PubMed Health⌕ Search

Biomedical subjects

W D Davidson

Publications and source records attributed to W D Davidson.

At least 19 recordsLinked to original sources
PubMed1991

Dimethyl sulfoxide enhances hexose monophosphate shunt activity in cultured glomerular mesangial cells, leukocytes and erythrocytes.

The effect of dimethyl sulfoxide (DMSO) on the rate of glucose oxidation by cultured rat glomerular mesangial cells, human erythrocytes and peritoneal exudate cells was studied. Mesangial cells, erythrocytes and peritoneal exudate cells incubated with DMSO showed enhancement of 14CO2 production from D-[1-14C] glucose but not from D-[6-14C] glucose. The concentration of DMSO required to stimulate respiratory burst activity was lowest for erythrocytes and highest for peritoneal exudate cells. Studies utilizing tritiated deoxyglucose revealed that the increased glucose oxidation associated with DMSO exposure was not due to increased transmembrane glucose movement at low concentrations of DMSO, and only partially responsible at high concentrations of DMSO. This study documents the ability of DMSO to specifically enhance the activity of the hexose monophosphate shunt pathway in all cells studied. The precise mechanism whereby DMSO stimulates shunt activity remains unknown.

Animals↗
PubMed1987

Evaluation of isradipine (PN 200-110) in mild to moderate hypertension.

The efficacy and safety of isradipine (PN 200-110), a new dihydropyridine calcium antagonist, was evaluated in 87 hypertensive patients in a placebo-controlled, double-blind, randomized multicenter trial. After a 3-week single-blind washout phase, isradipine (or matching placebo) was administered for 4 weeks, beginning at 2.5 mg b.i.d. with increments of 2.5 mg b.i.d. at weekly intervals if supine diastolic blood pressure remained greater than or equal to 90 mm Hg. At the end of 1 week average supine blood pressure in the isradipine group (n = 45) fell from a baseline of 156 +/- 13/104 +/- 4 mm Hg to 146 +/- 14/97 +/- 7 mm Hg. By week 4 blood pressure was reduced by 19/14 mm Hg compared with 4/5 mm Hg in the placebo group (P less than 0.001 between groups). Supine and standing pulse rates were slightly increased initially with isradipine therapy but returned to baseline with increasing isradipine doses. Blood pressure responses at week 4 were good or excellent (supine diastolic less than or equal to 90 mm Hg or greater than or equal to 10 mm Hg decrease from baseline) in 87% of isradipine-treated patients and in 26% of placebo-treated patients. Headache, edema, abdominal discomfort, and constipation occurred slightly more frequently in isradipine-treated patients than in placebo-treated control subjects. The results indicate that isradipine, administered as monotherapy in doses of 2.5 to 10 mg b.i.d., is safe and effective in patients with mild to moderate essential hypertension.

Adult↗
PubMed1987

Combined otolaryngological and neurosurgical approach in treating sinus fractures.

Frontal sinus injury in patients with closed head trauma is significant. Fractures of the anterior and posterior table as well as injury to the nasofrontal duct system requiring exploration, and often times obliteration of the frontal sinus, are not uncommon. Some patients present with frontal sinus damage along with intracranial pathology that requires craniotomy for treatment of the intracranial problem. In these patients, the neurosurgeon typically performs a bifrontal scalp flap to expose the cranium. A bone flap that transects the superior margin of the frontal sinus is then elevated and removed. This allows direct visualization of the anterior and posterior sinus walls and both nasofrontal ducts, subsequently facilitating reduction of fractures, debridement, and obliteration or ablation, if necessary, without creating another bone flap. The surgeon gets an overall picture of the sinus without the added trauma associated with the creation of an osteoplastic flap.

Adult↗
PubMed1986

Relationship between 201Tl uptake and oxidative metabolism in cultured myocardial cells.

The uptake of thallium-201 (201Tl) by myocardial cells in cultures was assessed in the presence of 10(-3) M potassium cyanide (KCN), an inhibitor of mitochondrial respiration, and 10(-4) M dinitrophenol (DNP), an uncoupler of oxidative phosphorylation. The cultures were incubated with 14C-glucose or 14C-octanoate, allowing the measurement of the oxidative metabolism and beta-oxidation from the production of 14CO2. The results demonstrated a moderate decrease in the ratio between the intra/extracellular concentration of 201Tl (Tl i/e) in the presence of KCN (28.9 +/- 8.1 versus 35.6 +/- 9.7 in the controls, n.s.) and no change with DNP (37.6 +/- 9.7). Glycolysis and fatty acid oxidation were lowered with KCN (-28 +/- 15 and -45 +/- 22% respectively, p less than 0.05 in both cases) and were non significantly increased with DNP (+37 +/- 23 and +10 +/- 52% respectively). These results show that 201Tl intracellular uptake is not related directly, but is not totally independent of glycolysis and fatty acid oxidation.

2,4-Dinitrophenol↗
PubMed1985

Effects of grisorixin on the distribution of thallium-201 and on the oxidative metabolism in cultured myocardial cells.

Previous experiments in the dog and guinea-pig have shown that grisorixin, a monocarboxylic ionophore, can significantly increase the coronary blood flow and the myocardial uptake of 201Tl, as well as have a stimulant effect on the heart. In this study, cultures of myocardial cells were used in order to isolate the cells from the vascular and extracardiac influences so that any ionophorous effect on 201Tl could be evidenced. The effects of grisorixin on the oxidative metabolism were simultaneously studied. The technique described by Harary was used to prepare the cultures. The activity of the 14CCO2 produced by oxidation of [14C]glucose and [14C]octanoate added to the medium of culture and the intra/extracellular ratio of 201Tl concentrations (Tl i/e) were measured. In the controls (n = 8), the Tl i/e was 40 +/- 10 while it was 17 +/- 6 (p less than 0.05) in the cells that received 201Tl and grisorixin at the same time (n = 4), and 19 +/- 5 (p less than 0.05) in the flasks where 201Tl was injected after grisorixin (n = 7). A significant decrease of the [14C]octanoate oxidation was found in the flasks treated with grisorixin (n = 4, -50 +/- 16%, p less than 0.01) while the [14C]glucose oxidation was not significantly lowered (n = 3; -11 +/- 12%). The conclusion is that grisorixin decreases both the intracellular concentration of 201Tl and the fatty-acids oxidation in cultured myocardial cells. The beneficial effects previously observed in vivo were probably the consequence of the strong coronary dilatation and of an indirect stimulation.

Animals↗
PubMed1984

Teaching dialysis kinetics with a minicomputer.

The quantitative aspects of dialysis kinetics are poorly understood by the majority of nephrology fellows in training. For this reason, we have developed three teaching programs for use on the Apple II computer. The programs, based on the dialysis equations of Gotch et al. [1] and Gotch [2], allow the student to alter each of the dialysis variables independently, and to graphically display the resulting dialysis curves, so that the effects of changing variables can be visually compared. The three teaching programs describe intradialysis kinetics, dialysis kinetics during a single intradialytic and interdialytic period, and dialysis kinetics during a 2-week interval.

Computer-Assisted Instruction↗
PubMed1984

Therapeutic percutaneous renal artery occlusion with a detachable balloon.

Bilateral nephrectomy is sometimes required for the control of severe hypertension or nephrotic syndrome. Surgical intervention in a patient with uncontrollable hypertension or the malnutrition and anasarca of nephrotic syndrome is associated with increased risk for the development of operative complications. We report 2 hemodialysis patients, 1 with uncontrollable hypertension and 1 with nephrotic syndrome, who were successfully treated with percutaneous renal infarction. Inflatable and detachable balloons were placed in each renal artery by percutaneous arterial catheterization. Neither patient experienced any significant complication from the procedure.

Adult↗
PubMed1983

Impaired pentose phosphate shunt function in sickle cell disease: a potential mechanism for increased Heinz body formation and membrane lipid peroxidation.

The red cells' antioxidant defense mechanisms were compared between individuals with sickle cell disease and those with hemolytic anemia and reticulocytosis. In sickle cell disease, there was a significant increase in incubated Heinz body formation (p less than .001), a decrease in reduced glutathione concentration (p less than .01), an increase in glucose-6-phosphate dehydrogenase activity (p less than .01), and a decrease in glutathione reductase activity (p less than .005). The patients with sickle cell disease hd an absolute increase in the activity of the pentose shunt in the intact red cell after methylene blue stimulation (p less than .05) and in red cell hemolysates (p less than .0250. Heinz body formation (r = .75) and pentose shunt activity in red cell hemolysates (r = .83) were strongly related to the degree of reticulocytosis. Although there was a correlation between the pentose shunt activity in the stimulated red cell and in red cell hemolysates for the patients with hemolytic anemia (r = .58), stimulated shunt activity did not increase as the hemolysate shunt activity increased for the patients with sickle cell disease. There were very strong relationships between the ATP concentration and the reticulocyte count (r = .80) and the hemolysate pentose shunt activity (r = .77) in sickle cel disease. These data suggest that in spite of an absolute increase in stimulated pentose shunt activity, there Is a relative suppression of stimulated shunt activity in the youngest sickle erythrocytes. This may be related, in part, to the inhibitory effects of high concentrations of ATP on the activity of glucose-6-phosphate dehydrogenase.

2,3-Diphosphoglycerate↗
PubMed1982

Pathogenesis of dialysis-induced hypoxemia.

Patients undergoing hemodialysis with acetate-containing dialysis solutions develop hypoxemia. To determine the cause of the hypoxemia, we studied and compared the ventilatory, gas-exchange and blood-gas responses in chronic renal failure patients undergoing hemodialysis with acetate and bicarbonate dialysis solutions. Seven stable chronic dialysis patients were dialyzed against acetate and bicarbonate solutions in a random order. Dialysis was carried out using a 1.5 m2 hollow fiber dialyzer at a blood flow rate of 200 ml/min and a dialysate flow rate of 500 ml/min. During acetate dialysis, PaO2 fell within 15 minutes from a mean control predialysis concentration of 84 = 6 (SEM) mmHg to a mean of 70 +/- 7.5 mmHg (P less than 0.05), and remained low throughout the study. PaO2 did not change significantly during bicarbonate dialysis. Total ventilation fell from a predialysis level of 7.2 +/- 0.7 L/min to 5.7 +/- 0.6 L/min within 15 minutes (P less than 0.05). PaCO2 was not significantly changed from predialysis levels with either acetate or bicarbonate dialysis. Measurement of blood concentration of CO2 and bicarbonate across the dialyzer indicated that the total CO2 loss (as CO2 and bicarbonate) through the dialyzer was 3 millimoles per minute or the equivalent of approximately 60 ml of CO2 per minute, i.e., about one third of the patient's metabolic production of CO2.

Acetates↗
PubMed1981

Instantaneous and continuous measurement of 14C-labeled substrate oxidation to 14CO2 by minute tissue specimens: an ionization chamber method.

The vibrating reed electrometer and ionization chamber have been adapted for the instantaneous and continuous measurement of 14C-labeled substrate oxidation to 14CO2 by minute quantities of isolated tissues. This modified technique, utilizing a "closed" circulation incubation system, is 10-50 times as sensitive as the previously described "open" circulation techniques. Substrate oxidation curves are described for human erythrocytes and polymorphonuclear leucocytes, canine parietal cells and isolated segments of the rat nephron. This apparatus should prove to be a useful tool for metabolic studies of small quantities of isolated tissue.

Animals↗
PubMed1981

Substrate oxidation by isolated single nephron segments of the rat.

Substrate oxidation was assessed by measuring 14CO2 production from 14C-labeled substrates in proximal convoluted tubules (PCT), medullary (MTAL), and cortical (CTAL) thick ascending limb of Henle, nephron segments rich in mitochondria and characterized by active solute transport. PCT, MTAL, and CTAL were dissected from the outer cortex, outer medulla, and the medullary rays of the cortex, respectively, of collagenase-treated rat kidney slices. Tubules were incubated at 37 degrees C in 150 microliters of Krebs-Ringer-bicarbonate buffer (pH, 7.4) with 14C-labeled substrate. 14CO2 production was linear up to 4 and 2 hours in PCT and MTAL, respectively. Freeze-thawing of the tubules markedly decreased 14CO2 production, and the addition of cyanide completely abolished it. The PCT demonstrated marked 14CO2 production from labeled succinate, 2-oxoglutarate, glutamate, glutamine, and malate (approximately 10 to 45 pmoles/mm/hr) and moderate 14CO/ production from citrate (approximately 3 pmoles/ml/hr). Little 14CO2 was released from labeled glucose and lactate in PCT. These results are consistent with the existence of gluconeogenesis in this nephron segment. By contrast, MTAL and CTAL oxidized glucose, 2-oxoglutarate, lactate, glutamate, and glutamine, but not malate, succinate, and citrate. The pentose shunt pathway accounted for approximately half of the 14CO2 produced from 1-14C glucose in MTAL and CTAL. Palmitate oxidation occurred in MTAL and CTAL but minimally in PCT. The results demonstrate a distinct pattern of substrate oxidation in PCT, MTAL, and CTAL where oxidative metabolism is critical to support active solute transport.

Animals↗
PubMed1981

Hexose monophosphate shunt metabolism in sheep: comparison of fetal, newborn and adult erythrocytes.

Glucose utilization through the hexose monophosphate shunt was measured in erythrocytes from fetal sheep, newborn lambs and adult pregnant sheep. Fetal erythrocytes demonstrate dramatically increased glucose oxidation in the presence of the oxidant new methylene blue. This response declines by birth and thereafter until adult sheep erythrocytes show no response. No stimulation was observed in adult sheep red cells under a number of conditions, although when adult sheep red cells were separated according to cell age, young cells were found to respond greatly to new methylene blue. When the rate of glucose oxidation after new methylene blue stimulation is correlated with in vitro glucose-6-phosphate dehydrogenase activity, a highly significant relationship is seen. This suggests that developmental changes in glucose oxidation by sheep red cells may be due to similar changes in glucose-6-phosphate dehydrogenase activity. The relationship also suggests that mature adult erythrocytes may be unable to respond to oxidants because of their low glucose-6-phosphate dehydrogenase activity.

Animals↗
PubMed1980

Effect of uremia on incorporation of acetate into rat plasma and tissue lipids.

Experimental uremia was induced in rats by means of bilateral nephrectomy or bilateral ureteral ligation. Incorporation of acetate-1-14C into expired 14CO2 and into plasma and tissue lipids was studied immediately after surgery and at 48 hr, when the rats were uremic. In rats studied immediately after surgery, bilateral nephrectomy, but not bilateral ureteral ligation, significantly decreased the conversion of acetate-1-14C into expired 14CO2. In uremic rats at 48 hr, acetate-1-14C metabolism to 14CO2 was not significantly altered in either group. Plasma triglyceride concentrations and 14C-acetate incorporation into triglycerides were increased in the 48-hr uremic groups, but plasma and liver triglyceride specific radioactivities were not significantly altered. Plasma free fatty acid concentrations and incorporation of acetate into free fatty acids were lower in the 48-hr uremic groups than in controls. Plasma cholesterol concentrations and specific radioactivities were increased in these uremic groups, as were liver free cholesterol specific activities. These results suggest that increased triglyceride and cholesterol synthesis from acetate may contribute to the hypertriglyceridemia and hypercholesterolemia observed in uremic rats.

Acetates↗
PubMed1980

Effect of hemodialysis with acetate vs bicarbonate on plasma lipid and lipoprotein levels in uremic patients.

A group of 18 stable hemodialysis patients were dialyzed alternately for 4 week periods against acetate or bicarbonate solutions. Total plasma cholesterol and triglyceride concentrations and the content of these lipids in the VLDL, LDL, and HDL lipoprotein fractions were not significantly different when these dialysis periods were compared. When patients were subgrouped according to whether they were normo or hypertriglyceridemic or whether they had an adequate or deficient lipolytic response to heparin infusion, there were also no differences apparent between the acetate vs. bicarbonate dialysis periods. The data indicates, therefore, that acetate is probably not a contributory factor to the hypertriglyceridemias observed in some chronic hemodialysis patients.

Acetates↗
PubMed1978

Comparison of acetate-1-14C metabolism in uremic and nonuremic dogs.

Acetate-1-14C was infused into six anephric uremic and six anephric nonuremic dogs during a 4-hr hemodialysis against a standard acetate containing (39.5 mM) dialysis solution. Arterial acetate (nonradioactive) levels achieved a steady state by the end of dialysis indicating that the maximum rate of acetate metabolism had not been exceeded. The mean arterial acetate level at the end of dialysis was 2.6 mM in both groups of dogs. Acetate disappearance after the cessation of dialysis followed first order kinetics with a mean half-life of 3.8 +/- 0.5 min in the uremic and 3.7 +/- 0.5 min in the nonuremic dogs. Most of the infused acetate-1-14C was metabolized to 14CO2 within 8 hr after dialysis. An average of 84 and 71% of the infused acetate-1-14C was metabolized to 14CO2 in the uremic and nonuremic dogs, respectively. Small but significant amounts of radioactivity were incorporated into lipids of plasma and other tissues. Incorporation of radioactivity into total lipids of liver, omental fat, and sciatic nerve was significantly greater in the uremic as compared to the nonuremic dogs. Incorporation of radioactivity into total lipids of heart, aorta, and plasma was the same in both groups of dogs.

Acetates↗
PubMed1978

Lipid metabolism in non-uremic and uremic dogs during and after hemodialysis with acetate.

Plasma triglyceride and cholesterol concentrations were elevated in dogs after nephrectomy induced uremia. Plasma triglyceride concentrations remained constant during a 4-hour period of hemodialysis of uremic and non-uremic dogs against an acetate concentration of 39.5 mM (delivering 3 mEq/Kg/hr) plus infusion of 12.5 muCi/Kg/hr of acetate-1-14C, but rose progressively following dialysis. Radioactivities in plasma phospholipids, triglycerides and cholesteryl esters increased during dialysis and continued to rise in the post dialysis period, whereas 14C activity in free fatty acids and free cholesterol increased during dialysis and decreased post-dialysis. Acetate 14-C incorporation into plasma triglycerides was similar in the uremic and non-uremic groups, but incorporation into plasma cholesterol was higher in the uremics. Liver triglyceride concentrations and radioactivities at 12 hours were higher in the uremic dogs. At this time, adipose tissue 14C incorporation was also higher in uremic dogs but no differences were observed in aorta, heart or sciatic nerve incorporation. The results suggest that acetate may contribute to the increased plasma triglyceride concentrations observed following dialysis, and that uremia further accentuates acetate incorporation into plasma cholesterol and liver triglycerides.

Acetates↗