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PubMed1989

Tyramine potentiation during treatment with MAO inhibitors: brofaromine and moclobemide vs irreversible inhibitors.

Healthy ambulatory subjects were treated p.o. for 2 to 4 weeks with 6 different MAO inhibitors (MAOI). MAOI drugs were given to (n) subjects. Brofaromine (Brof): 100-150 mg/d (39); moclobemide (Mocl): 450 mg/d (8); clorgyline (Clor): 5, 10, 15 mg/d (5); selegiline (Sel): 5, 20 mg/d (7); phenelzine (Phen): 30, 45, 60 mg/d (6); tranylcypromine (TCP): 20 mg/d (12). Pressor responsiveness to oral tyramine (TYR) was assessed before, during, and after treatment. In unmedicated subjects (Cont), doses of TYR to raise systolic blood pressure by at least 30 mm Hg (PD30), ranged between 200 and 800 mg. During treatment with MAOIs, the PD30 decreased. The median effective doses (ED 50) of TYR were: Cont (n = 55): 437 mg; Sel, 20 mg/d: 96 mg; Mocl 450 mg/d: 63 mg; Brof: 100-150 mg/d: 44 mg; Phen, 60 mg/d: 33 mg; Clor, 10 mg/d: 43 mg; CP: 8 mg. Pressor responsiveness to oral TYR normalized within 3 d (Mocl), 8 d (Brof), and 30 d (TCP). After Phen, in 2 subjects the potentiation persisted for 2 and 4 weeks, in 4 volunteers for 8 and more weeks. After Clor, only one of 4 subjects reached 83% of his early pressor sensitivity within 15 weeks. The results suggest that the two reversible MAO-A inhibitors Mocl and Brof may lessen the liability to TYR-related hypertensive reactions.

Adult↗
PubMed1989

Disposition of N-methyl-[ring-3,5-3H]tyramine in rabbits and mice.

After iv bolus injection of N-methyl-[ring-3,5-3H] tyramine ([3H]MT) 14.8 MBq/kg in rabbits, the plasma concentration-time data was found to be in accordance with the 2-compartment model. The pharmacokinetic parameters were: T1/2 alpha = 0.3 min, T1/2 beta = 5.6 min, K12 = 0.69/min, K21 = 0.21/min, K10 = 1.6/min, VC = 0.4 L/kg, Cl = 0.62 L/kg.min-1. [3H]MT was taken up by organs rapidly and extensively. Two min after administration, a large amount of radioactivity was detected in every organ sampled. The highest amounts were in the kidney and liver, followed by lung, small intestine, heart, skeletal muscle, spleen, brain and fat. The drug was metabolized extremely fast in vivo. The metabolites were found in the plasma chromatogram just 0.5 min after dosing, while over 80% were found in the urine within 1 h. After a 1 h collecting period, the radioactivity recovered in the urine amounted to 79% of the injected dose. By the end of a 6 h collection, almost no drug was detected in the body.

Animals↗
PubMed1988

The involvement of intestinal monoamine oxidase in the transport and metabolism of tyramine.

The monoamine oxidase activities were found to be similar in the crypt and villous cells of the different regions of rat small intestine. In all cases the activity of the A-form of the enzyme constituted more than 70% of the total. A similar proportion of that form of the enzyme was found in homogenates of biopsy samples of human intestine. Studies with everted intestines showed that at concentrations above 10 microM over 70% of tyramine was deaminated during transport and the use of selective inhibitors confirmed the A-form of monoamine oxidase to play the dominant role in that process.

Animals↗
PubMed1988

Tyramine pressor effect in man: studies with moclobemide, a novel, reversible monoamine oxidase inhibitor.

The pressor effect of tyramine (TYR) administered i.v. and orally was measured in healthy volunteers during treatment with different therapeutic doses of moclobemide, a new, reversible, preferential type A monoamine oxidase inhibitor. With moclobemide 3 X 100 mg/day the systolic blood pressure (SBP) increase produced by TYR administered i.v. was potentiated 2.4-fold and that in response to TYR p.o. in the fasting state was increased 4.1-fold, as determined from equieffective TYR doses before and during moclobemide treatment. Peak concentrations of free TYR in plasma after oral doses of TYR were increased 2.6-fold, and a 2.5-fold smaller plasma TYR concentration produced the same SBP rise as before moclobemide treatment. No SBP increase was observed at plasma TYR concentrations below 20 ng/ml or after p.o. TYR does smaller than 80 mg. The potentiation of the pressor effect of i.v. TYR by single moclobemide doses up to 300 mg had disappeared 24 hrs after moclobemide administration. Peak TYR plasma concentration and concomitant SBP increments were considerably smaller when TYR was administered with a meal than when administered as a bolus with tap water, 2.1 times higher oral TYR doses being required to achieve similar peak TYR plasma concentration as in the fasting condition. The pressor effect of TYR was further, but only slightly, increased during treatment with moclobemide 3 x 200 mg/day, however SBP rises were again significantly smaller when TYR was given together with a meal. In contrast, tranylcypromine produced a 20 to 40-fold potentiation of the pressor effect of oral TYR and this potentiation was only slightly smaller when TYR was given with a meal. In conclusion the potentiation by moclobemide of the pressor response to oral TYR corresponds roughly to a fourfold left shift of the TYR dose-pressor response curve and is about 10 times less marked than after tranylcypromine. In real life situations, the ingestion of TYR in amounts less than 100 mg is highly unlikely to produce a clinically relevant blood pressure elevation.

Adult↗
PubMed1988

Oral tyramine pressor test and the safety of monoamine oxidase inhibitor drugs: comparison of brofaromine and tranylcypromine in healthy subjects.

The pressor effect of orally administered tyramine (TYR) has been evaluated in 124 tests of 49 healthy unmedicated volunteers, in 99 tests of 29 subjects treated with the reversible selective monoamine oxidase (MAO) A inhibitor brofaromine (BROF), and in 73 tests of 12 subjects treated with tranylcypromine (TCP). In unmedicated subjects, pressor doses of TYR to raise systolic blood pressure (BP) by 30 mm Hg (PD30) ranged between 200 and 800 mg of TYR. There was no correlation of PD30 with sex, age, or weight. In repeated tests, the intraindividual coefficient of variation of the PD30 (+/- SD) was 10 +/- 9%. During treatment for 8 to 16 days with the two MAO inhibitors (MAOIs) BROF and TCP, seven-fold and 56-fold increases of TYR pressor sensitivity were estimated. A significant correlation was found between the individual PD30 before and during MAO inhibition with BROF. Cheese with a pressor content equal to the PD30 of TYR raised the systolic BP in only three of 10 volunteers during BROF inconsistently by not more than 20 mm. Therefore, the probability of "cheese reactions" during treatment with this reversible MAOI seems to be small. For complete normalization of oral pressor responsiveness, delays of 8 and 30 days after the last doses of BROF and TCP, respectively, are needed. The total incidence of systolic BP elevations by more than 60 mm Hg was 13% in a total of 296 oral tests given to 49 subjects. This incidence of easily controllable hypertensive reactions is outweighed by the importance of the test as predictor of clinical risks for drugs with TYR potentiating effects.

Adolescent↗
PubMed1985

Loci of catabolism of beta-very low density lipoprotein in vivo delineated with a residualizing label, 125I-dilactitol tyramine.

beta-Very low density lipoprotein (beta-VLDL) may be a major atherogenic lipoprotein, and knowledge of the sites of its catabolism should facilitate elucidation of mechanisms important in the regulation of its plasma concentrations. In this study, catabolic sites of beta-VLDL have been delineated in normolipidemic rabbits with a novel, radioiodinated, residualizing label, 125I-dilactitol tyramine (125I-DLT). Comparative studies of beta-VLDL and low density lipoprotein catabolism were performed with 125I-DLT conjugated to each lipoprotein and with lipoproteins iodine-labeled conventionally. Conjugation did not alter size distributions or charge characteristics of lipoprotein particles. The overall processing (binding and degradation) of lipoproteins by cultured rabbit skin fibroblasts was not influenced by 125I-DLT derivatization, suggesting that attachment of the label did not influence cell receptor-lipoprotein interactions. Furthermore, although degradation products of 125I-lipoproteins leaked out of the cells and into the medium, the degradation products of 125I-DLT lipoproteins were retained by the cells. The principal catabolic site of beta-VLDL in normolipidemic rabbits was found to be the liver with 54 +/- 4% of injected 125I retained in this organ 24 h after injection of 125I-DLT-beta-VLDL. When catabolism was normalized to tissue weight, the liver and adrenals were found to be approximately equally active in the metabolism of beta-VLDL. In agreement with results of other studies with residualizing labels, the principal organ of catabolism of 125I-DLT-LDL in vivo was the liver. The adrenals were the most highly catabolizing organ when results were normalized for tissue weight. The quantitative differences observed in the tissue distributions of injected 125I-DLT-beta-VLDL and 125I-DLT-low density lipoprotein suggested that a significant proportion of beta-VLDL is removed by tissues before conversion to low density lipoprotein.

Animals↗
PubMed1977

Tyramine-binding by synaptosomes from rat brain: effect of centrally active drugs.

Incubation of p-tyramine (TRM) with rat midbrain plus corpus striatum (MB+ CS) crude synaptosomal preparations, under conditions which reduce to a minimum amine uptake, results in appreciable binding of this amine by synaptosomes. This process is inhibited by preincubation with a number of drugs active in the CNS, e.g., chlorpromazine, desipramine, d-amphetamine, and diphenhydramine. Morphine, however, does not affect this binding. The Ki for each one of these compounds, as well as the K association constant and concentration of the binding sites of TRM, were determined. These results suggest a role for TRM in synaptic transmission mechanisms occurring in the nigrostriatal system, a function which could be regulated by a number of substances representing some of the major chemical classes of centrally active drugs (CD).

Animals↗
PubMed1980

[Treatment of neurogenic orthostatic hypotension by an association of tyramine and a monoamine oxidase inhibitor (author's transl)].

Metabolic and hormonal tests to assess plasma renin, aldosterone, and catecholamine activity were conducted in three patients with idiopathic orthostatic hypotension. Blood pressure readings were then taken in decubitus and orthostatism during treatment with 10 to 15 mg of tyramine and 30 mg of tranylcypromine. Marked functional improvement was observed, with an increase in mean blood pressure in decubitus and a less marked reduction in orthostatism avoiding the onset of severe discomfort. Therapeutic indications are limited, however, because of a possible hypertensive response.

Aged↗
PubMed1981

Effects of carotid body chemoreceptor stimulation by norepinephrine, epinephrine and tyramine on ventilation in the rabbit.

Effects of norepinephrine, epinephrine and tyramine on the carotid body chemoreceptor in the rabbit were studied by measuring reflex ventilatory responses. The basic pattern of the responses was transient inhibition with a decrease in tidal volume followed by sustained excitation, even though the predominant feature was excitation in the epinephrine-induced response. The initial inhibition which was either unaffected or slightly potentiated after phenoxybenzamine was completely blocked by haloperidol. The late excitation was enhanced after mecamylamine and haloperidol treatments and was abolished following administration of phenoxybenzamine. The results indicated possible participation of inhibitory dopamine receptors for the induction of the initial depression and reduction of blood flow in the vessels of the carotid body by vasoconstriction for the excitatory response.

Animals↗
PubMed1995

In vivo renal production and tubular secretion of tyramine.

Para-tyramine (p-TYM) is a predominant urinary amine in humans, rabbit, rat and dog, and its urinary excretion rate may reflect central nervous system pathophysiology. However, the source of urinary p-TYM is not known, nor have the mechanisms regulating its excretion been characterized. The present study, by using renal clearance techniques, examined the sources of urinary p-TYM and the mechanism of excretion in anesthetized rabbits. In all studies, the renal clearance of p-TYM was compared with that of norepinephrine (NE). Base-line delivery to the kidney of p-TYM in plasma was 8.6 +/- 1.6 ng/min (mean +/- S.E.M., n = 16), whereas the mean urinary excretion rate of p-TYM was 26.5 +/- 3.6 ng/min during the same period (P < .001 vs. delivery). In three separate series of experiments, either vehicle (n = 5) or a specific inhibitor of renal tubular organic cation secretion, cyanine 863 (6 mg/kg, n = 7), or a specific inhibitor of aromatic-amino acid-decarboxylase, alpha-mono-fluoromethyldopa (FMD, 4 mg/kg, n = 5), were infused i.v., Mean arterial pressure, glomerular filtration rate, renal plasma flow and urine flow rate were unchanged in all studies. The renal clearances of p-TYM (Cp-TYM) and NE (CNE) were unchanged only after vehicle. After cyanine 863, Cp-TYM was decreased to 36% of control (P < .01), whereas CNE decreased to 21% of its base-line value (P < .01). After FMD Cp-TYM was reduced to 2% of control (P < .05), whereas CNE decreased by 44% (P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Characterization of Drosophila tyramine beta-hydroxylase gene and isolation of mutant flies lacking octopamine.

Octopamine is likely to be an important neuroactive molecule in invertebrates. Here we report the molecular cloning of the Drosophila melanogaster gene, which encodes tyramine beta-hydroxylase (TBH), the enzyme that catalyzes the last step in octopamine biosynthesis. The deduced amino acid sequence of the encoded protein exhibits 39% identity to the evolutionarily related mammalian dopamine beta-hydroxylase enzyme. We generated a polyclonal antibody against the protein product of T beta h gene, and we demonstrate that the TBH expression pattern is remarkably similar to the previously described octopamine immunoreactivity in Drosophila. We further report the creation of null mutations at the T beta h locus, which result in complete absence of TBH protein and blockage of the octopamine biosynthesis. T beta h-null flies are octopamine-less but survive to adulthood. They are normal in external morphology, but the females are sterile, because although they mate, they retain fully developed eggs. Finally, we demonstrate that this defect in egg laying is associated with the octopamine deficit, because females that have retained eggs initiate egg laying when transferred onto octopamine-supplemented food.

Animals↗
PubMed1997

[Amplification of immunologic reactions using catalytic deposition at the reaction sites of tyramine derivatives. A decisive gain in sensitivity in immunohistochemistry and in situ hybridization].

In the catalyzed reporter deposition technique, horseradish peroxidase catalyzes the activation of conjugated phenolic compounds resulting in the covalent binding of the radicalized intermediates to electron rich moieties in the protein molecules present at the site of reaction. Comparing the biotinyl-, digoxigeninyl-, and fluoresceinyl-derivatives of tyramine and four immunohistochemical formats, we showed that the most sensitive detection system was that using biotinyl-tyramide and an immunohistochemical technique using a biotinylated secondary antibody followed by a streptavidin peroxidase. Amplification without background staining was obtained in most biotin rich tissues with digoxigeninyl-tyramide. With fluoresceinyl-tyramide, clear signal amplification was observed in the fluorescent microscope. Finally, when compared with standard methods, increased sensitivity was obtained with the fluorescent derivative for detection of hybridized sequences in interphase chromosomes.

Binding Sites↗
PubMed1976

Release of 3H-alpha-methyl-m-tyramine from rat striatum in vitro.

Release of 3H-d-alpha-methyl-m-tyramine (3H-MMTA), a false dopaminergic transmitter, from rat striatum was studied in vitro. After its initial uptake, 3H-MMTA was released by high K+ and by amphetamine. The release requirements were essentially the same as those known to exist for release of dopamine in vitro. These studies indicate that 3H-MMTA might serve as a useful tool with which to study dopamine release mechanisms in vitro.

Amphetamine↗
PubMed1986

Evidence that alpha-methyl-p-tyramine is implicated in behavioural augmentation to amphetamine.

Behavioural studies showed that administration of alpha-methyl-p-tyramine (AMT; 10 mg/kg i.p.) to rats 24 hr before treatment with d-amphetamine (AMPHET; 4 mg/kg i.p.) resulted in augmentation of AMPHET-induced stereotype activity. Parallel experiments involving electro-chemical estimation of dopamine metabolites in the striatum showed that the decrease in the concentration of homovanillic acid (HVA) produced by AMPHET (4 mg/kg) was enhanced in AMT (10 mg/kg) pretreated animals. These findings suggest that AMT derived from previous doses of AMPHET may play a role in the phenomena of behavioural augmentation observed after chronic administration of AMPHET.

Amphetamines↗
PubMed1999

Identification and characterization of cDNA clones encoding hydroxycinnamoyl-CoA:tyramine N-hydroxycinnamoyltransferase from tobacco.

The sequences of three cDNA clones that include the complete coding region of hydroxycinnamoyl-CoA:tyramine N-hydroxycinnamoyltransferase (THT) from tobacco are reported. The three cDNAs were isolated by antibody screening of a cDNA expression library produced from poly(A)+RNA purified from tobacco leaves (Nicotiana tabacum cv. Bottom Special), previously infiltrated with an incompatible strain of Ralstonia solanacearum. The identity of these clones was confirmed by the detection of THT activity in extracts of transformed Escherichia coli and by matching the translated polypeptides with tryptic enzyme sequences. cDNA clones tht4 and tht11 differ only by their 5' leader and 3' UTRs and therefore encode the same protein, whereas tht10 and tht11 exhibit 95 and 99% sequence identity at the DNA and deduced amino acid levels, respectively. The three clones encode proteins of 226 amino acids with calculated molecular masses of 26 kDa. The deduced amino acid sequences show no similarity with the sequence of anthranilate hydroxycinnamoyl/benzoyltransferase from Dianthus caryophyllus, the only enzyme exhibiting hydroxycinnamoyltransferase activity to be cloned so far in plants. In contrast, comparison of the THT amino acid sequence with protein sequence databases revealed substantial homology with mammalian diamine acetyltransferases. The THT clones hybridized to a 0.95-kb mRNA from elicited tobacco cell-suspension cultures and also to a mRNA of similar size from wound-healing potato tubers. The messengers for THT were also found to be expressed at relatively high levels in tobacco root tissues. Southern hybridization of tobacco genomic DNA with THT cDNA suggests that several copies of the THT gene occur in the tobacco genome. Inhibition experiments using amino-acid-specific reagents demonstrated that both histidyl and cysteyl residues are required for THT activity. In the course of these experiments THT was also found to be inhibited by (2-hydroxyphenyl) amino sulfinyl acetic acid 1,1-dimethylethyl ester, an irreversible inhibitor of cinnamyl alcohol dehydrogenase.

Acyltransferases↗
PubMed1995

Characterization of a cloned locust tyramine receptor cDNA by functional expression in permanently transformed Drosophila S2 cells.

The cDNA for Tyr-Loc, a G protein-coupled receptor that clearly shows homology to a number of mammalian and fruit fly receptors for biogenic amines, was cloned from the nervous system of Locusta migratoria. Functional expression of the cloned cDNA was obtained in cultured insect cells, i.e., in Spodoptera SF9 cells using a baculoviral expression system and in stably transformed Drosophila Schneider 2 (S2) cells. Multiple copies of the receptor expression construct are inserted into the genome of these permanently transformed cells. The expression of the receptor cDNA was driven by the upstream sequences of a Bombyx mori baculoviral immediate early gene. Tyramine shows a much higher binding affinity to this receptor than other possible endogenous ligands. It also reduces forskolin-induced cyclic AMP production in the permanently transformed S2 cells. The pharmacological profile of the Tyr-Loc receptor is distinct from that of any locust receptor-type described so far, but it is similar to that of the Drosophila tyramine/octopamine receptor. In the locust CNS, the Tyr-Loc mRNA is not present in the distal part of the optic lobes but has a widespread distribution in the brain and the ventral nerve cord.

Amino Acid Sequence↗
PubMed1978

Comparative immunological studies on arylsulfatase in bacteria of the family Enterobacteriaceae: occurrence of latent arylsulfatase protein regulated by sulfur compounds and tyramine.

The arylsulfatases of 21 strains of the family Enterobacteriaceae were compared by measuring their enzymatic activities and immunological reactivities. Enzyme formation under repressing, nonrepressing, and derepressing conditions was tested. Antiserum prepared against pure arylsulfatase from Klebsiella aerobgenes W70 was tested against the enzyme extracts from the strains using double diffusion, quantitative precipitation, and immunoelectrophoresis. No close relationship was found between arylsulfatase activity and immunological cross-reactionship was found between arylsulfatase activity and immunological cross-reactivity. The strains in the family Enterobacteriaceae could be divided into two groups on the basis of the immunological properties of their enzyme. Antisera formed a precipitin band with both active and inactive enzyme proteins from Escherichia, Citrobacter, Salmonella, Klebsiella, and Enterobacter, but not with the proteins from Serratia, Proteus, and Erwinia, even though some strains of these species had enzyme activity. It was also found that the formation of arylsulfatase proteins, irrespective of whether they had enzyme activity, were under regulation by sulfur compounds and tyramine.

Arylsulfatases↗