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Biomedical subjects

L Boon

Publications and source records attributed to L Boon.

At least 37 records · Page 2Linked to original sources
PubMed1997

Capillary-venous malformation in the labia majora in a 12-year-old girl.

The case of a capillary-venous malformation in the labia majora of a 12-year-old girl is reported. The tumour increased in volume with puberty. The authors present a differential diagnosis between immature haemangioma and vascular malformation. The diagnosis is based on clinical examination, ultrasound, nuclear magnetic resonance, arteriography and gynaecological exploration. This malformation can be excised locally.

Angiography↗
PubMed1997

In situ measurement of glutamate concentrations in the periportal, intermediate, and pericentral zones of rat liver.

We developed a quantitative histochemical assay for measurement of local glutamate concentrations in cryostat sections of rat liver. Deamination of glutamate by glutamate dehydrogenase (GDH) was coupled to the production of formazan and formazan precipitation was used for colorimetric visualization. The method was tested and validated with gelatin model sections with known glutamate concentrations. Calibration graphs showed linear relationships with high correlation coefficients (> 96%) between glutamate concentrations or section thickness and absorbance values. The method was reproducible, with a constant percentage of 60 +/- 5% of glutamate being converted in gelatin model sections containing glutamate concentrations of 2 mM and higher. Glutamate concentrations were estimated in periportal, intermediate, and pericentral zones of liver lobules that contain low, intermediate, and high GDH activity, respectively. In fed adult male rat livers, periportal zones contained the highest concentrations of glutamate (approximately 14 mM) and intermediate and pericentral zones approximately 13 and 9 mM, respectively. On starvation, glutamate concentrations increased only in the small rim of pericentral cells that express glutamine synthetase, to approximately 15 mM. In livers of fetal and newborn rats, glutamate was homogeneously distributed, with a concentration of approximately 5 mM. In suckling rat liver, distribution of glutamate was still homogeneous but the concentration was increased to approximately 8 mM. These glutamate distribution patterns were in agreement with those detected immunohistochemically.

Age Factors↗
PubMed1996

Regulation of glutamate dehydrogenase expression in the developing rat liver: control at different levels in the prenatal period.

To study the regulation of the expression of glutamate dehydrogenase (Glu-DH) in rat liver during development, the Glu-DH mRNA concentration in the liver of rats ranging in age from 14 days prenatal development to 3 months after birth was determined. This concentration increased up to two days before birth, decreased rapidly between two days before and one day after birth and increased again in the second and third postnatal week. The ratio of Glu-DH mRNA/protein decreased more than 10-fold in the prenatal period, whereas it did not change significantly after birth. Thus, whereas the ratio between the Glu-DH monomer protein molecules and Glu-DH mRNA molecules is found to be approximately 1400 at 14 days of prenatal development, it is approximately 1700 four weeks after birth. We argue than an increase in the translational efficiency after birth is the most likely cause of the observed developmental changes in Glu-DH mRNA/protein ratio. Our results suggest that the expression after birth is predominantly regulated at the pretranslational level, whereas the prenatal Glu-DH expression is regulated both at the translational level and at the pretranslational level.

Animals↗
PubMed1996

Response of hepatic amino acid consumption to chronic metabolic acidosis.

In a previous paper, we showed that an inhibition of amino acid transport across the liver plasma membrane is responsible for the decrease in urea synthesis in acute metabolic acidosis. We have now studied the mechanism responsible for the decline in urea synthesis in chronic acidosis. Chronic metabolic acidosis and alkalosis were induced by feeding three groups of rats HCl, NH4Cl, and NaHCO3 (8 mmol/day) for 7 days. Amino acids and NH4+ were measured in portal vein, hepatic vein, and aortic plasma, and arteriovenous differences were calculated. The rates of urinary urea and NH4+ excretion were also determined. Hepatic amino acid consumption was lower in both HCl and NH4Cl acidosis compared with NaHCO3-fed rats. Glutamine release was not different in the three conditions. Because intrahepatic concentrations of amino acids and intracellular protein degradation were similar under these conditions, it can be concluded that at low blood pH amino acid catabolism may be inhibited and might explain the observed decrease in urea excretion in HCl, but not NH4Cl, acidosis; urea excretion was comparable in the NH4Cl and NaHCO3 groups presumably because the increased NH4+ load in the former group was processed, uninhibited, to urea. Amino acids not used by the liver in acidosis could account for the 25-fold increase in NH4+ excretion in HCl and NH4Cl compared with alkalosis (P < 0.05). These findings indicate that urea synthesis is decreased in chronic HCl acidosis. They show that urea synthesis is controlled in chronic, as in acute, acidosis by amino acid uptake by the liver and/or intrahepatic degradation and that the ornithine cycle per se has only minor control of acid-base homeostasis.

Acidosis↗
PubMed1996

Gender-dependent regulation of glutamate dehydrogenase expression in periportal and pericentral zones of rat liver lobules.

We studied the level(s) at which glutamate dehydrogenase (GDH; EC 1.4.1.2) expression is regulated in the livers of fed male and female rats. The cellular content of GDH mRNA, protein, and enzyme activity was determined quantitatively using image analysis for measurement of the absorbance in consecutive serial sections that were processed for in situ hybridization, immunohistochemistry, and enzyme histochemistry. In both males and females, GDH protein and activity patterns were similar, with pericentral values being twice as high as periportal values. GDH mRNA distribution patterns in female liver lobules reflected those of GDH protein and activity, but GDH mRNA distribution patterns in male rat livers were found to be homogeneous owing to a more than twofold lower cellular mRNA content in pericentral zones than in female rats. We conclude that gender affects GDH expression selectively in pericentral zones at posttranscriptional and pretranslational levels.

Animals↗
PubMed1996

Osteoporosis-pseudoglioma syndrome, a disorder affecting skeletal strength and vision, is assigned to chromosome region 11q12-13.

Osteoporosis-pseudoglioma syndrome (OPS) is an autosomal recessive disorder characterized by severe juvenile-onset osteoporosis and congenital or juvenile-onset blindness. The pathogenic mechanism is not known. Clinical, biochemical, and microscopic analyses suggest that OPS may be a disorder of matrix homeostasis rather than a disorder of matrix structure. Consequently, identification of the OPS gene and its protein product could provide insights regarding common osteoporotic conditions, such as postmenopausal and senile osteoporosis. As a first step toward determining the cause of OPS, we utilized a combination of traditional linkage analysis and homozygosity mapping to assign the OPS locus to chromosome region 11q12-13. Mapping was accomplished by analyzing 16 DNA samples (seven affected individuals) from three different consanguineous kindreds. Studies in 10 additional families narrowed the candidate region, supported locus homogeneity, and did not detect founder effects. The OPS locus maps to a 13-cM interval between D11S1298 and D11S971 and most likely lies in a 3-cM region between GSTP1 and D11S1296. At present, no strong candidate genes colocalize with OPS.

Alleles↗
PubMed1994

Acute acidosis inhibits liver amino acid transport: no primary role for the urea cycle in acid-base balance.

To examine further the role of the liver in acid-base homeostasis, we studied hepatic amino acid uptake and urea synthesis in rats in vivo during acute acidosis and alkalosis, induced by infusion of 1.8 mmol of HCl or NaHCO3 over 3 h. Amino acids and NH4+ were measured in portal vein, hepatic vein, and aortic plasma, and arteriovenous differences of amino acids and urinary urea and NH4+ excretion were measured. In acidosis, urinary urea excretion was reduced 36% (P < 0.01), whereas urinary NH4+ excretion increased ninefold (P < 0.01), but the sum of urea and NH4+ excretion was unchanged. Total hepatic amino acid uptake, as determined from arteriovenous differences, was decreased by 63% (P < 0.01) in acidosis, with the major effect being noted with alanine and glycine. Only glutamine was released in both acidosis and alkalosis but was not significantly different in the two conditions. Since intracellular concentrations of readily transportable amino acids were not different at low pH despite accelerated protein degradation, these results indicate that hepatic amino acid transport was inhibited markedly and sufficiently to explain the observed decrease in urea synthesis. Total hepatic vein amino acid content was greater in acidosis than alkalosis (P < 0.01). Directly or indirectly, by conversion to glutamine elsewhere, these increased amino acids were degraded in kidney and accounted for the ninefold increase in urinary NH4+ excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗
PubMed1993

Cell swelling and the sensitivity of autophagic proteolysis to inhibition by amino acids in isolated rat hepatocytes.

In the isolated perfused rat liver, autophagic proteolysis is inhibited by hypo-osmotic perfusion media [Häussinger, D., Hallbrucker, C., vom Dahl, S., Lang, F. & Gerok, W. (1990) Biochem. J. 272, 239-242]. Here we report that in isolated hepatocytes, incubated in the absence of amino acids to ensure maximal proteolytic flux, proteolysis was not inhibited by hypo-osmolarity while the synthesis of glycogen from glucose, a process known to be very sensitive to changes in cell volume [Baquet, A., Hue, L., Meijer, A. J., van Woerkom, G. M. & Plomp, P. J. A. M. (1990) J. Biol. Chem. 265, 955-959], was stimulated under identical conditions. However, in isolated hepatocytes, hypo-osmolarity increased the sensitivity of autophagic proteolysis to inhibition by low concentrations of amino acids. The anti-proteolytic effect of hypo-osmolarity in our experiments was not due to stimulation of amino-acid transport into the hepatocytes: neither the consumption of most amino acids, nor the rate of urea synthesis was appreciably affected by hypo-osmotic incubation conditions. In the course of these studies we also found that hypo-osmolarity increased the affinity of protein synthesis for amino acids. In the presence of amino acids the intracellular level of ATP was not much affected. However, because of cell swelling under these conditions the intracellular concentration of ATP decreased. It is proposed that a small part of the inhibition of proteolysis by amino acids may be due to this fall in ATP concentration.

Adenosine Triphosphate↗
PubMed1993

Influence of tutors' subject-matter expertise on student effort and achievement in problem-based learning.

PURPOSE: To investigate the effects of tutors' subject-matter expertise on students' levels of academic achievement and study effort in a problem-based health sciences curriculum. Also, to study differences in tutors' behaviors and the influences of these differences on students' performances. METHOD: Data were analyzed from 336 staff-led tutorial groups involving student participants in seven four-year undergraduate programs at the University of Limburg Faculty of Health Sciences in 1989-90. Overall, 1,925 data records were studied, with each student participating in an average of 1.7 groups led by either content experts or non-experts. The basic analyses were of (1) students' achievement scores as a function of tutors' expertise levels and students' curriculum year; (2) students' estimates of self-study time as a function of tutors' expertise levels and students' curriculum year; and (3) the average ratings of the tutors' behaviors as a function of tutors' expertise levels. Statistical methods included analysis of variance and Pearson correlations. RESULTS: The students guided by subject-matter experts were shown to spend more time on self-directed study, and they achieved somewhat better than did the students guided by non-expert tutors. The effect of subject-matter expertise on achievement was strongest in the first curriculum year, suggesting that novice students are more dependent on their tutors' expertise than are more advanced students. Also, the content-expert tutors made more extensive use of their subject-matter knowledge to guide students. However, in addition to the tutors' knowledge-related behaviors, the tutors' process-facilitation skills affected student achievement. Moreover, these two sets of behaviors were correlated, indicating that both are necessary conditions for effective tutoring. CONCLUSION: The results indicate that, at least for the curriculum studied, the assumption in the literature that tutors do not necessarily need content knowledge so long as they are skilled in the tutoring process is not entirely justified: the students who were guided by content experts achieved somewhat better and spent more time on self-directed learning. More important, tutoring skill and content knowledge seemed to be necessary and closely related conditions for effective tutoring.

Achievement↗
PubMed1992

A comparative analysis of healing of surgical cleft lip corrected in utero and neonates.

We studied the healing process in surgically created cleft lips in fetal mice and compared it with that in newborn mice with cleft lips. Our purpose was to determine the time for optimal healing, defined as minimal scarring, for a repaired cleft lip. Full-thickness paramedian lip incisions were made in NMRI mice in utero, in 2- and 4-day-old neonates, and in adults (n = 10 in each experimental and control group). The healing process was studied by biochemical analysis of hyaluronic acid and hydroxyproline content in the repaired cleft tissue. We found that the production of hyaluronic acid remained stable during the healing period and was similar in all experimental groups. However, there was an unexplained but consistent depression in the hyaluronic acid content of fetal tissue 2 days after repair. Hydroxyproline was present in the fetal healing tissue, but in a low concentration, starting 4 days after surgical incision of the lip. The production of hydroxyproline in 2-day-old neonates was similar to that in the fetuses throughout the healing period (p less than 0.0005). However, the production of hydroxyproline increased in 4-day-old neonatal and adult tissues. In conclusion, we found an optimal healing period for mice with minimal collagen production in the late fetal stage, and this lasted 2 days after birth.

Aging↗
PubMed1991

Oxygen tension does not affect urea synthesis in perifused rat hepatocytes.

Perfusion of rat liver had led to the suggestion that oxygen tension, rather than the distribution of enzymes of urea synthesis, plays a key role in the regulation of urea synthesis in the periportal and pericentral areas of the liver lobule [F. W. Kari, H. Yoshihara and R. G. Thurman (1987) Eur. J. Biochem. 163, 1-7]. We have directly tested the effect of oxygen concentration on ureogenesis under steady-state conditions in isolated hepatocytes perifused with physiological concentrations of ammonia. We found that ureogenesis is independent of the oxygen concentration. Only at oxygen concentrations below 25 microM (which is below the oxygen concentration in liver) was urea synthesis decreased. This was because insufficient production of ATP led to decreased flux through carbamoyl-phosphate synthase. It is concluded that oxygen does not control urea synthesis.

Adenosine Triphosphate↗
PubMed1990

Stimulation of glycogen synthesis in hepatocytes by added amino acids is related to the total intracellular content of amino acids.

Katz et al. [Katz, J., Golden, S. & Wals, P.A. (1976) Proc. Natl Acad. Sci. USA 73, 3433-3437] were the first to report that in hepatocytes isolated from fasted rats and incubated with either dihydroxyacetone, glucose or other sugars, glycogen synthesis was greatly accelerated by addition of amino acids. We have looked for possible mediators responsible for this effect and have tested the effect of alanine, proline, asparagine, glutamine or a combination of ammonia with either pyruvate or lactate in activating glycogen synthesis from dihydroxyacetone. The following observations were made. 1. Stimulation of glycogen synthesis by alanine, proline or asparagine does not require production of glutamine since the effect also occurs in periportal hepatocytes which lack glutamine synthetase. 2. Under various conditions, stimulation of glycogen synthesis by added amino acids directly correlated with increases in the intracellular content of amino acids, expressed in osmotic equivalents. 3. 3-Mercaptopicolinic acid, the inhibitor of phosphoenolpyruvate carboxykinase, further enhances stimulation of glycogen synthesis by amino acids because it increases the intracellular accumulation of aspartate and glutamate. 4. The previously reported enhancement by leucine of the stimulation of glycogen synthesis by glutamine [Chen. K. S. & Lardy, H. A. (1985) J. Biol. Chem. 260, 14683-14688] can be ascribed to inhibition of urea synthesis by leucine which results in accumulation of glutamate and of ammonia, the essential activator of glutaminase. It is concluded that activation of glycogen synthesis by added amino acids is due to an increase in intracellular osmolarity following their uptake and the accumulation of intracellular catabolites. This results in an increase in hepatic volume which stimulates glycogen synthesis [Baquet, A., Hue, L., Meijer, A. J., van Woerkom, G. M. & Plomp, P. J. A. M. (1990) J. Biol. Chem. 265, 955-959].

Amino Acids↗
PubMed1988

Control by pH of urea synthesis in isolated rat hepatocytes.

Control by pH of urea synthesis has been studied in isolated rat hepatocytes incubated with a physiological mixture of amino acids. Inhibition of urea synthesis by decreasing the pH of the medium was caused by diminished production of ammonia and not, as suggested in the literature, by inhibition of entry of ammonia into the ornithine cycle. The decrease by low pH of the rate of degradation of the added amino acids, that of alanine being quantitatively the most important, was accompanied by a decrease in their intracellular concentration. It is concluded that inhibited transport of amino acids across the plasma membrane of the hepatocyte is responsible, at least in part, for the fall in urea synthesis with decreasing pH. It is proposed that inhibition by low pH of other steps in the ureogenic pathway, distal to the production of ammonia, does not affect flux through the ornithine cycle per se, but rather contributes to the buffering of the intrahepatic concentration of ammonia.

Amino Acids↗
PubMedDate not supplied

Intra-abdominal lymphatic malformation.

Intra-abdominal lymphangioma is a rare congenital lymphatic vascular malformation. It is found, most commonly, in adult patients who present with abdominal pain, and whom medical imaging (ultrasound, endoscopy and tomography) reveals a cystic intra-abdominal mass. Such masses may be on the mesentery, in contact with abdominal viscera or may be part of the visceral wall. Diagnosis of intra-abdominal lymphangioma is difficult because of its rarity, and because other pathologies may have the same radiological signs. The diagnosis is confirmed by anatomopathological examination with immunohistochemistry. The treatment is complete surgical excision, in order to prevent recurrence.

Abdominal Neoplasms↗