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Biomedical subjects

E Reynolds

Publications and source records attributed to E Reynolds.

At least 19 recordsLinked to original sources
PubMed1998

Vergence control across saccades in dyslexic adults.

Many aspects of vision have been investigated in developmental dyslexia. Some research suggests deficits in vergence control (e.g. Buzzelli, 1991, Optom. Vision Sci. 68, 842-846), although ability to control vergence across saccades has not yet been investigated. We have explored this question indirectly using Enright's (1996 Vision Res. 36, 307-312.) sequential stereopsis task. The task requires observers to set two adjacent targets (whose textures cannot be resolved simultaneously if either is fixated) to appear equi-distant. Enright has argued that sequential stereopsis stereoacuity thresholds offer an indication of vergence control across saccades. We report two experiments using a total of 17 dyslexic and 18 control adults. Performance was measured on a sequential stereopsis task and an ordinary 'simultaneous' stereopsis task. No significant differences between groups were found. However, whereas practice of the sequential task lowered control group thresholds on the simultaneous task, for the dyslexic group it significantly raised thresholds, suggesting that visual fatigue is especially important in investigations of visual functions in dyslexia. Although the small samples used limit conclusions at this stage, the main sequential stereopsis results suggest that, if Enright is correct, dyslexic adults can show normal vergence control across saccades.

Adult↗
PubMed1997

Bone resorption and serum levels of vitamin D metabolites in the hypophosphataemic rat.

The supplementation of a low phosphate diet with vitamin D has been shown to result in an increase in bone resorption in the hypophosphataemic rat. The aim of the present study was to determine if administration of vitamin D to rats fed a vitamin D- and phosphate-depleted diet would result in an increase in the circulatory levels of the active vitamin D metabolite 1,25(OH)2D3 and an associated increase in bone resorption. Three groups of weanling Sprague-Dawley rats were used. The first group consisted of control animals on a normal laboratory stock diet and the second and third groups were experimental animals receiving a vitamin D- and phosphate-deficient diet with the third group receiving vitamin D supplementation. All animals were housed in the dark. After 30 days on the diet the experimental animals received 0.1 mmol NaH2PO4 by intraperitoneal injection. Blood was sampled at zero, 3, 6, 18 and 48 h post-injection and analysed for the vitamin D metabolites 25(OH)D3 and 1,25(OH)2D3, calcium and inorganic phosphate (Pi). The serum analyses revealed that the level of 25(OH)D3 in the hypophosphataemic animals was significantly lower than that of the control animals. However, the 1,25(OH)3D3 level was initially significantly higher, then dropped to the control level at 18 h post-intraperitoneal injection of phosphate. Further, the serum levels of 25(OH)D3 and 1,25(OH)2D3, calcium and Pi in the hypophosphataemic animals supplemented with vitamin D were significantly higher than those of the vitamin D-deficient animals. Also the vitamin D-supplemented animals exhibited significantly greater levels of bone resorption. These results therefore, are consistent with a role of 1,25(OH)2D3 in bone resorption in hypophosphataemic rats.

Analysis of Variance↗
PubMed1996

Hypertension in women and the elderly. Some puzzling and some expected findings of treatment studies.

Almost 65% of the US population over age 60 has hypertension (systolic blood pressure > or = 140 mm Hg or diastolic blood pressure > or = 90 mm Hg), which is strongly related to increased rates of coronary artery disease (CAD), stroke, and death. The need for treatment seems obvious. However, in young and middle-aged women, treatment is not straightforward, and trials have not specifically targeted this group. Data extrapolated from existing studies suggest that treatment of hypertension does not confer the same protection against CAD and stroke in women as it does in men. In fact, a trend toward harm in young and middle-aged white women receiving stepped care for hypertension has been reported. Therefore, for now, treatment of women in this age-group should be conservative; drugs should be prescribed only after a focused trial of lifestyle modification has failed. Until recently, elderly subjects were also excluded from treatment studies, despite the fact that they are at high risk for morbidity and death from hypertension-related diseases. Recent studies have established that treatment of hypertension in the elderly is extremely effective, that elderly women should be treated as aggressively as elderly men, and that low-dose diuretic or beta-blocker therapy should be initiated if lifestyle modifications are not effective.

Adult↗
PubMed1993

ETA and ETB receptors coexist on rabbit pulmonary artery vascular smooth muscle mediating contraction.

The possibility that both ETA and ETB endothelin receptor subtypes could mediate contractile activity in the same tissue was investigated in isolated, endothelium denuded rabbit pulmonary arteries. The ETB selective agonist, sarafotoxin 6c (S6c), produced potent contractile activity, equal to the non-selective ETA and ETB receptor agonist endothelin-1 (ET-1), indicating a contractile role for ETB receptors in this tissue. In addition BQ-123 (10.0 microM), the ETA selective antagonist, was only partially effective in blocking ET-1 induced contractions further indicating a contractile role for ETB receptors. However, the partial blockade by BQ-123 suggested a possible contractile role for ETA receptors. To address this possibility, ETB receptors were desensitized with a 30 minute pretreatment of S6c (0.01 microM). Under these conditions, we were able to demonstrate full ET-1 contractile activity that was now sensitive to blockade by BQ-123. The coexistence of both ETA and ETB receptors was confirmed through receptor binding experiments indicating 40/60 ratio, respectively. We conclude that 1) both ETA and ETB receptors coexist on vascular smooth muscle of rabbit pulmonary artery, 2) activation of either receptors subtype results in contraction, and 3) prolong activation of the ETB receptor subtype produces tachyphylaxis preventing further activation by S6c or ET-1.

Animals↗
PubMed1991

Modulation of Na+/K+ exchange potentiates lipopolysaccharide-induced gene expression in murine peritoneal macrophages.

The role of Na+/K+ exchange in regulating lipopolysaccharide (LPS)-mediated induction of cytokine gene expression has been examined in murine peritoneal macrophages. Depletion of K+ from the culture medium resulted in a three- to five-fold potentiation of tumor necrosis factor-alpha (TNF alpha), KC (gro), and IP-10 mRNA expression in LPS-treated macrophages. The potentiating effect was apparently the result of inhibition of Na+/K+ exchange through the Na+/K(+)-adenosine triphosphatase (ATPase) because ouabain-mediated inhibition of Na+/K(+)-ATPase was also able to potentiate cytokine mRNA expression as much or more than did K+ depletion. The effects of K+ depletion or ouabain treatment were not caused by depolarization of the macrophage membrane because depolarization mediated by elevating extracellular K+ levels was inhibitory to cytokine mRNA expression. Depletion of Na+ by substitution with choline in the culture medium also markedly potentiated LPS-induced gene expression. The Na+/H+ antiporter was not, however, involved in potentiating cytokine expression because treatment of macrophages with amiloride either had no effect on or was inhibitory to the LPS-induced changes in mRNA levels. The potentiation of gene expression was selective and was at least partially the result of increased transcriptional activity of each gene. Whereas Na+ depletion and ouabain both inhibited 86Rb+ uptake by macrophages, treatment with LPS had no effect either on Rb+ uptake or on efflux. Thus altered Na+/K+ exchange is not a component of the primary signalling pathway(s) mediating response to LPS. Nevertheless, modulation of macrophage Na+/K+ exchange by agents encountered during an inflammatory response may be an important determinant of the magnitude and quality of specific gene expression.

Animals↗
PubMed1988

Effects of cholecystokinin and hydrocortisone on DNA and protein synthesis in immature rat pancreas.

To define the developmental pattern of the trophic effects of cholecystokinin octapeptide (CCK-8) and hydrocortisone on immature rat pancreas, we injected newborn rats, rats aged 4, 7, 11, 18, and 25 days and 3 months, and adult rats with CCK (5 and 10 micrograms/kg) in gelatin and hydrocortisone (10 mg/kg) for 3 days. Animals were killed, the pancreata were removed, and the concentrations of DNA and protein were measured and DNA and protein synthesis rates determined by incorporation of [3H]thymidine and [14C]leucine, respectively. These values were compared with those of saline-injected controls. DNA concentration was significantly increased over control at ages 2 days to adult by hydrocortisone and by CCK (10 micrograms/kg) in the adult. Protein concentration was increased on days 3-14 by hydrocortisone. DNA synthesis was increased by CCK and decreased by hydrocortisone at 3 months and adult. Protein synthesis was decreased by hydrocortisone at ages 3-14 days. Thus, each agent has its own developmental pattern with age on the rat pancreas.

Age Factors↗
PubMed1987

Ontogeny of secretory function and cholecystokinin binding capacity in immature rat pancreas.

Isolated acini were prepared from the pancreas of immature rats (age less than 1 hr. - 48 hrs) in order to study the development of the secretory process. The ultrastructural integrity of the acinar cells was maintained after digestion and stimulation with secretagogues. Acini prepared from rats aged 24 - 48 hours responded to both CCK-8 and carbachol with significant increases in amylase release. Although typical biphasic dose response curves were obtained, the curves were shifted to the right by 1 - 2 log units, compared to the responses of adult acini. At ages younger than 24 hours, acini were insensitive to secretagogues but were sensitive to the calcium ionophore A23187. CCK receptors were virtually absent from membranes prepared from newborn pancreases, but binding of CCK, although small, was measurable at 12 hours and slowly increased up to 48 hours. A greater amount of binding was seen at 72 hours, which appeared constant up to 14 days. At 21 days, adult levels of binding were found. These results confirm previous studies that the rat pancreas is insensitive to secretagogues in the first 24 hours of life. After age 24 hours the secretory process is intact but less sensitive to secretory agents than the more mature pancreas. In the case of CCK, this may be due to lesser numbers of CCK receptors and/or affinity of CCK for its receptor.

Age Factors↗
PubMed1987

DNA and protein synthesis in developing rat pancreas.

To define developmental patterns, we determined the rate of protein and DNA synthesis in rat pancreas at birth, 1, 2, 3, 7, 10, 14, 21, 28 days, 2 months, 3 months, and in adults. Fragments of freshly minced pancreas were incubated with [3H]-thymidine and [14C]-leucine and the DNA and protein synthesis rates were measured. We found that DNA content was lowest at birth, rose through day 3, plateaued at about 8 mg/g wet weight through day 14, then slowly decreased to the adult value of about 5 mg/g at 2 months; protein content, although high at birth, decreased rapidly to a value of 80 mg/g at day 3 and slowly rose to the adult value of 160 mg/g; protein synthesis, low at birth, rapidly increased to about five times the adult value by day 3, and remained elevated for the 1st month; DNA synthesis was 15 times the adult rate at birth, increased to 30 times at 3 days of age, then declined slowly in an exponential fashion to the adult value. We conclude that the pancreas at birth is poised biosynthetically to undergo a rapid hyperplastic and hypertrophic response, and this process reaches a maximal rate at about 3 days of age.

Aging↗
PubMed1987

Effect on intracranial pressure of furosemide combined with varying doses and administration rates of mannitol.

The first part of this study investigated the combined use of furosemide and mannitol in the treatment of elevated intracranial pressure (ICP). Two groups of dogs were studied to determine if renal excretion of mannitol was altered in the presence of furosemide. No significant difference in excretion was noted between the two groups. Fifteen animals were used in other studies to identify the most advantageous sequence of administration of furosemide and mannitol. Infusion of mannitol followed by furosemide 15 minutes later resulted in the most profound and sustained ICP reduction. The effect on ICP reduction of varying the mannitol dose was observed in studies using single doses of 0.5 gm/kg, 0.75 gm/kg, and 1 gm/kg. The larger mannitol dose, resulting in a greater blood-brain osmotic gradient, proved to be the most efficacious in ICP reduction. A further 15 animals were used in investigations to determine whether changing the rate of delivery of the most effective mannitol dose (1 gm/kg) influenced resultant ICP reduction. The results indicated that rapid administration (2 ml/kg/min) produced higher peak serum concentrations of mannitol and more profound lowering of ICP than the same dose delivered at slower rates.

Animals↗
PubMed1986

Ophthalmic needles. An engineering analysis.

Mechanical engineering formulas to predict the amount of flex and the bend strength expected for surgical needles are presented. Bend strength measurements were made on ophthalmic needles produced from two different materials and several shapes. The agreement between the data derived by measurement and the theoretical predictions is excellent. The force required to penetrate porcine corneas is also measured. A needle strength/penetration force ratio was developed from the data presented in this paper. This ratio reveals that needles produced from smaller wire sizes, if optimally designed, can perform as well as existing larger needles.

Animals↗
PubMed1985

Choroid plexus Na+/K+-activated adenosine triphosphatase and cerebrospinal fluid formation.

The quantitative relationship between intraventricular fluid formation and choroid plexus Na+/K+-activated (transport) adenosine triphosphatase (ATPase) was studied in rabbit and dog by perfusing the ventricular system with a solution containing ouabain (10(-8) to 10(-3) M). The effect of ouabain in the same range of concentrations on ATPase activity was also measured by the release of inorganic orthophosphate from in vitro choroid plexus tissue. Normally, about 20 to 25% of ATPase activity in lateral ventricle plexus is Na+/K+-activated, and this component is almost completely inhibited by ouabain in a concentration of 10(-4) M. At this concentration, the rate of intraventricular cerebrospinal fluid (CSF) formation is decreased some 70 to 80% in dog and rabbit. The results of this study suggest that a portion of the intraventricular fluid formation is insensitive to cardiac glycoside inhibition and that either there are two different mechanisms responsible for choroid plexus fluid formation or there is a significant non-ATPase dependent extrachoroidal source of CSF.

Animals↗