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Biomedical subjects

L C Tang

Publications and source records attributed to L C Tang.

At least 37 records · Page 2Linked to original sources
PubMed1991

Linking phospholipase A2 to phospholipid turnover and prostaglandin synthesis in mast cell granules.

Rapid incorporation of exogenous arachidonic acid into phospholipid has been detected in conjunction with eicosanoid synthesis by purified mast cell granules [Chock, S. P. & Schmauder-Chock, E. A. (1988) Biochem. Biophys. Res. Commun. 156, 1308-1315]. The species of phospholipid formed has now been identified primarily as phosphatidylinositol. A calcium-dependent phospholipase A2 has also been detected in the secretory granule. This enzyme, like the cyclooxygenase [Schmauder-Chock, E. A. & Chock, S. P. (1989) J. Histochem. Cytochem. 37, 1319-1328], appears to bind tightly to the granule matrix components. It is heat resistant and requires millimolar concentrations of calcium for optimal activity. It prefers phosphatidylinositol over phosphatidylcholine as substrate. Since the granule contains a large amount of phospholipid, the action of this phospholipase A2 can provide the required substrate for the arachidonic acid cascade. These findings provide the basis for linking phospholipase A2 to the production of eicosanoids during granule exocytosis. Since the granule also contains both an active acylating system that can rapidly reacylate lysophosphatidylinositol to form phosphatidylinositol, and an active phospholipase A2 which hydrolyzes phosphatidylinositol, a rapid turnover involving the fatty acid at the sn-2 position of phosphatidylinositol may occur. These findings are consistent with our postulation that the secretory granule is the source and/or the cause of many of the early biochemical events associated with the process of stimulus-secretion coupling.

Animals↗
PubMed1991

Human erythrocyte as a model for investigating muscarinic agonists and antagonists.

1. Human erythrocyte muscarinic receptor is further classified as M1 subtype by its binding of [3H]pirenzepine (a specific M1 antagonist). Conversely, binding of [3H]piperidinyl AF-DX116 (a specific M2 antagonist) is not detected. 2. There are high correlations between the binding efficacies of 25 known or putative cholinergic agents using either human erythrocyte membrane or mouse caudate homogenate. Also the in vitro data corresponds satisfactorily with in vivo data measuring the protective effect of these compounds against organophosphate poisoning. 3. The human erythrocyte membrane is an efficient model for investigating cholinergic agonists and antagonists.

Animals↗
PubMed1987

The modulation of dopamine-sensitive adenylate cyclase activity in the mouse caudate nucleus by estradiol.

When levodopa (L-DOPA) is administered to mice, the central nervous system responses to the dopamine stimulation were less sensitive in female than in the male mice. The sensitivity is reflected both behaviorally and biochemically. The behavioral response were measured by scores recorded after intraperitoneal injection of a standard dose of L-DOPA. The biochemical studies included the determination of the cyclic AMP produced by in vitro experiments after incubating dopamine with mouse caudate nucleus homogenates. This insensitivity to dopamine stimulation in female animals can be reversed by ovariectomy. Estradiol treatment in vivo suppressed the dopamine stimulation, while estradiol directly added to the caudate nucleus homogenate does not affect the dopamine-sensitive adenylate cyclase activity. These findings indicate that the estradiol-induced effects on the brain enzyme are indirect. The female sex hormone does have an effect on the central dopaminergic system. However, the underlying mechanism(s) cannot be delineated by the present studies.

Adenylyl Cyclases↗
PubMed1986

Identification and characterization of human erythrocyte muscarinic receptors.

Cholinergic muscarinic but not nicotinic receptors could be detected on the outer surface of the human red blood cell membrane by direct labelled ligand binding. This 3H-QNB binding could be inhibited by atropine. The erythrocyte cholinergic receptor was similar to brain muscarinic receptor in regard to stimulation of cGMP production.

Calcium Chloride↗
PubMed1986

Seminal plasma transferrin and seminiferous tubular dysfunction.

Seminal plasma transferrin levels were assayed in 158 random semen samples collected from normospermic, oligospermic, and azoospermic men, and their relationships with seminal characteristics, sperm fertilizing capacity as assessed by the zona-free hamster ova penetration assay, and serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were evaluated. The concentrations of seminal plasma transferrin in azoospermic, oligospermic and postvasectomy samples were significantly lower than those in normospermic samples. Seminal plasma transferrin concentrations were similar in azoospermia due to obstruction of the reproductive tract or damage to the germinal epithelium. No significant difference in seminal plasma transferrin concentrations was observed in the groups of subjects with normal and elevated FSH or normal and elevated LH. A positive correlation was observed between seminal plasma transferrin concentration and sperm density and between total semen transferrin content and the total number of sperm in the ejaculate. There were no significant correlations between seminal plasma transferrin concentration and sperm motility, percent normal sperm, sperm fertilizing capacity, and serum FSH or LH concentration. The results indicate that seminal plasma transferrin is not a useful marker for Sertoli cell or seminiferous tubular dysfunction. In addition, it is doubtful that measurement of seminal plasma transferrin will yield additional information regarding the fertility potential of semen samples.

Follicle Stimulating Hormone↗
PubMed1986

Thymectomy in myasthenia gravis during pregnancy.

A 24 year old woman with myasthenia gravis suffered an antepartum exacerbation which failed to respond to increasing dosages of pyridostigmine. Thymectomy performed in the second trimester was followed by clinical improvement and full term vaginal delivery with no puerperal deterioration.

Adult↗
PubMed1985

Pregnancy in patients with mitral valve prolapse.

The obstetrical performances and outcomes of 37 pregnancies in women with mitral valve prolapse between 1979 and 1982 are reviewed. Thirteen patients were diagnosed before pregnancy and 24 patients were detected at antenatal examinations. Three ended in cesarean sections for obstetrical complications and 34 in uneventful vaginal deliveries at term. No cardiac complications occurred in these patients. There was no maternal mortality. Thirty-six babies were born without congenital abnormalities. One baby was hydropic due to haemoglobinopathy and died. Prophylactic antibiotics is recommended in selected cases. Early detection and treatment of cardiac arrhythmias is mandatory.

Adult↗
PubMed1985

Effect of clomiphene citrate on human spermatozoal motility and fertilizing capacity in vitro.

The effect of clomiphene citrate (CC) at various concentrations (0.005, 0.05, 0.5, 5, and 50 micrograms/ml) on the in vitro motility and fertilizing capacity of human spermatozoa was studied. Spermatozoa collected from 14 normal men were washed in modified Krebs-Ringer solution (Biggers, Whitten and Whittingham [BWW] medium) and incubated with CC for 5 hours, the period required for spermatozoal capacitation. The percent motilities of spermatozoa were recorded at 0 and 5 hours during incubation with CC. After incubation, the spermatozoa were washed with BWW medium to remove CC before insemination of the zona-free hamster ova. CC caused a significant dose-dependent decrease in the penetration of denuded hamster ova in comparison with the control (P less than 0.05). Significant depressive effect on spermatozoal motility was observed with CC at 0.05 micrograms/ml or higher concentrations (P less than 0.05). These results indicate that (1) CC decreases human spermatozoal fertilizing capacity in vitro and (2) the inhibitory effect on fertilizing capacity could be due to the sperm-immobilizing activity of CC.

Animals↗
PubMed1985

Clomiphene citrate does not improve spermatozoal fertilizing capacity in idiopathic oligospermia.

Clomiphene citrate (CC) was given to 24 men with idiopathic oligospermia at a daily dose of 25 mg (10 subjects) or 50 mg (14 subjects). Sperm concentration increased slightly after CC treatment in both groups. Sperm motility and morphology remained unchanged. Spermatozoal fertilizing capacity as assessed by the zona-free hamster ova penetration test showed no significant change throughout the treatment period. Two pregnancies occurred in the partners of the subjects treated with 50 mg CC/day, but none occurred in the other group. We conclude that oral administration of CC does not improve fertilizing capacity of sperm as measured by the zona-free hamster ova penetration test in idiopathic oligospermia.

Adult↗