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Biomedical subjects

G Davis

Publications and source records attributed to G Davis.

At least 145 records · Page 8Linked to original sources
PubMed1991

A study of the action of angiotensin II on perfusion through the cortex and papilla of the rat kidney.

The effect of angiotensin II on blood pressure and perfusion of blood through the cortex and papilla regions of the kidney was determined in pentobarbitone-anaesthetized rats which were subjected to laser-Doppler flowmetry to estimate regional renal haemodynamics. Angiotensin II was infused at 10, 45 and 150 ng (kg body weight-1 min-1) which caused dose-related increases in blood pressure of 3, 12 and 24%, respectively, and decreases in cortical perfusion of 9, 15 and 24%, respectively. Papillary perfusion did not change at any dose of angiotensin II. This pattern and magnitude of responses to angiotensin II in blood pressure, cortical and papillary perfusions was essentially unaffected (a) following blockade of cyclo-oxygenase activity with indomethacin (1.3 mg kg-1 plus 2 mg kg-1 h-1), (b) during infusion of a bradykinin antagonist, at 1.3 micrograms min-1, (c) when renal perfusion pressure was regulated at control levels and (d) following Methylene Blue administration to inhibit potential endothelial-derived relaxing factor production. By contrast, infusion of phenylephrine at 5, 10 and 20 micrograms kg-1 min-1 caused dose-related increases in blood pressure and decreases in both cortical and papillary perfusions reaching some 28, 7 and 17% respectively at the highest dose of phenylephrine used. These results showed that both cortex and papilla were sensitive to vasoconstrictor agents. They are compatible with the suggestion that angiotensin II regulates cortical but not papillary perfusion in the kidney, and that these responses do not depend on prostaglandin, bradykinin, renal perfusion pressure or endothelium-derived relaxing factor.

Angiotensin II↗
PubMed1991

Effect of somatic nerve stimulation on the kidney in intact, vagotomized and carotid sinus-denervated rats.

1. The influence of cardiopulmonary and arterial baroreceptors on the renal nerve-dependent functional responses of the kidney to electrical stimulation of somatic afferent nerves was studied in pentobarbitone-anaesthetized rats. 2. Electrical stimulation of the left brachial nerve plexus at 3 Hz, 0.2 ms and 15 V in the intact animals increased blood pressure by 22%, and while renal perfusion pressure was maintained at pre-stimulus levels, renal blood flow and glomerular filtration rate decreased by 14 and 22% respectively. At the same time urine flow rate and absolute and fractional sodium excretion decreased by 36, 42 and 27% respectively. In animals subjected to acute renal nerve section these renal functional responses could not be elicited. 3. Following bilateral vagotomy the systemic and renal haemodynamic responses to brachial nerve stimulation were similar to the intact group. However, urine flow rate and absolute and fractional sodium excretions decreased by 50, 59 and 47% respectively, responses which were significantly greater than in the intact group. 4. In a group of rats in which the carotid sinus nerves had been sectioned, stimulation of the brachial plexus caused reductions of renal blood flow and glomerular filtration rate of the same magnitude as in the intact group; however, urine flow rate and absolute and fractional sodium excretion fell by 51, 60 and 48%, respectively, which were significantly larger than in the intact group. 5. These results demonstrate that the afferent nerve information arising from muscle joints and skin and carried via the brachial plexus caused reflex renal nerve-dependent reductions in renal haemodynamics and an antidiuresis and antinatriuresis. The cardiopulmonary and carotid sinus baroreceptors exert a tonic inhibitory action on these reflex renal responses insofar as they appeared to attenuate the antidiuretic and antinatriuretic responses to somatic afferent nerve stimulation.

Animals↗
PubMed1991

Gains of cardiorespiratory fitness with arm-crank training in spinally disabled men.

Cardiorespiratory responses to four patterns of arm-crank training (thrice weekly sessions at 50 or 70% of peak oxygen intake, 20 or 40 min per session) were examined over 8, 16, and 24 weeks in 24 initially inactive subjects with paraplegia. Training was associated with a significant increment of the peak oxygen intake during arm-crank tests except in control subjects and those combining a low intensity (50% of peak) with short-duration training (20-min sessions). There were associated increases in cardiac stroke volume, as assessed by a carbon dioxide rebreathing technique during submaximal exercise. It is suggested that the performance of inactive wheelchair users is limited by a pooling of blood in paralysed regions, with a reduction of cardiac preloading; nevertheless, substantial gains of performance are possible through prolonged arm-crank exercise of moderate intensity.

Adolescent↗
PubMed1990

Purification of human smooth muscle filamin and characterization of structural domains and functional sites.

A method was developed to purify human smooth muscle filamin in high yield and structural domains were defined by using mild proteolysis to dissect the molecule into intermediate-sized peptides. Unique domains were defined and aligned by using high-resolution peptide mapping of iodinated peptides on cellulose plates. The amino- and carboxyl-terminal orientation of these domains within the molecule was determined by amino acid sequence analysis of several aligned peptides. In addition to the three unique domains which were identified, a number of smaller and larger fragments were also characterized and aligned within the intact molecule. These structural domains and related peptides provide a useful set of defined fragments for further elucidation of structure-function relationships. The two known functionally important binding sites of filamin, the self-association site and the actin-binding site, have been localized. Self-association of two monomers in a tail-to-tail orientation involves a small protease-sensitive region near the carboxyl terminal of the intact polypeptide chain. Sedimentation assays indicate that an actin-binding site is located near the blocked amino terminal of the filamin molecule. Sequences derived from large peptides mapping near the amino terminal show homology to the amino-terminal actin-binding site of alpha-actinin (chicken fibroblast and Dictyostelium), Dictyostelium 120-kDa actin gelation factor, beta-spectrin (human red cell and Drosophila), and human dystrophin. This homology is particularly interesting for two reasons. The functional form of filamin is single stranded, in contrast to alpha-actinin and spectrin which are antiparallel double-stranded actin cross-linkers. Also, no homology to the spectrin-like segments which comprise most of the mass of spectrin, alpha-actinin, and dystrophin was found. Instead, the sequence of a domain located near the center of the filamin molecule (tryptic 100-kDa peptide, T100) shows homology to the published internal repeats of the Dictyostelium 120-kDa actin gelation factor. On the basis of these results, a model of human smooth muscle filamin substructure is presented. Also, comparisons of human smooth muscle filamin, avian smooth muscle filamin, and human platelet filamin are reported.

Amino Acid Sequence↗
PubMed1990

Role of cryptic receptors (cryptitopes) in bacterial adhesion to oral surfaces.

Progress in characterizing the receptors that promote bacterial attachment to teeth and oral epithelial cells has suggested that hidden molecular segments may frequently be involved. Such cryptic receptors, referred to as 'cryptitopes', may become exposed by several mechanisms. Hidden segments of salivary acidic proline-rich proteins evidently become exposed when the molecules undergo a conformational change as they adsorb to apatitic mineral. Adhesins of Actinomyces viscosus and certain other prominent dental plaque bacteria are able to bind to these cryptitopes, and this enables these organisms to bind to proline-rich proteins on apatitic surfaces while avoiding interactions with these proteins in solution. Cryptitopes may also become exposed as a result of enzymatic action. Thus, several bacteria, including Fusobacterium nucleatum, Eikenella corrodens, A. viscosus, A. naeslundii and Bacteroides intermedius, have adhesins that bind to galactosyl receptors which become exposed after treatment with neuraminidase. Similarly, the adhesion of some Gram-negative bacteria, such as Bact. gingivalis, is enhanced when tissue surfaces are treated with certain proteases, or lysosomal enzymes derived from human polymorphonuclear leucocytes. It seems likely that elevated levels of enzymes present in gingival fluid as sequelae of poor oral hygiene and gingivitis may generate cryptitopes for potentially periodontopathic bacteria, and thereby contribute to modulation of the gingival flora.

Actinomyces↗
PubMed1990

Induction of erythrocyte HLA expression during interferon treatment and HIV infection.

Although HLA antigens are present on the surface membrane of most cells, erythrocytes express little or no HLA. Occasionally red cells from normal individuals or patients with certain diseases express elevated levels of these molecules. The reasons for such variations are currently not understood. We report here that the expression of very high levels of HLA on erythrocytes occurs in response to interferon alpha given as a therapeutic agent for viral hepatitis. Increased expression became apparent after the second or third week of treatment, peaked at 3-4 months, and decreased at the end of the treatment period. This chronology suggests that elevated HLA expression is originated during erythropoiesis and persists throughout the lifetime of the erythrocyte. Furthermore, erythrocyte HLA expression did not correlate with changes of plasma HLA or beta 2-microglobulin concentrations and was not affected by in vitro chloroquine treatment, ruling out the possibility that HLA was adsorbed from plasma. Increased expression of HLA on erythrocytes was also demonstrated in patients infected with the human immunodeficiency virus, a disease in which increased production of endogenous interferon has been previously documented. We conclude that high HLA expression in red cells occurs in response to persistent interferon stimulation. Further studies will determine if this effect can also be produced by interferon tau or other factors.

Adult↗
PubMed1990

Accessible sialic acid content of oral epithelial cells from healthy and gingivitis subjects.

The purpose of the present study was to determine if there were differences in the quantity of accessible sialic acid on superficial epithelial cells collected from different areas of the mouth, and from healthy subjects with good oral hygiene, as compared to subjects with gingivitis. Superficial epithelial cells were collected by gently scraping the tongue dorsum, hard palate, free gingiva and buccal epithelium. The cells were washed and treated with clostridial neuraminidase to release accessible sialic acid; this was quantitated using a fluorometric assay. Buccal cells released an average of 62.6 ng sialic acid per 10,000 cells, which was nearly 3-fold more than cells from the hard palate (24.1 ng), free gingiva (21.9 ng), or tongue (15.4 ng). Buccal and free gingival cells collected from 5 healthy subjects had significantly higher levels of accessible sialic acid on their surface than cells collected from 5 subjects with gingivitis. These differences were significant at the p less than 0.001 and p less than 0.01 levels, respectively. The data obtained suggest that the oral hygiene status of an individual can influence the quantity of accessible sialic acid residues on oral epithelium; this would be expected to influence the attachment and colonization of bacteria which bind to sialic acid-containing receptors.

Adolescent↗
PubMed1990

Effect of insulin on renal sodium handling in hypertensive rats.

Spontaneously hypertensive rats have reduced peripheral insulin sensitivity. To determine whether hypertensive rats demonstrate reduced response to the antinatriuretic effect of insulin, urinary sodium excretion was determined in hypertensive and normotensive rats (n = 7 per group) before and during euglycemic insulin administration at two infusion rates (21 milliunits/kg load and 4 milliunits/kg/min or 85 milliunits/kg load and 8 milliunits/kg/min). Hypertensive and normotensive time controls received the vehicle for insulin administration. Mean arterial pressure was greater (p less than 0.05) and inulin clearance was less (p less than 0.05) in hypertensive than normotensive rats before insulin infusion. Baseline fractional sodium excretion was not different between groups. Low dose insulin infusion reduced (p less than 0.05) fractional sodium excretion from 0.81 +/- 0.43% to 0.31 +/- 0.07% in hypertensive rats and from 1.05 +/- 0.37% to 0.47 +/- 0.18% in normotensive rats. High dose insulin infusion reduced (p less than 0.05) fractional sodium excretion from 0.67 +/- 0.22% to 0.21 +/- 0.08% in hypertensive rats and from 0.81 +/- 0.15% to 0.30 +/- 0.09% in normotensive rats. Sodium excretion was unchanged in time controls. The reduction in sodium excretion was similar in both rat groups during low dose and high dose insulin infusions. Mean arterial pressure and inulin clearance were unchanged from baseline values during insulin infusion in all rat groups. Glucose requirement to maintain euglycemia was greater (p less than 0.05) in normotensive than hypertensive rats at both insulin infusion rates. Thus, while hypertensive rats have reduced sensitivity to the hypoglycemic effects of insulin, the antinatriuretic response to insulin is not different from that of normotensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Percutaneous transcatheter embolization of symptomatic renal angiomyolipomas: a report of four cases.

Successful percutaneous transcatheter embolization of renal angiomyolipoma is reported in four female patients. The angiomyolipomas measured more than 4 cm in diameter. Three patients had severe haemorrhage and one patient had a growing angiomyolipoma in a solitary kidney. This patient had percutaneous transcatheter embolization to prevent further deterioration of kidney function. Three patients had multiple renal angiomyolipomas as part of tuberous sclerosis. Two of them had selective transcatheter embolization of more than one angiomyolipoma. After embolization, one patient had partial loss of kidney function and one patient developed an abscess that could successfully be drained percutaneously under ultrasound guidance. The following conclusions can be drawn. All patients with tuberous sclerosis should be screened for renal angiomyolipomas. All symptomatic renal angiomyolipomas and all angiomyolipomas that measure more than 4 cm in diameter require treatment. Embolization should be considered as a primary therapeutic modality for multiple angiomyolipomas.

Adult↗
PubMed1989

The major human rhinovirus receptor is ICAM-1.

The major human rhinovirus receptor has been identified with monoclonal antibodies that inhibit rhinovirus infection. These monoclonal antibodies recognize a 95 kd cell surface glycoprotein on human cells and on mouse transfectants expressing a rhinovirus binding phenotype. Purified 95 kd protein binds to rhinovirus in vitro. Protein sequence from the 95 kd protein showed an identity with that of intercellular adhesion molecule-1 (ICAM-1); a cDNA clone obtained from mouse transfectants expressing the rhinovirus receptor had essentially the same sequence as ICAM-1. Thus, the major human rhinovirus receptor is ICAM-1. The gene for this receptor maps to human chromosome 19, which also contains the genes for a number of other picornavirus receptors.

Alkaloids↗
PubMed1989

Intravascular exchange and bolus transfusion in the severely isoimmunized fetus.

Eight Rh-sensitized fetuses, between 21 weeks 2 days and 35 weeks of gestation, received 31 intravascular transfusions (13 exchange and 18 bolus) and one intraperitoneal transfusion under ultrasonographic guidance. The interval between transfusions was 13.4 +/- 4.7 days. Posttransfusion hematocrit dropped at a rate of 1.0% +/- 0.6% per day. Procedure time for the bolus transfusion was shorter than for the exchange transfusion (t test, p less than 0.001). Bleeding from the puncture site complicated 10 of the 31 intravascular transfusions, without apparent maternal or fetal consequences. Fetuses were delivered between 33 and 36 weeks of gestation, after lung maturity was achieved.

Adult↗
PubMed1989

Growth and reproduction of mice developed from bisected embryos.

Embryos from three groups of mice, ICR (I), a synthetic (S), and an F(1) hybrid from C57BL males and S females (F), were used to examine effects of embryo bisection on subsequent viability, postnatal growth and reproduction. In two experiments, Group S females used as recipients received the following combinations of whole (W) and/or bisected (B) embryos: W(I) and W(F), W(I) and B(F), B(I) and W(F), and B(I) and B(F) in Experiment 1 and W(I) and W(S), W(I) and B(S), B(I) and W(S), and B(I) and B(S) in Experiment 2. Eight to 12 embryos of both types were transferred surgically to two horns of the uterus. Overall survival rate of whole embryos (32.6%) was significantly greater (P < 0.001) than that for demi-embryos (13.2%). The gestation period after transfer was significantly longer (P < 0.05) for demi-embryos (17.5d) than for whole embryos (16.4 d). Mice developed from demi and whole embryos were not different in mean body weight at birth and at 21, 42 and 63 d of age. Fertility and litter size at first parity of mice that developed from bisected embryos were comparable with those that developed from whole embryos. Hence, bisection decreased embryo viability, increased gestation period of recipients but did not affect postnatal growth and reproduction.

Journal Article↗
PubMed1989

Growth of rubella virus in a glass bead propagator.

A glass sphere propagator with an air lift pump to circulate the medium, has been successfully used to produce large volumes of rubella virus. The system was productive, flexible and easy to operate.

Animals↗
PubMed1989

Evidence for the involvement of a specific cell wall layer in regulation of deep supercooling of xylem parenchyma.

Current theory indicates that the structure of the cell wall is integral to the ability of a tissue to exhibit deep supercooling. Our previous work has indicated that the structure of the pit membrane and/or amorphous layer (protective layer), rather than the entire cell wall, may play a major role in deep supercooling (21, 22). The present study indicates a shift in the low-temperature-exotherm of current year shoots of peach can be induced by soaking twigs in water over 3 to 10 days. Alternatively, these shifts can be inhibited by exposing tissues to 10(-4) molar cycloheximide. Ultrastructural observations indicated a marked alteration of the amorphous layer in xylem parenchyma of water-soaked tissue. Alterations consisted of an apparent loosening or partial dissolution of portions of the amorphous layer. Changes in the density or uniformity of the amorphous layer in cycloheximide-treated tissues were not as readily apparent. The appearance of the protoplast in tissue soaked in water for up to 10 days was characteristic of deacclimated cells. However, in tissue soaked in cycloheximide for the same period these changes were not evident. These observations further support our contention that the structure of the amorphous layer may play a key role in establishing and regulating the ability of a cell to exhibit deep supercooling.

Journal Article↗
PubMed1989

Pulsed-spray pharmacomechanical thrombolysis: preliminary clinical results.

Pulsed-spray pharmacomechanical thrombolysis was used to treat 41 patients with 47 complete thrombotic occlusions of hemodialysis grafts (n = 29), arterial bypass grafts (n = 10), or peripheral native arteries (n = 8). The procedure involves the use of small pulses of highly concentrated urokinase, which are forcefully sprayed throughout the thrombus during systemic heparinization. Virtually complete lysis was achieved in 46 of 47 occlusions. In the 46 thrombi that lysed, mean time for completion of lysis was 63 +/- 35 min and initial partial return of flow required 26 +/- 18 min. Complications included small peripheral emboli in one treated bypass graft (which cleared promptly after further pulse-spray therapy) and bleeding in three cases (one case of hematoma in the infused field at the site of recent surgery, one case of bilateral hematomas at the femoral puncture site, and one minor delayed self-limited gastrointestinal hemorrhage). Results to date suggest that the pulsed-spray pharmacomechanical method augments the speed, consistency, safety, and cost efficacy of clinical thrombolysis. Further study is warranted.

Arteriovenous Shunt, Surgical↗