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Biomedical subjects

A Chen

Publications and source records attributed to A Chen.

At least 451 records · Page 25Linked to original sources
PubMed1984

Sulpiride isomers exhibit reversed stereospecificity for D-1 and D-2 dopamine receptors in the CNS.

We have investigated the stereospecificity of the interaction of (-) and (+)sulpiride with [3H]cis-flupentixol and [3H]spiperone binding to D-1 and D-2 dopamine receptors respectively in rat striatum. Both isomers of sulpiride compete more potently at D-2 vs. D-1 dopamine receptors. (-)Sulpiride is 50-fold more potent than (+)sulpiride in blocking D-2 receptors, while (+)sulpiride is 3-fold more potent than (-)sulpiride at D-1 receptors. This reversed stereospecificity of sulpiride interactions with CNS D-1 and D-2 dopamine receptors is similar to the stereospecificity of sulpiride interactions at DA1 and DA2 dopamine receptors in peripheral vascular beds.

Animals↗
PubMed1983

Metabolic clearance rate and half-time disappearance rate of human N-terminal and adrenocorticotropin of pro-opiomelanocortin in the rat: a comparative study.

In metabolic clearance rate (MCR) and plasma half-time disappearance rate (t 1/2) of human N-terminal (1-76) and adrenocorticotropin(hACTH 1-39) of pro-opiomelanocortin were compared after intravenous bolus injection of both peptides simultaneously into rat. The level of immunoreactive (IR) hNT and IR-ACTH in plasma and urine samples were measured by specific and homologous radioimmunoassays (RIAs). The MCR and hNT and hACTH were 3.01 +/- 0.20 ml/min (M +/- S.D., N = 4) and 2.04 +/- 0.06 ml/min, respectively (p less than 0.05), The curve for the disappearance rate of IR-hNT was triphasic (rapid t 1/2 = 0.96 +/- 0.39 min, intermediate t 1/2 = 6.7 +/- 2.25 min, and slow t 1/2 = 74 +/- 15.8 min), while that of IR-ACTH was biphasic (rapid t 1/2 = 3.3 +/- 0.68 min, and slow t 1/2 = 41.5 +/- 3.03 min) as analyzed by the non-linear least-squares methods. Statistically significant difference (p less than 0.01) was found between IR-hNT and IR-hACTH in the rapid t 1/2 and in the slow t 1/2. Subsequent analysis of pooled plasma sample (30 min post-injection) by molecular sieve chromatography on Sephadex G-50 superfine column revealed that the majority of IR-hNT (90-95%) and IR-ACTH (60-70%) are co-chromatographed with [125I]iodo hNT and [125I]iodo ACTH respectively. Similarly, gel filtration of pooled urine sample (120 min post-injection) on Sephadex G-50 superfine revealed that 80-90% of IR-hNT and less than 50% of IR-ACTH co-eluted with [125I]iodo hNT and [125I]iodo ACTH, respectively. Smaller molecular forms of IR-hNT and IR-ACTH were definitely apparent in the urine sample. In conclusion, hNT has a larger MCR and a longer half-time disappearance rate (t 1/2) than IR-hACTH in rat plasma and it appears that hNT is more resistant to degradation by plasma and by kidney than hACTH.

Adrenocorticotropic Hormone↗
PubMed1982

Identification of beta-endorphin-6(16-17) as the principal metabolite of des-tyrosin-gamma-endorphin (DTgammaE) in vitro and assessment of its activity in neurotransmitter receptor binding assays.

Des-tyrosine-gamma-endorphin (beta-endorphin-(2-17); DTgamma E) lacks direct in vitro activity at dopaminergic receptors, but does inhibit in vivo [3H]spiperone binding in various rat brain areas. The principal objective of these studies was to test the hypothesis that DTgammaE may exert its selective, neuroleptic-like activity through an active metabolite. Accordingly, DTgammaE was incubated at 37 degrees C in a whole rat brain homogenate of neutral pH after which samples were prepared for HPLC analysis. The major, heat-stable metabolite of DTgammaE was identified as the clinically active, beta-endorphin related fragment, beta-endorphine-(6-17). The beta-endorphin sequences 4-17, 5-17, l0-17, 12-17 and 2-16 were also present but in minor amounts. Identical results were obtained studying DTgammaE metabolism using rat striatal tissue slices. Neurotransmitter receptor binding experiments showed that beta-endorphin-(6-17) was inactive at central dopaminergic, serotonergic, muscarinic, benzodiazepine and opiate receptors measured in vitro. Thus, like DTgammaE, beta-endorphin-(6-17) differs from classical neuroleptics in that it does not inhibit in vitro [3H]spiperone binding in the corpus striatum, frontal cortex or mesolimbic areas of the rat brain. It may be that DTgammaE and beta-endorphine-(66-17) exert their selective neuroleptic-like activity through an indirect inhibition of central dopaminergic activity, possibly in combination with an in vivo antagonism of the postsynaptic dopamine receptor.

Animals↗
PubMed1982

High performance liquid chromatography of pharmacologically active amines and peptides in biological materials.

Precise and quantitative reversed-phase high performance liquid chromatographic (HPLC) procedures are described which can be used in biogenic amine and neuropeptide research. The amine procedure was applied to various pharmacological matrices including plasma, heart tissue and brain. The use of peptide HPLC as an analytical tool for various neuropeptides is illustrated by studies on des-tyrosine-gamma-endorphin (DT gamma E) metabolism in the brain and the stability of an ACTH (ORG-2766) analogue during a chronic infusion in rats. The power of HPLC as a research tool in peptide pharmacology is described, discussed and demonstrated as an aid in the understanding of the pharmacological effects of exogenous peptides and the function of the brain.

Adrenocorticotropic Hormone↗
PubMed1982

Modulation of benzodiazepine receptor binding: insight into pharmacological efficacy.

The effects of GABA on the binding of analogues of benzodiazepines, triazolopyridazines, beta-carbolines and imidazodiazepines were examined in ligand/[3H] flunitrazepam competition experiments. GABA increased the potency of anxiolytics, like flunitrazepam, whereas the potency of benzodiazepine antagonists, like Ro15-1788, was largely insensitive to the influence of GABA. Several other agents including pyrazolopyridines, barbiturates and etomidate caused a chloride dependent enhancement of [3H] flunitrazepam binding but not an enhancement of [3H] propyl-beta-carboline-3-carboxylate binding.

Animals↗
PubMed1982

A test and calibration process for microcalorimeters used as thermal power meters.

A test and calibration process for microcalorimeters is described. The method has been developed with particular reference to instruments used for measurements of thermal power produced by suspensions of living cells. The process investigated is the hydrolysis of triacetin in imidazole/acetic acid buffer. The power levels are regulated by changing the buffer composition. The power will decrease slowly and very nearly linearly with time. Five test solutions, power levels 7-90 microW X ml-1, have been characterized at 37 degrees C and one of them at 25 degrees C (13 microW X ml-1). The power values for these reaction mixtures can be accurately calculated (+/- 0.5%) as a function of time during extended reaction periods, about 20 h or more.

Buffers↗
PubMed1982

Simultaneous determination of delta G, delta H and delta S by an automatic microcalorimetric titration technique. Application to protein ligand binding.

A methodological study has been made with a syringe titration unit attached to an LKB batch microcalorimeter. The precision and accuracy of the instrument assembly have been evaluated by neutralization reactions and by dilution of sucrose solutions. As an example, heat quantities on the order of 10 mJ accompanying the addition of 10 microliter titrant solution could be determined with an accuracy of better than 1%. A stepwise titration procedure was used to characterize the binding of indole-3-propionic acid to alpha-chymotrypsin. The following thermodynamic data were obtained (25 degrees C, acetate buffer, pH 5.80): delta G0=-18.46 +/- 0.17 kJ X mol-1, delta H0=-15.26 +/- 0.20 kJ X mol-1, delta S0 = 10.85 +/- 1.21 JK-1 X mol-1.

Calorimetry↗
PubMed1982

Change in auditory asymmetry with amobarbital: evidence of cerebral pharmacological asymmetry?

Eleven right-handed subjects were administered a dichotic listening test to assess cerebral hemispheric dominance, both under a drug-free condition and following systemic injection of the barbiturate, amobarbital. The finding of increased right ear advantage during the drug period reflects increased left cerebral dominance, and suggests that amobarbital may have an asymmetric, pharmacological effect on the two cerebral hemispheres.

Adult↗
PubMed1981

Characterization of clones of tumorigenic feline cells transformed by a chemical carcinogen.

Tumorigenic clonal lines derived from soft agar colonies induced by DMBA-transformed feline embryo cells were isolated and characterized. The morphologically altered clonal cells formed large aggregates, growing in this aggregate form when suspended in liquid growth medium above an agar base and forming colonies in soft agar with high efficiency. When inoculated into athymic nude mice, chemically altered clonal cells produced progressively growing sarcomas. Cells established from the tumors morphologically resembled the DMBA-transformed feline embryo cells and were characterized as cat cells by karyological analysis. The tumorigenic lines were negative for feline oncornavirus-associated cell membrane antigen (FOCMA), and for "gag-X" the transformation-related polyprotein which is encoded by the replication defective feline sarcoma virus.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1976

Thyroid hormones: effect of physiological concentrations on cultured cardiac cells.

Cultured cardiac cells prepared from newborn rat heart will respond in vitro to physiological concentrations of L-triiodothyronine. The cells are grown in a culture medium that contains hypothyroid calf serum. A dose response relationship of L-triiodothyronine indicates that this system may be a useful model for elucidation of the mechanism of thyroid hormone effects on the heart.

Animals↗