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A Chiu

Publications and source records attributed to A Chiu.

At least 55 records · Page 3Linked to original sources
PubMed1988

Assessment of rat brain alpha 1-adrenoceptor binding and activation of inositol phospholipid turnover following chronic imipramine treatment.

Chronic (21 days) treatment of rats with imipramine (10 mg/kg) did not change the density or affinity of alpha 1-adrenoceptors as measured by the specific binding of [3H]prazosin in rat cortical membranes, but produced the expected significant decrease in the density of beta-adrenoceptors labeled by [125I]iodocyanopindolol. The functional status of brain alpha 1-adrenoceptors was also assessed by measuring the noradrenaline (NA)-induced accumulation of [3H]inositol 1-phosphate (IP1) in brain slices from these animals. No apparent change was observed in the concentration-response relationship between NA and [3H]IP1 accumulation in rat cerebral cortex after chronic treatment with imipramine. At concentrations higher than 1 microM in vitro, imipramine and its metabolite, desipramine, produced a concentration-dependent decrease in the [3H]IP1 accumulation elicited by NA. This inhibitory effect is likely mediated by direct blockade of alpha 1-adrenoceptors by these drugs. As the endogenous drug concentration would not reach 1 microM in our preparation, the lack of changes in alpha 1-adrenoceptor response following chronic imipramine treatment are not likely attributable to residual imipramine or desipramine retained in the tissues. In conclusion, the above findings do not support previous suggestions that brain alpha 1-adrenoceptors are upregulated following chronic imipramine administration.

Animals↗
PubMed1988

Enzymatic properties of the 15-lipoxygenase of human cultured keratinocytes.

The arachidonic acid 15-lipoxygenase or linoleic acid omega-6 lipoxygenase of human neonatal foreskin cultured keratinocytes converts arachidonic acid to 15-hydroxy-eicosatetraenoic acid and linoleic acid to 13-hydroxy-linoleic acid. A mean of 93% of the 15-lipoxygenase activity in sonicates of cultured keratinocytes was recovered in the 400,000 X g supernatant, attesting to the cytosolic localization of this enzyme. Optimal 15-lipoxygenase activity in the 400,000 X g supernatant was expressed at pH 6.7-7.3 and in the presence of calcium at a concentration of 2 mM or higher. Keratinocyte 15-lipoxygenase metabolized arachidonic acid (Km = 10.6 microM) and linoleic acid (Km = 9.5 microM) with similar efficiency. Nordihydroguaiaretic acid and 5,8,11,14-eicosatetraynoic acid both inhibited the conversion of arachidonic acid to 15-HETE with respective 50% inhibitory concentrations of 2.0 microM and 0.9 microM, while ATP, GTP, and cyclic AMP had no effect on activity at pH 6.8-7.2. The enzymatic properties of human keratinocyte 15-lipoxygenase thus resemble those of PMN leukocyte 15-lipoxygenase and the mediators generated may contribute to the regulation of cutaneous sensation and inflammation.

Arachidonate 15-Lipoxygenase↗
PubMed1982

Simultaneous determination of norepinephrine, dopamine and serotonin in rat brain regions by ion-pair liquid chromatography on octyl silane columns and amperometric detection.

A highly sensitive and specific ion-pair liquid chromatography-electrochemical detection method is described for the simultaneous determination of rat brain regional norepinephrine, dopamine and serotonin levels using octylsilane (C8) columns. These amines were first isolated from tissue homogenates by adsorption on Amberlite CG-50 resin followed by separation on RP-8 columns with a mobile phase consisting of 0.05 M NaH2PO4 (pH 3.0) 0.02 mM EDTA, 1 mM heptanesulphonate-methanol (92:8, v/v) at 1.8 ml/min. Using 3,4-dihydroxybenzylamine as the internal standard, tissue recoveries (mean +/- S.D.) for norepinephrine, dopamine and serotonin were 87.5 +/- 2.6%, 61.8 +/- 10.5% and 72.9 +/- 7.5%, respectively. Assay sensitivities were sufficient for reliable quantitation of at least 200 pg of these compounds in a brain sample. The procedure is readily adaptable to determination of brain epinephrine and normetanephrine levels, as well. Finally, the reversed-phase system employed is highly flexible in that the same column and mobile phase conditions may be used for assay of biogenic amine metabolites.

Animals↗
PubMed1982

The biological role of enzyme attachment and immobilization.

The state of enzymes in the living cell is considered: it is not clear whether some, if any, enzymes are naturally present in the "soluble" state. The evidence for enzyme binding to cellular constituents, and its effects on function and properties of enzyme and isoenzymes, is reviewed.

Animals↗
PubMed1981

Multiple binding sites for [3H]clonidine and [3H]WB-4101 in rat brain.

Binding of the alpha-adrenergic agonist [3H]clonidine and the alpha-adrenergic antagonist [3H]WB-4101 exhibited multiple binding site characteristics in both rat frontal cortex and cerebellum. Kinetic analysis of the dissociation of both radioligands in rat frontal cortex suggests two high affinity sites for each ligand. Competition of various noradrenergic agonists and antagonists for [3H]WB-4101 binding yielded shallow competition curves, with Hill coefficients ranging from 0.45 to 0.7. This further suggests multiplicity in [3H]WB-4101 binding. In the rat cerebellum, competition of various noradrenergic drugs for [3H]clonidine binding yielded biphasic competition curves. Furthermore Scatchard analysis of [3H]clonidine binding in rat cerebellum showed two high affinity sites with KD = 0.5 nM and 1.9 nM, respectively. Competition of various noradrenergic drugs for [3H]WB-4101 binding in the rat cerebellum yielded biphasic competition curves. Lesioning of the dorsal bundle with 6-hydroxydopamine did not significantly affect the binding of either [3H]clonidine or [3H]WB-4101. These findings for both [3H]clonidine and [3H]WB-4101 binding in rat frontal cortex and cerebellum can be explained by the existence of postsynaptic binding sites for both 3H ligands.

Adrenergic alpha-Agonists↗
PubMed1980

Fractionation and reconstitution of vitamin K-dependent carboxylation activity in rat liver microsomes.

Attempts to purify the vitamin K-dependent carboxylation system from rat liver microsomes have not yet met with success. Purification procedures result in low yields of activity even after relatively mild separation methods. We have been able to demonstrate that one reason for these failures is that there are at least two components (which can be separated) necessary for the reaction. Recombination of the separated components is possible if the detergent (Triton X-100) concentration is lowered and ethylene glycol is added to the system. Under these conditions, vitamin K-dependent carboxylation of synthetic pentapeptide (Phe-Leu-Glu-Glu-Leu) can be totally reconstituted.

Animals↗
PubMed1980

Regulation of vitamin K-dependent carboxylation.

Vitamin K-dependent carboxylation activity measured with pentapeptide substrate (Phe-Leu-Glu-Glu-Leu) gradually decreases upon in vivo injection of vitamin K to vitamin K-deficient rats. A decrease in pentapeptide carboxylation can also be observed by the in vitro addition of antibodies against prothrombin and other vitamin K-dependent proteins to the soluble system derived from vitamin K-deficient rat liver microsomes. In both cases, adding back in vitro partially decarboxylated vitamin K-dependent proteins or purified hepatic prothrombin precursor restores the level of pentapeptide carboxylation. After warfarin treatment, a 3-fold increase in carboxylation results, which can be abolished by giving cycloheximide along with the warfarin. However, the resulting decreased activity is restored by the in vitro addition of partially decarboxylated vitamin K-dependent proteins. These data are consistent with the hypothesis that (after warfarin treatment) increased peptide carboxylation is primarily due to activation of the system by precursor proteins, rather than synthesis of an increased amount of enzyme.

Animals↗
PubMed1976

Localization of angiotensin converting enzyme (kininase II). II. Immunocytochemistry and immunofluorescence.

The cellular and subcellular sites of angiotensin converting enzyme (kininase II) in lung tissue and endothelial cells in culture were examined by immunocytochemical and immunofluorescence techniques. Converting enzyme is capable of inactivating bradykinin and of converting angiotensin I to its potent lower homolog, angiotensin II. Immunocytochemistry at the electron microscope level used goat anti- (pig lung and angiotensin converting enzyme) coupled to 11-MP (11-microperoxidase) via glutaraldehyde or to 8-MP (8-microperoxidase) via a bifunctional active ester, bis-succinyl succinate. The latter conjugate, which does not contain complex polymers, has been characterized in detail in terms of immunoreactivity and peroxidase activity.

Animals↗