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Biomedical subjects

H H Tai

Publications and source records attributed to H H Tai.

197 records · Page 11Linked to original sources
PubMed1976

Biosynthesis of prostaglandins in rabbit kidney medulla. Properties of prostaglandin synthase.

A simple radioactive-substrate assay for prostaglandin synthase (EC 1.14.99.1), which uses t.l.c. to measure simultaneously different prostaglandins synthesized from one precursor substrate, was developed. Rabbit kidney-medulla prostaglandin synthase catalyses the formation of prostaglandin E2, prostaglandin F2alpha and prostaglandin D2 from arachidonic acid. Fractionation of crude homogenates indicated that the microsomal fraction possessed the highest specific activity of prostaglandin synthase, whereas the soluble fraction exhibited little enzyme activity but rather contained a heat-labile inhibitory macromolecular factor(s), which might be attributed to the serum albumin present in this fraction. The microsomal fraction possessed low intrinsic enzyme activity, but the actvity could be fully stimulated by the presence of both GSH (reduced glutathione) and a phenolic cofactor. Only cysteine could partially replace GSH, whereas other thiols were inactive and some were even inhibitory. A variety of phenolic compounds, including catecholamines, dopamine (3,4-dihydroxyphenethylamine), 5-hydroxytryptamine and quinol, were active in stimulating prostaglandin synthase. In all cases, the stimulation was reflected in the synthesis of all three prostaglandins with ratios not significantly altered by different phenolic cofactors. The synthesis of each of the different prostaglandins appeared to have similar pH optima. The enzyme system was not inhibited by thiol-group inhibitors or a variety of metal chelators except for cyanide and 8-hydroxyquinoline. Characterization of the kidney-medulla prostaglandin synthase system indicated that it exhibited properties similar to those of the enzyme system present in seminal vesicles.

Animals↗
PubMed1976

Observations of plasma secretin levels by radioimmunoassay in response to duodenal acidification and to a meat meal in humans.

The endogenous release of secretin in healthy human subjects was studied by measuring plasma secretin levels by radioimmunoassay (RIA) before, during, and following duodenal acidification and eating a meal. The sensitivity of our RIA was assessed by measuring plasma secretin levels during constant intravenous infusions of 4 graded doses of secretin. Our RIA detected significant increases (P less than 0.001) in plasma secretin with each dose, including a low dose of 0.125 U (41.3 ng)/kg hr. Intraduodenal infusion of 0.1 N HCl resulted in marked increases (P less than 0.001) in plasma secretin levels whenever pH in the second portion of the duodenum was reduced to less than 3.5. In contrast, following a meal, pH in the second portion of the duodenum remained consistently greater than 4.5 and plasma secretin levels showed no changes from basal levels. These studies confirm that endogenous release of secretin depends on an acidic pH of the duodenum, and insigificant changes in the plasma secretin level following ingestion of a meal suggest that endogenous release of secretin in the postprandial period is probably to small in quantity to be detected by the present radioimmunoassay method.

Adolescent↗
PubMed1976

Plasma secretin and gastrin responses to a meat meal and duodenal acidification in dogs.

In five conscious dogs with gastric fistula and two duodenal cannulas, plasma RIA secretin and gastrin levels were determined in response to 1) infusion of 0.1 N HCl in the proximal duodenal cannula, 2) ingestion of a meal, and 3) intraduodenal infusion of 0.1 N HCl following ingestion of a meal. Significant increases in plasma RIA secretin levels occurred during duodenal acidification. However, no significant change occurred in the secretin levels after ingestion of a meal, whereas significant increase in plasma gastrin level was observed. Postprandial duodenal pH remained above 4.5 for 3 h.

Animals↗
PubMed1976

Kinetic evidence of a distinct regulatory site on 15-hydroxyprostaglandin dehydrogenase.

15-Hydroxyprostaglandin dehydrogenase was inhibited by xylocaine, furosemide, and ethacrynic acid, but was activated by imipramine and other related drugs. Inhibition by xylocaine was uncompetitive with respect to both NAD+ and PGE1. Activation by imipramine was also uncompetitive with respect to both substrates. Kinetic studies on mixed inhibitor and activator showed a competitive pattern of inhibition of xylocaine vs imipramine activation. These studies suggest that either inhibitors or activators interact with the enzyme at a site distinct from substrate and coenzyme binding sites, and that inhibitors and activators probably interact with the enzyme at the same regulatory site.

Alcohol Oxidoreductases↗
PubMed1974

Mechanisms of lysosomal enzyme release from human leukocytes. II. Effects of cAMP and cGMP, autonomic agonists, and agents which affect microtubule function.

Selective release of inflammatory materials from leukocyte lysosomes is reduced by compounds which increase cyclic 3',5'-adenosine monophosphate (cAMP) levels in suspensions of human leukocytes and is augmented by agents which increase cyclic 3',5'-guanosine monophosphate (cGMP) levels in these cell suspensions. Lysosomal enzymes are released in the absence of phagocytosis when cytochalasin B (5 mug/ml) converts polymorphonuclear leukocytes (PMN) to secretory cells: lysosomes merge directly with the plasma membrane upon encounter of PMN with zymosan, and cells selectively extrude substantial proportions of lysosomal, but not cytoplasmic enzymes. beta-Adrenergic stimulation of human leukocytes produced a dose-related reduction in beta-glucuronidase release (blocked by 10(-6) M propranolol) whereas alpha-adrenergic stimulation (phenylephrine plus propranolol) was ineffective. In contrast, the cholinergic agonist carbamylcholine chloride enhanced enzyme secretion, an effect blocked by 10(-6) M atropine. Incubation of cells with exogenous cAMP or with agents that increase endogenous cAMP levels (prostaglandin E1, histamine, isoproterenol, and cholera enterotoxin) reduced extrusion of lysosomal enzymes; in contrast, exogenous cGMP and carbamylcholine chloride (which increases endogenous cGMP levels), increased beta-glucuronidase release. Whereas colchicine (5 x 10(-4) M), a drug which impairs microtubule integrity, reduced selective enzyme release, deuterium oxide, which favors microtubule assembly, enhanced selective release of lyosomal enzymes. The data suggest that granule movement and acid hydrolase release from leukocyte lysosomes requires intact microtubules and may be modulated by adrenergic and cholinergic agents which appear to provoke changes in concentrations of cyclic nucleotides.

Atropine↗
PubMedDate not supplied

Morphine and etorphine: XIV. Detection by ELISA in equine urine.

We have raised antibodies to morphine and etorphine and developed one-step enzyme-linked immunosorbent assays (ELISA) for these drugs as part of a panel of post race tests for drugs in racing horses. These tests are simple, can be completed in 2 h, and can be read by visual inspection. The morphine ELISA has an I50 for morphine of about 1.5 ng/mL, while the etorphine ELISA has an I50 for etorphine of 250 pg/mL. Cross-reactivity studies show that the antimorphine antibody cross-reacts well with levorphanol, hydromorphone, and oxycodone, while the anti-etorphine antibody showed no cross-reactivity with buprenorphine, diprenorphine, oxymorphone, morphine, or thebaine. The morphine test readily detected parent morphine or its metabolites in equine urine for at least 8 h after administration of 50 mg/horse, while a 0.1 micrograms/kg dose of etorphine was detectable for up to 48 h post dosing. For each test the background activity in post-race urines was equal to or less than the I50 for the standard curves, making them useful equine forensic tests. Each of these tests has detected "positives" in post race urine samples and as such these tests are capable of substantially improving the speed and efficacy of both pre-race and post-race testing for morphine, etorphine, and their congeners in racing horses.

Animals↗
PubMedDate not supplied

Immunoassay detection of drugs in racing horses: detection of ethacrynic acid and bumetanide in equine urine by ELISA.

We have raised antibodies and developed one-step enzyme-linked immunosorbent assays (ELISA) for the diuretics ethacrynic acid and bumetanide as part of a panel of pre- and post-race tests for high potency drugs in racing horses. These ELISA tests are rapid (completed within one hour), sensitive, and can be read by eye. The ELISA detects ethacrynic acid at a drug concentration for half-maximal inhibition (I-50) of about 2.5 ng/mL for the parent drug. After dosing horses intravenously with 5 mg ethacrynic acid per horse, the parent drug or its metabolites are detectable in urine for at least 8 hours. The bumetanide ELISA has an I-50 for the parent drug of about 2.0 ng/mL and will detect bumetanide or its metabolites for about 8 hours in urine after intravenous administration of a 1.7-mg dose per horse. Both antibodies are relatively specific for each drug and do not cross-react with other commonly used diuretics or other acidic compounds often found in post-race equine urine samples. Ethacrynic acid and bumetanide are potent diuretics suspected of being illegally substituted for furosemide in certain racing jurisdictions. Development of these rapid, sensitive, and simple tests for these agents will allow more effective pre- and post-race control of the use of these agents in racing horses. Both tests have recently uncovered several "positives" for these medications in a midwestern racing jurisdiction.

Animals↗