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Biomedical subjects

M Leung

Publications and source records attributed to M Leung.

At least 55 records · Page 3Linked to original sources
PubMed1990

Low-dose doxycycline therapy: effect on gingival and crevicular fluid collagenase activity in humans.

Tetracyclines are now recognized to have non-antimicrobial properties with therapeutic potential--for example, these agents can inhibit pathologic collagenolysis by blocking mammalian collagenases and other matrix-degrading metalloproteinases. In the current study, adult human subjects with moderate chronic periodontitis were administered specially formulated capsules of doxycycline, containing lower-than-usual amounts of this semi-synthetic tetracycline, on a daily basis for 2 weeks prior to a full-thickness flap procedure; control subjects were administered placebo capsules. The gingiva excised during this surgical procedure were extracted, the extracts partially purified and analyzed for collagenase activity using [3H-methyl] collagen as substrate and the techniques of SDS-PAGE/fluorography or liquid scintillation spectrometry. In the absence of any drug pre-treatment, or after a 2-wk regimen of placebo capsules, the gingival extracts exhibited pathologically-excessive mammalian collagenase activity. The 2-wk regimen of low-dose doxycycline capsules reduced this activity by approximately 60-80% (p less than 0.05 and less than 0.01, respectively); in vitro exposure of the gingival extract to doxycycline also inhibited its collagenase activity. Collagenase activity in the crevicular fluid of periodontal pockets of an additional group of subjects was also significantly reduced, as was the severity of inflammation at the same gingival sites. The results suggest that a regimen of low-dose doxycycline capsules may provide a safe (other studies indicate that this regimen may not induce tetracycline resistance in the subgingival plaque) and effective adjunct to instrumentation therapy in the management of pathologic collagenolysis in the periodontal patient. However, further studies are necessary to confirm this hypothesis.

Adult↗
PubMed1988

Repair of tricuspid atresia: utility of right ventricular incorporation.

During a 10-year period, 62 patients underwent the following modifications of the Fontan operation for repair of tricuspid atresia: direct atriopulmonary connection (N = 15), atriopulmonary connection using a conduit (N = 5), direct atrioventricular (AV) connection (N = 22), and AV connections with a valved conduit (N = 20), including 2 with combined Fontan-arterial switch procedures. The overall hospital mortality was 16.1% (10/62) (70% confidence limits, 11.2 to 22.4%). By multivariate analysis, the risk factors for early and late death included increasing right atrial pressure after repair, use of an atriopulmonary connection, and previous pulmonary artery banding (all variables, p less than 0.05). Postoperative catheterization was performed in 22 patients including 15 with AV valved-conduit connections. Right ventricular (RV) work based on pulmonary artery pressure minus right atrial pressure was correlated with the preoperative RV to left ventricular volume ratio computed from the four-chamber angiographic projection (p = 0.025), and was appreciable only with ratios exceeding about 30%. In 6 of 19 eligible patients, severe conduit obstruction has developed. Considering the survival data, the risk of reoperation, and postoperative hemodynamic findings, analysis of our experience supports the preferential use of nonvalved AV connections in most patients with tricuspid atresia and ventriculoarterial concordance.

Adolescent↗
PubMed1987

Expression of herpes simplex virus thymidine kinase gene in aquatic filamentous fungus Achlya ambisexualis.

We have constructed a plasmid vector pSV2neo-MK alpha G in which the structural tk gene for Herpes simplex virus thymidine kinase (HSV-TK) was placed downstream from the metallothionein-I promoter. The vector also contained the selection marker aminoglycoside 3'-phosphotransferase (Km). This vector was able to transform the filamentous fungus Achlya ambisexualis and G-418-resistant colonies were obtained. Southern blot analyses revealed that multiple bands hybridizing to the HSV tk gene probe were present in the genomic DNA of the transformants. Upon analysis by gel electrophoresis, one of the transformants exhibited TK activity bearing electrophoretic mobility similar to that of the HSV-TK. An increase of approx. 40% of [3H]thymidine uptake and incorporation into cellular DNA was also observed in this transformant. This study suggested that the HSV tk gene can be expressed in the fungus A. ambisexualis that can be considered as a candidate host cell for further gene-expression studies.

Chytridiomycota↗
PubMed1987

Reversed offsetting of the septal attachments of the atrioventricular valves and Ebstein's malformation of the morphologically mitral valve.

Ebstein's anomaly of the tricuspid valve is characterised by downstream displacement of the tricuspid leaflets. In the case of the septal leaflet, the result is exaggerated offsetting of the atrioventricular valves. Thus it might be supposed that in Ebstein's anomaly of the mitral valve, downstream displacement of the aortic (septal) leaflet of the mitral valve could move its attachment beyond that of the tricuspid valve, resulting in reversed offsetting. To examine this hypothesis three patients each with a concordant atrioventricular connection were studied. The first, with Marfan's syndrome and without an abnormal mitral valve, had reversed offsetting shown by echocardiography. The second, without Marfan's syndrome and with Ebstein's anomaly of the mitral valve, showed echocardiographically normal offsetting but a displaced mural leaflet. The third, in whom Ebstein's anomaly of the mitral valve was confirmed at necropsy, showed all the features of the second case, with normal offsetting of the atrioventricular valves. Thus reversed offsetting is not a feature of Ebstein's anomaly of the mitral valve and in the first case this feature was caused by upward displacement of the tricuspid valve secondary to dilation of the aortic root.

Abnormalities, Multiple↗
PubMed1986

Bromocriptine inhibits incorporation of [3H]thymidine into rat pituitary tumor cells.

The effects of bromocriptine on GH3 pituitary tumor cell [3H]thymidine incorporation were studied. Cells were grown in the presence of bromocriptine, then exposed to a short-term pulse of [3H]thymidine in serum-free medium containing deoxycytidine (10 microM) to prevent deoxythymidine triphosphate (dTTP) pooling. After 48 h exposure to bromocriptine, basal prolactin (PRL)-secretion during 45 min was inhibited by 50% by 10 microM bromocriptine and thyroid releasing hormone-induced PRL stimulation was suppressed. Incorporation of radiolabelled thymidine into acid-precipitable DNA increased progressively from 15 to 60 min and was abolished by simultaneous incubation with excess unlabelled thymidine (100 microM). Bromocriptine (10 microM) inhibited incorporation of 5-50 microM [3H]thymidine, but this was not reversed by simultaneous incubation with metoclopramide (10 microM). Aminopterin, an inhibitor of endogenous de novo DNA synthesis, stimulated [3H]thymidine incorporation twofold and this increased DNA salvage pathway activity was also blocked by bromocriptine. As incorporation of [3H]thymidine into acid-soluble cell nucleotides was also inhibited by bromocriptine, the data suggest that in these cells the drug inhibits thymidine kinase activity, a salvage pathway of DNA synthesis.

Animals↗
PubMed1984

Dietary intakes of preschoolers.

Between 1977 and 1979, the H.J. Heinz Company of Canada Ltd conducted a longitudinal survey of infant nutrition from birth to 18 months. In 1980, 189 of the original 403 infants were recruited in a follow-up study. The age of the children in the follow-up study was 3.5 to 4 years. This article describes the food and nutrient intakes of the preschool children. Food intake information was obtained by the 4-day dietary record method. The mean energy intake of the children was adequate to support normal growth. The mean nutrient intakes were above the recommended daily intakes of the Canadian Dietary Standard. All children ate three regular meals and at least one in-between meal snack. Milk was the primary source of energy, protein, fat, calcium, phosphorus, sodium, potassium, and riboflavin. Meat contributed a substantial amount of protein, fat, and niacin. Cereal and cereal products were the primary source of iron and were good sources of carbohydrates, sodium, and the B vitamins. Fruit and fruit juices were the primary sources of carbohydrate and vitamin C. Vitamin supplements provided large amounts of vitamin A and the B vitamins. Since foods alone included sufficient nutrients to provide the recommended daily nutrient intakes, vitamin supplements were largely unnecessary.

Child Nutritional Physiological Phenomena↗
PubMed1983

Isolation of molluscan opioid peptides.

An acid extract of neural tissues of the mollusc, Mytilus edulis, was fractionated by high-pressure chromatography. Peak fractions with retention times of that of Met-enkephalin, Leu-enkephalin and Met-enkephalin-Arg-Phe were subjected to competitive displacement assays in the same neural tissues. The results showed that these fractions have the same binding activities as the authentic neuropeptides. The peptides from these fractions were purified by high-pressure liquid chromatography under isocractic conditions. Sequential amino acid analyses showed these peptides to have the same primary structures as Met-enkephalin, Leu-enkephalin and Met-enkephalin-Arg-Phe.

Animals↗
PubMed1982

Purification of opioid peptides from molluscan ganglia.

1. Acid extracts from pedal ganglia of Mytilus edulis was fractionated by high-pressure liquid chromatography (HPLC). 2. Components were recovered which had the same retention times as met- and leu-enkephalin. 3. When tested in an in vitro assay, these components inhibited dopamine-stimulated adenylate cyclase activity in a naloxone-reversible manner. 4. These results suggest that molluscan neural tissue contains opioid peptides similar, perhaps identical, to the mammalian enkephalins.

Adenylyl Cyclases↗
PubMed1982

Sodium intakes of infants from 1 to 18 months of age.

The daily sodium content in the diets of infants was determined. Milk and milk products were the main contributor of sodium during early infancy. Commercial baby foods contributed little sodium. As table foods were introduced, the daily sodium intake of the infants rose dramatically. The main sources of sodium in table foods were salt-containing canned foods and added table salt.

Age Factors↗
PubMed1981

Iron intake of infants: the importance of infant cereals.

Since 1976 many baby foods have been reformulated and the iron used to fortify infant cereals has been changed to a more bioavailable form. Therefore, the dietary intake of iron by infants from 1 to 18 months of age was assessed in a longitudinal survey conducted in Toronto and Montreal between 1977 and 1979. Except in the 1st and 18th months the mean daily iron consumption of the infants was above that recommended in the Dietary Standard for Canada. The main source of this nutrient was infant cereals. Examination of the diets of the infants who did not have the recommended daily intake of iron showed that they did not consume sufficient amounts of infant cereals and other iron-rich foods. These results indicate that without such cereals it is difficult to provide infants with the amount of iron they need. Therefore, infants should receive these cereals during the first 2 years of life.

Biological Availability↗
PubMed1981

Pichinde virus L and S RNAs contain unique sequences.

Using oligodeoxyribonucleotides produced by limited DNase I digestion of calf thymus DNA as a primer, we synthesized complementary DNA (cDNA) from the L and the S RNAs of Pichinde virus. The reaction conditions for in vitro cDNA synthesis were optimized to allow transcription of about 90% of either L or S RNA. No significant hybridization was observed when the L cDNA was hybridized to the S RNA, or when the S cDNA was hybridized to the L RNA. The results indicate that the L and S RNAs of Pichinde virus contain unique nucleotide sequences.

Arenaviridae↗
PubMed1981

Infant fatness and feeding practices: a longitudinal assessment.

In recent years, bottle feeding and the early introduction of solid foods in infants' diets have been proposed as factors contributing to overweight in infancy that might continue into childhood. These hypotheses were examined in a longitudinal survey of 403 infants from birth to 18 months of age. Results from this survey do not support either (a) a relationship between type of milk feeding or time of introduction of solid food and fatness at 6 months of age or (b) the hypothesis that fat infants remain fat.

Breast Feeding↗
PubMed1980

Reappraisal of protein losses in patients undergoing continuous ambulatory peritoneal dialysis.

Dialysate effluent protein content was measured in 22 patients undergoing continuous ambulatory peritoneal dialysis (9 with and 13 without previous peritonitis). The average amount of protein in those patients without peritonitis was 1.3 g/2 liters exchanged over a 6-hour period, while that of patients with previous peritonitis was 2.6 g/2 liters exchanged over the same period. 71% of protein found in the dialysate of 2 patients was albumin. Despite the difference in the amount of protein lost between those without and those with peritonitis, there was no significant difference in their mean serum albumin levels (3.2 and 3.4 g%, respectively) which were only slightly below the normal range. The previously reported high protein losses in patients undergoing CAPD are probably the result of frequent episodes of peritonitis and a higher number (five) of daily exchanges.

Adolescent↗
PubMed1978

Measurement of free and free-plus-peptide hydroxyproline fractions in plasma.

Plasma hydroxyproline fractions--free-plus-peptide and free--were determined by a method involving centrifugal ultrafiltration and the procedure of Kivirikko et al. [Anal. Biochem. 19, 249 (1967)]. Within- and between-day precision (CV) for the combined fractions was 4--5% and 2.8--6%, respectively. Mean analytical recoveries of free hydroxyproline were 95.2% (87--109%) in the normal range, and 97% (91--108%) in the above-normal range. Normal ranges for plasma hydroxyproline fractions, based on data for 11 men and 19 women, were free-plus-peptide, 7.5--25.3; free, 4.9--22.7; and peptide (calculated), 0.1--5.1 mumol of hydroxyproline per litre, respectively. These ranges showed no sex-related differences and were gaussian in distribution. A factor was derived to transform data on concentrations in ultrafiltrate into plasma concentrations.

Humans↗
PubMed1977

Measurement of serum and plasma ionic calcium with the "Space-Stat 20 Ionized Calcium Analyzer".

Ca2+ was measured in sera and plasma from 36 normal subjects (18 men 23-57 years old, and 18 women 20-52 years old) with the Space-Stat 20 Ionized Calcium Analyzer. Within-day and between-day precision (CV) for commercial serum-based specimens varied from 0.64-0.96% and 1.1-3.8%, respectively, depending on their mean concentrations. Plasma and serum showed within-day CV's of 1.05 and 0.79%, respectively. The linear regression of serum Ca2+ (y) on plasma Ca2+ (x) was y = 0.63x + 0.45 mmol/litre with a highly significant (P less than 0.001) coefficient of correlation (r) of 0.69. An approximate 5% increase in the mean Ca2+ concentration in serum over that found in plasma is probably due to heparin complexing. No significant sex-related difference was observed for either serum or plasma. The mean Ca2+ concentration of 29 refrigerated specimens tended to decrease in seven days (by 2.3%, not statistically significant). The normal Ca2+ range in serum and plasma (n = 35) was 1.08-1.18 and 1.02-1.14 mmol/litre, respectively.

Adult↗