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Biomedical subjects

A Quan

Publications and source records attributed to A Quan.

At least 37 records · Page 2Linked to original sources
PubMed1998

Bone mineral density in children with myelomeningocele.

BACKGROUND: Difficulties with ambulation in patients with myelomeningocele often lead to physical inactivity, osteoporosis, and subsequent development of pathologic fractures. OBJECTIVE: The purpose of this study was to examine bone mineral density and biochemical markers of bone metabolism in patients with myelomeningocele. DESIGN AND METHODS: A total of 35 patients between 6 and 19 years of age with myelomeningocele (ambulatory and nonambulatory) were randomly chosen at the Texas Scottish Rite Hospital for Children. We measured bone mineral density of the distal radius in these patients using single photon absorptiometry and measured the biochemical markers of bone metabolism including parathyroid hormone, 1,25 vitamin D, osteocalcin, urinary pyridinolines/deoxypyridinolines, and urinary calcium excretion. RESULTS: Bone mineral density of the distal radius in the patients with myelomeningocele was approximately 1 to 2 standard deviation units below the mean of the normal population. There were no significant differences between ambulators and nonambulators. However, bone mineral density of the 8 patients who suffered multiple fractures (19) was significantly lower than that for those remaining patients without fractures. Elevated urinary pyridinoline levels, which indicate elevated bone reabsorption, were found more frequently in both non- and limited ambulators than in full-time ambulators. Urinary calcium excretion also was greater than twofold higher in nonambulatory patients versus ambulatory patients. There were no other differences in the biochemical markers of bone metabolism (osteocalcin, parathyroid hormone, 1,25 vitamin D, and urinary deoxypyridinolines) between ambulators and nonambulators. Bone mineral density rises in normal growing children 6 to 19 years of age. When the boys and girls were considered separately, bone mineral density rises with age in boys, but not in girls. CONCLUSION: Patients with myelomeningocele have decreased bone mineral density and are at risk of suffering pathologic bone fractures. The measurement of bone mineral density may help to identify those patients at greatest risk of suffering multiple fractures. The urinary calcium excretion of nonambulators was higher than that of ambulators and likely contributes to their decreased bone mineral density. Bone mineral density increases with age in boys, but not in girls.

Adolescent↗
PubMed1997

Endothelial dysfunction exacerbates the impairment of relaxation by lysophosphatidylcholine in porcine coronary artery.

1. Current evidence suggests that lysophosphatidylcholine (LPC), a component found in oxidized low-density lipoprotein (Ox-LDL), inhibits endothelium-dependent relaxation (EDR) mediated by endothelium-derived relaxing factor (EDRF) and endothelium-derived hyperpolarizing factor (EDHF). An objective of the present study was to characterize the roles of the different elements of EDR in LPC-induced impairment within the porcine coronary artery. Concomitantly, we sought to determine whether impairment of one component of EDR would increase the sensitivity of the endothelium to LPC. 2. Bradykinin (0.1 nmol/L -0.3 mumol/L) relaxed U46,619 (30 nmol/L)-precontracted porcine coronary artery rings in a concentration-dependent manner. A reduction in the bradykinin-elicited response was observed in NG-nitro-L-arginine methyl ester (L-NAME; 300 mumol/L)- and ouabain (50 mumol/L)-treated rings. Pretreatment with LPC (20 mumol/L), which on its own had no effect on normal endothelial relaxation, resulted in further inhibition of EDRF- and EDHF-induced relaxations. 3. Our results demonstrate that EDRF and EDHF are the primary mediators of EDR in the porcine coronary artery. Our data also show that while a low concentration of LPC (20 mumol/L) does not impair EDR, it can evoke vascular dysfunction following blockade of either the effects of EDRF or EDHF. Therefore, these data suggest that the partially damaged vascular endothelium could be more sensitive to threshold levels of this atherogenic phospholipid.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1997

Serum creatinine is a poor marker of glomerular filtration rate in patients with spina bifida.

Serum creatinine is used to estimate the glomerular filtration rate (GFR). The serum creatinine, however, may not accurately reflect the GFR in spina bifida patients, who often have decreased overall muscle mass resulting from spinal cord abnormalities. The relationship between the serum creatinine and GFR (obtained by [(125)I]iothalamate clearance) was examined in a population of spina bifida patients. Age-matched patients without spina bifida were used as controls. Results demonstrate that, for serum creatinines above 0.5 mg/dL, serum creatinine is a very poor predictor of GFR. Two patients with serum creatinines of 2.2 mg/dL are near end-stage renal disease with GFRs of 12.5 and 13 mL/minute per 1.73m2 and two patients were initiated on dialysis at the conclusion of the study. It is concluded that obtaining a GFR from a clearance study and not serum creatinine is the only reliable method to assess renal function in spina bifida patients once the serum creatinine is greater than 0.5 mg/dL.

Adolescent↗
PubMed1997

Effect of luminal angiotensin II on rabbit proximal convoluted tubule bicarbonate absorption.

The present in vitro microperfusion study examined the effect of luminal angiotensin II on proximal convoluted tubule (PCT) volume absorption and bicarbonate transport. Neither 10(-11) M, 10(-10) M, nor 2 x 10(-8) M luminal angiotensin II significantly affected PCT transport. When tubules were first perfused with enalaprilat to inhibit endogenous angiotensin II production, addition of 10(-10) M luminal angiotensin II increased volume absorption (0.72 +/- 0.08 vs. 0.86 +/- 0.07 nl x mm(-1) xmin(-1), P < 0.01) and bicarbonate transport (52.3 +/- 3.7 vs. 67.9 +/- 4.2 pmol x mm(-1) min(-1), P < 0.01). Addition of 10(-6) M losartan, an AT1 inhibitor, to the luminal perfusate inhibited volume absorption (0.95 +/- 0.14 vs. 0.72 +/- 0.11 nl x mm(-1) x min(-1), P < 0.05) and bicarbonate transport (65.0 +/- 7.3 vs. 54.7 +/- 9.2 pmol x mm(-1) x min(-1), P < 0.05). Addition of 10(-4) M luminal PD-123319, an AT2 inhibitor, was without effect. In tubules perfused with 10(-4) M luminal enalaprilat and 10(-4) M luminal PD-123319, addition of 10(-10) M luminal angiotensin II in the experimental period resulted in a stimulation in volume absorption (0.61 +/- 0.08 vs. 0.81 +/- 0.10 nl x mm(-1) x min(-1), P < 0.01) and bicarbonate transport (49.9 +/- 6.3 vs. 77.4 +/- 14.3 pmol x mm(-1) x min(-1), P < 0.01). In tubules perfused with 10(-6) M losartan and 10(-4) M enalaprilat, addition of luminal 10(-10) M angiotensin II resulted in no change in transport. These data are consistent with endogenous angiotensin II affecting PCT bicarbonate transport in vitro via luminal AT1 receptors.

Absorption↗
PubMed1997

Regulation of proximal tubule transport by angiotensin II.

Angiotensin II maintains extracellular volume homeostasis, in part, by regulating proximal tubule transport. Physiological doses of angiotensin II stimulate volume and solute transport in the proximal tubule independent of changes in the glomerular filtration rate. Stimulation of bicarbonate transport primarily occurs via increasing activity of the sodium/hydrogen exchanger and the sodium/bicarbonate cotransporter. The effects of circulating angiotensin II are mediated by angiotensin II receptors on the basolateral membrane of the proximal tubule. Recently, the proximal tubule was found to synthesize and secrete angiotensin II into the lumen. The luminal membrane contains angiotensin II receptors and luminal angiotensin II levels are 100 to 200-fold higher than that found in plasma. Luminal angiotensin II receptor blockade or luminal inhibition of angiotensin II synthesis both significantly diminish proximal tubule transport, consistent with stimulation of proximal tubule transport by endogenously produced and luminally secreted angiotensin II. These data provide evidence for an autocrine/paracrine role for angiotensin II that functions independent of circulating angiotensin II.

Angiotensin II↗
PubMed1996

Effects of heparin on the properties of solubilized and reconstituted rat brain AMPA receptors.

Heparin was found to bind to alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors and to alter their functional properties. AMPA receptors solubilized in 0.4% Triton X-100 bound to a heparin-agarose column and were eluted by 0.4 M NaCl. Soluble heparin inhibited 10 nM [3H]AMPA binding to detergent-solubilized receptors by 75% (IC50 = 10 micrograms/ml), but had little effect on binding to membrane-associated receptors. The inhibition of [3H]AMPA binding to detergent-solubilized receptors was not observed when binding was measured in the presence of 0.4 M NaCl, and no effect of heparin was observed on binding of the AMPA receptor antagonist [3H]6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Scatchard analyses of [3H]AMPA binding to solubilized receptors revealed that the inhibition induced by heparin was caused by a decrease in the apparent affinity of a portion of the total binding sites. Studies on AMPA receptors reconstituted in artificial lipid bilayers indicated that 10 micrograms/ml heparin enhanced cooperativity between channels and prolonged the lifetime of the open channel, but did not affect the amplitude of single channel currents. Thus, heparin may be added to the list of compounds known to modulate AMPA receptor function. These data also raise the possibility that heparin-containing proteoglycans, which are known to be concentrated at synaptic junctions, might be able to bind AMPA receptors and influence their functional characteristics.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1996

Endogenous production of angiotensin II modulates rat proximal tubule transport.

There is evidence that angiotensin II is synthesized by the proximal tubule and secreted into the tubular lumen. This study examined the functional significance of endogenously produced angiotensin II on proximal tubule transport in male Sprague-Dawley rats. Addition of 10(-11), 10(-8), and 10(-6) M angiotensin II to the lumen of proximal convoluted tubules perfused in vivo had no effect on the rate of fluid reabsorption. The absence of an effect of exogenous luminal angiotensin II could be due to its endogenous production and luminal secretion. Luminal 10(-8) M Dup 753 (an angiotensin II receptor antagonist) resulted in a 35% decrease in proximal tubule fluid reabsorption when compared to control (Jv = 1.64 +/- 0.12 nl/mm.min vs. 2.55 +/- 0.32 nl/mm.min, P < 0.05). Similarly, luminal 10(-4) M enalaprilat, an angiotensin converting enzyme inhibitor, decreased fluid reabsorption by 40% (Jv = 1.53 +/- 0.23 nl/mm.min vs. 2.55 +/- 0.32 nl/mm.min, P < 0.05). When 10(-11) or 10(-8) M exogenous angiotensin II was added to enalaprilat (10(-4) M) in the luminal perfusate, fluid reabsorption returned to its baseline rate (Jv = 2.78 +/- 0.35 nl/mm.min). Thus, addition of exogenous angiotensin II stimulates proximal tubule transport when endogenous production is inhibited. These experiments show that endogenously produced angiotensin II modulates fluid transport in the proximal tubule independent of systemic angiotensin II.

Angiotensin II↗
PubMed1996

Ultraviolet radiation, thiol reagents, and solubilization enhance AMPA receptor binding affinity via a common mechanism.

The binding properties of membrane-bound or solubilized AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid)-type glutamate receptors from rat brain were tested following exposure to ultraviolet (UV) radiation or incubation with the thiol reagent p-chloromercuriphenyl-sulfonic acid (PCMBS). Brief exposure to UV radiation (254 nm) increased [3H]AMPA binding to brain membranes, while binding to soluble fractions decreased. The increase in brain membrane binding was caused by an apparent interconversion of low-affinity [3H]AMPA binding sites into a higher-affinity state. Incubation with PCMBS caused a significant increase in [3H]AMPA binding to brain membranes but had no significant effect on [3H]AMPA binding to solubilized receptors. There was an interaction between the PCMBS and UV effects in the brain membranes such that prior exposure to one of the treatments reduced the relative magnitude of the other's effects. The present results suggest that ultraviolet radiation, PCMBS and solubilization all increase AMPA receptor binding affinity via a common mechanism.

4-Chloromercuribenzenesulfonate↗
PubMed1996

Protein losses in children on continuous cycler peritoneal dialysis.

Peritoneal dialysis can result in significant protein losses through the dialysate effluent. Although protein loss in chronic ambulatory peritoneal dialysis has been examined, it has not been extensively studied in patients on continuous cycler peritoneal dialysis. Such losses can contribute to protein calorie malnutrition, especially in infants and children, many of whom are on continuous cycler peritoneal dialysis. We measured protein loss during continuous cycler peritoneal dialysis in patients ranging in age from 2 months to 18 years. There was an inverse correlation between body surface area and peritoneal protein loss, expressed both as milligrams of protein per kilogram body weight per day (P < 0.0001) and as milligrams of protein per meter square body surface area per day (P < 0.05). Peritoneal fluid protein losses in patients greater than 50 kg were similar to those previously reported in adults treated with chronic ambulatory peritoneal dialysis. In contrast, infants had nearly twofold greater peritoneal protein losses per meter square body surface area than older children weighing more than 50 kg. Such protein losses in infants impair normal growth and may contribute to permanent loss of growth potential. Infants on peritoneal dialysis require early and aggressive nutritional supplementation with higher caloric and protein intake to compensate for such dialysate protein losses and maximize growth.

Adolescent↗
PubMed1996

Effects of a centrally active benzoylpyrrolidine drug on AMPA receptor kinetics.

A newly developed benzoylpyrrolidine drug (BDP-20) that increases the size of fast, excitatory synaptic responses was examined for its effects on the kinetic properties of alpha-amino-3-hydroxy-5-methyl-4-isoxalepropionic acid (AMPA)-type glutamate receptors. When long pulses of glutamate were applied to excised hippocampal patches of the rat, the compound BDP-20 caused an approximately 15-fold reduction in the rate at which responses desensitized and a similar size increase in steady-state currents. In experiments using 1-ms glutamate pulses, BDP-20 prolonged response deactivation by a factor of about four and greatly reduced the depression in the second response when two consecutive glutamate pulses were given. Two types of equilibrium binding assays indicated that BDP-20 causes a measurable increase in the affinity of AMPA receptors; the EC50 values for this effect were similar to those obtained in excised patch studies. The actions of BDP-20 on physiology and ligand binding could be adequately reproduced in a receptor model by slowing the rate of desensitization and increasing the affinity of the sensitized states. The biochemical and physiological effects of this benzoylpyrrolidine compound were qualitatively different from those obtained with cyclothiazide, although both types of drug increased AMPA receptor-mediated synaptic responses. Moreover, interactions between the drugs were at most only partially competitive; AMPA receptors may thus have multiple modulatory sites with distinct drug preferences and different effects on receptor kinetics.

Animals↗
PubMed1996

Renal tubular acidosis and deafness: report of a large family.

The syndrome of distal renal tubular acidosis (dRTA) and sensorineural deafness has been reported in consanguineous families and is believed to be inherited in an autosomal recessive pattern. All affected patients also have nephrocalcinosis. We report here a family with 6 of 12 children affected with this syndrome. The parents are unaffected and are not blood related. This is the largest family described to date with distal renal tubular acidosis and sensorineural deafness.

Acidosis, Renal Tubular↗
PubMed1996

Effect of cyclothiazide on binding properties of AMPA-type glutamate receptors: lack of competition between cyclothiazide and GYKI 52466.

The effects of cyclothiazide on the properties of (R,S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors were studied using equilibrium binding techniques and interactions with other compounds known to modulate the receptors. Cyclothiazide caused a reduction in [3H]AMPA binding in assays carried out in the presence of thiocyanate, a chaotropic ion that markedly increases the affinity of AMPA receptors and accelerates their desensitization. In the absence of thiocyanate, however, cyclothiazide had no reliable effect on the binding of [3H]AMPA or on the affinity for this agonist assessed from the displacement of [3H]CNQX. The interaction of cyclothiazide with the receptor appears not to be changed by the presence of thiocyanate. Analysis of the results with a kinetic model of the AMPA receptor suggests that cyclothiazide does not block receptor desensitization by making the desensitized state inaccessible but rather by stabilizing the active state, i.e., by increasing the affinity of the latter to a point where it becomes energetically more favorable than the desensitized state. GYKI 52466, an atypical benzodiazepine that blocks AMPA receptor-gated currents, did not reverse the changes in binding affinity produced by cyclothiazide in the presence of thiocyanate. Physiological experiments conducted in excised patches collected from hippocampal pyramidal cells indicated that thiocyanate does not block access of GYKI 52466 to AMPA receptors. These results point to the conclusion that cyclothiazide acts at a site on the AMPA receptor different from that for GYKI 52466.

Animals↗
PubMed1995

Resolution of hepatitis B virus-related membranoproliferative glomerulonephritis after orthotopic liver transplantation.

The most well-described renal disease associated with hepatitis B virus (HBV) infection is membranous glomerulonephritis; membranoproliferative glomerulonephritis is described much less frequently. The course of HBV-associated renal disease after liver transplantation has not been described to date. We present a 15-year-old girl with HBV-associated membranoproliferative glomerulonephritis and end-stage liver disease, in whom, after cadaver liver transplantation, clinical and histological resolution of renal disease was observed. Resolution was associated with diminution of circulating HBV surface antigen levels.

Adolescent↗
PubMed1993

Cyclothiazide decreases [3H]AMPA binding to rat brain membranes: evidence that AMPA receptor desensitization increases agonist affinity.

The effects of cyclothiazide, a drug which blocks AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor desensitization, were tested on binding of [3H]AMPA to rat brain membranes. Cyclothiazide reduced [3H]AMPA binding by lowering the apparent affinity of the AMPA receptor. The magnitude of the decrease was temperature dependent and greater for membrane-bound than for solubilized receptors. These data provide evidence that desensitization increases the affinity of the AMPA receptor for agonists and indicate that a significant percentage of AMPA receptors in conventional equilibrium binding assays are in a desensitized state.

Animals↗
PubMed1983

The use of thioesterase II as a rat mammary epithelial cell-specific marker.

The avidin-biotin-peroxidase complex immunoperoxidase technique was employed to determine the intercellular distribution of thioesterase II in rat mammary glands. This enzyme is responsible for shifting the product specificity of the fatty-acid synthetase enzyme complex from long to medium chain fatty acids. Thioesterase II was found exclusively in the cells lining the lumen of the ductal and alveolar structures in glands from mature virgin (150 days old) and pregnant rats. The ductal cell staining intensity was considerably less than that of the alveolar cells in the mature virgin rat glands. No immunoreactive thioesterase II was found in the stromal, adipose, vascular, or myoepithelial components of the gland in the developmental stages examined. In the glands from immature virgin rats (40-45 days old) thioesterase II was again found only in the epithelial cells lining the lumen of the ductal and end-bud structures although this layer was usually more than one cell thick. Quantitative determination of thioesterase II activity in cytosol preparations revealed similar levels in mammary fragments from enzymatically-dissociated glands obtained from mature virgins and in end buds derived from immature virgins, but somewhat higher levels in mammary structures derived from late-pregnant animals. These immunohistological and biochemical results demonstrate thioesterase II's usefulness as a mammary epithelial cell-specific marker.

Animals↗
PubMed1977

Laparoscopic sterilization after "spontaneous" abortion.

One hundred eighty-nine patients were evaluated to assess the safety of laparoscopic sterilization after completion of a "spontaneous" abortion by curettage. Some of the "spontaneous" abortions had probably been illegally initiated outside the hospital and were septic. The laparoscopic sterilization procedures used tubal rings to achieve tubal occlusion. They were performed 4 to 48 hours after completion of the abortion. Patients were discharged from the hospital on the day the procedure was performed. Surgical difficulties and complications associated with the laparoscopy were infrequent. Undergoing a curettage prior to sterilization with tubal rings by laparoscopy did not appear to result in increased rates of complications.

Abortion, Septic↗
PubMed1977

Homogeneity of protein serotype antigens in Neisseria meningitidis group A.

Serotype antigens (STA), which have been shown to be constituents of outer-membrane protein, were extracted from group A meningococci with 0.2 M LiCl and pelleted by centrifugation at 150,000 X g. The STAs from 100 group A strains, which had been isolated from cases and carriers in various geographical locations, were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Every STA produced three major protein bands with molecular weights of approximately 35,000, 39,000, and 45,000, respectively. This SDS-PAGE pattern is clearly distinct from that produced by the serotype of group B and C meningococci most commonly isolated from cases (group B type 2 and group C type 2). The group A STAs were also indistinguishable by immunodiffusion. However, differences in bactericidal reactions were demonstrated, suggesting that there are other antigens that play a role in antibody response.

Antigens, Bacterial↗