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PubMed1979

Mechanism of hyperosmolarity inhibition of vascular contractility.

Studies were made of the responses of the vascular bed of cat hind leg to intraarterial injection of noradrenaline, angiotensine, tyramine and vasopressine, as well as of carotid occlusion upon increasing the tissue osmolarity through intraarterial hypertonic infusion. The limb was perfused at constant blood flow. Hyperosmolarity inhibited the contractile effects of all stimuli studied. The inhibition of the contractility was greater in the case of tyramine and identical in the case of the remaining vasoconstrictor agents. Increased KCl content or the addition of L-ascorbic acid to the hypertonic solution with preservation of the same hyperosmolarity reduced the inhibition of the contractile responses to noradrenaline and angiotensine. The restoration of the contractility was much more pronounced upon simultaneous increase in the KCl content and addition of L-ascorbic acid. No recovery of the contractile effect of tyramine was observed. The mechanism of hyperosmolarity inhibition of the vascular contraction is discussed. In all vasoconstrictor stimuli the inhibition is connected primarily with disruption of the transmembrane exchange of Na+ and Ka+. In some vasoconstrictor agents, e. g. tyramine, there is disturbance in the specific mechanism connected secondarily with vascular contraction.

Angiotensin II↗

PubMed1979

Effects of dopaminoceptor agonists and antagonists on the rat vas deferens "in vitro".

Dopamine, noradrenaline, tyramine, amantadine and apomorphine produced concentration-related contractions of the rat vas deferens "in vitro". pD2 values of 5.35 +/- 0.12, 5.20 +/- 0.08, 4.50 +/- 0.06, and 4.50 +/- 0.10 were obtained for dopamine, noradrenaline, tyramine and apomorphine respectively. Phentolamine, haloperidol and pimozide blocked the effects of dopamine, tyramine, amantadine and apomorphine, however, noradrenaline-induced contractions were resistant to pimozide. Guanethidine (4 micrograms/ml) induced supersensitivity towards noradrenaline, almost abolished the effect of tyramine, but did not influence the effects of dopamine, amantadine and apomorphine at this concentration. These results confirm earlier reports that there are distinct dopaminoceptors in the rat vas deferens in addition to the conventional noradrenoceptors.

Animals↗

PubMed1981

Pharmacological responses by different portions of guinea pig vas deferens circular muscle preparation.

The different segments of the guinea pig vas deferens circular muscle exhibit differential response patterns upon pharmacological stimulation. Namely, apart from barium chloride, the affinity and intrinsic activity of certain agonists and the strength of maximum contractions they induce appear to decrease along the path from the epididymis toward the prostate. If one subdivides the vas deferens into 3 parts of equal length such as epididymal, medial and prostatic portions, then adrenaline, acetylcholine, acetyl-beta-methylcholine, dopamine, histamine and bradykinin induce contractions on each of the 3 parts; whereas tyramine, ephedrine elicit responses in the epididymal and medial portions; amphetamine, DMPP, serotonin and PGF2 alpha in turn provoking contractions exclusively on the epididymal portion. The effects of adrenaline and noradrenaline are blocked by phentolamine and tolazoline; the responses to acetylcholine, acetyl-beta-methylcholine and carbamyl-beta-methylcholine are antagonized by atropine over a specific concentration range. The effects of tyramine, ephedrine and amphetamine are inhibited by phentolamine in an remarkably low dose range (pA2 = 13.51 +/- 0.09; 14.54 +/- 0.31; 14.35 +/- 0.12). The situation was the same when tyramine-dibenamine and tyramine-phenoxybenzamine combinations were tested (pD'2 = 14.03 +/- 0.37; 13.26 +/- 0.03). Based on these findings the presence of a peculiar alpha adrenergic receptor is suggested on the sympathetic postganglionic fibres. In addition to the already identified alpha adrenergic, muscarinic cholinergic and histamine H1 receptors, we could show the presence of dopaminergic receptors too in the vas deferens circular muscle.

Acetylcholine↗

PubMed1984

Alternate substrates of dopamine beta-hydroxylase. III. Stoichiometry of the inactivation reaction with benzyl cyanides and spectroscopic investigations.

Dopamine beta-hydroxylase was incubated with p-hydroxybenzyl cyanide, ascorbate, and O2 and the products of the hydroxylation reaction were monitored by high performance liquid chromatography. At early times, p-hydroxymandelonitrile was the sole product but this compound slowly decomposed to p-hydroxybenzaldehyde and cyanide. Dopamine beta-hydroxylase was also inhibited under these reaction conditions but the amount of cyanide produced was insufficient to account for the extent of enzyme inhibition. Incubation of dopamine beta-hydroxylase with [ring-3H]p-hydroxybenzyl cyanide, ascorbate, and O2 resulted in incorporation of detectable radiolabel into enzyme only when 100% O2 (0.4 X Km) was present. The amount of incorporated radiolabel was substoichiometric with respect to enzyme subunits (approximately 30%) and also did not correlate with the total amount of inhibited dopamine beta-hydroxylase. These data suggest two different modes of inhibition: covalent-adduct formation at early times and inhibition due to cyanide generated at the active site. Separate K14CN binding studies with dopamine beta-hydroxylase corroborated the latter suggestion since 2 mol of cyanide were bound per tetramer. Tyramine stabilized [14C]cyanide binding to dopamine beta-hydroxylase, consistent with the lack of enzyme reactivation observed under certain conditions (Colombo, G., Giedroc, D. P., Rajashekhar, B., and Villafranca, J. J. 1984) J. Biol. Chem. 259, 1601-1606). EPR data for dopamine beta-hydroxylase-bound Cu2+ directly demonstrated that a quaternary complex with tyramine and cyanide was formed, since the spectrum of dopamine beta-hydroxylase-Cu2+-tyramine-cyanide is distinct from that of dopamine beta-hydroxylase-Cu2+-cyanide and dopamine beta-hydroxylase-Cu2+-tyramine. A comprehensive mechanism for dopamine beta-hydroxylase inhibition by benzyl cyanides is presented.

Acetonitriles↗

PubMed1982

[P-hydroxyphenylacetic acid concentrations in cerebrospinal fluid].

Using reversed-phase high-performance liquid chromatography and electrochemical detection with a rapid one-step purification on Sephadex G-10 column, we have developed a sensitive technique to measure p-hydroxyphenylacetic acid (PHPA), the oxidatively deaminated metabolite of p-tyramine, in cerebrospinal fluid (CSF). The method has been shown to offer simplicity, high sensitivity and low cost for the analysis of PHPA. By using this method PHPA can be measured concurrently with the dopamine metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in small amounts of CSF (0.5 ml or less). The concentrations of PHPA ranged 4.2 to 17.0 ng/ml with a mean value of 7.8 ng/ml+/-1.1 SEM in lumbar CSF of non-neurological control patients. PHPA value is consistent with the results of earlier studies using different methods. PHPA concentrations in both schizophrenic (4.7+/-0.6 ng/ml, n=11) and epileptic patients (5.8+/-0.4 ng/ml, n=28) were significantly lower than those in control patients. A concentration gradient of PHPA was found along the ventricular-lumbar axis. Probenecid markedly increased PHPA in lumbar CSF. These observations suggest that PHPA in lumbar CSF is derived at least in part from the brain and eliminated from CSF by a probenecid-sensitive transport mechanism. There was a significant correlation between PHPA and HVA concentrations in CSF. This is an interesting finding since a reciprocal relationship between dopamine turnover and p-tyramine concentrations has been found in the striatum of experimental animals. A number of recent studies suggest that p-tyramine may act as neurotransmitter or neuromodulator in specific neuronal systems. The present method should be useful in clinical investigations to clarify a functional role of p-tyramine in the brain.

Adolescent↗

PubMedDate not supplied

[Monoamine oxidase inhibitors and pressor response to dietary amines].

Because gastro-intestinal monoamine oxidase (MAO) effectively prevents dietary pressor amines, typically tyramine, from entering the tissues, a marked hypertensive response (the "cheese reaction") can occur when subjects treated with antidepressant MAO inhibitors ingest foods or beverages rich in such amines. Although tyramine is a substrate for both MAO-A and -B, it is only inhibitors of the former enzyme, which are also the effective antidepressants, that give rise to the cheese reaction. This has be shown to be owing to MAO-A being the major form of MAO in intestine and stomach. Selective inhibition of that form of the enzyme results in substantial amounts of unchanged tyramine passing through the intestine. The development of reversible inhibitors of monoamine oxidase-A (RIMAs) has reduced this hypertensive response since rising tyramine concentrations can displace the inhibitor from the enzyme and thus allow some metabolism to occur. This has led to the development of MAO-inhibitory antidepressants that may, apparently, be used without dietary restriction. However, reversibility of the inhibitory process is not sufficient and the analysis of inhibitory behaviour presented here indicates that such safety will only be obtained with inhibitors that are competitive with respect to the amine substrates. Noncompetitive inhibitors might be expected to offer no safety advantage in this respect, whereas uncompetitive could actually exacerbate the pressor response.

Blood Pressure↗

PubMed1998

Modulation of vasoconstriction by insulin.

OBJECTIVE: To test the hypothesis that insulin differently modifies vasoconstriction and recovery from vasoconstriction induced by endogenously released versus circulating norepinephrine, and to investigate the time-dependency of its effect METHODS: Healthy male subjects were studied. Norepinephrine was infused for 10 min into the brachial artery with 40 min pauses in between, three times with vehicle and three times during concurrent intra-arterial infusion of 0.1 mU/kg per min insulin, inducing locally high, above physiologic, concentrations of insulin. We infused tyramine, to release endogenous norepinephrine from sympathetic nerve endings, similarly into six other subjects. Ratios of infused: control arm forearm blood flow (FBFi: FBFc) were determined during the infusions of agonists and for 10 min after their cessation. Because of insulin's vasodilator effect, responses to norepinephrine after vasodilatation by isoproterenol or sodium nitroprusside were also determined for six other subjects. RESULTS: Exogenous norepinephrine induced a transient peak vasoconstriction and then a partial recovery from vasoconstriction that remained stable throughout the infusion. Administration of norepinephrine decreased the FBFi: FBFc ratio by 29+/-7% (mean +/- SEM) before and 45+/-4% during infusion of insulin (P < 0.01). After cessation of the norepinephrine infusions blood flow rapidly recovered, which even resulted in an overshoot vasodilatation during infusion of insulin. Administration of tyramine induced only a plateau vasoconstrictor phase; the FBFi: FBFc ratio decreased by 49+/-6% before and 63+/-5% during infusion of insulin (P < 0.01). After cessation of the tyramine infusions, vasoconstriction slowly and only partially recovered, which was not affected by infusion of insulin. No time-dependency was observed for the repeated infusions of agonist. Infusion of insulin significantly reduced the apparent concentrations of norepinephrine and tyramine at which half maximal effect occurs (EC50). Dilatation with isoproterenol or sodium nitroprusside beforehand dose-dependently also reduced the EC50 of norepinephrine, with a correlation coefficient of 0.613 (P < 0.001) for relationship between individual EC50 values and baseline flows. CONCLUSIONS: Vasoconstriction induced by exogenous or endogenous norepinephrine is augmented by a high concentration of insulin. This augmentation is not time-dependent This augmentation is, however, an unspecific effect insofar as other vasodilators also enhance norepinephrine-induced vasoconstriction. The finding that hyperinsulinemia stimulates norepinephrine's vasoconstrictor effect implies that these two growth-stimulating and vascular hypertrophy-stimulating factors may act synergistically on vascular remodeling in patients with hypertension and hyperinsulinemia.

Adult↗

PubMed1983

Autoradiographic localization of newly synthesized octopamine to retinal efferents in the Limulus visual system.

The biogenic amine octopamine is synthesized from both tyrosine and tyramine in the lateral, median, and ventral eyes of Limulus. The autoradiographic studies presented here were designed to locate the sites of octopamine synthesis in the ventral and lateral eyes. We found that efferent fibers, which project to ventral and lateral eyes from the central nervous system, became intensely and selectively labeled during in vitro incubations with 3H-tyramine. In the ventral eye, more than 95% of the efferent fibers were labeled. Results of biochemical analyses suggested that most of the radioactive substance within these efferent fibers was newly synthesized octopamine. The selective labeling of efferent fibers during incubation with 3H-tyramine was used as an anatomical tool to study the number and distribution of efferent fibers within the ventral eye. Light microscopic (LM) reconstructions of the distribution of label in serial longitudinal sections through ventral optic nerves together with electron microscopic (EM) autoradiographic analyses revealed between 70 and 200 efferent axons. The results of these studies and of reconstructions of efferent innervation to photoreceptor somata suggest that each ventral photoreceptor cell or each small cluster of cells is innervated by a separate efferent fiber. Both LM reconstructions and EM analyses showed that efferent fibers ramify extensively and specifically in and near the internal rhabdom of ventral photoreceptor cells. In EM autoradiographs of lateral eyes incubated with 3H- tyramine, the silver grains that were located over ommatidia were concentrated exclusively over efferent fibers. All of these efferent fibers, which lay near rhabdoms and in partitions between retinular cells, were labeled. The results of our present studies support our hypothesis that octopamine is a neurotransmitter in Limulus retinal efferent fibers. This amine may modulate the biochemistry and physiology of ventral photoreceptor cells and may mediate many of the known effects of circadian efferent innervation to the lateral eye.

Animals↗

PubMed1977

Properties of monoamine oxidase (MAO) in human blood platelets, plasma, lymphocytes and granulocytes.

The properties of monoamine oxidase in plasma, platelets, lymphocytes and granulocytes have been studied using cells prepared from a single small (about 20 ml) sample of blood. The three substrates, 5-hydroxytryptamine, tyramine and benzylamine, have been used to obtain a more complete picture of blood monoamine oxidase than was previously possible. Measurement of Michaelis constants, use of selective inhibitors, and activity against the three substrates distinguished three types of activity. The monoamine oxidases in platelets and lymphocytes are very similar, being most active with tyramine or benzylamine as substrate and inhibited by low concentrations of deprenil. The enzymes in plasma and granulocytes are similar in their relatively high activity against 5-hydroxytryptamine and in their inhibition by semicarbazide and cuprizone with tyramine or benzylamine as substrates. They differ in their affinities for 5-hydroxytryptamine and their activity against tyramine. The activity in platelets, plasma, lymphocytes and granulocytes has been measured in a group of 15 normal subjects using three substrates.

Adult↗

PubMed1981

Human platelet phenolsulphotransferase: separate control of the two forms and activity range in depressive illness.

Human phenolsulphotransferase exists in two forms, one specific for dopamine and tyramine, termed "M" and one for phenol, termed "P". In this study we have shown that these two forms are under separate control by correlating their activities in different individuals using different substrates. There was a highly significant correlation between the activities with dopamine, p-tyramine and 4-hydroxy-3-methoxyphenylglycol, but no significant correlation between the activities with any of these three substrates and that with phenol. Neither age nor sex had any effect on platelet phenolsulphotransferase "M" or "P" activities. Nor was there any significant correlation between platelet monoamine oxidase activity and phenolsulphotransferase "M" or "P" activities. Human platelet phenolsulphotransferase "M" was found to be unstable at temperatures above 35 degree C and it lost substantial activity when stored deep frozen in isotonic saline. However it was stable for up to four months when stored in isotonic sucrose or 10 mmol/l phosphate buffer (pH 7.4). Phenolsulphotransferase "M" amd "P" activities were measured in platelets from depressed patients of a diagnostic type characterized by low output of tyramine-O-sulphate after oral tyramine loading but their enzyme activities were not different from those in two control groups.

Arylsulfotransferase↗

PubMed1998

Effect of enhanced proteolysis on formation of biogenic amines by lactobacilli during Gouda cheese ripening.

The effect of enhanced proteolysis on amine formation by amino acid decarboxylase positive Lactobacillus sp. during Gouda cheese ripening was examined. A commercial proteolytic enzyme preparation was added to pasteurized milk prior to cheese preparation. The effect of this manipulation on the formation of putrescine, histamine and tyramine was investigated in the presence and absence of amino acid decarboxylase-positive strains during a 12-week ripening period. Four batches were supplemented with a proteolytic enzyme. Batch I contained the proteolytic enzyme only, whereas batches II-IV were additionally supplemented with Lactobacillus delbrueckii LTH 1260 (batch II), Lactobacillus buchneri LTH 1388 (batch III) or Lactobacillus brevis LTH 2560 (batch IV). In batch I putrescine was detected with 4 mg/kg, in batch II, 42 mg/kg putrescine, 238 mg/kg histamine and 636 mg/kg tyramine were found. Batch III contained 13 mg/kg putrescine and 418 mg/kg histamine, whereas in batch IV, 26 mg/kg putrescine and 776 mg/kg tyramine were present. Batch V was supplemented with all three lactobacilli but did not contain the proteolytic enzyme. In this experiment, 4 mg/kg putrescine, 179 mg/kg histamine and 337 mg/kg tyramine were detected. A control cheese batch (VI) without addition of amine forming lactobacilli or a proteolytic enzyme was produced and only 4 mg/kg putrescine were detected. An increase in amine concentration during cheese ripening under conditions of enhanced proteolysis in the presence of starter and spoilage lactobacilli was evident from the experiments.

Amino Acids↗

PubMed1999

Protective effect of imidaprilat, an angiotensin-converting enzyme inhibitor on *OH generation in rat myocardium.

We used a flexibly mounted microdialysis technique to the hearts of rats and examined the protective effect of imidaprilat, an angiotensin-converting enzyme (ACE) inhibitor, on the production of hydroxyl free radical (*OH) generation. A microdialysis probe was implanted into the left ventricular myocardium, and dialysate norepinephrine (NE) concentrations were measured as an index of myocardial interstitial NE levels. Sodium salicylate in Ringer's solution (0.5 nmol/microl/min) was directly infused through a microdialysis probe to detect the generation of *OH reflected by the formation of dihydroxybenzoic acid (DHBA) in rat myocardium. When tyramine (1 mM) was directly infused through the microdialysis probe, the level of NE significantly increased in the dialysate and the level of NE increased by 128 +/- 43%. Imidaprilat (5, 25 and 50 microM) decreased the level of tyramine (1 mM)-induced NE in a concentration-dependent manner. Tyramine clearly produced an increase in *OH formation. In the presence of imidaprilat (50 microM), tyramine failed to increase both 2,3- and 2,5-dihydroxylation. Therefore, the effects of imidaprilat on the *OH generation in the sympathetic nerve blockaded hearts by reserpine treatment were not observed. Moreover, to examine the effect of imidaprilat on *OH formation by ischemia/reperfusion of the myocardium, the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery. When the heart was reperfused, elevation of NE and 2,3- and 2,5-DHBA in imidaprilat (50 microM)-pretreated animals was not observed in the heart dialysate. Imidaprilat 2.5 mg/kg i.p. pretreatment at 5 h before coronary occlusion significantly blunted the rise of serum creatine phosphokinase and improved the electrocardiogram 2 h after coronary occlusion. These results suggest that imidaprilat, an ACE inhibitor, is associated with cardioprotective effect due to the suppression of NE-induced *OH generation.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2000

Effects of octopamine on lipolysis, glucose transport and amine oxidation in mammalian fat cells.

Octopamine is known to exert adrenergic effects in mammals although specific octopamine receptors have been cloned only in invertebrates. It has been shown that octopamine can stimulate alpha(2)-adrenoceptors (ARs) in Chinese hamster ovary cells transfected with human alpha(2)-ARs. More recently, we reported that octopamine stimulates lipolysis through beta(3)-rather than beta(1)-or beta(2)-AR activation in white adipocytes from different mammalian species. The present study was thus undertaken to further characterize the adrenergic properties of octopamine. For this purpose, several biological processes known to be regulated by adrenergic stimulation were studied in response to octopamine, noradrenaline, adrenaline and tyramine in white adipocytes from different mammals. First, octopamine was fully lipolytic in garden dormouse and Siberian hamster while tyramine was ineffective. Although being around one hundred-fold less potent that noradrenaline, octopamine was slightly more potent in these hibernators known for their high sensitivity to beta(3)-AR agonists than in rat and chiefly more active than in human adipocytes known for their limited responses to beta(3)-AR agonists. Second, octopamine reduced insulin-dependent glucose transport in rat fat cells, a response also observed with noradrenaline and selective beta(3)-AR agonists but not with beta(1)-or beta(2)-agonists. Third, human adipocytes, which endogenously express a high level of alpha(2)-ARs, exhibited a clear alpha(2)-adrenergic antilipolytic response to adrenaline but not to octopamine. Moreover, octopamine exhibited only a very weak affinity for the alpha(2A)-ARs labeled by [3H]RX821002 in human adipocyte membranes. In Syrian hamster adipocytes, which also possess alpha(2)-ARs, octopamine induced only a weak antilipolysis. Finally, octopamine was a substrate of fat cell amine oxidases, with an apparent affinity similar to that of noradrenaline. All these results demonstrate that octopamine, tyramine noradrenaline and adrenaline can be degraded by adipocyte amine oxidases. However these biogenic amines interact differently with adipocyte adrenoceptors: tyramine is inactive, adrenaline and noradrenaline activate both beta- and alpha(2)-ARs while octopamine activates only beta(3)-ARs and is devoid of alpha(2)-adrenergic agonism. Thus, octopamine could be considered as an endogenous selective beta(3)-AR agonist.

Adipocytes↗

PubMed2004

A catalysis-based selection for peroxidase antibodies with increased activity.

A biotin-tyramine conjugate (1) was found to covalently cross-link with peroxidase antibody 7G12 upon the catalytic oxidation of the tyramine moiety in the presence of hydrogen peroxide (H2O2). On the basis of this observation, a novel strategy was developed to select mutants of 7G12 Fab with enhanced peroxidase activity from a library of phage displayed antibodies. In such a selection, tyramine is oxidized by hydrogen peroxide in a process catalyzed by peroxidase antibodies displayed on phage. Antibodies with higher peroxidase activity are preferentially labeled with biotin through irreversible adduct formation between oxidized biotin-linked tyramine molecules and phenolic side chains of the antibody. The corresponding phage particles can then be selected via biotin-streptavidin interactions. Using this strategy, phage displayed libraries of antibody 7G12 were selected for higher peroxidase activity. As a result, mutations of antibody 7G12 that led to 10 to 20-fold increases in the peroxidase activity (kcat/Km) were identified, suggesting the validity of this method for the evolution of peroxidase antibodies based directly on catalytic turnover.

Antibodies, Catalytic↗

PubMed1994

Binding of fluorescent-labeled low molecular mass heparin to latex microspheres and to rat and human leukocytes.

Fluorescent-labeled LMMH may be used to investigate the pharmacokinetics of heparins. FITC has been specifically bound by endpoint attachment to LMMH-tyramine. In the present article two in vitro methods are described with the intention of developing new ex vivo test systems. To determine the concentration of heparin, protamine has been bound to the surface of magnetic latex particles. LMMH-tyramine-FITC bound dose dependently in a linear range from 0.1 to 30 micrograms/mL to the protamine-coated latex particles. The fluorescence intensity of the latex particles was analyzed using flow cytometry. No differences in the dilution curves were observed between buffer system, rat and human plasma. This indicated that no interference of heparin binding took place with plasma proteins with respect to the binding to protamine. In the second method the binding of LMMH-tyramine-FITC on rat and human leukocytes was analyzed using flow cytometry. LMMH-tryamine-FITC bound dose dependently to rat and human granulocyes, monocytes, and lymphocytes. A linear relationship of binding was obtained for all three cell lines; the sensitivity was 0.1 microgram/mL for monocytes and lymphocytes and 0.03 microgram/mL for granulocytes without differences between rat and human cells. The data demonstrate a dose-dependent binding of LMMH-tyramine-FITC to protamine coated latex beads and to rat and human leukocytes.

Animals↗

PubMed1997

Measurement of fluorescent-labeled LMM-heparin in biological fluids using protamine-linked microbeads.

A quantitative assay for fluorescent heparin in a purified system and in plasma was developed (Piazolo et al: Semin Thromb Hemostas 20:227-235, 1994). The protamine microbeads (1.6 microns) showed a broad size distribution and a large standard variation in low concentrations. Our aim was to optimize these protamine microbeads for the measurement of fluorescent heparin. The following results were obtained: Paramagnetic protamine microbeads of different average diameters (0.8, 1.6, 2.8, and 4.5 microns) were synthesized by cyclocarbodiimide and tosyl activation. These microbeads bind heparin and are assayed using flow cytometry. The protamine concentration on the surface of the beads ranged between 2.0 and 61 mg/mL. The protamine microbeads bound fluorescent heparin and were analyzed by flow cytometry. The protamine microbeads bound LMM-heparin-tyramine-FITC dose dependently in saline solution, plasma, and blood. There are substantial differences between the microbeads of different origins with regard to the amount of protamine bound, the sensitivity of the detection, and the reliability for the determination of heparins in plasma and blood. The minimal sensitivity of the final method was 0.001 U/mL LMMH-tyramine-FITC in saline solution and in plasma. Human blood cells were not bound to protamine microbeads. The half-maximal binding of LMMH-tyramine-FITC of the different protamine-coated microbeads ranged from 1.7 to 8.0 micrograms/mL in saline solution, 2.3 to 8.7 micrograms/mL in plasma, and 3.1 to 6.4 micrograms/mL in blood. We conclude that all protamine microbeads can be used to quantify the concentration of LMMH-tyramine. Protamine Dynabeads M-450 (diameter 4.5 microns) have advantages over other microbeads because of their more homogeneous size distribution, a higher selectivity, and they can be measured together with leukocytes. They are currently used to develop a competitive binding assay for heparin in plasma.

Binding, Competitive↗

PubMed1989

Food and food additives in severe atopic dermatitis.

In this study the role of food additives, tyramine and acetylsalicylic acid, was investigated by double-blind placebo-controlled challenges (DBPCC) in 25 children with severe atopic dermatitis (AD). All children challenged with foods (n = 24), except one, showed one or more positive reactions to the DBPCC with foods. Positive reactions presented as different combinations of flares of skin symptoms, intestinal symptoms and respiratory symptoms. Seventeen children (70.8%) showed a positive challenge to egg, 12 to wheat (50%), eight to milk (33.3%) and eight to soya (33.3%). Six children underwent DBPCC with food additives, tyramine and acetylsalicylic acid. All were found to demonstrate positive skin and/or intestinal reactions to at least one of the food additives. Two children reacted to tartrazine, three to sodium benzoate, two to sodium glutamate, two to sodium metabisulfite, four to acetylsalicylic acid and one to tyramine. It is concluded that some foods, food additives, tyramine and acetylsalicylic acid, can cause positive DBPCC in children with severe AD.

Animals↗

PubMed1995

Monitoring norepinephrine levels by microdialysis in the white adipose tissue of spontaneously hypertensive rats.

1. To investigate whether microdialysis is suitable to monitor catecholamine in white adipose tissue of conscious rat and to assess eventual differences in norepinephrine (NE) interstitial levels, two groups of 12 male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, 14-16 weeks old, were compared. 2. A flexible microdialysis probe was implanted subcutaneously in the parascapular region, and perfused with Ringer solution (flow rate: 2.0 mu L/min). After a 20 min equilibration period, NE levels were monitored over a 120 min period; then, tyramine hydrochloride (0.1 nmol/min) was perfused for 80 min. Dialysates from each 20 min collection period were analysed by HPLC with electrochemical detection for NE. 3. Basal levels of NE (adjusted for the recovery) were higher in SHR compared to WKY (1210.0 +/- 140.5 pg/mL dialysate vs 573.3 +/- 75.8 pg/mL dialysate; P < 0.001, ANOVA). In both strains tyramine perfusion increased NE concentration in dialysates; the net (i.e. baseline subtracted) NE output was lower (76.3 pg/h, s.e.m. 22.3) in SHR compared with that shown by WKY rats (201.0 pg/h, s.e.m 18.4, P < 0.01). 4. The increased basal levels of NE observed in SHR are associated with a blunted response to tyramine challenge. Since tyramine is known to cause NE release from the cytosol but not from vesicle stores, such a blunted response is consistent with an increased turnover rate of NE or with an accelerated uptake in pre-synaptic vesicles which, together with the higher basal levels, would suggest increased noradrenergic activity.

Adipose Tissue↗