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Biomedical subjects

M B Youdim

Publications and source records attributed to M B Youdim.

At least 307 records · Page 17Linked to original sources
PubMed1975

Human platelet monoamine oxidase activity in iron-deficiency anaemia.

1. The activity of monoamine oxidase, when assayed with four substrates, was significantly lowered in platelets prepared from the blood of patients with iron-deficiency anaemia. 2. Treatment with oral iron preparations restored platelet monoamine oxidase activity to normal in those patients whose serum iron concentrations also returned to normal. 3. Platelet monoamine oxidase activity remained low if treatment failed to restore serum iron concentration to within normal limits.

Adult↗
PubMed1975

Effects of monoamine oxidase inhibition by clorgyline, deprenil or tranylcypromine on 5-hydroxytryptamine concentrations in rat brain and hyperactivity following subsequent tryptophan administration.

1 The effect of various doses of tranylcypromine on the degree of inhibition of rat brain monoamine oxidase (MAO) using 5-hydroxytryptamine (5-HT), dopamine and phenylethylamine as substrates has been examined 120 min after injection of the inhibitor. The concentration of brain 5-HT was also examined both after tranylcypromine alone and also when L-tryptophan (100 mg/kg) had been given 30 min after the tranylcypromine. 2 All doses of tranylcypromine greater than 2.5 mg/kg totally inhibited MAO oxidation of 5-HT, phenylethylamine and dopamine as measured in vitro and produced a similar rise of brain 5-HT in vivo. When tryptophan was also given, there was a further rise of brain 5-HT, which was comparable after all doses of tranylcypromine above 2.5 mg/kg and the characteristic syndrome of hyperactivity made is appearance. 3 Clorgyline (a "Type A" MAO inhibitor), in doses up to 10 mg/kg, did not totally inhibit MAO activity towards phenylethylamine although it did inhibit 5-HT oxidation by 100%. Deprenil (a "Type B" MAO inhibitor) at doses up to 10 mg/kg did not fully inhibit 5-HT oxidation although phenylethylamine oxidation was inhibited almost completely. Administration of either compound alone did not produce as great an accumulation of brain 5-HT as that seen after tranylcypromine (2.5 mg/kg) and subsequent administration of tryptophan did not cause hyperactivity or the rise of brain 5-HT seen after tranylcypromine (2.5 mg/kg) plus tryptophan. 4 Administration of clorgyline plus deprenil (2.5 mg/kg of each) almost totally inhibited oxidation of both 5-HT and phenylethylamine; subsequent tryptophan administration resulted in a rise of brain 5-HT nearly as great as that seen following tranylcypromine (2.5 mg/kg) plus tryptophan and the animals became hyperactive. 5 No evidence was found pointing to the formation of any other 5-substituted indole in the brain following tranylcypromine plus L-tryptophan administration as suggested by others. 6 It is concluded that while 5-HT may normally be metabolized in the brain by "Tye A" MAO in vivo, when this form is inhibited, 5-HT can still be metabolized by "Type B" enzyme. It is only when both forms are almost totally inhibited that the largest rise of brain 5-HT is seen and subsequent tryptophan administration produces the hyperactivity syndrome.

Animals↗
PubMed1975

Variation in activity of monoamine metabolizing enzymes in rat liver during pregnancy.

1. Catechol-0-methyltransferase (COMT) and monoamine oxidase (MAO) activities in rat liver were measured during pregnancy, parturition and postpartum. Compared with activity in non-pregnant controls, both enzymes showed a significant decrease in activity which was most pronounced at day 18. 2. The metabolism of intravenously infused [3H]-adrenaline to [3H]-metanephrine and to [3H]-acidic metabolites was also significantly depressed during pregnancy but had returned to control values by the 21st day. 3. The effects of reserpine and/or nialamide on hepatic COMT and MAO were studied in control and 20-day-pregnant rats. Their action on COMT activity differed in the two groups. MAO was inhibited to a similar extent in these groups whether the drugs were given separately or in combination. 4. It seems possible that the changes in endocrine function which occur during pregnancy are responsible for the observed alterations in enzyme activity.

Animals↗
PubMed1975

In vitro inhibition of brain mitochondrial monoamine oxidase by 6-hydroxydopamine.

6-Hydroxydopamine (6-OHDA) inhibits rat brain mitochondrial monoamine oxidase (MAO) when kynuramine or dopamine are used as substrates. The effect is competitive and reversible giving Ki values of 74 and 176 muM with the respective substrates. At high concentrations (5 mM) of each substrate, inhibition of MAO was not observed.

Animals↗
PubMed1975

Monoamine oxidase. Its inhibition.

Some 50 years ago the enzyme MAO was discovered by Hare and in the early 1930s Blaschko suggested that MAO may play an important role in the catabolism of monoamines in the central nervous system. With the discovery of iproniazid as an inhibitor of MAO and its introduction as an anti-depressant, many aspects of MAO activity and biogenic amine metabolism in experimental animals and man were examined. Although many other inhibitors of MAO were discovered and used therapeutically as anti-depressants, these drugs fell into disrepute largely because of their side-effects. Furthermore, their anti-depressant properties were questioned. After some years of relative inactivity there is now a revival of interest in the functional role of MAO in the central nervous system and drugs that inhibit or stimulate its activity "specifically". The basic reason for the upsurge of interest is that the enzyme from many tissues, including the brain of animals as well as man, has been purified and characterised. The evidence that neuronal MAO exist with different substrate and inhibitor specificities has led to the suggestion that they have physiological function and that deamination of non-methylated biogenic monoamines can take place in neurons. These findings have led to the advent of new drugs (clorgyline and depranil) with "selective" inhibition of enzyme forms. Their possible usage in the chemotherapy of depressive illness should be considered seriously. Fluctuation in peripheral organs as well as brain MAO is well documented. Recently they have been associated with changes in naturally occurring steroids. Although a decrease in platelet and brain MAO activity has been reported in a number of affect disorders (schizophrenia and bipolar depression) the results of these findings have recently been questioned (20, 141). Obviously further study in this area of research discussed is badly needed.

Bipolar Disorder↗
PubMed1975

Platelet monoamine oxidase in children with infantile autism.

Platelet monoamine oxidase activity was measured in 9 autistic subjects and 9 controls. There were no significant differences in the rates of metabolism of 5-hydroxytryptamine, dopamine or tyramine between the two groups, although the rate of metabolism of tyramine was more rapid than 5-hydroxytryptamine or dopamine within each group. It is concluded that the data presented do not support the view that measurement of platelet monoamine oxidase can be used as a biochemical index to aid in the clinical diagnosis of infantile autism.

Adolescent↗