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PubMed1975

Inhibition of pancreatic islet monoamine oxidase by adrenergic antagonists and ethanol.

Although the alpha-adrenergic antagonist phentolamine potentiates glucose-stimulated insulin secretion of intact animals, it either does not alter, or it inhibits in vitro insulin secretion. This may be because in the higher concentration used in in vitro studies, phentolamine exerts a second pharmacological effect that counterbalances its primary effect of blocking monoamine action. We recently demonstrated that pancreatic islets contain substantial amounts of monoamine oxidase (MAO), and that MAO inhibitors such as iproniazid and tranylcypromine can alter insulin secretion. In the present study, we determined if other drugs that affect insulin secretion, alter the MAO activity of homogenates of rabbit pancreatic islets (collagenase technique) or liver. Phentolamine, phenoxybenzamine and propranolol (10 muM and 100 muM) inhibit islet and hepatic MAO. Haloperidol (10muM) inhibits hepatic but not islet MAO, while haloperidol (10muM) does not inhibit MAO in either tissue. Ethanol (270 to 2.7mM) inhibits islet MAO. Hepatic MAO is inhibited by high (270 to 180mM) but not by low (27 to 2.7mM) concentrations of ethanol. Collagenase digestion does not increase the sensitivity of islet and liver MAO to inhibition by phentolamine or ethanol. In the absence of added monoamines, phentolamine and phenoxybenzamine do not alter basal or glucose-stimulated insulin secretion from rabbit pancreas. Preincubation of rabbit pancreas with the serotonin precursor 5-hydroxytryptophan (5-HTP) increases the beta cell serotonin content and inhibits glucose-stimulated insulin secretion. Alpha adrenergic antagonists not only fail to block, but actually potentiate the serotonin inhibition of insulin secretion. We conclude that inhibition of islet MAO may cause an increase in islet monoamine content and these monoamines may alter in vitro insulin secretion. One mechanism through which adrenergic antagonists and ethanol modify in vitro insulin secretion may be by inhibiting pancreatic islet MAO.

5-Hydroxytryptophan↗
PubMed2000

Anaphylaxis and monoamine oxidase inhibitors--the use of adrenaline.

A 67 year old woman taking a monoamine oxidase inhibitor (MAOI) presented to the accident and emergency department with an anaphylactic reaction to flucloxacillin. This case highlights the uncertainty regarding the use of adrenaline (epinephrine) in the context of concurrent MAOI use. A summary of the evidence is presented to clarify this.

Aged↗
PubMed1977

Brain and vascular monoamine oxidase activity in the deoxycorticosterone-salt hypertensive rat.

1 The role of monoamine oxidase (MAO) in the maintenance of deoxycorticosterone-sodium chloride (DOCA-salt) hypertension was investigated by assaying the MAO activity both in central as well as peripheral blood vessels and in brain tissue. 2 The results suggest that the activity of MAO in the DOCA-salt hypertensive rat is similar to the activity present in the normotensive rat.

Animals↗
PubMed1991

Is the oxidation of milacemide by monoamine oxidase a major factor in its anticonvulsant actions?

The anticonvulsant drug milacemide (2-n-pentylaminoacetamide) is known to be oxidized by monoamine oxidase-B to yield glycinamide which then breaks-down to give glycine. It has been postulated that it is this liberation of glycine in the brain that accounts for the anticonvulsant effects. In order to test this hypothesis, and since amines bearing a methyl-group in the alpha-position have been shown to be resistant to oxidation by monoamine oxidase, the effects of milacemide were compared with those of alpha-methyl-milacemide. Although the latter compound was found to be toxic at higher concentrations, it was found to antagonize bicuculline-induced convulsions in mice. When milacemide was administered to mice (0.5 mmol/kg, p.o.) there was a substantial increase in urinary glycinamide excretion. No such increase was observed after the administration of the same dose of alpha-methyl-milacemide. Furthermore, alpha-methyl-milacemide was not oxidized by either monoamine oxidase-A or -B in vitro to any detectable extent, although it was a competitive inhibitor of both forms of the enzyme. The findings that alpha-methyl-milacemide has anticonvulsant properties in the bicuculline test but is not a substrate for monoamine oxidase or a source of urinary glycinamide cast doubt on the importance of the oxidation or milacemide to form glycinamide as a major factor in its anticonvulsant action.

Acetamides↗
PubMedDate not supplied

Monoamine oxidase activity in the pituitary of mice after estrogen, progesterone and centchroman treatment.

Monoamine oxidase activity (MAO) was estimated in the pituitary of ovariectomized mice after a single administration of estradiol-dipropionate (0.01 mg/kg; im), progesterone (1 mg/kg; im) and centchroman (1.25 mg/kg ip). Estrogen and progesterone were found to decrease the enzymic level, as compared to control, while centchroman remarkably increased it. The significance of dissimilarity in the pituitary threshold for steroidal and nonsteroidal molecule is discussed.

Animals↗
PubMed1982

Tricyclic antidepressants and monoamine oxidase inhibitors in the treatment of agoraphobia.

The efficacy of tricyclic antidepressants and monoamine oxidase inhibitors for the treatment of agoraphobia and other panic disorders is reviewed with an emphasis on controlled prospective studies. After methodological biases are taken into account, there is strong evidence that antidepressants suppress panic attacks. This effect is not dependent on the presence of concomitant depressive symptoms. The clinical issues of dosage, delay in response, and relapse with discontinuation of treatment are also reviewed.

Agoraphobia↗
PubMed1978

Effects of aging on monoamine oxidase activity of mouse and rabbit tissues.

The effect of aging on the monoamine oxidase (MAO) activity in tissues of mice and rabbits was evaluated. There were no alterations in the MAO activity of liver, kidney, pancreas and brain (adult mice and rabbits) or testis and heart (adult mice) with aging. There were no alterations in the norepinephrine content of the brain, kidney and heart of older mice. The present study indicates that increased MAO activity is not inevitably associated with aging in all species.

Aging↗
PubMed1995

Effect of disease and drug treatment on blood serotonin and monoamine oxidase B activity in Parkinson's disease.

Serotonin (5-hydroxytryptamine, 5HT) content and monoamine oxidase (MAO) activity were determined in whole blood of patients with Parkinson's disease (PD) with and without drug treatment and compared with controls. From that comparison a significant reduction in platelet 5HT became apparent in PD. Selegiline, which was always used in combination with L-dopa, not only inhibited MAO activity, as expected, but it also appeared to induce an increase in 5HT content.

Adult↗
PubMed1990

Monoamine oxidase activity in embryos of pike (Esox lucius).

1. Mitochondrial MAO specific activity was measured in eggs and early embryos of the teleostean fish Esox lucius using tryptamine, 5-hydroxytryptamine (5-HT) and phenylethylamine (PEA) as substrates. 2. Tryptamine is the most readily deaminated substrate in mitochondria isolated from unfertilized eggs and embryos at the stages of cleavage, blastula and gastrula. 3. Monoamine oxidase activity gradually decreases during development and at the gastrula stage it is respectively 80% (tryptamine), 70% (5-HT) and 50% (PEA) of that found in the egg using the corresponding substrate. 4. The inhibition of egg MAO activity by clorgyline and deprenyl measured in E. lucius eggs using tryptamine as substrate, indicates the presence of a single form of MAO not corresponding to the MAO A and MAO B described in terrestrial vertebrates.

Animals↗
PubMed1989

Brain monoamine oxidase (MAO) B: a unique neurotoxin and neurotransmitter producing enzyme.

The notion that monoamine oxidase (MAO) functions solely to inactivate neurotransmitter and other biogenic amines needs to be re-evaluated. It is now apparent that MAO-B is capable of oxidizing inert non-polar amines such as MPTP (N-methyl-4-phenyl-1,2,3,6, tetrahydropyridine) and milacemide (2-n-pentylaminoacetamide) into neuroactive substances giving rise to Parkinson inducing dopaminergic neurotoxin, MPP+ and inhibitory amino acid neurotransmitter, glycine respectively. These findings accord new prospectives for neuropsychotherapy with selective MAO-B inhibitors and substrates.

Animals↗
PubMed1985

Platelet monoamine oxidase activity in patients with panic disorder.

Preliminary reports have indicated that platelet monoamine oxidase (MAO) activity is elevated in patients with anxiety disorder. We compared MAO activity in 20 drug-free patients with panic disorder with 20 age- and sex-matched normal controls. MAO activity in patients was significantly higher than in normals. MAO activity was not correlated with age or plasma catecholamine levels. The authors speculate about the possible significance of elevated MAO activity in patients with panic disorder.

Adult↗
PubMed1975

A new colimetric assay for monoamine oxidase in serum and its clinical application.

A new colimetric assay for serum monoamine oxidase and clinical findings based on this method are described. This rapid, precise procedure employs 1-[(4-aminomethylphenyl)azol]-2-naphthol as a substrate. The enzymatically generated 1-[(4-formyl phenyl)azo]-2-naphthol is extracted into cyclohexane to form a colored solution whose absorbance is determined at 500 nm. The method proved to be extremely simple, and the results obtained correlated well with those given by the standard method of McEwen.

Aldehydes↗
PubMed1976

Alpha-methyl derivatives of biogenic amines as inhibitors of monoamin oxidase.

The values of Km app and Vmax for three natural substrates of monoamine oxidase have been determined at various stages in the isolation of the enzyme from rat liver tissue. The results are consistent with the presence in the enzyme preparation of at least two distinct molecular forms of the enzyme. Using the alpha-methyl derivatives of the natural substrates as inhibitors of the enzyme, the substrate dependence of Ki further substantiates this view. In addition, the kinetics of the inhibition suggest that the value of Km app may not for all substrates, necessarily be a measure of the affinity of the substrate for the enzyme.

Amphetamines↗
PubMed1998

The oxidation of dopamine and epinine by the two forms of monoamine oxidase from rat liver.

Information on the "in vitro" oxidation of epinine by monoamine oxidase (MAO) compared to dopamine is very poor. The aim of this work was to study the oxidative deamination of epinine and dopamine by rat liver MAO-A and MAO-B. The contributions of MAO-A and B to the metabolism of dopamine (55% and 45%, respectively) and epinine (70% and 30%, respectively) were similar. The results of this study show that epinine is a substrate for both forms of MAO in rat liver, although the contribution of MAO A to the deamination of this secondary amine appears to be slightly more important than that of MAO B.

Animals↗