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Biomedical subjects

R S Chang

Publications and source records attributed to R S Chang.

At least 91 records · Page 5Linked to original sources
PubMed1988

Genetic polymorphism of natural Epstein-Barr virus isolates from infectious mononucleosis patients and healthy carriers.

We analyzed Epstein-Barr virus (EBV) genomes from lymphoblastoid cell lines isolated from patients with infectious mononucleosis and from healthy subjects from California, Hawaii, and Hong Kong between 1970 and 1987. Using genetic polymorphism as epidemiological markers, we found that several genotypes of EBV cocirculate in a community and that although most EBV strains isolated from California and Southern China may be differentiated genotypically, there was no specific association between genotype and disease or time of isolation.

B-Lymphocytes↗
PubMed1988

Dextran sulfate as an inhibitor against the human immunodeficiency virus.

Dextran sulfate (DS) is a potent inhibitor of the growth of human immunodeficiency virus type 1 (HIV-1) in the H9 cell. Its minimal inhibitory concentration is about 1 microgram/ml. Its therapeutic index is greater than or equal to 200 which is higher than that of 38 for zidovudine. At the ID100 range, DS blocks the synthesis of HIV-1 antigens completely for at least 21 days; zidovudine at the subtoxic concentration of 3 micrograms/ml is incapable of achieving such a complete blockage. DS is still active when added to H9 cell cultures 4 hr after the addition of HIV-1. DS does not inactivate extracellular HIV-1 and is incapable of inducing interferons. It interferes partially with the infection of the H9 cells by the HIV-1. It inhibits the activity of HIV-1 reverse transcriptase. These activities may account, at least in part, for the inhibitory activity of dextran sulfate against the HIV-1. DS has a narrow antiviral spectrum; it is noninhibitory to the herpes simplex, vesicular stomatitis, polio, or adeno viruses. Dextran is not inhibitory to HIV-1. After sulfonation, the sulfonated dextran is highly inhibitory. Therefore, the sulfate group in the DS molecule appears to be essential for its anti-HIV-1 activity. The molecular weights of DS within the range 4000 to 12,000 do not appear to influence its anti-HIV potency.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Characterization of [3H](+/-)L-364,718 binding to solubilized cholecystokinin (CCK) receptors of rat pancreas.

The binding of [3H](+/-)L-364,718 (3S(-)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3-yl )-1H-indole-2-carboxamide), an extremely potent nonpeptide cholecystokinin (CCK) receptor antagonist, to digitonin-solubilized CCK receptors from rat pancreas was characterized. [3H](+/-)L-364,718 binding to digitonin-solubilized receptors was assayed using polyethylene glycol precipitation followed by rapid filtration to separate free and bound [3H](+/-)L-364,718. Specific [3H](+/-)L-364,718 binding to solubilized receptors was dependent on the digitonin and receptor concentration and, under optimal conditions, represented greater than 90% of the total binding. Scatchard analysis indicated a single class of binding sites with a Kd of 0.53 nM and a Bmax of 3.1 pmol/mg protein. Specific [3H](+/-)L-364,718 binding to solubilized CCK receptors was inhibited by both CCK receptor agonists and antagonists in a stereospecific manner. After solubilization, the affinities of various antagonists to displace specific [3H](+/-)L-364,718 binding were similar to those obtained with membrane-bound receptors; however, the affinities of CCK agonists were reduced 10-100 times. Collectively, the data presented indicate that [3H](+/-)L-364,718 represents a new antagonist ligand which has apparent advantages over the agonist ligand [125I]CCK in assaying digitonin-solubilized receptors. Gel filtration of the digitonin-solubilized CCK receptors followed by [3H](+/-)L-364,718 binding determinations revealed an estimated molecular weight of 400,000 daltons.

Animals↗
PubMed1987

Computer programs for the analysis of protein fluorescence quenching data.

Educational computer programs for analysis of fluorescence quenching studies of proteins have been developed. The program is written according to the classical Stern-Volmer equation and some modified Stern-Volmer equations. The static and dynamic quenching constants as well as the accessibility of the quencher molecules to the fluorescence groups are calculated. The experimental data are plotted on a high resolution graph. The calculated data or the graphs can be printed out to obtain a hard copy for filing.

Kinetics↗
PubMed1987

In vivo pharmacology of L-364,718, a new potent nonpeptide peripheral cholecystokinin antagonist.

The in vivo pharmacological activity of L-364,718, a new, potent peripheral cholecystokinin (CCK) antagonist, was characterized in several species using assay systems that measure various well known actions of CCK upon the gastrointestinal system. Administered p.o., L-364,178 was highly potent in antagonizing cholecystokinin octapeptide (CCK-8)-induced inhibition of gastric emptying in mice (ED50 = 38 micrograms/kg), rats (ED50 = 140 micrograms/kg) and dogs (ED50 = 91 micrograms/kg) as well as CCK-8-induced reduction in food consumption in rats (ED50 = 321 micrograms/kg). Administered i.v., L-364,718 effectively antagonized the contractile effects of CCK on the colon in rabbits (ED50 = 34 micrograms/kg) and the gallbladder in cats (ED50 = 210 micrograms/kg). Secretion of pancreatic protein and amylase elicited by CCK in cats was also antagonized by L-364,718 (ED50 less than 1.0 mg/kg i.v.). The CCK antagonism produced by L-364,718 in all species persisted for at least 2 to 5 hr. In the absence of exogenously administered CCK-8, L-364,718 per se had no effect in any of the assay systems studied, indicating a lack of CCK-like agonist properties. Specificity for CCK was demonstrated by the inability of L-364,718 (1.0-5.0 mg/kg) to antagonize either amino acid- or atropine-induced inhibition of gastric emptying in rats and dogs, respectively. L-364,718 also did not antagonize motilin-induced gallbladder contractions or secretin-induced pancreatic secretion in cats.(ABSTRACT TRUNCATED AT 250 WORDS)

Amylases↗
PubMed1986

Tifluadom, a kappa-opiate agonist, acts as a peripheral cholecystokinin receptor antagonist.

Tifluadom, a benzodiazepine kappa-opiate agonist, stereoselectively inhibited the binding of 125I-CCK to pancreatic membranes (IC50 = 47 nM). Several other opiate agonists were ineffective. Scatchard analysis indicated the inhibition of CCK binding by tifluadom was competitive in nature. Tifluadom (1 microM) did not displace 125I-CCK binding to brain tissue or 125I-gastrin binding to fundic glands. In the isolated guinea pig gallbladder, tifluadom antagonized CCK-8 induced contractions with an estimated pA2 of 6.8. These data demonstrate that tifluadom is a peripherally selective CCK antagonist. This unique action could contribute to its reported analgesic and appetite stimulatory properties.

Animals↗
PubMed1986

Increased neuropeptide Y (NPY) receptor binding in hippocampus and cortex of spontaneous hypertensive (SH) rats compared to normotensive (WKY) rats.

Specific 125I-NPY binding in various brain regions of spontaneous hypertensive (SH) rats and age-matched normotensive (WKY) rats was compared. SH rats exhibited significantly greater 125I-NPY binding than WKY rats in the hippocampus (43%) and cortex (18%), but not hypothalamus, midbrain, striatum or pons-medulla. Scatchard analysis indicated that the increased 125I-NPY binding in the hippocampus of SH rats represents a greater number of NPY binding sites.

Animals↗
PubMed1986

Thyrotropin-releasing hormone receptors in gut tissues resemble pituitary receptors.

The relative order of activity of thyrotropin-releasing hormone (TRH) and various analogs in contracting the isolated guinea pig antrum and duodenum correlated with their potencies in activating thyroid-stimulating hormone (TSH) release. The action of TRH in both tissues was selectively antagonized by the putative pituitary TRH receptor antagonist, chlordiazepoxide (10 microM). The data indicate that the contractions produced by TRH in these gut tissues are mediated by TRH receptors with similar characteristics as the pituitary TRH receptors responsible for TSH release.

Animals↗
PubMed1986

Characterization of [3H]pentagastrin binding in guinea pig gastric glands--an alternative convenient ligand for receptor binding assay.

The binding of [3H]pentagastrin to guinea pig gastric glands was specific, saturable and of high affinity (Kd = 5 nM). The relative order of potencies for gastrin and CCK analogs in displacing [3H]pentagastrin binding correlated well with those obtained using [125I]gastrin and their reported biological potencies for stimulating acid secretion. Nonselective CCK/gastrin antagonists including carbobenzoxy-CCK (26-32), proglumide and benzotript, but not the selective peripheral CCK antagonist, asperlicin, inhibited specific [3H]pentagastrin binding. The results indicate that [3H]pentagastrin labels physiologically relevant gastrin receptors in guinea pig gastric glands.

Animals↗
PubMed1986

Relative sensitivity of cell culture systems in the detection of herpes simplex viruses.

Guinea pig embryonic fibroblasts were more sensitive and McCoy and Hep-2 cells were less sensitive than human foreskin fibroblasts in parallel titrations of herpes simplex virus. No difference in sensitivity was found for five lines of human fetal lung fibroblasts (including WI-38 cells), two lines of human embryo fibroblasts, one line of human foreskin fibroblasts, cells from a human fetal kidney, amnion cells from a human placenta, the Chang liver cell, the HeLa cell, and a line of mink cells. The cell doubling level of human or guinea pig fibroblast lines did not affect their sensitivity. One hundred ninety-five clinical specimens submitted for herpes simplex virus isolations were tested in parallel in primary rabbit kidney, guinea pig embryo, and human fetal lung fibroblast cultures. The percentages of positive or false-negative cultures were essentially the same for the three types of cells.

Amnion↗
PubMed1986

Cholecystokinin antagonists. Synthesis of asperlicin analogues with improved potency and water solubility.

Seventeen analogues of the selective, competitive cholecystokinin (CCK) antagonist asperlicin 1 were prepared. These compounds were tested as inhibitors of the binding of [125I]CCK to rat pancreas and guinea pig brain receptors. Compounds 4, 7, and 8 were more potent than asperlicin on the pancreatic CCK receptor. One analogue, 17, displayed potency equivalent to asperlicin on the pancreas CCK receptor and showed a marked improvement in aqueous solubility, thereby facilitating the use of this class of CCK antagonists in physiological and pharmacological studies.

Animals↗
PubMed1986

Biochemical and pharmacological characterization of an extremely potent and selective nonpeptide cholecystokinin antagonist.

3S(-)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4- benzodiazepine-3-yl)-1H-indole-2-carboxamide (L-364,718) interacted in a competitive manner with rat pancreatic cholecystokinin (CCK) receptors as determined by Scatchard analysis of the specific binding of 125I-labeled CCK. The affinity of L-364,718 for both pancreatic (IC50, 81 pM) and gallbladder (IC50, 45 pM) CCK receptors in radioligand binding assays greatly exceeded that of other reported nonpeptide CCK antagonists and was similar to that of CCK itself. In vitro functional studies utilizing CCK-induced contractions of the isolated guinea pig ileum and colon further demonstrated that L-364,718 acts as a competitive CCK antagonist, which lacks agonist activity and has a similar high affinity in these tissues (pA2, 9.9). L-364,718 exhibited a very high selectivity for peripheral CCK receptors relative to brain CCK, gastrin, and various other peptide and nonpeptide receptors in both in vitro radioligand and isolated tissue assays. In vivo, low intravenous doses of L-364,718 (0.1 mg/kg) markedly antagonized the contractions of the guinea pig gallbladder produced by intravenous administration of CCK for at least 2 hr. Administered orally, L-364,718 (ED50, 0.04 mg/kg) was highly effective as an antagonist of CCK-induced inhibition of gastric emptying in mice. The biochemical and pharmacological properties of L-364,718--namely, very high affinity and selectivity for peripheral CCK receptors, long-lasting in vivo efficacy, and oral bioavailability--makes this compound a powerful tool for investigating the physiological and pharmacological actions of CCK, and possibly its role in gastrointestinal disorders.

Animals↗
PubMed1986

Evidence that cholecystokinin octapeptide (CCK-8) acts as a potent, full agonist on gastrin receptors for acid secretion in the isolated mouse stomach: lack of antagonism by the specific CCK antagonist asperlicin.

Cholecystokinin octapeptide (CCK-8) (EC50 = 5 nM) was considerably more potent than pentagastrin (EC50 = 161 nM) in stimulating acid secretion in the isolated perfused mouse stomach suspended in a medium containing a phosphodiesterase inhibitor. The maximum acid response to CCK-8 was not significantly different from that produced by pentagastrin. The nonselective CCK/gastrin antagonist, proglumide, but not the selective CCK antagonist, asperlicin, antagonized the acid response to both pentagastrin and CCK-8. The data suggest that CCK-8 acts as a potent, full agonist on gastrin receptors for acid secretion in the isolated mouse stomach.

Animals↗
PubMed1986

Characterization of the binding of [3H]-(+/-)-L-364,718: a new potent, nonpeptide cholecystokinin antagonist radioligand selective for peripheral receptors.

[3H]-(+/-)-L-364,718 a new, potent and selective nonpeptide peripheral cholecystokinin (CCK) antagonist bound saturably and reversibly to rat pancreatic membranes. The radioligand recognized a single class of binding sites with a high affinity (Kd = 0.23 nM). The binding of [3H]-(+/-)-L-364,718 was stereospecific in that the more biologically active (-)-enantiomer demonstrated greater potency than the (+)-enantiomer. The rank order of potency of various CCK agonists and antagonists in displacing [3H]-(+/-)-L-364,718 correlated with their ability to displace [125I]CCK-8 and their known pharmacological activities in peripheral tissues. However, the absolute potencies of agonists were greater in displacing [125I]CCK-8 than [3H]-(+/-)-L-364,718. As described for other physiologically relevant receptor systems, the potency for displacement of [3H]-(+/-)-L-364,718 binding by CCK agonists, but not antagonists, was reduced by guanosine 5'-(beta, gamma-imido)triphosphate and NaCl and enhanced by MgCl2. [3H]-(+/-)-L-364,718 also demonstrated specific binding to bovine gall bladder tissue but not guinea pig brain or gastric glands, consistent with its selectivity as a peripheral CCK antagonist. [3H]-(+/-)-L-364,718 binding to pancreatic membranes was not affected by various pharmacological agents known to interact with other common peptide and nonpeptide receptor systems. These data indicate that [3H]-(+/-)-L-364,718 represents a new potent nonpeptide antagonist radioligand for the study of peripheral CCK receptors which may allow differentiation of agonist and antagonist interactions.

Animals↗