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Biomedical subjects

J S Edwards

Publications and source records attributed to J S Edwards.

At least 37 records · Page 2Linked to original sources
PubMed1996

A comparison of three subjective tests for astigmatism and their interexaminer reliabilities.

BACKGROUND: Astigmatism is a common cause of blurred vision and asthenopia. Several different tests for the measurement of astigmatism have been described in the literature, but there are few studies that have compared the results of various tests. METHODS: The results of three astigmatism tests performed on 40 subjects by two examiners were compared. Two of the tests, the Jackson cross cylinder (JCC) and the Humphriss immediate contrast (HIC), utilized distance targets; one test, the Pratt test, involved a near target. RESULTS: The mean differences between all tests were less than 0.25D. There was a slight tendency for higher cylinder power to be found on the Pratt test. The three tests agreed within +/- 0.25D on cylinder power 80 to 98 percent of the time and within 10 degrees of cylinder axis 85 to 98 percent of the time. Interexaminer reliability showed mean differences less than 0.12D for each of the three tests, agreement within +/- 0.25D on cylinder power 88 to 90 percent of the time and within 10 degrees on cylinder axis 85 to 93 percent of the time. CONCLUSIONS: The results suggested that any of the three techniques could be substituted for another for astigmatism testing. On theoretical grounds, a binocular refraction method for cylinder axis determination, such as the HIC, is advisable for patients with cyclophorias and significant amounts of astigmatism. The results showed good reliability for each of the three methods.

Adolescent↗
PubMed1995

The effect of age and liver disease on the pharmacokinetics of the calcium antagonist, nisoldipine.

Two studies were performed-one in elderly, hypertensive patients and one in patients with chronic liver disease-to investigate the effect of age and liver disease upon the pharmacokinetics of nisoldipine, a dihydropyridine-type calcium antagonist. The effect of acute and chronic administration of nisoldipine (once and twice daily) was investigated in 17 elderly hypertensive patients. Compared with previously published data from young healthy volunteers, the values for Cmax and AUC appear to be higher in elderly hypertensive patients while Tmax and half-life were unchanged. Nisoldipine significantly reduced both systolic and diastolic blood pressure when given acutely to elderly hypertensive patients. Major alterations in the pharmacokinetics of nisoldipine were found in 7 patients with chronic liver disease when compared with the elderly hypertensives and healthy volunteers. The values for AUC, Cmax, half-life and volume of distribution were all higher than expected from the volunteer data while clearance was lower. One patient receiving primidone had very low nisoldipine levels, suggesting that the concomitant administration of agents that may induce the metabolism of nisoldipine should be discouraged. Nevertheless, comparisons of nisoldipine plasma levels after acute and chronic administration showed no evidence of any accumulation in either patient population in the doses used. The drug was generally well tolerated although 1 patient with chronic liver disease was withdrawn due to fluid retention.

Administration, Oral↗
PubMed1994

Selective expression of glionexin, a glial glycoprotein, in insect mechanoreceptors.

The distribution of a glial cell-associated glycoprotein, glionexin (GX), on sensory receptors of the adult cricket Acheta domesticus is described, using the monoclonal antibody 5B12 as an immunohistochemical probe. GX was previously shown to be widely distributed in the embryo and to persist in the postembryonic to adult central nervous system. Here we demonstrate that it is restricted in the adult periphery to three subclasses of mechano-receptor sensilla: large socketed hair mechanoreceptors, their associated campaniform sensilla, and chordotonal organs. GX was not detected in photoreceptors, chemoreceptors, or other mechanoreceptors. The pattern of distribution differs significantly within the three subclasses of mechanoreceptors. In the hair and campaniform receptors GX is restricted to the extracellular space among glial cells clustered around the axon hillock region, but in chordotonal organs it surrounds the scolopidium at the tip of dendrites. The highly restricted distribution of GX in the periphery suggests possible functions that include mechanical stability of the sensory apparatus and ionic homeostasis in the respective neuronal spike-generating regions. The developmental modulation of GX expression is taken to imply multiple functions for the molecule during the life of the insect.

Animals↗
PubMed1994

Effect of cytoplasmic pH on Ca(2+)-stimulated eicosanoid biosynthesis in human platelets.

1. We have investigated the effect of cytoplasmic pH (pHi) on the relationship between platelet cytoplasmic Ca2+ concentration ([Ca2+]i) and eicosanoid biosynthesis. Stirred gel-filtered human platelets loaded with fluorescent indicators of Ca2+ and H+ were suspended in balanced salt solutions at 37 degrees C. [Ca2+]i was controlled by calcium ionophore (ionomycin). Increased [Ca2+]i was associated with increased production of thromboxane A2 (TXA2) as determined by radioimmunoassay of its stable hydrolysis product TXB2, and of 12-hydroxy eicosatetraenoic acid (12-HETE) measured by high performance liquid chromatography. 2. Varying pHi with a K+/H+ ionophore (nigericin) in platelets suspended in K+ rich solutions of pH 6.8, 7.4 or 7.8 with subsequent resuspension in solution of pH 7.4 containing albumin (1 g l-1) and Ca2+ (1 mM) resulted in pHi of 6.72 +/- 0.05, 7.31 +/- 0.02 and 7.71 +/- 0.04 (mean +/- s.e. mean, n = 5). Ionomycin (1.2 microM) increased [Ca2+]i by 97.1 +/- 17.6, 191.9 +/- 48.7 and 322.8 +/- 55.7 nM at the different values of pHi respectively; TXB2 production was 0.7 +/- 0.2, 2.1 +/- 0.4 and 10.7 +/- 3.3 ng micrograms-1 protein, and 12-HETE production was 150.9 +/- 68.2, 184.4 +/- 77.9 and 302.3 +/- 62.8 ng micrograms-1 protein. 3. Ammonium chloride (50 mM) caused a small reduction in pHo while increasing pHi from 7.32 +/- 0.04 to 7.89 +/- 0.05 and increasing ionomycin (1.2 microM)-induced [Ca2+]i responses from 94.1 +/- 67.3 to 721.6 +/- 288.3 nM. TXB2 production increased from 3.1 +/- 2.1 to 17.3 +/- 8.2 and 12-HETE production increased from 100.5 +/- 26.7 to 203.2 +/- 36.4 ng microg-1 protein. Responses of [Ca2+]i and TXB2 production to epoxymethano prostaglandin H2 (U46619, an endoperoxide-thromboxane receptor agonist) increased significantly in the presence of NH4C1.4. Alterations of pHi (such as may occur under pathological conditions) influence [Ca2+]i responses and eicosanoid synthesis in human platelets.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1994

Intestinal carbohydrate absorption and permeability at high altitude (5,730 m).

To investigate the effects of high altitude on intestinal function, the absorption and permeation of nonmetabolizable carbohydrates were measured in 14 volunteers (median age 21 yr, range 19-37 yr) at sea level in Oxford, UK; at 1,050 m in Nepal; at 5,570 m after 5 days at > 5,500 m; and at 5,730 m after 11 days at > 5,500 m. Body weight decreased 5.7 +/- 1.19 kg from sea level to 5,570 m (P < 0.001 by paired t test) despite 72-h dietary records showing no change in energy intake. Absorption of carbohydrates by mediated transport was measured by urinary xylose and 3-O-methyl-D-glucose excretion. Xylose excretion (%oral dose) decreased from 31.4 +/- 4.5% to 20.7 +/- 4.5% (P < 0.001) and 3-O-methyl-D-glucose excretion decreased from 39.7 +/- 6.1 to 33.7 +/- 7.0% (P = 0.003) from sea level to 5,730 m. Monosaccharide permeation measured by L-rhamnose excretion decreased from 11.3 +/- 2.5 to 6.2 +/- 2.0% (P = 0.001). Intestinal permeability, a measure of barrier function (ratio of lactulose to L-rhamnose), increased from 0.036 +/- 0.014 at sea level to 0.084 +/- 0.042 at 1,050 m (P = 0.006), possibly due to infective enteropathy after arrival in Nepal, but reverted to normal (0.045 +/- 0.013; P = 0.062) at 5,730 m. Absorption of all carbohydrates returned to normal after return to the UK. This study showed that a decrease in mediated (D-xylose or 3-O-methyl-D-glucose) and diffusional (L-rhamnose) monosaccharide absorption occurs at high altitude but that intestinal permeability at 5,730 m is unchanged.

3-O-Methylglucose↗
PubMed1994

A comparison of once daily versus twice daily nisoldipine as monotherapy in patients over 65 years of age.

The antihypertensive effect of the calcium antagonist nisoldipine was investigated in 33 elderly hypertensive patients. This randomised double-blind study involved a dose titration of both once and twice daily nisoldipine from 5 mg up to a maximum of 20 mg/day, with placebo treatment both before and after nisoldipine. Blood pressure measurements were made 12/24 h post-dose to assess 24 h blood pressure control. The majority of patients required a daily dose of 20 mg. There were no significant differences seen between the two treatment regimens. Nisoldipine given either once or twice daily, significantly reduced blood pressure when compared to baseline values. Three patients withdrew from the study because of adverse events whilst on nisoldipine once daily treatment. Overall the incidence of adverse event was higher on once daily treatment, although the majority were mild and did not require withdrawal of treatment. Nisoldipine effectively lowered the blood pressure of these elderly hypertensive patients and was reasonably well-tolerated.

Aged↗
PubMed1994

Cold-weather field feeding: an overview.

Extremely cold environments are a challenge to military field feeding operations due to freezing and inadequate intakes of rations and water. The U.S. Army Research Institute of Environmental Medicine conducted a series of three cold-weather field feeding studies to test, modify, and contribute data for the development of Cold-Weather Feeding Doctrine. Conclusions from these studies show that command emphasis is essential for ration and water storage and distribution to prevent freezing, and adequate ration and water consumption to prevent weight loss and dehydration. Since any ration mix can be configured to meet cold-weather feeding requirements, the decision of which ration to use should be based on logistical support and constraints, mission requirements, and water availability.

Dehydration↗
PubMed1993

The differentiation between neuroglia and connective tissue sheath in insect ganglia revisited: the neural lamella and perineurial sheath cells are absent in a mesodermless mutant of Drosophila.

Two morphogenetic mutations, twist and Delta, that affect the embryonic development of Drosophila in known ways were used to examine the derivation and function of the outer layers of the central nervous system (CNS). Both the extracellular neural lamella, which ensheaths the CNS, and its source, the underlying perineurial sheath cell layer, fail to develop in Drosophila embryos that are homozygous for a loss of function mutation in the twist gene, and which thus lack mesodermal derivatives. The cell layer immediately below the perineurial sheath cells, here termed barrier glial cells, constitute the ion permeability barrier in wild-type embryos. They are present in twist mutant embryos, appear to be normal at the ultrastructural level, and function as a blood-brain ion barrier. The apparent derivation of perineurial sheath cells from mesodermal precursors distinguishes them from neurons, glia and other nonneural components of the CNS, such as tracheae, all of which are of ectodermal origin. We confirm Scharrer's interpretation of the relationship between the perineurium and underlying neuroglia. In embryos homozygous for the neurogenic mutant Delta, an embryonic lethal in which excess ventral blastoderm gives rise to neuroblasts, the CNS forms as an amorphous cell mass, with discontinuous perineurial sheath and barrier glial cell layers. We propose that the cell mass is permeable to lanthanum ions and fails to form a blood-brain barrier because volume growth prevents the formation of continuous surface cell layers.

Animals↗
PubMed1993

Inhibition by nitroprusside of platelet calcium mobilization: evidence for reduced sensitivity to nitric oxide in essential hypertension.

OBJECTIVE: Although platelets from patients with moderate hypertension are abnormally sensitive to agonist-induced aggregation, their sensitivity to antagonists is not known. Nitric oxide (NO) is an endogenous antagonist of platelet function. The objective of this study was to determine whether platelet sensitivity to the inhibitory activity of sodium nitroprusside, a donor of NO, is abnormal in hypertension. DESIGN AND METHODS: Untreated patients with uncomplicated essential hypertension (mean arterial pressure > 120 mmHg) were studied. The rise in cytosolic calcium in response to 9,11-deoxy-11 alpha, 9 alpha-epoxymethanoprostaglandin F2 alpha (U46619, a thromboxane mimetic) was measured in fura-2-loaded platelets from 20 patients and 15 normotensive healthy subjects. Inhibition by sodium nitroprusside was measured in a further group of 14 patients and 20 normotensive subjects. RESULTS: Basal cytosolic calcium concentration and the rise in this parameter induced by U46619 were significantly greater in platelets from hypertensive patients than in those from normotensive controls. The mean half-maximal inhibitory concentration of nitroprusside to calcium mobilization induced by 3 mumol/l U46619 was 3.1-fold greater in platelets from hypertensive patients than in those from controls (95% confidence interval 1.6-6.0). CONCLUSION: The sensitivity of platelets to nitroprusside is reduced in essential hypertension. This reduced sensitivity to NO might influence the risk of arterial thrombosis in hypertensives.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1993

Thromboxane A2 receptor antagonism and synthase inhibition in essential hypertension.

Short-term effects of ridogrel, a combined thromboxane synthase inhibitor and receptor antagonist, were investigated in 16 patients with uncomplicated essential hypertension. After a 2-week placebo period without antihypertensive medication, patients were admitted to the hospital overnight on two occasions 3 weeks apart. On each occasion, they received two doses of either placebo or ridogrel (300 mg) 12 hours apart according to a double-blind crossover protocol. Renal and systemic thromboxane A2 and prostacyclin biosynthesis were investigated by measuring urinary excretion of thromboxane B2, 6-oxo-prostaglandin F1 alpha, and their respective 2,3-dinor metabolites using gas chromatography/mass spectrometry. Responses of platelets to a thromboxane A2 mimetic and to adenosine diphosphate were studied turbidometrically. Blood pressure was measured automatically at 20-minute intervals. Ridogrel reduced excretion of 2,3-dinor-thromboxane B2 and thromboxane B2 compared with placebo (21 +/- 6 versus 279 +/- 28 and 14 +/- 4 versus 39 +/- 9 ng/g creatinine, respectively; P < .0001 and P < .05). Excretion of 2,3-dinor-6-oxoprostaglandin F1 alpha and 6-oxoprostaglandin F1 alpha was increased by ridogrel compared with placebo (184 +/- 20 versus 146 +/- 11 and 86 +/- 9 versus 58 +/- 6 ng/g creatinine, respectively; P < .05). Ridogrel selectively antagonized platelet aggregation to the thromboxane mimetic (P < .0001). Blood pressure did not differ significantly between ridogrel and placebo treatment periods. Thus, in patients with essential hypertension, acute administration of ridogrel reduces renal and extrarenal thromboxane A2 biosynthesis, increases renal and extrarenal prostacyclin biosynthesis, inhibits thromboxane receptor-activated platelet aggregation, but has no effect on systemic arterial pressure.

Adult↗
PubMed1991

Neural repair and glial proliferation: parallels with gliogenesis in insects.

There is a growing recognition, stemming from work with both vertebrates and invertebrates, that the capacity for neuronal regeneration is critically dependent on the local microenvironment. That environment is largely created by the non-neuronal elements of the nervous system, the neuroglia. Therefore an understanding of how glial cells respond to injury is crucial to understanding neuronal regeneration. Here we examine the process of repair in a relatively simple nervous system, that of the insect, in which it is possible to define precisely the cellular events of the repair process. This repair is rapid and well organised; it involves the recruitment of blood cells, the division of endogenous glial elements and, possibly, migration from pre-existing glial pools in adjacent ganglia. There are clear parallels between the events of repair and those of normal glial development. It seems likely that the ability of the insect central nervous system to repair resides in the retention of developmental capacities throughout its life and that damage results in the activation of this potential.

Animals↗
PubMed1991

Effects of CO2 laser beam on cortical bone.

Sixteen bone blocks from two freshly amputated legs were used to study the effect of CO2 laser on cortical bone. They were divided into two groups. In Group I, the blocks were treated with CO2 laser using 1 mm spot (focused mode). In Group II, they were treated with CO2 laser using 3 mm spot (defocused mode). Two other variables were investigated: the power and time of exposure. Three histologic zones were observed: a superficial zone with black particle deposits (carbonization), an intermediate zone with fibrillations and enlarged empty lacunae, and a deep zone with normal appearing bone. The bony changes in the first two zones combined were superficial in all specimens and did not exceed 200 microns. Increased energy, a focused beam, and time of exposure were all associated with increased matrix changes. CO2 laser can be applied to cortical bone in vitro with minimal residual thermal damage.

Bone and Bones↗
PubMed1991

A comparison of the pharmacokinetics of nisoldipine in elderly and young subjects.

Nine young and 12 elderly healthy volunteers received nisoldipine 10 mg once a day for 7 days. Plasma nisoldipine concentrations were measured on Day 1 and on Day 7. Higher plasma drug concentrations were observed in the elderly group than in the young group with the values for AUC being approximately doubled in the elderly group. There was no evidence of significant accumulation in either age group.

Adult↗
PubMed1991

The influence of a calorie supplement on the consumption of the meal, ready-to-eat in a cold environment.

There is a dichotomy between calories issued to soldiers in their daily field rations and the amounts actually consumed. Soldiers frequently consume insufficient calories to maintain body weight. A supplemental pack (740 kcal) was developed, to increase field calorie consumption, and tested with the old and new versions of the Meal, Ready-to-Eat on a 10-day field study in Alaska. Initial and final measurements included body weights, heights, blood, and urine parameters. Daily measurements included the collection of urine samples and completion of a dietary intake log. Energy intakes of the supplemented groups were 4%-11% higher (p less than 0.05) although the calorie intakes were still below the recommended 4,500 kcal/day for cold weather operations. Mean body weight loss ranged from 3.0 lb (1.7%) to 4.8 lb (2.8%). Two groups of the four groups became hypohydrated by day 3, due to low water intake, and only improved after direct intervention to increase drinking. Water and food intakes were strongly correlated (p less than 0.05). Results confirm the success of the supplemental pack as a means of increasing food intake and underscore the importance of water discipline in a cold environment.

Alaska↗
PubMed1990

Conservation of antigen 3G6: a crystalline cone constituent in the compound eye of arthropods.

A monoclonal antibody (MAb), 3G6, highly selective for neuropil glia in the CNS of the house cricket Acheta domesticus, also demonstrates remarkable selectivity for the nonneuronal crystalline cone cells of the compound eye. MAb 3G6 labels cone cells in eucone eyes throughout Insecta, from ancestral forms such as the bristle tail to the more recent honeybee; eucone structures are also recognized in Crustacea. Analogous nonneural structures found in pseudocone or acone eyes also express detectable 3G6 immunoreactivity. Immunoblot analysis demonstrates that MAb 3G6 binds to similar Mr85 kDa glycoproteins in the cricket CNS and retina, corresponding to the glial and crystalline cone forms of the antigen. Further, polypeptides of similar relative mass are also recognized in the eucone eye of the butterfly Pieris and the pseudocone eye of the fly Calliphora. The properties and function of glycoprotein 3G6 in the CNS and retina are yet to be explored. However, the finding that a unique antigen is highly conserved within the crystalline cone or analogous regions of the retina throughout the Arthropoda lends support at the molecular level to the notion that the arthropod compound eye has a monophyletic origin.

Animals↗
PubMed1990

The effect of appendage and scale loss on instar duration in adult firebrats, Thermobia domestica (Thysanura).

The loss of appendages immediately following a moult shortens the subsequent intermoult interval in adult Thermobia domestica. The loss of increasing numbers of appendages accelerates the ensuing moult incrementally. Leg amputation at sites distal to the trochanter-femoral autotomy plane has comparable effects in accelerating the moult. Functional legs regenerated at the first moult following amputation are at least 80% of normal length, while abdominal cerci are regenerated at a slower pace, attaining about 20% of normal length at the first post-operative moult. Scale loss also causes an acceleration of the following moult. It is proposed that changes in diffuse sensory input, rather than specific proprioceptive feedback, mediate the acceleration of the moult cycle.

Animals↗