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Biomedical subjects

P Lau

Publications and source records attributed to P Lau.

At least 73 records · Page 4Linked to original sources
PubMed1985

Modifications in the alditol acetate method for analysis of muramic acid and other neutral and amino sugars by capillary gas chromatography-mass spectrometry with selected ion monitoring.

Two alditol acetate methods for the gas chromatographic (GC) analysis of neutral and amino sugars were compared. Following sodium borohydride reduction, one method uses methylimidazole as an acetylation catalyst without prior removal of water or borate salts and the other method uses sodium acetate after removal of borate and water. Depending on the acetylation conditions, muramic acid produced different derivatives. With methylimidazole, reliable derivatization of muramic acid was not possible, although other sugars derivatized reliably. With sodium acetate, all sugars tested were reproducibly derivatized. The utility of the sodium acetate method is shown by the trace GC-mass spectrometric analysis of muramic acid and rhamnose derived from bacterial peptidoglycan-polysaccharide complexes in mammalian tissue.

Acetylation↗
PubMed1985

Heat myringotomy.

Heat myringotomy using a commercially available, battery powered device produced an opening in the tympanic membrane that persisted 1 to 3 weeks. The procedure was performed to treat chronic otitis media with effusion (COME) in lieu of ventilation tubes in 10 pediatric and 15 adult ears under office iontophoretic anesthesia. These patients were followed for a minimum of 3 months to assess efficacy. Fifty percent of pediatric ears were controlled, eliminating the need for general anesthesia and tube insertion. Forty percent of adult ears were controlled with heat myringotomy. A description of the procedure, discussion of possible reasons for failure, and analysis of potential cost savings are included.

Adolescent↗
PubMed1983

Paroxysmal cold hemoglobinuria in a patient with Klebsiella pneumonia.

A case of paroxysmal cold hemoglobinuria (PCH) occurring in a patient with Klebsiella pneumonia is described. The first sign of PCH in the patient was erythrophagocytosis. The Donath-Landsteiner (D-L) antibody exhibited anti-P specificity both serologically and biochemically. The appearance of D-L antibody during fulminating Klebsiella pneumonia strongly suggests their causal relationship.

Bronchopneumonia↗
PubMed1980

Post-transfusion purpura: an enigma of alloimmunization.

A patient with post-transfusion purpura is reported. This female patient, sensitized by previous blood transfusion, developed symptomatic thrombocytopenia seven days after a second blood transfusion. A platelet antibody, which had anti-P1A1 specificity, was identified by 51Cr-release assay and by indirect immunofluorescence. Hemorrhage stopped abruptly after plasma exchange therapy. Thrombocytopenia did not recur when the patient was further challenged with P1A1-positive blood and plasma. Anti-P1A1 antibody, detectable by immunofluorescence but not by complement-dependent platelet cytoxicity, persisted in high titer for at least one year after recovery. The heterogeneity and pathogenesis of this clinical syndrome are discussed.

Aged↗
PubMed1977

Identification of semen in 500 patients seen because of rape.

Of 500 patients seen because of rape, semen was identified in vaginal secretions by the identification of spermatozoa in 61%, by an acid phosphatase value of 50 units or more in 40%, and by the identification of a foreign blood group substance or a high titer of own blood group substance in 16%. The addition of the determination of the acid phosphatase to the search for spermatozoa identified semen in only 1.4% more patients, or a total of 62.4%. Identification and titers of blood group substance were confirmatory only, but further characterized the source of the semen in 25% of those patients with spermatozoa. Spermatozoa were identified for as long as 48 hours, and elevated acid phosphatase was not found after 18 hours. Acid phosphatase was elevated in only 62% of patients with spermatozoa.

ABO Blood-Group System↗
PubMed1976

Spin label studies on conformational changes of aphohemoglobin due to heme binding.

Human apohemoglobin (globin) was spin-labeled at the beta-93 sulfhydryl groups with 2,2,5,5-tetramethyl-3-aminopyrrolidine-I-oxyl. Spin-labeled globin exhibited an EPR spectra that is less immobilized than that of spin-labeled hemoglobin, indicating the conformational difference in the vicinity of the label between hemoglobin and globin. Spectrophotometric titration of spin-labeled globin with protohemin showed that 1 mol of globin (on the tetramer basis) combines with 4 mol of hemin, producing a holomethemoglobin spectrophotometrically indistinguishable from native methemoglobin. The EPR spectrum was also changed strikingly upon the addition of protohemin. This change, however, was not proportional to the amount of hemin added, but marked changes occurred after 3 to 4 mol of hemin were mixed with 1 mol of spin-labeled globin. The EPR spectrum of spin-labeled hemoglobin thus prepared was identical with that prepared by direct spin labeling to methemoglobin. These results suggest the preferential binding of hemin to alpha-globin chains in the course of heme binding by globin. This assumption was further confirmed by preparing spin-labeled semihemoglobin in which only one kind of chain contained hemin (alpha h betaO SL and alpha O beta h SL). The EPR spectrum of the alpha h beta O SL molecule showed a slightly immobilized EPR spectrum, similar to that of spin-labeled globin mixed with 50% of the stoichiometric amount of hemin. On the other hand, the alpha O beta h SL molecule showed a distinctly different EPR signal from that of globin half-saturated with hemin, and showed an intermediate spectrum between those of beta h SL and alpha h beta h SL. These results indicate that heme binding to globin chains brings about a major conformational change in the protein moiety and that chain-chain association plays a secondary role. We conclude that hemin binds preferentially to alpha-globin chains and that the conformation of globin changes rapidly to that of methemoglobin after all four hemes are attached to globin heme pockets.

Apoproteins↗
PubMed1976

Positive direct antiglobulin reaction in a patient population.

This study was undertaken to ascertain the incidence, the associated clinical diseases, and the serologic characteristics and significance of positive direct antiglobulin tests (DAT) in a hospital population. Forty-one (0.9%) of 4,664 medical-surgical patients had positive DAT's on admission. Eight of these 41 people also had antibodies in their sera. Twelve patients were taking alpha-methyldopa and one cephalothin, seven had malignant tumors, nine had immunologic disease, and 12 had miscellaneous conditions. Elution of antibodies from the erythrocytes of 36 patients was attempted: 17 eluates failed to react with panel cells; anti-K antibody was found in the eluates from two patients who had recently received transfusions; five eluates showed no blood-group specificity; and 12 agglutinated all panel cells. Eleven of the last 12 eluates, after absorption with Rh-negative cells, were tested with Rh cells of various phenotypes, and weaker or negative results with Rhnull cells were obtained with seven absorbed eluates. Three of the 41 patients had mild to overt hemolysis.

Adolescent↗
PubMed1975

Effects of scopolamine, physostigmine and chlordiazepoxide on punished and extinguished water consumption in rats.

It has been postulated that behavioral inhibition due to punishment or extinction may be mediated by brain acetylcholine, and drugs which have disinhibitory action are thought to interact with this system. This notion was tested by comparing the effects of scopolamine, physostigmine and chlordiazepoxide on punished and extinguished water consumption. Scopolamine hydrobromide (0.3, 0.5 mg/kg, i.p.), a centrally and peripherally acting antimuscarinic agent and physostigmine sulfate, (0.3 mg/kg, i.p.), a centrally and peripherally acting acetylcholinesterase inhibitor, lowered both non-punished and punishment suppressed water intake and lick rate, whereas their quaternary analogs which primarily act in the periphery, had no significant effect at comparable dose levels. Scopolamine and physostigmine suppressed punished water consumption at lower dose levels than nonpunished intake. In contrast, chlordiazepoxide (5.0, 10.0, 20.0 mg/kg, i.p.) enhanced punished as well as non-punished water intake. In a further experiment comparing punishment and extinction suppression, scopolamine and physostigmine did not affect punished or extinguished water intake; chlordiazepoxide (5.0, 10.0, 20.0 mg/kg) reliably increased punished, but not extinguished licking on the water nozzle. These results suggest (1) that scopolamine and chlordiazepoxide do not act via a common mechanism, and (2) that punishment and extinction suppression are not a pharmacological entity.

Acetylcholine↗
PubMedDate not supplied

Coagulation defects in rabbits after infusion of dispersed fluorochemicals.

Coagulation parameters were studied in rabbits during and after intravenous infusion of suspensions of dispersed fluorochemicals. Blood samples from rabbits given dispersed perfluorobutyltetrahydrofurane or perfluorotributylamine showed thrombocytopenia, prolongation of activated partial thromboplastin time, and decreases in Factors X and XI. The possible presence of an inhibitor of coagulation was suggested by the prolongation of prothrombin time when measured with serial dilutions of thromboplastin reagent. These abnormalities were not found in whole blood or platelet-rich plasma after incubation in vitro with dispersed fluorochemical.

Animals↗
PubMedDate not supplied

The effect of centrifugation time on cellular residues in fresh plasma.

Cellular residues were present in all fresh plasma prepared by a standard technique with centrifugation times of 5, 7, or 10 minutes. The amounts of cellular residues in the plasma were inversely proportional to the time of centrifugation. Platelet contamination was statistically different in the three times tested. In contrast, the residual amounts of erythrocytes and leukocytes were significantly different only when 5- and 10-minute centrifugation times were compared.

Blood Platelets↗
PubMedDate not supplied

Studies on the blood of an MsHe/MSu proposita and her family. Serological evidence that Henshaw-producing genes do not code for the 'N' antigen.

The serum of a black woman has been found to contain a potent alloanti-N that reacted in direct agglutination tests with the 'N' antigen carried on Ss-active sialoglycoprotein. Thus far, such antibodies have been observed only in the sera of MSu/MSu individuals. However, our proposita had red cells that lacked 'N'. Her blood type was M+, N-, S-, s+, U+, He+. Results of family studies indicate that she is of the genotype MsHe/MSu. Our findings are consistent with recently reported data on the structure of the Henshaw antigen, which is located on a Ss-active sialoglycoprotein that does not carry 'N'.

Blood Group Incompatibility↗