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Abstract
The concept of reversible type A monoamine oxidase (MAO-A) inhibitors as effective antidepressant drugs with a minimal side effect profile has been vindicated in practice. Despite this, the pharmacological basis for their actions is unclear. Studies with the irreversible inhibitor clorgyline have shown that chronic but not acute treatment of rats leads to a significant enhancement of noradrenaline release from peripheral sympathetic nerves and cerebral cortex together with a more effective inhibition of MAO-A, as shown by reduction in levels of deaminated metabolites in cortical microdialysis fluid. Reversible inhibitors, however, do not have a cumulative effect on MAO inhibition and may have different effects on noradrenaline release. Reversible inhibitors did not produce the acute reduction in sympathetic nerve activity seen with clorgyline, which may be one factor in explaining their milder side effect profile. Other aspects of the pharmacology of reversible and irreversible selective inhibitors of MAO-A are reviewed.
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Affiliation(s)
- J P Finberg
- Department of Pharmacology, Faculty of Medicine, Technion, Haifa, Israel
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2
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Oxenkrug GF, Requintina PJ, McIntyre IM, White K. Chronic effect of the irreversible and reversible selective MAO-A inhibitors on rat pineal melatonin biosynthesis. JOURNAL OF NEURAL TRANSMISSION. SUPPLEMENTUM 1994; 41:381-4. [PMID: 7523585 DOI: 10.1007/978-3-7091-9324-2_51] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Acute administration of the irreversible MAO-A inhibitor, clorgyline (2.0 mg/kg, s.c.) and the reversible MAO-A inhibitor, moclobemide (10 mg/kg, s.c.), increased rat pineal melatonin and related indoles content (HPLC-fluorimetric method). Chronic (21 days) administration of clorgyline attenuated the acute effect of clorgyline on pineal melatonin biosynthesis. The acute effect of moclobemide on melatonin biosynthesis was not affected by chronic moclobemide administration. The observed difference in the chronic effects of irreversible and reversible selective MAO-A inhibitors on melatonin biosynthesis could have clinical implications.
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Affiliation(s)
- G F Oxenkrug
- Pineal Research Laboratory, VAMC, Providence, Rhode Island
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3
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Finberg JP, Pacak K, Kopin IJ, Goldstein DS. Chronic inhibition of monoamine oxidase type A increases noradrenaline release in rat frontal cortex. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1993; 347:500-5. [PMID: 8391652 DOI: 10.1007/bf00166742] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Chronic but not acute treatment of rats with MAO inhibitors, as with other antidepressant drugs, has been shown to down-regulate the number of cerebro-cortical beta-adrenoceptors. In order to establish whether this effect is associated with an increase in cortical noradrenaline release, rats were treated for 1, 3 or 21 days with clorgyline (2 mg/kg i.p. single injection; 1 mg/kg i.p. repeated injections), and the frontal cortex was then perfused by microdialysis in the awake animal. Control animals were injected with saline. The concentration of noradrenaline in the microdialysate increased only slightly after 1 or 3 days of clorgyline treatment but increased fourfold over control levels after 21 days treatment. Yohimbine (20 mumol/l) added to the perfusing solution caused a similar degree of enhancement in microdialysate noradrenaline concentration in all groups of rats. Tetrodotoxin (10 mumol/l) reduced noradrenaline concentration to low levels in all groups of animals, but noradrenaline was still detectable in the microdialysate in rats treated with clorgyline for 21 days. Concentrations of the deaminated metabolites dihydroxyphenylacetic acid, dihydroxyphenylglycol and methoxy-hydroxyphenylglycol were lowest after the 21 day clorgyline treatment. Determination of enzyme activity ex vivo showed that MAO-A was inhibited more than 95% by all clorgyline treatments with less than 10% inhibition of MAO-B. The results indicate that cerebrocortical noradrenaline release increases gradually during chronic MAO inhibition. This may be the result of more complete inhibition of the enzyme with time, not detectable by the ex vivo assay, but shown by the progressive reduction in metabolite levels.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J P Finberg
- Clinical Neurochemistry Section, N.I.N.D.S., N.I.H., Bethesda, MD 20892
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4
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Abstract
Release of endogenous noradrenaline (NA) and functional activity of presynaptic alpha 2-adrenoceptors were measured in isolated rat vas deferens following acute (2 mg/kg) or chronic (21 * 1 mg/kg daily, i.p.) treatment with clorgyline. Noradrenaline tissue content was higher in rats treated chronically with clorgyline than in those treated acutely. In vitro experiments done in the presence of 1 microM desipramine and 0.5 microM yohimbine showed that NA release, elicited by electrical field stimulation, was higher in chronic clorgyline rats than in controls, while no significant difference was found between acute clorgyline and control rats. Yohimbine enhanced evoked release of NA in all treatment groups, provided that desipramine was present in the Krebs solution, and the enhancement was non significantly higher in chronic clorgyline than in acute clorgyline and control rats. Efflux of 3,4-dihydroxyphenylglycol was lower in chronic clorgyline rats than in other groups. No difference was found between the treatment groups in a 1 min [3H]NA uptake into the tissue, nor in the ability of desipramine (1 microM) to block the uptake. The results indicate that following chronic treatment with clorgyline, evoked release of NA increased, and there was no reduction in the ability of the presynaptic alpha 2-adrenoceptor inhibitory mechanism to reduce nerve stimulation induced release of NA.
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Affiliation(s)
- G Ari
- Department of Pharmacology, Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
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5
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García-Roldán JL, Torres J, Marín J. Alpha-adrenoceptors involved on the cardiovascular response induced by mianserin in the pithed rat. GENERAL PHARMACOLOGY 1992; 23:509-14. [PMID: 1324869 DOI: 10.1016/0306-3623(92)90120-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
1. The effects of the antidepressant drug mianserin on the cardiovascular responses induced by preganglionic electrical stimulation, and i.v. infusion of the adrenergic agonists noradrenaline (NA, alpha 1 and alpha 2), phenylephrine (alpha 1) and xylazine (alpha 2) in the pithed normotensive rat were studied. 2. Mianserin inhibited in a dose-dependent manner the pressor effect caused by electrical stimulation of spinal cord (Th7-Th9) and the infusion of NA, phenylephrine and xylazine. Cocaine increased the inhibitory effect of mianserin on the pressor effect caused by electrical stimulation and NA. 3. Mianserin blocked the xylazine-induced inhibition of cardiac nerve stimulation effect. 4. These results suggest that mianserin blocks the NA uptake, and it is more effective in blocking presynaptic alpha 2- than postsynaptic alpha-adrenoceptors.
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Affiliation(s)
- J L García-Roldán
- Departamento de Farmacología, Facultad de Medicina, Universidad de Valladolid, Madrid, Spain
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Norman TR, Judd FK, Burrows GD. New pharmacological approaches to the management of depression: from theory to clinical practice. Aust N Z J Psychiatry 1992; 26:73-81. [PMID: 1580888 DOI: 10.3109/00048679209068311] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A review of the clinical efficacy of four structurally distinct antidepressant drugs is presented. Their antidepressant activity can be rationalised within current pharmacological hypotheses of drug action, despite markedly different effects on "in vitro" testing. Fluoxetine, a specific serotonin re-uptake inhibitor, has proven safe, effective treatment for depressive illness and may have a role to play in the treatment of obsessive-compulsive disorder and panic attacks. While it has few of the anticholinergic side effects of the tricyclic antidepressants, nausea, tremor, headache, weight loss, nervousness and sweating are side effects most frequently reported. Minaprine, a compound with weak MAO inhibiting properties and effects on serotonergic receptors, has clinical efficacy in the treatment of depression based on several comparative studies. It is claimed that minaprine lacks anticholinergic and sedative properties. Moclobemide, a specific, reversible inhibitor of MAO-A, has been extensively evaluated in depressive illness. The major advantage of this agent over other irreversible, non-specific MAO inhibitors, is the significant attenuation of the so-called "cheese effect" with doses of tyramine likely to be encountered in foodstuffs. Rolipram, a phosphodiesterase inhibitor, represents a new approach to antidepressant treatment. Limited clinical data suggest that the drug may be an effective antidepressant with few side effects. The place of these agents in therapy is yet to be established.
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Affiliation(s)
- T R Norman
- Department of Psychiatry, University of Melbourne, Austin Hospital, Heidelberg, Victoria
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Cesura AM, Pletscher A. The new generation of monoamine oxidase inhibitors. PROGRESS IN DRUG RESEARCH. FORTSCHRITTE DER ARZNEIMITTELFORSCHUNG. PROGRES DES RECHERCHES PHARMACEUTIQUES 1992; 38:171-297. [PMID: 1609114 DOI: 10.1007/978-3-0348-7141-9_3] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Irreversible and unspecific inhibitors of MAO were the first modern antidepressants, but after an initial success they fell into discredit due to adverse side effects. In the past two decades interest in MAO inhibitors has been renewed because of progress in basic research, a milestone being the finding that there are two subtypes of MAO, MAO-A and MAO-B. These are distinct proteins with high amino acid homology, coded by separate genes both located on the short arm of the human chromosome X. The enzyme subforms show different substrate specificities in vitro and different distributions within the central nervous system and in peripheral organs. In the central nervous system of man MAO-A seems to be mainly involved in the metabolism of 5 HT and noradrenaline, whereas 2-phenylethylamine and probably dopamine are predominantly deaminated by MAO-B. In the intestinal tract tyramine is mainly metabolized by MAO-A. These characteristics indicate distinct physiological functions of the two MAO-subforms. Several irreversible and reversible non-hydrazine inhibitors with relative selectivities for one of the MAO-subforms have been developed. They belong to various chemical classes with different modes of enzyme inhibition. These range from covalent mechanism based interaction (e.g. by propargyl- and allylamine derivatives) to pseudosubstrate inhibition (e.g. by 2-aminoethyl-carboxamides) and non-covalent interaction (e.g. by brofaromine, toloxatone and possibly moclobemide). The most important pharmacological effects of the new types of MAO inhibitors are those observed in neuropsychiatric disorders. The inhibitors of MAO-A show a favorable action in various forms of mental depression. The drugs seem to have about the same activity as other types of antidepressants, including tricyclic and related compounds as well as classical MAO inhibitors. The onset of action of the MAO-A inhibitors is claimed to be relatively fast. Other possible indications of these drugs include disorders with cognitive impairment, e.g. dementia of the Alzheimer type. In subjects with Parkinson's disease the MAO-B inhibitor L-deprenyl exerts a L-dopa-sparing effect, prolongs L-dopa action and seems to have a favorable influence regarding on-off disabilities. The action is in general transitory (months to several years). In addition L-deprenyl has been shown to delay the necessity for L-dopa treatment in patients with early parkinsonism. Whether the drug influence the progression of the disease is still a matter of debate. L-deprenyl also appears to have some antidepressant effect (especially in higher doses) and to exert a beneficial influence in other disorders, e.g. dementia of the Alzheimer type.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- A M Cesura
- Pharma Division, Preclinical Research, F. Hoffmann-La Roche Ltd., Basel, Switzerland
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Piletz JE, Andorn AC, Unnerstall JR, Halaris A. Binding of [3H]-p-aminoclonidine to alpha 2-adrenoceptor states plus a non-adrenergic site on human platelet plasma membranes. Biochem Pharmacol 1991; 42:569-84. [PMID: 1677571 DOI: 10.1016/0006-2952(91)90320-5] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Characterization of the binding of [3H]p-aminoclonidine ([3H]PAC) to purified plasma membranes from human platelets has revealed multiple binding sites. [3H]PAC identified site-1 in the picomolar affinity range (site-1 KD estimates ranged from 13 to 94 pM). Site-1 displayed a rank order of competition by various compounds for [3H]PAC, indicative of an alpha 2-adrenoceptor, and was sensitive to 0.1 mM GTP. [3H]PAC also identified a second site with nanomolar affinity (site-2 KD estimates ranged from 0.7 to 1.7 nM). In the presence of 0.1 mM GTP, site-2 was not diminished significantly. Also in contrast to site-1, site-2 displayed low affinity for yohimbine (YOH), (-)-epinephrine and (-)-norepinephrine (NE). Therefore, site-2 could not be an active alpha 2-adrenoceptor; instead it had properties similar to a previously reported imidazoline-preferring binding site. A third site (site-3) bound [3H]PAC with a KD for site-3 of 26.6 +/- 10.0 nM (SD). Site-3 had a rank order of competition by various compounds for 5 nM [3H]yohimbine ([3H]YOH) binding which was indicative of an alpha 2-adrenoceptor. (-)-NE competed for 5 nM [3H]YOH binding at two sites: site-1 Ki = 32 pM, site-3 Ki = 239 nM. Treatment with 0.1 mM GTP completely removed site-1 and transferred the competitive binding of (-)-NE to low affinity (Ki = 437 nM). Thus, site-3 appears to be a free alpha 2-adrenoceptor. Bmax estimates for untreated membranes, derived from simultaneous multi-experiment curve-fitting analyses, were site-1 = 36 +/- 29 fmol/mg plasma membrane protein, site-2 = 95 +/- 34 fmol/mg and site-3 = 154 +/- 35 fmol/mg. We are the first to report a site for [3H]PAC binding on platelets (site-2) with properties uncharacteristic of an adrenoceptor. This observation appears to be due to our use of purified plasma membrane and low ionic strength buffer. These studies relate to reports of increased binding of [3H]PAC to platelets from depressed patients.
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Affiliation(s)
- J E Piletz
- Department of Psychiatry, Case Western Reserve University, School of Medicine, Cleveland, Ohio
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Affiliation(s)
- H Y Meltzer
- Department of Psychiatry, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106
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Finberg JP, Ari G, Lavian G, Hovevey-Sion D. Modification of alpha-2 presynaptic receptor activity and catecholamine release following chronic MAO inhibition. JOURNAL OF NEURAL TRANSMISSION. SUPPLEMENTUM 1990; 32:405-12. [PMID: 1965197 DOI: 10.1007/978-3-7091-9113-2_55] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Neuronal release of noradrenaline from the isolated rat vas deferens has been studied following long-term MAO inhibition. Fractional release of 3H-noradrenaline in response to electrical field stimulation was reduced following chronic clorgyline treatment, but yohimbine equalised the fractional release to that of control animals. Endogenous release of noradrenaline was increased 1.8 fold in yohimbine-treated tissues from rats treated chronically with clorgyline, while tissue noradrenaline content increased 2.3 fold. Electrophysiological activity measured from the renal nerve of anaesthetised rats decreased following acute treatment with clorgyline. This effect was absent following pretreatment with yohimbine. From isolated tissue studies, there was no conclusive evidence for down-regulation of alpha 2-presynaptic receptors by long-term MAO inhibition. Acute MAO inhibition with clorgyline produces distinct physiological effects in the CNS, but not in peripheral sympathetic nerves.
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Affiliation(s)
- J P Finberg
- Rappaport Family Institute for Research in the Medical Sciences and Faculty of Medicine, Technion, Haifa, Israel
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Rowan MJ, O'Connor JJ, Anwyl R. Changes in auditory evoked responses and in the inhibitory action of 5-hydroxytryptophan following chronic treatment with imipramine in the rat. Psychopharmacology (Berl) 1988; 96:408-13. [PMID: 3146776 DOI: 10.1007/bf00216071] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The neurophysiological effects of acute and chronic treatment with the tricyclic antidepressant drug imipramine were investigated. Brainstem (BAER) and middle latency (MLR) auditory evoked responses were monitored in the alert and immobile rat. Daily injection of imipramine (10 mg/kg, IP) for 2 weeks produced a 13% increase in the latency and a 35% reduction in the amplitude of the N17 component of the MLR. Acute imipramine treatment had no effect. There was no observable change in the BAER after either acute or chronic drug administration. Serotonergic function was assessed by studying the inhibitory effects of 5-hydroxytryptophan on the BAER and MLR. Chronic application of imipramine caused an apparent reduction of the effects of 5-hydroxytryptophan (75 mg/kg, IP) on the N17 component of the MLR. This may, however, be due to the shift in baseline latency and amplitude. Inhibition of the BAER by 5-hydroxytryptophan was unaltered by long term exposure to imipramine. Acute treatment with imipramine was without effect on the modulation of the BAER and the MLR by 5-hydroxytryptophan. These results provide evidence that chronic, as opposed to acute, administration of imipramine had an inhibitory effect on auditory processing at the level of the MLR and that this may be associated with a change in the net output of the serotonergic system.
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Affiliation(s)
- M J Rowan
- Department of Pharmacology and Therapeutics, Trinity College, Dublin, Ireland
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