Effects of amiridin and tacrine, drugs effective in Alzheimer's disease, on synaptosomal uptake of neuromediators]

The study of the drugs effective in the treatment of cognitive deficits and memory loss associated with senile dementia of the Alzheimer's type--tacrine and amiridin, acetylcholinesterase inhibitor physostigmine and nootrop piracetam on uptake of 3H-serotonin (3H-5-HT), 3H-adrenaline (3H-AD), 3H-noradrenaline (3H-HA), 2H-dopamine (3H-DA), 3H-gamma-aminobutyric acid (3H-GABA), 3H-glutamic acid (3H-GLU), 3H-aspartic acid (3H-ASP) and 3H-glycine (3H-GLI) showed that tacrine and amiridin (5 x 10(-5) M) statistically significantly (P less than 0.05) inhibited the uptake of 3H-DA and 3H-5-HT. Physostigmine at concentration 5 x 10(-4) M statistically significantly (P less than 0.05) inhibited uptake of 3H-5-HT only. Piracetam at concentration range 1-5 x 10(-3) M had no effect on uptake of all investigated neurotransmitters. The above finding suggest that the uptake of neurotransmitter in nerve terminals is not the main target of amiridin and tacrine.     

Effect of chlorpromazine, imipramine and lithium on MAO-A and MAO-B activity in rat brain mitochondria

Drugs with efficacy in psychiatric disorders affect the function of central neurotransmitter amines, which are inactivated primarily by monoamine oxidase (MAO). Effect of these drugs on the two types of MAO (MAO-A and MAO-B) has been studied in rat brain. The result showed that chlorpromazine (CPZ) and imipramine (IMI) at concentrations of 1x10(-2), 5x10(-3) and 2.5x10(-3) M inhibited rat brain mitochondrial MAO-A activity in vitro by 82, 50, 39 and 86, 74, 38 %, respectively. CPZ at concentrations of 5x10(-3), 2.5x10(-3), 1x10(-3) M inhibited rat brain mitochondrial MAO-B activity in vitro by 83, 55, 39 %, respectively, while IMI at concentrations of 5x10(-4), 2.5x10(-4), 1x10(-4) M inhibited the in vitro enzyme activity by 43, 35, 21 %, respectively. Lithium at concentration of 5x10(-3) M could not either inhibit MAO-A or MAO-B in the mitochondrial fraction of rat brain.     

Serotonin Metabolism by Monoamine Oxidase in Rat Primary Astrocyte Cultures

The oxidative deamination of serotonin (5-HT) to 5-hydroxyindoleacetic acid (5-HIAA) by rat primary astrocyte cultures was investigated in intact cells using HPLC. All detectable 5-HIAA accumulated in the extracellular medium, and its rate of production was proportional to the 5-HT concentration over the tested range of 5 x 10(-7) to 10(-4) M. At 5 x 10(-7) M 5-HT, intracellular 5-HT was detectable only in astrocytes treated with monoamine oxidase (MAO) inhibitors. These findings are consistent with the idea that 5-HT taken up into astrocytes is not stored for re-release, but is rapidly metabolized to 5-HIAA, which is then extruded from the cell. At 5 x 10(-7) M 5-HT, 5-HIAA formation in intact cells was blocked 63% by the selective high-affinity 5-HT uptake inhibitor fluoxetine. 5-HT oxidation to 5-HIAA is carried out principally by MAO-A, because clorgyline was more effective at inhibiting the production of 5-HIAA than was pargyline. Radioenzymatic determinations of MAO activity in cell homogenates supported these findings, because under these conditions clorgyline was 1,000-fold more effective than pargyline at inhibiting MAO activity toward 14C-labelled 5-HT. However, the relatively selective MAO-B substrate beta-phenylethylamine (PEA) was also oxidized, showing that these cultures also contained MAO-B activity; the Km values for MAO-A oxidation of 5-HT and MAO-B oxidation of PEA were 135 and 45 microM, and Vmax values were 88 and 91 nmol/mg of total cell protein/h, respectively. Higher concentrations of PEA (greater than 20 microM) were oxidized by both MAO-A and MAO-B isozymes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modification of substrate-inhibitor affinities of human platelet monoamine oxidase B in vitro

The rate of benzylamine utilization by monoamine oxidase (MAO)-B from human blood platelets was 2-4 times higher than that for octopamine. Both activities were inhibited 100% by 10(-7) M deprenyl (a specific MAO-B inhibitor) and were not affected by clorgyline (a specific MAO-A inhibitor) or by polyclonal antibodies to MAO-A. The preincubation of platelet MAO-B with purified MAO-A from mitochondrial membranes of human placenta resulted in appearance of excess octopamine activity. This additional activity was not precipitated by antibodies to MAO-A or inhibited by deprenyl but was inhibited by clorgyline. Incubation of the MAO-A preparation from placenta at 45 degrees C for 15 min before its preincubation with MAO-B caused 50% loss of both activities. Protease inhibitors had no effect on the modification of MAO. These data indicate that MAO-A or a factor tightly bound to it can modify MAO-B yielding a form of the enzyme with both MAO-A and MAO-B substrate and inhibitor affinities and MAO-B immunospecificity.     

Design,synthesis and evaluation of 2-(indolylmethylidene)-2,3-dihydro-1-benzofuran-3-one and 2-(indolyl)-4H-chromen-4-one derivatives as novel monoamine oxidases inhibitors

A series of 2-(indolylmethylidene)-2,3-dihydro-1-benzofuran-3-ones (aurone-indole hybrids) and 2-(indolyl)-4H-chromen-4-ones (flavone-indole hybrids) were designed, synthesized, and their monoamine oxidase (MAO) A and B inhibitory activities were evaluated. Compounds 5b and 11b showed potent inhibitory activities against MAO-A, comparable to that of pargyline used as a positive control, and most of the compounds, except for 2a and 10b, showed potent inhibitory activities against MAO-B. Compound 9a was the most potent and highly selective inhibitor of MAO-B (IC₅₀ value for MAO-B: 0.0026 μM, and MAO-A: >100 μM). Comparison of the inhibitory activities of 1a vs. 9a vs. 13a and 1b vs. 7b vs. 11b suggested that methoxy substitution at R¹ on the A-rings of flavonoids increases MAO-A inhibition whereas methoxy substitution at R² increased MAO-B inhibition. Comparison of 4a vs. 10a, 6a vs. 11a, 3b vs. 8b and 4b vs. 9b showed incremental increases in MAO-B inhibitory activity by R² substitution on the A ring. Comparison of the MAO-B inhibitory effects of the flavone-indole hybrids and aurone-indole hybrids showed that most of the aurone-indole hybrids were stronger inhibitors than the corresponding flavone-indole hybrids. Molecular docking analysis of compounds 1a and 9a with MAO-B further supported the above structural effects of these compounds on MAO-B inhibitory activity.This is the first report identifying aurone-indole hybrids as potent MAO-B inhibitors. The results reported here suggest that 2-(1H-indol-1-ylmethylene)-6-methoxy-3(2H)-benzofuranone (9a) might be a useful lead for the design and development of novel MAO-B inhibitors     

Effects of polymethylene derivatives of 4-aminopyridine on functional properties of hippocampal neurons

The effects of amiridin (9-amino-2,3,5,6,7,8-hexahydro-IH-cyclopenta(b) quinoline) and tacrine (1,2,3,4-tetrahydro-9-aminoacridine) on Schaffer collaterals--CAI field potentials were compared in rat hippocampal slice preparations. Similar dose-dependent increase in pop-spike amplitude was observed during slice perfusion with low concentrations of amiridin (5-50 microM) or tacrine (0.5-10 microM). This facilitation was not always fully reversible. The effect was accompanied by slight decrease in pop-EPSP amplitude suggesting membrane depolarization as a possible mechanism of pop-spike facilitation. Further increase in drug concentrations led to the depression and full blockade of pop-spike, that was associated with significant decrease in the pop-EPSP and fiber potential amplitudes. In contrast structurally related 4-aminopyridine evoked dose-dependent increase in both pop-EPSP and pop-spike amplitudes with all the concentrations tested (0.05-1000 microM), this facilitation was transformed into epileptiform response with 4-aminopyridine concentration about 500 microM. Possible mechanisms of drug actions on hippocampal neuron reactivity are discussed. It is suggested that amiridin might turn to be as effective as tacrine in symptomatic treatment of Alzheimer disease.     

Study of anti-amnesic activity of amiridin in a model of amnesic syndrome

The model of amnestic syndrome obtained by treatment with scopolamine during 20 days in rats was used to study anti-amnesic activity of amiridin in comparison with that of tacrine, physostigmine and piracetam. Multiple injection of Sc resulted in significant deterioration of rats, performance in passive avoidance test. Behavioral disorders were accompanied by such changes in lipid composition of brain synaptosomes which indicated a decreased membrane fluidity. Amiridin and tacrine as well as piracetam showed anti-amnesic action which in the course of treatment correlated with their normalizing effect on lipid content of synaptosomes. The diverse effect of amiridin and tacrine with respect to physostigmine implies that the former drugs can't be attributed to anticholinesterase preparations which are traditionally used in the treatment of Alzheimer disease.     

Potent in vivo but not in vitro inhibition of monoamine oxidase by 3-chloro-alpha-phenylpyrazinemethanol.

3-Chloro-alpha-phenylpyrazinemethanol (3-CPM) inhibited monoamine oxidase (MAO) types A and B in vivo in mouse brain, heart and liver. The inhibition was dose-dependent at doses of 0.3-32 mg/kg i.p. and occurred within 1 h after the compound was injected. 3-CPM was a very weak inhibitor of mouse brain mitochondrial MAO activity in vitro, even when preincubated with the enzyme; MAO-A was inhibited only about 50% at a high concentration of 3-CPM (1 mM), and MAO-B was inhibited even less. After a 10 mg/kg i.p. dose of 3-CPM in mice, both MAO-A and MAO-B were inhibited at day 1, but activity had largely recovered within a few days in brain, liver and heart. 3-CPM at doses of 1, 3, 10 and 32 mg/kg i.p. caused dose-dependent antagonism of the depletion of striatal dopamine and of cortical norepinephrine by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. 3-CPM is therefore a potent inhibitor of MAO-A and of MAO-B in mice in vivo despite its weak effect on the enzyme in vitro. A metabolite of the drug may be involved in the in vivo effects.     

Sulfonyl hydrazones derived from 3-formylchromone as non-selective inhibitors of MAO-A and MAO-B: Synthesis,molecular modelling and in-silico ADME evaluation

A series of sulfonyl hydrazones derived from 3-formylchromone was synthesized and discovered to be effective, non-selective inhibitors of monoamine oxidases (MAO-A and MAO-B). The compounds are easily (synthetically) accessible in high yields, by simple condensation of 4-methylbenzenesulfonohydrazide with different (un)substituted 3-formylchromones. All compounds had IC₅₀ values in lower micro-molar range (IC₅₀ = 0.33–7.14 μM for MAO-A, and 1.12–3.56 μM for MAO-B). The most active MAO-B inhibitor was N′-[(E)-(6-fluoro-4-oxo-4H-chromen-3-yl)methylidene]-4-methylbenzenesulfonohydrazide (3e) with IC₅₀ value of 1.12 ± 0.02 μM, and N′-[(E)-(6-chloro-4-oxo-4H-chromen-3-yl)methylidene]-4-methylbenzenesulfonohydrazide (3f) was the most active MAO-A inhibitor with IC₅₀ value of 0.33 ± 0.01 μM. From enzyme kinetic studies, the mode of inhibition against MAO-B was found to be competitive, whereas against MAO-A, it was found to be non-competitive. Molecular docking studies indicated a new binding pocket for non-competitive MAO-A inhibitors. The activity of these compounds is optimally combined with highly favorable ADME profile with predicted good oral bioavailability.     

Synthesis and inhibitory effect of piperine derivates on monoamine oxidase

A series of piperine derivates (1-19) have been designed, synthesized and evaluated in vitro for their monoamine oxidase (MAO) A and B inhibitory activity and selectivity. It is worth noting that most of the small amine moieties substituted on the piperidine ring proved to be potent and selective inhibitors of MAO-B rather than of MAO-A. 5-(3,4-methylenedioxyphenyl)-2E,4E-pentadienoic acid n-propyl amide (3) showed the greatest MAO-B inhibitory activity (IC(50)(MAO-B)=0.045 μM) and good selectivity (IC(50)(MAO-A)=3.66 μM). The conjugated double bond and carbonyl group of piperine are proved to be an essential feature for piperine and related alkylamides to exhibit MAO-inhibitory activity. Binding mode of the titled compounds was predicted using FlexX algorithm. The design and optimization of novel small molecule monoamine oxidase inhibitors will be guided by the results of this report.     

Anti-thyroid hormonal activity of tetrabromobisphenol A, a flame retardant, and related compounds: Affinity to the mammalian thyroid hormone receptor, and effect on tadpole metamorphosis

The thyroid hormone-disrupting activity of tetrabromobisphenol A (TBBPA), a flame retardant, and related compounds was examined. TBBPA, tetrachlorobisphenol A (TCBPA), tetramethylbisphenol A (TMBPA) and 3,3'-dimethylbisphenol A (DMBPA) markedly inhibited the binding of triiodothyronine (T3; 1 x 10(-10) M) to thyroid hormone receptor in the concentration range of 1 x 10(-7)-1 x 10(-4) M, while bisphenol A and 2,2-diphenylpropane were inactive. TBBPA, TCBPA, TMBPA and DMBPA did not exhibit thyroid hormonal activity in a thyroid hormone-responsive reporter assay using a Chinese hamster ovary cell line (CHO-K1) transfected with thyroid hormone receptor alpha1 or beta1, but TBBPA and TCBPA showed significant anti-thyroid hormone effects on the activity of T3 (1 x 10(-8) M) in the concentration range of 3 x 10(-6) - 5 x 10(-5) M. The thyroid hormone-disrupting activity of TBBPA was also examined in terms of the effect on amphibian metamorphosis stimulated by thyroid hormone. TBBPA in the concentration range of 1 x 10(-8) to 1 x 10(-6) M showed suppressive action on T3 (5 x 10(-8) M)-enhancement of Rana rugosa tadpole tail shortening. These facts suggest that TBBPA, TCBPA, TMBPA and DMBPA can act as thyroid hormone-disrupting agents.     

Novel multifunctional neuroprotective iron chelator-monoamine oxidase inhibitor drugs for neurodegenerative diseases. In vivo selective brain monoamine oxidase inhibition and prevention of MPTP-induced striatal dopamine depletion

Several multifunctional iron chelators have been synthesized from hydroxyquinoline pharmacophore of the iron chelator, VK-28, possessing the monoamine oxidase (MAO) and neuroprotective N-propargylamine moiety. They have iron chelating potency similar to desferal. M30 is a potent irreversible rat brain mitochondrial MAO-A and -B inhibitor in vitro (IC50, MAO-A, 0.037 +/- 0.02; MAO-B, 0.057 +/- 0.01). Acute (1-5 mg/kg) and chronic [5-10 mg/kg intraperitoneally (i.p.) or orally (p.o.) once daily for 14 days]in vivo studies have shown M30 to be a potent brain selective (striatum, hippocampus and cerebellum) MAO-A and -B inhibitor. It has little effects on the enzyme activities of the liver and small intestine. Its N-desmethylated derivative, M30A is significantly less active. Acute and chronic treatment with M30 results in increased levels of dopamine (DA), serotonin(5-HT), noradrenaline (NA) and decreases in DOPAC (dihydroxyphenylacetic acid), HVA (homovanillic acid) and 5-HIAA (5-hydroxyindole acetic acid) as determined in striatum and hypothalamus. In the mouse MPTP (N-methy-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease (PD) it attenuates the DA depleting action of the neurotoxin and increases striatal levels of DA, 5-HT and NA, while decreasing their metabolites. As DA is equally well metabolized by MAO-A and -B, it is expected that M30 would have a greater DA neurotransmission potentiation in PD than selective MAO-B inhibitors, for which it is being developed, as MAO-B inhibitors do not alter brain dopamine.     

Monoamine Oxidase-Inhibiting Properties of SR 95191, a New Pyridazine Derivative, in the Rat: Evidence for Selective and Reversible Inhibition of Monoamine Oxidase Type A In Vivo but Not In Vitro

In rodents, SR 95191 [3-(2-morpholinoethylamino)-4-cyano-6-phenylpyridazine] has been shown to be active in animal models of depression. The profile of activity of SR 95191 suggests that the compound is a selective and short-acting type A monoamine oxidase (MAO) inhibitor (MAOI) in vivo. In the present study, the interaction of SR 95191 with MAO-A and MAO-B activity was further examined in vivo and in vitro. In brain, liver, and duodenum of pretreated rats, SR 95191 selectively inhibited MAO-A (ED50 = 3-5 mg/kg, p.o.), whereas MAO-B was only weakly inhibited for doses as high as 300 mg/kg, p.o. In vivo, SR 95191 (1-100 mg/kg, p.o.) antagonized, in a dose-dependent fashion, the irreversible inhibition of brain and liver MAO-A induced by phenelzine. Finally, dopamine and 5-hydroxytryptamine depleted from their striatal stores by tetrabenazine were able to displace SR 95191 from the active site of MAO-A. However, ex vivo, kinetic studies showed that the inhibitory effect of SR 95191 (1-10 mg/kg) towards MAO-A was noncompetitive and was unchanged after dilution or dialysis. In vitro, the inhibition of brain MAO-A, but not MAO-B, by SR 95191 was time dependent, with a 19-fold decrease in the IC50 values being observed over a 30-min incubation period (140 to 7.5 microM). At this time, the SR 95191-induced inhibition of MAO-A was not removed by repeated washings. When the reaction was started by adding the homogenate without prior preincubation with SR 95191, the inhibition of brain MAO-A was fully competitive (Ki = 68 microM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental study of the effects of amiridin and tacrine on learning and memory

The authors studied the influence of amiridin and tacrine on learning and memory in mice and rat by passive avoidance conditioning test at norm and under scopolamine induced amnesia as well as of their effect on acetylcholine esterase (AChE) activity in brain cortex homogenates. Amiridin in doses 0.1 and 0.2 mg/kg showed a beneficial action on conditioning in untreated animals, its effect being comparable with that of piracetam. Tacrine was ineffective. In scopolamine treated animals amiridin and tacrine showed anti-amnestic action at dose of 0.1 mg/kg which was found ineffective with respect to AChE activity. The data suggests that the ameliorating effect of amiridin and tacrine on cognitive abilities in patients with senile dementia is not related their anticholinesterase properties.     

Histochemical investigation of criteria for the distinction between monoamine oxidase A and B in various species

The superior cervical ganglion (SCG), pineal body (PB), and liver (L) of the rat, rabbit and cat were stained for monoamine oxidase (MAO) A and B by the tetranitro blue tetrazolium (TNBT) and coupled peroxidase ( PerOx ) methods, using 5-hydroxytryptamine (5HT), tryptamine ( Tryp ), tyramine (Tyr), and benzylamine (Bz) as substrates, and clorgyline (Cl) and deprenyl (Dep), both at 10(-7) M, as selective inhibitors. The nodose ganglion (NG) and dorsal root ganglion (DRG) of the rabbit and cat were also studied. The results with rat tissues were consistent with published quantitative findings (SCG, MAO-A much greater than B; PB, MAO-A less than or equal to B; L, MAO-A = B). In the rabbit, the findings with the SCG were similar; the MAO activities of the PB were relatively resistant to both inhibitors; the MAO of the liver required 10(-4) M concentrations of both inhibitors to produce near total inhibition, suggesting that the liver contains an MAO distinct from MAO A and B. All cat tissues examined appeared to contain almost exclusively MAO-B. In this species 5HT, which is generally considered a selective substrate for MAO-A, was oxidized by MAO-B. The findings indicate that criteria for MAO-A, -B, and other subgroups must be defined for each species and tissue.     

Design,synthesis and biological evaluation of N-methyl-N-[(1,2,3-triazol-4-yl)alkyl]propargylamines as novel monoamine oxidase B inhibitors

Different azides and alkynes have been coupled via Cu-catalyzed 1,3-dipolar Huisgen cycloaddition to afford a novel family of N₁- and C₅-substituted 1,2,3-triazole derivatives that feature the propargylamine group typical of irreversible MAO-B inhibitors at the C4-side chain of the triazole ring. All the synthesized compounds were evaluated against human MAO-A and MAO-B. Structure–activity relationships and molecular modeling were utilized to gain insight into the structural and chemical features that enhance the binding affinity and selectivity between the two enzyme isoforms. Several lead compounds, in terms of potency (submicromolar to low micromolar range), MAO-B selective recognition, and brain permeability, were identified. One of these leads (MAO-B IC₅₀ of 3.54 μM, selectivity MAO-A/MAO-B index of 27.7) was further subjected to reversibility and time-dependence inhibition studies, which disclosed a slow and irreversible inhibition of human MAO-B. Overall, the results support the suitability of the 4-triazolylalkyl propargylamine scaffold for exploring the design of multipotent anti-Alzheimer compounds endowed with irreversible MAO-B inhibitory activity.     

A comparative study on the effects of amiridin on learning and memory of old rats during passive avoidance test]

18-month rats showed much less learning ability in comparison with that of 3-month rats. 20-days treatment of old rats with amiridin, tacrine, and piracetam improved latency in passive avoidance test to the level of 3-month rats. The activity of acetylcholine esterase (AChE) from homogenates of old rat cortex was reduced as compared with that of young rats. After treatment with amiridin the activity of the enzyme remained unchanged, tacrine stimulate the decrease of activity of AChE while piracetam increased activity of AChE to the level of 3-month rats. The aging of rats is followed by the reduction of unsaturated fatty acids, the increase of cholesterol content and the increase of microviscosity of membranes of brain synaptosomes. Multiple treatment with amiridin, piracetam and tacrine normalized these indices.     

Differences in monoamine oxidase activity between cultured noradrenergic and cholinergic sympathetic neurons

Two types of monoamine oxidase activity (MAO-A and MAO-B) help regulate the levels of biogenic amines such as catecholamines and serotonin. Although MAO-A has greater activity toward most catecholamines than MAO-B, no direct experiments have determined the types and levels of MAO activity that are normally expressed in noradrenergic neurons. Noradrenergic neurons from neonatal rat superior cervical ganglia were isolated and cultured under conditions that permit either continued expression of the noradrenergic phenotype or promote a transition to a predominantly cholinergic phenotype. After 14-21 days in vitro, neurons from both types of cultures were assayed for the type and amount of monoamine oxidase activity using tryptamine, a common substrate for both MAO-A and MAO-B. Neurons cultured under noradrenergic conditions expressed sevenfold greater MAO activity than neurons cultured under cholinergic conditions. Essentially all MAO activity in the noradrenergic cultures was inhibited by preincubation with 10(-8)-10(-9) M clorgyline, which indicated that this activity was primarily MAO-A. Cultures grown under cholinergic conditions exhibited 6- to 10-fold lower MAO-A activity and an 8- to 10-fold lower level of catecholamine synthesis from labeled precursors compared to neurons grown under noradrenergic conditions. These results directly demonstrate that high MAO-A activity is expressed in noradrenergic neurons in vitro. The corresponding decreases in both MAO-A specific activity and catecholamine synthesis as neurons become cholinergic in vitro suggest that the expression of the noradrenergic phenotype involves the coordinate regulation of degradative as well as synthetic enzymes involved in catecholamine metabolism.     

Inhibition of type A monoamine oxidase by coptisine in mouse brain

The inhibitory effects of coptisine, a protoberberine isoquinoline alkaloid, on type A and type B monoamine oxidase (MAO-A and MAO-B) activities in mouse brain were investigated. Coptisine showed an inhibitory effect on MAO-A activity in a concentration-dependent manner using a substrate kynuramine, but coptisine did not inhibit MAO-B activity. Coptisine exhibited 54.3% inhibition of MAO-A activity at 2 microM. The values of Km and Vmax of MAO-A were 151.9 +/- 0.6 microM and 0.40 +/- 0.03 nmol/min/mg protein, respectively (n=5). Coptisine competitively inhibited MAO-A activity with kynuramine. The Ki value of coptisine was 3.3 microM. The inhibition of MAO-A by coptisine was found to be reversible by dialysis of the incubation mixture. These results suggest that coptisine is a potent reversible inhibitor of MAO-A, and that coptisine functions to regulate the catecholamine content.     

Effects of the compounds 2-methoxynaphthoquinone, 2-propoxynaphthoquinone, and 2-isopropoxynaphthoquinone on ecdysone 20-monooxygenase activity

The effects of the natural compound 2-methoxy-1,4-naphthoquinone, isolated from the leaves of Impatiens glandulifera and the synthetic compounds 2-propoxy-1,4-naphthoquinone and 2-isopropoxy-1,4-naphthoquinone on ecdysone 20-monooxygenase (E-20-M) activity were examined in three insect species. Homogenates of wandering stage third instar larvae of Drosophila melanogaster, or abdomens from adult female Aedes aegypti, or fat body or midgut from fifth instar larvae of Manduca sexta were incubated with radiolabelled ecdysone and increasing concentrations (from 1 x 10(-8) to 1 x 10(-3) M) of the three compounds. All three compounds were found to inhibit in a dose-dependent fashion the E-20-M activity in the three insect species. The concentration of these compounds required to elicit a 50% inhibition of this steroid hydroxylase activity in the three insect species examined ranged from approximately 3 x 10(-5) to 7 x 10(-4) M.