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Biomedical subjects

B Ellis

Publications and source records attributed to B Ellis.

At least 37 records · Page 2Linked to original sources
PubMed1995

Media calcium attenuates mitochondrial 1,25(OH)2D production in phosphorus or vitamin D-deprived rats.

Although PTH and hypophosphatemia are the best known stimulators of 25-hydroxyvitamin D-1 alpha-hydroxylase, 1,25(OH)2D3 production in rats and humans can be modulated by circulating calcium, independent of PTH. To test whether calcium modulates this function directly in mitochondria, we examined effects of calcium on 1 alpha-hydroxylase in isolated mitochondrial preparations under basal and stimulated conditions. Rats were fed a low phosphorus (or matched control) diet for 4 or 7 d or a vitamin D-deficient (or matched control) diet for 2, 4, or 7 wk. Renal mitochondria were isolated and assayed for 1 alpha-hydroxylase activity in the presence or absence of added calcium. Calcium did not alter 1 alpha-hydroxylase in rats on control diets. After 4 d of low phosphorus diet, 1 alpha-hydroxylase was increased 2-fold over basal activity; media calcium prevented this stimulatory response. By 7 d the calcium effect was not evident. After 4 wk of vitamin D deprivation, activity was approximately 30-fold greater than controls; calcium reduced this response significantly (15-fold). A significant, but less marked inhibition of activity by calcium was present in rats subjected to 7 wk of vitamin D deprivation. Extramitochondrial calcium can directly modulate 1,25(OH)2D3 production, but this effect appears to be secondary to the primary physiologic regulators of this function. The calcium effect can be overcome after longer term exposure to phosphorus deprivation, but is sustained in the presence of long term vitamin D deprivation.

Animals↗
PubMed1995

Effects of extreme pH on the physiology of the Australian 'yabby' Cherax destructor: acute and chronic changes in haemolymph carbon dioxide, acid-base and ionic status

Freshwater habitats throughout the world are becoming increasingly threatened by the likelihood of acidification, but little consideration has been given to the importance of severe alkalization. Acute and chronic fluctuations in haemolymph acid­base status (PCO2, CCO2 and pH), [Na+] and [Ca2+] were monitored for up to 504 h (21 days) in the Australian freshwater crayfish Cherax destructor exposed to low- and high-pH water. The importance of carapace [Ca2+] during acid exposure was assessed. Crayfish were exposed to pH 7.1, pH 4.5 and pH 8.0 water containing calcium at 500 µmol l-1 while the effect of a lower calcium concentration (50 µmol l-1) was assessed in pH 4.5 water. Cherax in acid water containing 50 µmol l-1 Ca2+ exhibited a significant decrease in CO2 content after 2 h (mean decrease 1.13 mmol l-1, venous; 1.57 mmol l-1, arterial) and large ranges in PCO2 throughout the treatment (2.4­7.3 mmHg). The overall acid­base response was a metabolic acidosis compensated by a respiratory alkalosis. The haemolymph Na+ concentration in both control (pH 7.1, 50 µmol l-1) and acid-exposed animals in lower-Ca2+ water was up to 50 % reduced compared with that in animals in pH 7.1, 500 µmol l-1 Ca2+ water. Ion regulatory mechanisms, causing a subsequent increase in haemolymph [Na+] after 288 h, were implicated as an important component in acid­base homeostasis. Crayfish in acid, low-Ca2+ water also exhibited a 3.2 mmol l-1 increase in haemolymph [Ca2+] and showed a haemolymph alkalosis compared with animals in acid water with higher [Ca2+]. At higher water [Ca2+] in pH 4.5 water (500 µmol l-1 Ca2+), the haemolymph pH of Cherax was only 0.1 unit lower than that of animals in 50 µmol l-1 Ca2+ acid water after 96 h, and both CaCO2 and CvCO2 were unchanged compared with the initial condition. As with low-Ca2+ acid-exposure, the potential haemolymph acidosis appeared largely to be compensated by respiratory alkalosis. There was a transient 31 % reduction in haemolymph [Na+], although osmolality was unchanged (control 411±7.29 mosmol kg-1). Acid­base equilibrium recovered rapidly, probably in association with changes in ion flux and the re-establishment of normal haemolymph Na+ concentration. Alkaline-exposed Cherax destructor exhibited a mixed respiratory alkalosis and metabolic acidosis. Whereas haemolymph [Ca2+] increased by 1.8 mmol l-1 after only 1 h, haemolymph Na+ levels increased by 36 % after 2 h, possibly as part of a net H+ loss from the haemolymph. Increased HCO3-/Cl- exchange could contribute to the 4.3 mmol l-1 decrease in haemolymph CO2 level after 0.5 h of alkaline exposure. The responses of Cherax to extreme pH are different from those of the European and North American crayfish species studied to date.

Journal Article↗
PubMed1995

Effects of extreme pH on the physiology of the Australian 'yabby' Cherax destructor: acute and chronic changes in haemolymph oxygen levels, oxygen consumption and metabolic levels

Respiration and metabolism of the freshwater crayfish Cherax destructor were investigated with respect to the acidification and alkalization of its environment. Crayfish were exposed for up to 504 h (21 days) to pH 4.5, pH 7.1 (control) or pH 8.0 water and oxygen consumption rate, haemolymph oxygen transport and haemolymph glucose and lactate concentrations were determined. The effect of reducing environmental [Ca2+] in acid water from 500 to 50 µmol l-1 was also examined. In acid water (500 µmol l-1 Ca2+), oxygen uptake by Cherax was reduced by 79 % after 504 h (21 days) compared with 'control' animals (pH 7.1, 500 µmol l-1 Ca2+). Haemolymph lactate concentration (mean 0.6 mmol l-1) remained constant, indicating that anaerobiosis was not important, while glucose concentrations were regulated within the range of control values (0.32±0.01 mmol l-1). The arterial-venous CO2 difference of Cherax haemolymph decreased after 288 h and PaO2 increased from 11.1±0.5 mmHg to 42.4±1.0 mmHg between 96 h and 288 h. Decreased oxygen uptake and delivery without compensatory increases in anaerobiosis or glucose levels describe a hypometabolic response to low pH. The hypometabolic response of Cherax was greater in alkaline water as shown by a 53 % reduction in O2 uptake rate compared with a 44 % reduction in acid-exposed (500 µmol l-1 Ca2+) animals after 96 h. This decrease in M(dot)O2 of alkaline-exposed animals was correlated with decreased haemolymph glucose levels (from 0.32±0.01 at 0 h to 0.06±0.01 mmol l-1 at 96 h). Lowering the [Ca2+] of the water both increased the magnitude of the effects of acid exposure and elicited further changes in haemolymph oxygen transport. The maintenance of high haemolymph PO2 during pH stress appears to reduce the involvement of haemocyanin, since this promotes decreased a­v CO2. Hypometabolism probably permits Cherax to conserve resources that might otherwise be used, however, for growth and reproduction. The implications for the fitness of the animal are discussed.

Journal Article↗
PubMed1994

Trial of labor following cesarean delivery.

OBJECTIVE: To examine several variables that may affect the success rate for a trial of labor after previous cesarean delivery, as well as those affecting the rate of uterine rupture. METHODS: Between June 1, 1990 and December 31, 1991, we performed a consecutive, prospective study of 593 pregnant women who had had at least one abdominal delivery in the past, and attempted a trial of labor in each. Particular attention was given to the success rate of vaginal delivery, the type of previous uterine incision, use of oxytocin, estimated maternal blood loss, 5-minute Apgar scores, and reason for the previous cesarean operation. RESULTS: Four hundred seventy-eight patients (81%) had a successful vaginal delivery. Oxytocin induction or augmentation was successful in 46 of 67 (69%) and 117 of 167 cases (70%), respectively. Estimated maternal blood loss was less than 500 mL in 453 cases (95%). Five patients (0.8%) experienced true uterine rupture, resulting in severe neurologic sequelae in one infant. The only consistent indication of uterine rupture was an abrupt and prolonged fetal bradycardia. The majority (463; 97%) of infants who were delivered vaginally had 5-minute Apgar scores of 8 or greater. CONCLUSION: Our success rate of 81% suggests that a trial of labor after previous cesarean delivery is a safe and desirable option, but only after thorough patient counseling. An abrupt and persistent fetal bradycardia may be the only indication that uterine rupture has occurred.

Apgar Score↗
PubMed1994

Mechanism of electrical enhancement of efficacy of antibiotics in killing biofilm bacteria.

The bioelectric effect, in which electric fields are used to enhance the efficacy of biocides and antibiotics in killing biofilm bacteria, has been shown to reduce the very high concentrations of these antibacterial agents needed to kill biofilm bacteria to levels very close to those needed to kill planktonic (floating) bacteria of the same species. In this report, we show that biofilm bacteria are readily killed by an antibiotic on all areas of the active electrodes and on the surfaces of conductive elements that lie within the electric field but do not themselves function as electrodes. Considerations of electrode geometry indicate that very low (< 100 microA/cm2) current densities may be effective in this electrical enhancement of antibiotic efficacy against biofilm bacteria, and flow experiments indicate that this bioelectric effect does not appear to depend entirely on the possible local electrochemical generation of antibacterial molecules or ions. These data are expected to facilitate the use of the bioelectric effect in the prevention and treatment of device-related bacterial infections that are caused by bacteria that grow in biofilms and thereby frustrate antibiotic chemotherapy.

Anti-Bacterial Agents↗
PubMed1994

Testing antimicrobial susceptibilities of adherent bacteria by a method that incorporates guidelines of the National Committee for Clinical Laboratory Standards.

Membrane filters (0.22-microns pore size) were colonized with 10(4) CFU of logarithmic-phase bacteria per filter under laminar flow conditions in a Modified Robbins Device. Colonized filters were then placed upon agar dilution plates for MIC determinations. Subsequently, filters were transferred to control plates and incubated to obtain MBCs.

Bacterial Adhesion↗
PubMed1994

Physicians' perspectives of HMOs and marketing: implications and recommendations.

The authors compare physicians in HMOs and those not in HMOs in order to determine how HMOs have affected their practices. Physicians in HMOs see more patients per day, but receive less income per patient than physicians not in HMOs; however, both groups of physicians agree that HMOs have not changed marketing practices. In fact, both groups report uncertainty as to the best way to market their practice, and in their understanding of marketing. The physicians do agree that patient referrals are the most important means of patient acquisition; however, both groups report a surprisingly low use of patient questionnaires. Implications and recommendations for HMOs, physicians, and health care marketing researchers are discussed.

Attitude of Health Personnel↗
PubMed1993

Purification and characterization of sinapine synthase from seeds of Brassica napus.

1-O-Sinapoylglucose:choline sinapoyltransferase ("sinapine synthase") has been purified from immature seeds of Brassica napus by sequential hydroxylapatite absorption, ion-exchange chromatography, and gel filtration. The purified enzyme has an apparent molecular weight of 65 kDa on gel filtration and a subunit structure on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 28 kDa. Sinapine synthase has Km values in the high micromolar range for both substrates (1-O-sinapoylglucose and choline chloride) but these values are sensitive to the concentration of the second substrate. The enzyme displays a marked substrate specificity for 1-O-sinapoylglucose among other related glucose esters. No requirements for thiol protectants or divalent cations were found, but sinapine synthase activity is inhibited by Cu2+ and Hg2+ ions. Partial amino acid sequence data have been obtained from a tryptic digest of the 28-kDa polypeptide.

Acyltransferases↗
PubMed1993

Changing competition in health care marketing: a method for analysis and strategic planning.

As the cost and importance of healthcare continue to increase, competition in the medical industry is taking new forms and becoming more intense. The driving trends behind this competition are analyzed in the framework of Porter's Five Forces of Competition Model. The authors then discuss how the widely accepted strategies of cost, differentiation, focus, and domestication can be utilized to counter the implications of these trends and how to capitalize on opportunities in medical practice in the 1990's.

Consumer Behavior↗
PubMed1992

Cellular variability in the development of tight junctions after activation of protein kinase C.

Phorbol 12-myristate 13-acetate (PMA) decreases the tight junction conductance (TJC) during the reorganization of LLC-PK1A monolayers, but has the opposite effect in LLC-PK1B4, MDCK, and MDCK4 cells. Because no protein synthesis was required for the effects of PMA on the TJC of LLC-PK1A monolayers, we conclude that the regulation of the tight junction by protein kinase C (PKC) is a posttranslational event. In LLC-PK1A monolayers with existing tight junctions, PMA produced an initial increase in the TJC that reverted later to control values despite the continuous presence of PMA and cycloheximide. The inhibitory effect of PMA on the other cell lines was not revertible. A downregulation of total PKC activity and phorbol ester receptors was only observed during the reorganization of LLC-PK1A monolayers. PMA further increases this downregulation. This indicates that the peculiar response to PMA observed in LLC-PK1A monolayers is the result of two concurrent events: 1) the early activation of the enzyme just before the reorganization of the tight junctions begin, and 2) its late downregulation induced after prolonged exposure to phorbol esters. We conclude that PKC regulates the development of the occluding junctions, but through different mechanisms dependent on the characteristics of the cells.

Animals↗
PubMed1991

Biofilm and scleral buckle-associated infections. A mechanism for persistence.

Scleral buckle infections tend to be persistent as well as resistant to antimicrobial treatment. Often, scleral buckle infections require removal of the buckling elements for resolution. To determine if bacteria are able to persist on scleral buckles by elaborating a glycocalyx matrix or biofilm that offers protection against host defenses and antimicrobial treatment, the authors cultured 28 scleral buckle elements removed for infection and extrusion. Bacteria were isolated from 18 elements (64%). The most frequently isolated bacteria were Staphylococcus epidermidis and other coagulase-negative staphylococci (8), Staphylococcus aureus (3), corynebacteria (3), Mycobacterium chelonei (3), and Proteus mirabilis (3). Eleven (65%) of 17 buckles evaluated with scanning electron microscopy demonstrated the presence of bacteria encased in biofilm. Biofilm was demonstrated on the surfaces and ends of solid silicon elements. In the silicon sponges, biofilm also extended into the matrix of the sponges. The authors believe that bacterial production of biofilm offers an explanation for the persistence of scleral buckle infections and their ability to withstand antimicrobial treatment.

Adult↗
PubMed1991

Idiotypic characterisation of monoclonal antibodies with restricted epitope specificity for retinal S-antigen.

This paper describes the idiotypic specificities of eight murine monoclonal antibodies directed to three independent epitopes on retinal S-antigen. The antigenic sites recognised by these monoclonal antibodies have previously been localised to a small region near the C-terminal of bovine S-antigen. Xenogeneic, site-related anti-idiotypes prepared against each of the monoclonal antibodies recognised common idiotypes only amongst those monoclonal antibodies which reacted with the same epitope on S-antigen. Two of the three idiotypes were detected in the sera of BALB/c mice but not in two strains of rat immunised with xenogeneic S-antigen and none could be detected in the sera of patients with anti-photoreceptor autoantibodies. Our results demonstrate that the idiotypes of murine monoclonal antibodies to retinal S-antigen exhibit restricted epitope specificity but are species-restricted and imply that the S-antigen lacks a dominant antigenic epitope.

Antibodies, Monoclonal↗
PubMed1990

Fluoride penetration into dentine abutments in vitro.

The diffusion of fluoride ions from various concentrations of sodium fluoride solution into the dentine of decoronated human canine teeth, prepared as for reception of overdentures, was studied in vitro. The decoronated preparations were immersed for 7 days in 2.0, 1.5, 1.0, 0.5 and 0.05% solutions of neutral-pH sodium fluoride and then fluoride penetration into the prepared transverse face of the dentine was assessed by electron microprobe. Only with high concentrations of fluoride (2.0%) was there significant penetration. In peritubular dentine, fluoride penetration could be measured to a depth of 400 microns, but in intertubular dentine penetration did not take place beyond 100 microns. These findings call into question the efficacy of patient-administered caries prophylaxis with low-concentration fluoride treatments in overdenture cases.

Cuspid↗