supplementing the maternal diet with 18:3n-6.

Animals↗
PubMed1991

Cloning and expression of a functional rat liver D-beta-hydroxybutyrate dehydrogenase-beta-galactosidase fusion protein in Escherichia coli.

A rat liver bacteriophage lambda expression library was probed using polyclonal antibodies raised to purified rat liver D-beta-hydroxybutyrate dehydrogenase (BDH). A clone was selected that contained a 1.2-kb insert. The insert placed in an expression plasmid was utilized to transform Escherichia coli. These cells were shown to possess phosphatidylcholine-dependent BDH activity. Cells transformed with only the plasmid had no detectable BDH activity in the presence of phosphatidylcholine. The expressed activity in E. coli could be inhibited in a dose-dependent manner by BDH antiserum.

Animals↗
PubMed1990

Comparison of D-beta-hydroxybutyrate dehydrogenase from rat liver and brain mitochondria.

The properties of D-beta-hydroxybutyrate dehydrogenase (BDH) from rat liver and brain mitochondria were compared to determine if isozymes of this enzyme exist in these tissues. The BDHs from these tissues behaved similarly during the purification process. The enzymes were indistinguishable by sodium dodecyl sulfate-polyacrylamide or acid-urea-polyacrylamide gel electrophoresis and they had identical isoelectric points. The BDHs from rat liver and brain were also quite similar in functional parameters determined by kinetic analysis and phospholipid activation of apo-BDH (i.e., the lipid-free enzyme). Antiserum against rat liver BDH inhibited both enzymes to an equivalent extent in a titration assay. The enzymes had similar patterns of peptide mapping by partial digestion with Staphylococcus aureus V8 protease, followed by immunoblotting using antiserum against the liver enzyme. These results suggest that the BDHs in rat liver and brain are very similar and possibly identical.

Animals↗
PubMed1989

Developmental regulation of D-beta-hydroxybutyrate dehydrogenase in rat liver and brain.

The activities of ketone-metabolizing enzymes in rat brain increase 3- to 5-fold during the suckling period before decreasing to the adult level after weaning. We have observed that a similar developmental pattern also exists for D-beta-hydroxybutyrate dehydrogenase (BDH) in rat liver. Utilizing antibodies prepared against the purified protein we determined that the changes in BDH activities in both brain and liver are due to changes in the amount of BDH in the mitochondria. In vitro translations of isolated RNA followed by immunoprecipitation revealed that the increase in BDH activity and content was correlated with an increase in the level of functional BDH-mRNA in both liver and brain.

Age Factors↗
PubMed1989

Regulation of D-beta-hydroxybutyrate dehydrogenase in rat hepatoma cell lines.

Quantitation of D-beta-hydroxybutyrate dehydrogenase (BDH) in normal rat hepatocytes was compared with that in two rat hepatoma cell lines, H4-II-EC3 and RLT-3C. BDH activity in normal rat hepatocyte mitochondria was 321 nmol/min/mg, which was greatly reduced to 10.7 nmol/min/mg and 1.7 nmol/min/mg in H4-II-EC3 and RLT-3C cell mitochondria, respectively. The cell growth rate and L-[35S]methionine incorporation rate showed that RLT-3C cells had the highest growth rate (32.4-h doubling time) and the fastest protein biosynthesis rate (2.65 x 10(5) cpm/min/10(6) cells). The H4-II-EC3 cell line grew more slowly (48.5-h doubling time) and had lower protein biosynthesis rate (1.46 x 10(5) cpm/min/10(6) cells). The protein synthesis rate in hepatocytes was 1.25 x 10(5) cpm/min/10(6) cells. These results suggest that there is a reciprocal correlation between BDH activity and cell growth and protein synthesis rates. Immunochemical quantitation of BDH showed the amount of BDH in H4-II-EC3 and RLT-3C cells was about 4.8 and 0.5% of that in normal rat hepatocytes, respectively. Quantitation of BDH by biosynthesis indicated that BDH content in H4-II-EC3 cells and RLT-3C cells was 9.3 and 4.0% of that of normal hepatocytes, respectively. Precursor BDH synthesized by in vitro translation primed with RNA of H4-II-EC3 cells or RLT-3C cells was 3.0 and 1.1% of that translated from normal rat hepatocyte RNA. These results suggest that the decrease in BDH content in hepatoma cells results from a decrease in functional BDH-mRNA. The coupling of a decrease in BDH activity with an increase in activity of succinyl-CoA: acetoacetyl-CoA transferase in hepatoma cells may play a role in generating additional energy required for the rapid growth of tumor cells.

Animals↗
PubMed1987

Characterization of purified rabbit uterine renin: influence of pregnancy on uterine inactive renin.

Using specific antibody raised against renal renin, we have documented that the majority of the uterine renin-like activity in gravid and nongravid uteri is immunoreactive renin. To characterize its physiochemical properties, we obtained highly purified uterine renin by two affinity chromatographic steps, pepstatin and antirenin. Uterine renin has a pH optimum of 6, an apparent mol wt of 38K, and a Km of 1.7 microM for homologous substrate. These properties are identical to those of renal renin and are not influenced by the pregnant state. In the basal state, an inactive form of the uterine enzyme constitute 55 +/- 10% of the total uterine renin. During pregnancy, active renin increased 40-fold as inactive renin fell to 4 +/- 3% of the total renin concentration. The renal renin concentration fell as plasma renin increased during pregnancy. These data suggest that the increased uterine renin concentrations during pregnancy are probably due to increased local production and conversion of renin precursor to the active enzyme. This stimulation of the uterine renin level appears to be independent of renal renin.

Animals↗
PubMed1987

Vasopressin antagonism in the squirrel monkey (Saimiri sciureus).

Vasopressin antagonism and water diuresis (aquaresis) is demonstrated after i.p. or i.v. administration of vasopressin antagonists in a primate species, the squirrel monkey (Saimiri sciureus). Antagonism of vasopressin-stimulated renal medullary adenylate cyclase activity was evaluated in vitro; the most potent antagonists were those with D-tyrosine (alkyl) substitutions at position 2. Aquaresis was evaluated in vivo; the most potent aquaretic agents were again those with D-tyrosine (alkyl) substitutions at position 2. Correlation of in vitro vasopressin antagonist and in vivo aquaretic potencies for a series of antagonists was r = 0.7880 (P less than .05). Renal excretion of electrolytes, creatinine and urea tended to increase slightly as a function of vasopressin antagonist dose; the rates of solute excretion approached but seldom exceeded those rates associated with water diuresis in squirrel monkeys. The vasopressin antagonists antagonized the antidiuretic activity of exogenous vasopressin in vivo. Onset of the aquaretic response to i.v. administration of desGlyd(CH2)5D-Tyr(Et)VAVP was within 30 min; duration was greater than 120 min. These studies establish vasopressin antagonism and aquaresis associated with administration of vasopressin antagonists in a primate species.

Adenylyl Cyclases↗
PubMed1985

Phospholipid protection against proteolysis of D-beta-hydroxybutyrate dehydrogenase, a lecithin-requiring enzyme.

D-beta-Hydroxybutyrate dehydrogenase is a lipid-requiring enzyme which is localized on the inner face of the mitochondrial inner membrane. The apodehydrogenase, i.e. the purified enzyme devoid of lipid, has been purified from beef heart mitochondria and as such is inactive. It can be reactivated by insertion into phospholipid vesicles containing lecithin. Proteolytic digestion with different proteases has been carried out to obtain insight into the orientation of the enzyme in the membrane and to assess the extent of immersion of the protein into the phospholipid bilayer. Digestion of the apodehydrogenase with either trypsin, chymotrypsin, Staphylococcus aureus protease, thermolysin, carboxypeptidases A and Y, or Pronase (from Streptomyces griseus) leads to loss of activity, as assayed with phospholipid. Limited digestion with carboxypeptidase results in complete inactivation. Of the proteases tested, only Pronase and chymotrypsin cleave and inactivate the enzyme inserted into phospholipid vesicles (enzyme-phospholipid complex). For the enzyme-phospholipid complex, the loss of activity with Pronase digestion follows a single exponential decay to less than 10% of the initial activity. With chymotrypsin digestion, the staining intensity of the original approximately 31,500-dalton polypeptide decreases more rapidly than the loss of enzymic activity. The enzyme-phospholipid complex, after limited cleavage with chymotrypsin, retains enzymic activity and resonance energy transfer from protein to bound NADH and an approximately 26,000-dalton polypeptide is observed. Phospholipid alters the cleavage pattern with both chymotrypsin and Pronase, and the rate of inactivation of the enzyme-phospholipid complex is slowed in the presence of NAD(H). Moreover, the rate of inactivation of the apodehydrogenase with chymotrypsin is diminished approximately 3-fold in the presence of NAD+. Digestion of submitochondrial vesicles with either trypsin, chymotrypsin, or Pronase rapidly inactivates D-beta-hydroxybutyrate dehydrogenase; the addition of NAD+ or NADH, together with dithiothreitol and increased salt (to 50 mM), decreases the rate of inactivation, and with trypsin, virtually eliminates inactivation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

Role of aldosterone in sodium retention of pregnancy in the rat.

The purpose of this study was to test whether the absence or inhibition of aldosterone would alter the Na retention of pregnancy in the rat. We performed metabolic balance studies during the last 2 wk of the 3-wk rat pregnancy in the following four groups of saline-drinking rats: nonpregnant, sham adrenalectomized; pregnant, sham adrenalectomized; nonpregnant, adrenalectomized; and pregnant, adrenalectomized. Significant net Na retention was not found during the 2nd wk in any of the groups. During the final week, however, both pregnant groups retained between 8 and 11 meq Na more than their respective control groups. In addition, we measured plasma aldosterone concentration in these rats at term. The mineralocorticoid was not detectable in the nonpregnant adrenalectomized rats but was present in the pregnant adrenalectomized rats at a concentration of about 50% of that found in the pregnant sham-adrenalectomized rats. Serial measurements revealed that aldosterone was measurable by day 18 and nondetectable by 2 days postpartum in these pregnant adrenalectomized rats. Comparable balance studies were also performed in three groups of water-drinking rats: nonpregnant, pregnant, and pregnant rats that received large daily doses of spironolactone. During the 3rd wk both pregnant groups were in significant positive Na balance. Net Na retention for untreated pregnant rats was 8.4 meq and for the spironolactone treated, 6.9 meq, values that were not significantly different. We conclude that is is unlikely that aldosterone plays a critical role in the Na retention found during rat pregnancy.

Adrenal Glands↗
PubMed1980

Renal hemodynamics and volume homeostasis during pregnancy in the rat.

We believe that in pregnant rats, GFR is elevated at term, whereas renal plasma flow appears not to be increased. The mechanism for this increment is unclear, as is the specific time during gestation when renal hemodynamics increase. Rats increase their salt appetite and significantly positive sodium balance occurs, which is most pronounced during the last week of gestation. The retained sodium is distributed in part to the products of conception and in part to the mother, particularly in increasing her extracellular fluid volume. Although chronic volume expansion is present, absolute tubular sodium reabsorption remains elevated. The mechanism for this elevated tubular reabsorption appears no to be related to aldosterone because reduction or inhibition of this mineralocorticoid does not affect sodium balance significantly.

Aldosterone↗
PubMed1977

Normal renocortical blood flow in experimental acute renal failure.

Renal cortical blood flow of rats with postischemic, myohemoglobinuric, and mercury-induced acute renal failure was measured by the hydrogen washout technique using implanted platinum electrodes. Total renal blood flow was determined by venous cannulation in separate series of rats. The values obtained with the two methods were in excellent qualitative agreement (r=0.99, P less than 0.001), although venous cannulation gave values that were constantly lower than those calculated for whole kidney from the cortical flow rate and assumed cortical mass. Myohemoglobinuria produced by glycerol injection caused cortical blood flow to fall from a control value of 7.37+/-0.23 (SEM) ml/min X g of cortex to approximately one-half that value for four hours after injection (P less than 0.001). Flow rates 12 and 24 hr after glycerol injection were 85% (P less than 0.001) and 90% (P less than 0.05) of control, respectively. Cortical flow was reduced to 5.49+/-0.39 (SEM) ml/min X g of cortex four hours after release of one hour's total bilateral renal arterial occlusion (P less than 0.001), but rose to normal within 24 hr. Poisoning with 4.7 mg/kg of body wt of mercuric chloride produced a cortical blood flow value that was 30% higher than control 24 hr after injection (P less than 0.01), while a 12 mg/kg of body wt dose gave a normal flow value. Inulin clearance was severely depressed in all models at all study times. Thus, in contrast to human acute renal failure, marked renal cortical ischemia is not an essential feature of these different forms of murine acute renal failure.

Acute Kidney Injury↗
PubMedDate not supplied

Purification and characterization of D-beta-hydroxybutyrate dehydrogenase expressed in Escherichia coli.

D-beta-Hydroxybutyrate dehydrogenase (BDH), a lipid-requiring enzyme, has been cloned into pUC18, expressed in Escherichia coli, and purified to homogeneity. The apoenzyme, i.e., the enzyme devoid of phospholipid, has no activity, but can be activated by phospholipid to a specific activity of 129 mumol/(min.mg). The functional properties of the enzyme expressed in E. coli were compared with the enzyme purified from rat liver. The specific activities, kinetic parameters, and phospholipid activation profiles were virtually identical. These results indicate that the expression of the enzyme in E. coli is a viable method for producing active functional BDH and should allow for the production of specifically altered BDH molecules.

3-Hydroxybutyric Acid↗