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S X Xu

Publications and source records attributed to S X Xu.

68 records · Page 4Linked to original sources
PubMed1986

Different effects of enantiomers of tetrahydropalmatine on dopaminergic system.

Tetrahydropalmatine (THP) has two enantiomers with different effects on the brain dopaminergic system. Using [3H]spiperone for DA receptor binding assay, it was found that l-THP had an affinity to DA receptors (Ki = 0.2 microM). Neither d-THP nor reserpine showed such an effect even at concentrations higher than 100 or 1000 microM. Based on the fact that the presynaptic DA receptors take part in feed-back regulation on tyrosine hydroxylase activity, DOPA accumulation could be observed in rat striatum after injection of benserazide. A small dose of l-THP (2.5, 5, 10 mg/kg, ip.) caused an elevation of DOPA level by 49-282% versus the control value, and could reverse the decrease of DOPA level induced by apomorphine, a DA receptor agonist. On the contrary, d-THP displayed a biphasic effect on DOPA level, slight decrement (26-37%) at 10 and 25 mg/kg, naught at 50 mg/kg, and a 91% increment at 100 mk/kg, which was less than that of l-THP at 5 mg/kg. Moreover, measured by pulse voltammetry, DOPAC level in the striatum was raised by 88 or 190% at 2.5 or 10 mg/kg respectively. By means of spectrofluophotometry, l-THP at 50-100 mg/kg reduced DA level by 24-26%. However, the DA content reduction induced by d-THP is much more dose-dependent. At a small dose (10 mg/kg), d-THP predominantly reduced the DA level but left 5-HT and NA level unaffected. It caused an 80% reduction of DA at 100 mg/kg. From the above findings, it might be concluded that l-THP is a DA receptor antagonist, while d-THP is probably a DA depletor.

Alkaloids↗
PubMedDate not supplied

Pharmacology of functional endogenous IP prostanoid receptors in NCB-20 cells: comparison with binding data from human platelets.

The objective of these studies was to characterize the effects of a broad range of prostanoid agonists upon the stimulation of cAMP production in National Cancer Bank (NCB-20; mouse neuroblastoma/hamster brain hybridoma) cells. The pharmacology of these functional responses in NCB-20 cells was compared with that of the classic endogenous IP receptor present on human platelets using [3H]-iloprost binding techniques. In both assay systems, agonists from the IP prostanoid class exhibited the highest affinities and functional potencies. Specific prostanoids exhibited the following rank order of potency (EC50 +/- SEM) in stimulating cAMP production in the NCB-20 cells: carbaprostacyclin (4.3 +/- 0.9 nM) = PGI2 (6.6 +/-1.5 nM) > iloprost (75+/-13 nM) > 11-deoxy PGE, (378+/-138 nM) > misoprostol (1,243+/-48) > PGE2 (3020+/-700 nM) > ZK-118182 (7265+/-455 nM). Iloprost wasthe most potent compound in the human platelet binding assay while prostanoidsfromthe DPand EP receptor classes showed modest affinity. These studies provide functional and binding information for a broad range of both natural and synthetic prostanoid receptor ligands at the endogenous IP receptor in two different cell types.

Alprostadil↗