Search PubMed⌕ Search

Biomedical subjects

T Z Liu

Publications and source records attributed to T Z Liu.

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

Histologic, morphometric, and biochemical evolution of vein bypass grafts in a nonhuman primate model. III. Long-term changes and their modification by platelet inhibition with aspirin and dipyridamole.

The objectives of this study were to elucidate the long-term influence on vein bypass grafts of platelet inhibition and its late discontinuation. Cephalic vein grafts were interposed bilaterally in the femoral arteries of stump-tailed macaque monkeys fed a diet that sustains plasma cholesterol levels of approximately 225 mg/dl. Fifteen animals were divided into three groups of five animals each. Group I received no medications and served as a control group. Group II received for the full duration of the study a combination of aspirin, 80 mg/day, and dipyridamole, 50 mg/day. Group III received the same regimen of platelet inhibition as in group II during the first 9 months, but were not treated during the subsequent 9-month interval. Grafts were excised for analysis from groups I and II at both 9 and 18 months and from group III at 18 months. Cholesterol content in group I grafts was 470 +/- 89 micrograms/100 mg at 9 months and 388 +/- 127 micrograms/100 mg at 18 months. In group II grafts, cholesterol content was 208 +/- 72 micrograms/100 mg at 9 months (p less than 0.001 compared with group I) and 266 +/- 84 micrograms/100 mg at 18 months. In group III grafts, cholesterol content was 249 +/- 71 micrograms/100 mg at 18 months. Differences in cholesterol content among the three groups of grafts at 18 months were not found to be statistically significant. Stepwise regression analysis at 18 months showed that cholesterol content was best predicted by medial fibrosis (r2 = 0.66) followed by abundance of foam cells (increase in r2 = 0.26) in group I, by fibrin in group II (r2 = 0.63), and by prevalence of macrophages in group III (r2 = 0.74). In all groups, platelets, fibrin, and polymorphonuclear leukocytes were less abundant than they had been at 3 months. Cross-sectional area occupied by the intima was not influenced by platelet inhibition.

Animals↗
PubMed1989

Operative factors, not hemodynamics, modify hormones in repair of coarctation.

This study was designed to evaluate separately the influence of restoration of distal pulse pressure and the influence of factors related to operation upon hemodynamic and hormonal alterations accompanying repair of canine aortic coarctation. Eight normal adult dogs underwent a sham operation and served as controls. In 10 dogs the thoracic aorta was transfected and reanastomosed. In 10 dogs aortic coarctation was created within 1 week of birth by banding the aorta just proximal to the ductus ligament, thereby fixing lumenal diameter at 1 to 2 mm. Studies were performed in the latter animals 18 months after operation. These dogs were subdivided into two groups: one (n = 6) underwent surgical repair of the coarctation; in the other (n = 4), the coarctation was repaired and an occluder was placed on the aorta to maintain distal aortic pulse pressure at its diminished preoperative level. Normal distal pulse pressure was restored in these animals by releasing the occluder 1 week after recovery from the repair of coarctation. Each dog was studied in the conscious state before the definitive procedure and again 24 hr later. Plasma renin activity increased significantly after operation in the sham and in the transection groups. Renin activity and proximal blood pressure were significantly elevated and distal pulse pressure was diminished preoperatively in both the repair and the occluder groups. After their respective definitive procedures, the elevation in renin activity and in proximal pressure persisted in the repair group but decreased in the occluder group.(ABSTRACT TRUNCATED AT 250 WORDS)

Anastomosis, Surgical↗
PubMed1984

A new variant of lactate dehydrogenase isoenzyme in human saliva.

A hitherto unreported lactate dehydrogenase isoenzyme, which migrates electrophoretically to the relative position between LDH4 and LDH5, is detected in 100% of human saliva specimens obtained from a group of apparently healthy individuals. Despite the fact that 70% (14 of 20) of all specimens analyzed have LDH5 as the predominant isoenzyme, it has been observed that this newly discovered isoenzyme has anomalously emerged as the predominant isoenzyme in 20% (4 of 20) of the total specimens quantified.

Adolescent↗
PubMed1982

Specific spectrophotometry of ascorbic acid in serum or plasma by use of ascorbate oxidase.

We describe a specific enzymatic spectrophotometric method for ascorbic acid in serum or plasma. Samples are analyzed indirectly by measuring the absorbance at 593 nm of a reaction product, a complex of ferrous ion and 2,4,6-tris(2-pyridyl)-s-triazine (Fe2+-TPTZ). This product is formed by reduction of the corresponding ferric ion complex (Fe3+-TPTZ), which is nonspecifically reduced by various biological reducing agents under acidic conditions. Ascorbic acid is specifically quantified by pretreating one of a pair of replicate samples with ascorbate oxidase (EC 1.10.3.3), to oxidize the ascorbic acid, then reacting both samples with Fe3+-TPTZ and measuring the difference between the absorbances at 593 nm of the treated and untreated samples. This difference is linearly related to ascorbic acid concentrations from 10 to 100 mg/L. Ten repeat determinations of a serum pool with added ascorbic acid yielded a CV of 2.8% and a mean of 47.2 mg/L. The correlation (r) between the proposed method and the dinitrophenylhydrazine method was 0.93 for 32 samples analyzed by both methods. The present method is specific for ascorbic acid and requires no deproteinization.

Ascorbate Oxidase↗
PubMed1980

Spectrophotometric screening method for acetaminophen in serum and plasma.

We describe a simple, economical procedure for rapidly detecting acetaminophen in serum or plasma. The method is based upon the reduction by the drug of ferric 2,4,6-tris(2-pyridyl)-s-triazine, at an acidic pH, to ferrous 2,4,6-tris(2-pyridyl)-S-triazine complex, which absorbs maximally at 593 nm. Absorbance and acetaminophen concentration are linearly related from 25 to 400 mg/L, and so therapeutic and toxic concentrations can be measured. The method is accurate; day-to-day CV's for two pooled control specimens (103 and 227 mg/L) were 4.4 and 6.6%. Correlation studies, with an established nitration method and with the free-radical diphenylpicrylhydrazyl dye method, showed correlation coefficients of 0.985 and 0.915, respectively. Of 25 commonly used drugs tested, only levodopa, oxyphenylbutazone, and phenylephrine interfere significantly. Interference from salicylate, salicylamide, and phenylbutazone was insignificant.

Acetaminophen↗
PubMed1980

Fluorometric quantitation of glutamine in cerebrospinal fluid.

We describe a rapid, relatively simple-procedure for fluorometry of glutamine in cerebrospinal fluid. Glutamine is de-aminated with diluted sulfuric acid at 100 degrees C. The ammonia liberated is then reacted with a buffered o-phthalaldehyde--mercaptoethanol solution, pH 7.4, to form a fluorochrome. Fluorescence is linearly related to the concentration of glutamine from 0.10 to 0.60 g/L (0.68 to 4.10 mmol/l). To prevent interference by endogenous ammonia, each specimen was corrected for its own background fluorescence. The mean analytical recovery was 99.8%. Within-day variation (CV) for pooled, enriched cerebrospinal fluid controls at 0.33 g/L (2.22 mmol/L) and 0.53 g/L (3.63 mmol/L) were 2.2 and 5.1%. Day-to-day variation (CV) for the same controls was 4.4 and 4.8%, respectively. Data obtained by our method correlate excellently (r = 0.980) with those by an established procedure based on the Berthelot (phenol--hypochlorite) reaction.

Drug Stability↗
PubMed1979

Positive interference of catecholamine metabolites with quantitation of urinary uric acid by the direct acid ferric-reduction method.

We report the effect of major catecholamine metabolites such as homovanillic acid and vanilmandelic acid, normally present in urine, on quantitation of urinary uric acid by the direct acid ferric-reduction procedure [(Am. J. Clin. Pathol. 60, 691 (1973)]. When aqueous uric acid standards containing a mixture of these two metabolites, in concentrations comparable to those in a normal human 24-h urine, were added to Fe3+-phenanthroline or Fe3+-2,4,6-tripyridyl-s-triazine reaction mixture, the resulting absorbances at 505 or 593 nm considerably exceeded those of standards without such additions. Moreover, quantitation of urinary uric acid by the direct acid ferric-reduction procedure gave values that significantly exceeded those determined by the uricase method. Interference by the two metabolites was eliminated by extracting urine specimens with ethyl acetate before quantitation. Spectral scans revealed that homovanillic acid or vanilmandelic acid alone could also effectively reduce Fe3+-chelator complex and that the effect of these compounds on the analytical reaction was additive.

Homovanillic Acid↗