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Biomedical subjects

H Xu

Publications and source records attributed to H Xu.

At least 811 records · Page 45Linked to original sources
PubMed1987

The ouabain receptor in animal tissues and its endogenous ligand.

Cardiac glycosides bind to the Na+,K+-ATPase and inhibit its activity. Low concentrations (less than 10(-7) M) of ouabain stimulate the activity of Na+,K+-ATPase in whole homogenates of rat brain. The magnitude of this stimulation varies from 5 to 70%. The concentration of ouabain which induces maximal stimulation is also highly variable and ranges between 10(-9) to 10(-7) M. This stimulation may be explained by the presence of an endogenous ouabain-like compound (OLC) in the brain homogenate. Mammalian tissues and body fluids including brain, heart, kidney, plasma, urine and cerebrospinal fluid contain a unidentified OLC. An endogenous OLC was also demonstrated in toad skin and plasma. This compound was purified to homogeneity and identified using UV, NMR and Mass spectroscopies to be 3-hydroxy-14, 15-epoxy-20,22-dienolide glycoside (resibufogenin). Several reports have suggested that unsaturated fatty acids are the ouabain-like regulators of the Na+,K+-ATPase. Furthermore, Saline infusion to WKY rats, which was shown to increase OLC in the plasma causes also an elevation of free fatty acids. Thus, the interaction of fatty acids with several plasma membrane components was studied. Ouabain binding, opiate binding and binding to the beta-adrenergic receptor were all inhibited by micromolar concentrations of the unsaturated fatty acids, linoleic, oleic and arachidonic. Binding to the opiate receptor was inhibited with IC50 of 40-90 microM and binding to beta-adrenergic receptor with IC50 of 350-450 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Liquid and solid two-phase radioimmunoassay--simultaneous measurement of levels of triiodothyronine and thyroxine of human serum in a single specimen.

The principle of the liquid and solid two-phase radioimmunoassay and its application to measuring the concentrations of triiodothyronine and thyroxine of human serum in a single sample at the same time are described in this paper. Rabbit anti-triiodothyronine antiserum was immobilized on the inner surface of a plastic tube as solid-phase radioimmunoassay system of testing triiodothyronine and donkey anti-rabbit gamma globulin antiserum was used to separate immunocomplex in liquid-phase radioimmunoassay system of thyroxine reaction. In both systems, radioiodine-125-labelled antigens were used as tracer. Through simple calculation, we can get the results of serum concentrations of triiodothyronine and thyroxine in a single sample. Compared with classical single-component radioimmunoassay of triiodothyronine and thyroxine and by methodological appraisal of two-phase radioimmunoassay itself, this method has the advantages of very high efficiency, reliability and also has the same specificity and precision.

Humans↗
PubMed1986

Characterization of two classes of cardiac glycosine binding sites in rat heart and brain membrane preparations, using quantitative computer modelling.

Cardiac glycoside binding to rat heart and brain membrane preparations was measured by a rapid filtration technique. Data were analysed using quantitative computer analysis. The experimental results were consistent with a model in which cardiac glycoside-specific binding occurs at two independent classes of sites. The high-affinity sites in heart membranes were characterized by dissociation constants (Kd) of 40, 50, and 61 nmol/l for ouabain, digoxin and digitoxin, respectively, and the lower-affinity sites were characterized by Kd of 2.3 mumol/l, 67 nmol/l and 71 nmol/l for ouabain, digoxin and digitoxin, respectively. Comparable results were obtained using brain membranes. Potassium ions inhibit [3H]-ouabain binding in a dose-dependent manner with an IC50 of 500 mumol/l. Quantitative computer modeling indicated that potassium inhibits ouabain binding to approximately the same extent at both classed of binding sites, consistent with the hypothesis that the two classes of binding sites for cardiac glycosides might be associated with the Na+K+-ATPase.

Animals↗
PubMed1985

The effect of intracerebroventricular 3-mercaptopropionic acid on blood pressure and heart rate in the rat.

Intracerebroventricular (i.c.v.) injection of 3-mercaptopropionic acid (3-MP, 250 micrograms/10 microliter) elicited an elevation of blood pressure in a dose-dependent manner in anaesthetized rats. This elevation of blood pressure could be blocked by treatment with amino-oxyacetic acid (AOAA, 25 mg/kg, i.p.) 5 h prior to the i.c.v. injection of 3-MP. Given intraperitoneally (i.p.), 3-MP (75 mg/kg) had no effect on blood pressure or heart rate. I.c.v. injection of 3-MP produced a selective decrease in GABA content in the diencephalon and mesencephalon, whereas i.p. injection of 3-MP caused a decrease in GABA content in all regions of brain, including telencephalon, diencephalon, mesencephalon, pons and medulla. The results suggest that the elevation of blood pressure induced by i.c.v. injection of 3-MP may be the result of a selective depletion of GABA in diencephalon and/or mesencephalon. Decreases in GABA content in brain regions other than diencephalon and mesencephalon may lead to an opposite effect in modulating blood pressure.

3-Mercaptopropionic Acid↗
PubMed1985

Differentiation of vasodilator and sudomotor responses in the cat paw pad to preganglionic sympathetic stimulation.

We monitored sweat secretion (using skin potential) and blood flow (using skin temperature) in the hind-paw skin of chloralose-anaesthetized cats pre-treated with guanethidine, and studied the responses to electrical stimulation of the ipsilateral lumbar sympathetic trunk. Stimulation caused sweat secretion and an increase in skin blood flow which was almost entirely restricted to the paw pads and was completely ipsilateral. Stimulation of the tibial nerve trunk produced similar effects, except that the increase in blood flow was more prolonged. The vasodilator effect of sympathetic trunk stimulation was not affected by chronic deafferentation of the paw. Atropine methonitrate (0.5-1 mg/kg I.V.) abolished the sudomotor response to sympathetic stimulation, but did not attenuate the blood flow response. Hexamethonium (1-2 mg/kg I.V.) abolished the vasodilator response to sympathetic stimulation, but did not affect the sudomotor response. Larger doses of hexamethonium (10-20 mg/kg) abolished both responses. The data suggest that the lumbar post-ganglionic neurones mediating vasodilatation in the skin of the cat paw pad are distinct from those that mediate sudomotor secretion.

Animals↗
PubMed1985

Ohmefentanyl--a new agonist for mu-opiate receptor.

Ohmefentanyl (F 7302, N[1-(beta-hydroxy-beta-phenylethyl)-3-methyl-4-piperidyl]-N -phenylpropionamide) is a potent synthetic analgesic agent. The analgesic activity of ohmefentanyl in mice is 6300 times more potent than that of morphine. The potency of ohmefentanyl in competing with specific binding of 3H-naloxone is reduced by Na+ (100 mM) and GTP (50 microM), thus suggesting the agonist properties of this compound. Binding characteristics of 3H-ohmefentanyl with mice brain P2 fraction are studied. An important saturable, specific and reversible binding is demonstrated. Scatchard analysis indicates the existence of two classes of binding sites (KD1 = 0.32nM, KD2 = 3.91nM). Various opiate drugs strongly inhibit the binding of 3H-ohmefentanyl, but nonopiate drugs have negligible affinity. Comparison of the relative potencies of morphine, DSTLE(Tyr-D-Ser-Gly-Phe-Leu-Thr, a specific ligand for the delta-opiate receptor) and ohmefentanyl in competing with 3H-dihydromorphine (mu) and 3H-[D-Ala2, D-Leu5]-enkephalin (delta) binding to crude synaptic plasma membranes of mice brain shows that the inhibitory potencies of morphine, DSTLE and ohmefentanyl on 3H-DHM binding are 79, 0.11 and 81.5 times those on 3H-DADLE binding respectively. This suggests that ohmefentanyl has potent mu-agonist properties.

Analgesics↗
PubMed1983

Color-rendering capacity of illumination.

A new measure called color-rendering capacity is developed, by applying some of the concepts used in communication engineering, to describe another aspect of the color-rendering properties of illumination, i.e., the maximum possible number of different colors that can be displayed by a given illumination. It is a relative measure expressed as a dimensionless parameter between zero and unity, depending only on the spectral power distribution of the illumination. The computer program involved in calculating this parameter and calculated examples for several different light-source types are presented. By reference to this parameter, the prediction for four different fluorescent lamps about the extent to which a lamp can make an average chromatic environment appear colorful and bright is in general agreement with the existing observation. Another potential use of this parameter, in collaboration with the luminous efficacy, as a relevant indicator of the visual efficiency of illumination is also discussed.

Color↗
PubMed1981

Studies on synthesis and relationship between analgesic activity and receptor affinity for 3-methyl fentanyl derivatives.

In the present paper, the synthesis and analgesic activity (mice, i.p. hot plate test) of the derivatives of 3-methyl fentanyl are briefly described. Compound 7302, cis-N-[1-(2-hydroxy-2-phenylethyl)-3-methyl-4-piperidyl]-N-phenylpropionamide (cis: 3-methyl/4-N-phenylpropionamide) is found to be the most potent analgesic agent in this series synthesized by our laboratory (ED50 = 0.0022 mg/kg). The analgesic activity of 7302 is 28 times more potent than that of fentanyl and 6300 times more than that of morphine. The partition coefficients of 10 compounds in the series are determined by high performance liquid chromatography (HPLC) and their log p values are about 3. There are no regular relationships between the analgesic activity and partition coefficients. Study on the specific binding of 8 out of the above 10 compounds to crude synaptic plasma membrane (P2-fraction) of mouse brain demonstrates that there is an excellent statistical linear correlation (r = 0.998) between the analgesic potency and the specific binding affinity. The result shows that the analgesic potency of the derivatives of this series is mainly dependent on binding affinity for opiate receptor.

Analgesics↗