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At least 1,423 records · Page 79Linked to original sources
PubMed1976

The effects of adrenaline injections on human platelet monoamine oxidase and related measures.

A double-blind, placebo-controlled, cross-over study in ten normal volunteers assessed the effects of the subcutaneous administration of adrenaline on platelet MAO activity, in an attempt to replicate previous findings of increased MAO activity following adrenaline. Platelet counts, cortisol plasma concentrations, and uptake of metaraminol by the platelets were also determined to elucidate possible mechanisms of action. Blood pressure and heart rate were used as indices of the concentration of adrenaline effectively in circulation. MAO activity towards benzylamine was significantly increased by adrenaline. Non-significant increases were noted in the deamination of tyramine and tryptamine, in platelet counts, cortisol concentrations and metaraminol uptake. Increases in MAO activity were also noted early in the experimental sessions suggesting that other experimental variables such as venepuncture may affect platelet MAO activity. Possible mechanisms for this adrenaline effect are discussed and it is suggested that variables such as "arousal" and "stress" must be taken into account when interpreting clinical data on platelet MAO.

Adult↗
PubMed1979

The central action of pizotifen.

The central action of the potential antidepressant drug pizotifen (Sandomigran) was studied in mice, rats and rabbits. Pizotifen in doses up to 10 mg/kg i.p. was ineffective in classic tests for antidepressant activity. It neither antagonized the effects of reserpine in rats (hypothermia, ptosis) nor potentiated the effects of amphetamine (in mice and rats), nialamide or L-dopa (in mice) on locomotor activity. However, its antidepressant activitiy was found in the 'despair test' in rats. On the other hand, pizotifen inhibited the head twitch reaction induced by L-5-hydroxytryptophan in mice (ED50 = 0.009 mg/kg, i.p.) and by 5-methoxytryptamine (+ tranylcypromine) in rats (ED50 = 0.45 mg/kg, i.p.). It also antagonized tryptamine-induced clonic convulsions of fore-paws in rats (ED50 = 0.35 mg/kg, i.p.), and in doses of 5--10 mg/kg s.c. inhibited hyperthermia produced by LSD in rabbits. Finally, pizotifen (0.1--0.3 mg/kg, i.v.) inhibited or abolished LSD- or quipazine-induced stimulation of the hind limb flexor reflex of spinal rats; the above effect was not due to noradrenolytic action of the drug. These results suggest that pizotifen strongly blocks the central postsynaptic serotonin receptors.

Amphetamine↗
PubMed1979

Studies on human blood platelets in affective disorder.

Platelets were examined to enable a simultaneous investigation to be made of indolylamine and electrolyte metabolism in affective disorder. No significant differences were detected in either platelet membrane ATPase or adenyl cyclase specific activity in any of the groups of patients studied, when compared with appropriate controls. A reduced Vmax and y for the 5-hydroxy-tryptamine uptake process into platelets was observed in both unipolar and bipolar depressed groups. The Km for this process was not significantly different in any of the patients from that found in control subjects. Lithium therapy was shown not to influence significantly any of the platelet parameters examined. It is suggested that membrane enzyme changes found in some peripheral cells in patients suffering from affective disorder, i.e. reduced Na+ + K+ - ATPase activity in erythrocytes in depression, is not common to all peripheral cells and may or may not reflect central nervous system changes.

Adenosine Triphosphatases↗
PubMed1979

Zimelidine: a therapeutic and pharmacokinetic study in depression.

Zimelidine, a bicyclic compound with a strong effect on the neuronal reuptake of 5-hydroxy-tryptamine and with weak anticholinergic actions, was evaluated for its antidepressant efficacy in a double-blind comparative trial with amitriptyline. In doses of 200 mg a day it was found to be as effective as 150 mg amitriptyline, but with significantly less subjective side-effects. The plasma concentration of zimelidine and its metabolite, norzimelidine, showed no significant correlation with therapeutic outcome.

Allylamine↗
PubMed1982

Psilocybin as a discriminative stimulus: lack of specificity in an animal behavior model for 'hallucinogens'.

Fifteen rats were trained to discriminate between the tryptamine hallucinogen psilocybin (4-phosphoryloxy-N,N-dimethyltryptamine; 1.0 mg/kg) and saline in a two-lever choice task. Dose-response and time-response curves were obtained. The psilocybin cue generalized to psilocin (the dephosphorylated congener of psilocybin) and to the prototypical indoleamine hallucinogen LSD, but not to the phenylethylamine hallucinogen mescaline. These results indicate that the hallucinogenic effects of these drugs in humans may not be identical with their discriminative stimulus functions in animals, and that these four compounds may not be members of a single drug class. The term 'hallucinogen' may thus be a misnomer in the context of drug discrimination studies in nonhumans.

Animals↗
PubMed1975

The effects of protriptyline and clomipramine in vitro on the uptake of 5-hydroxytryptamine and dopamine in human platelet-rich plasma.

The effects of protriptyline and clomipramine, at concentrations of 10(-7)M to 10(-4)M, were studied in vitro on the uptake of 5-hydroxytryptamine and dopamine uptake in human platelet-rich plasma. It was found that the tertiary amine, clomipramine, was a more potent inhibitor of 5-hydroxytryptamine uptake than the secondary amine, protriptyline. The activity of both compounds was competitive but it was thought unlikely that they acted through tryptamine receptor sites as methysergide 2.5 X 10(-8)M had very little effect on 5-hydroxytryptamine uptake. Neither tricyclic antidepressant had any marked effect on dopamine uptake.

Binding, Competitive↗
PubMed1979

Modification of spontaneous ECoG and behavior in cat by monoamine precursors.

The effects of increasing the brain monoamine content on the three types of localized rhythms identified in somatic area I ("mu-type rhythms") were studied in freely moving cats. Increases in brain monoamines (catecholamines and serotonin) were produced by injecting L-Dopa and 5-HTP, L-tyrosine, L-tryptophan and tryptamine were also tested. It is concluded that the two subsets of rhythms, one accompanying high levels of alertness and vigilance and the other appearing during quiet wakefulness, are related to the catecholaminergic systems, while those characterizing drowsiness seem to be controlled by a serotoninergic system. The latter, however, is distinct from that controlling slow sleep.

5-Hydroxytryptophan↗
PubMed1983

Selective inhibition of monoamine oxidase in monoaminergic neurons in the rat brain.

The prevention by six reversible and selective monoamine oxidase-A (MAO-A) inhibitors (alpha-ethyl-tryptamine, harmaline, 4-methoxyamphetamine, amiflamine [FLA 336(+)], N-desmethylamiflamine [FLA 788(+)] and N,N-desmethylamiflamine [FLA 668(+)] of the phenelzine-induced irreversible MAO inhibition in the rat brain was examined. By using crude synaptosome preparations of hypothalamus and striatum incubated with low substrate concentrations of 14C-serotonin (1 X 10(-7) M), 14C-noradrenaline (2.5 X 10(-7) M) and 14C-dopamine (2.5 X 10(-7) M) in the absence and presence of selective amine uptake inhibitors (alaproclate, maprotiline and amfonelic acid, respectively), it was possible to determine the deaminating activities inside and outside the specific aminergic synaptosomes. Thus, with this technique the protection of MAO by the reversible inhibitors administered orally 1 h prior to the subcutaneous injection of phenelzine against the phenelzine effect could be determined inside and outside the specific aminergic neurons. It was found that alpha-ethyltryptamine, 4-methoxyamphetamine and particularly amiflamine and FLA 788(+) were more potent inside than outside the serotonergic neurons. FLA 668(+) was a selective inhibitor of noradrenergic MAO, to which also 4-methoxyamphetamine, amiflamine and FLA 788(+), but not alpha-ethyltryptamine had some preference. Harmaline had no certain preference for MAO in any of the aminergic neurons. At high doses of FLA 668(+) a preference for dopaminergic MAO was observed. Since pretreatment of the rats with norzimeldine or desipramine antagonized the preferences for serotonergic or noradrenergic MAO, it is plausible to conclude that the compounds showing these preferences are accumulated in the neurons by the membranal uptake systems.

Animals↗
PubMed1983

Thermolabile and thermostable human platelet phenol sulfotransferase. Substrate specificity and physical separation.

Human platelets contain at least two forms of phenol sulfotransferase (PST), a thermolabile (TL) form for which dopamine is a substrate and a thermostable (TS) form for which micromolar concentrations of phenol can serve as substrate. At higher concentrations phenol is also a substrate for the TL form. Studies of the regulation and the possible clinical value of measurements of platelet PST have been hampered because there is no specific substrate for the TS form of the enzyme. The purposes of these experiments were to determine whether there might be a better substrate than phenol for use in measurement of the activity of the TS form of platelet PST, and to attempt to physically separate the two forms of the platelet enzyme. The results of substrate kinetic, thermal stability, and inhibitor studies performed with platelet homogenates were all compatible with the conclusion that p-nitrophenol and 6-OH-melatonin were substrates for both the TS and TL forms of platelet PST. Norepinephrine, epinephrine and 5-OH-tryptamine were substrates for only the TL form. The apparent Km constants of the two forms of PST for p-nitrophenol differed by 7,100-fold when measured in platelet homogenates. This difference was 200 times greater than that which has been reported for phenol. Therefore, p-nitrophenol is the preferred substrate for measurement of the TS PST activity if interference by the TL activity is to be avoided. This information made it possible to use p-nitrophenol as a substrate in experiments designed to separate the two forms of platelet PST.(ABSTRACT TRUNCATED AT 250 WORDS)

Arylsulfotransferase↗
PubMed1977

Influence of enkephalin on K+-evoked efflux of putative neurotransmitters in rat brain. Selective inhibition of acetylcholine and dopamine release.

In rat brain slices preincubated with various radiolabelled putative neurotransmitters, methionine-enkephalin diminished the potassium-evoked release of dopamine and acetylcholine. The effect was antagonised by naloxone. The potassium-induced effux of three other neurotransmitters, histamine, 5-hydroxy-tryptamine and gamma-aminobutyric acid, were unaffected by methionine-enkephalin. A probable physiological function for the endogenous ligands in specifically affecting the catecholaminergic and cholinergic transmission is suggested.

Acetylcholine↗
PubMed1979

Extracellular 5-hydroxytryptamine inhibits 5-hydroxytryptamine release from rat brain cortex slices.

Rat brain cortex slices preincubated with 3H-5-hydroxytryptamine were superfused with physiological salt solution and stimulated electrically, or they were superfused with Ca2+-free solution containing 25 mM K+ and stimulated by introduction of 1.3 mM CaCl2 for 2 min. After blockade of neuronal 5-hydroxy-tryptamine (5-HT) uptake with clomipramine or paroxetine, the 3H overflow evoked by both methods of stimulation was decreased by unlabelled 5-HT and increased by methiothepin. The inhibition caused by 5-HT was antagonized by simultaneous administration of methiothepin. The inhibition by 5-HT of Ca2+-induced overflow was also observed in the presence of tetrodotoxin. These results suggest that 5-HT regulates its own release from central serotoninergic neurones by activating presynaptic 5-HT autoreceptors, thus decreasing the availability of Ca2+ for stimulus-release coupling.

Animals↗
PubMed1975

New characteristics of harmaline inhibition of intestinal transport systems.

Harmaline strongly inhibits the uptake of phenylalanine by slices of guinea-pig intestine in vitro. The lowest concentration having a significant effect is 0.1 mM. The drug also inhibits the unidirectional flux of phenylalanine from the mucosal to serosal face of the tissue provided it is added to the solution bathing the mucosal surface. The unidirectional flux of sodium from the mucosa to the serosa was similarly reduced. Ion and water absorption in the perfused dog intestine in vivo is also diminished in the presence of harmaline. These results support the hypothesis, previously proposed in view of the rapid onset of harmaline inhibition of sodium-dependent uptake mechanisms in a variety of tissues, that harmaline interacts with the sodium-site of non-electrolyte carrier complexes. The effect of harmaline on phenylalanine uptake by the intesting is duplicated by other psychotropic indole analogues. The actions of harmine and harnalol are similar to that of harmaline, despite great differences in the liposolubility of the different compounds. N:N-dimethyl-tryptamine is equally inhibitory, but serotonin is inactive. Mescaline and lysergic acid diethylamide also inhibit phenylalanine transport, but to a much lesser extent than harmaline.

Alkaloids↗
PubMed1986

Autoreceptors and alpha 2-adrenoceptors at the serotonergic axons of rabbit brain cortex.

Slices of the rabbit occipito-parietal cortex were preincubated with 3H-serotonin and then superfused and stimulated electrically (2 min at 3 Hz). In the absence of drugs, the stimulation-evoked overflow of tritium was approximately 3% of the tritium content of the tissue. Unlabelled serotonin and 5-carboxamido-tryptamine, when administered in the presence of 6-nitroquipazine, reduced the evoked overflow of tritium. Their effects were antagonized by metitepin (apparent pA2 value 8.1) and (+/-)-cyanopindolol (apparent pA2 value 6.4). Metitepin, but not cyanopindolol, increased evoked tritium overflow; the effect of metitepin was greater in the presence than in the absence of nitroquipazine. The evoked overflow of tritium was also depressed by clonidine, an effect antagonized by idazoxan (apparent pA2 value 7.0) but not by prazosin. Phenylephrine caused a decrease only at high concentrations that simultaneously accelerated basal tritium efflux. Prazosin and idazoxan did not change evoked tritium overflow, and phentolamine increased it significantly only when administered in the presence of (+)-oxaprotiline. Rauwolscine produced an inhibition that was prevented by metitepin. It is concluded that the serotonergic axons of the rabbit occipitoparietal cortex possess presynaptic, release-inhibiting serotonin autoreceptors and alpha 2-adrenoceptors. The receptors appear to receive an input of endogenous serotonin and, to a lesser extent, noradrenaline, under the conditions of these in vitro experiments.

Adrenergic alpha-Agonists↗
PubMed1976

Inhibition of the reuptake of serotonin by tryptoline.

Tryptoline, a metabolite of tryptamine, competitively inhibits serotonin accumulation in nuclei-free homogenate of rat "forebrains". After intraventricular injection the drug elicits an increase of serotonin levels in the same part of the brain whereas the monoamine oxidase activity is not altered.

Animals↗
PubMed1978

Tetrahydronorharmane (tetrahydro-beta-carboline), a physiologically occurring compound of indole metabolism.

In the present paper a sensitive method is described to measure tetrahydronorharmane (THN) in the urine of man and rats as well as in the forebrain of rats. The compound is extracted into diethyl ether, separated by thin layer chromatography (TLC), acetylated with radiolabelled acetic anhydride and further isolated by two-dimensional TLC development. The existence of THN in urine of man was proven by using chromatography with different solvent systems, cocristallisation, isotope dilution technique as well as mass-spectrometry. The amount of THN in the urine varied over a wide range. With the same method it was demonstrated that THN occurs also in the forebrain of rats. The concentration increases after loading with tryptamine. The findings are discussed in view of the hypothesis that THN acts as a compound modulating neuronal mechanism.

Adult↗
PubMed1986

On the nature of the receptor mediating the action of 5-hydroxytryptamine in potentiating responses of the mouse urinary bladder strip to electrical stimulation.

Superfused mouse bladder strip responded to electrical stimulation (ES) by twitch contractions. These contractions were potentiated by 5-hydroxytryptamine (5-HT; 0.03-3.0 microM). Three tryptamine analogues were tested for their ability to potentiate the responses to ES and their relative activities were compared with values in the literature. 5-Carboxamidotryptamine was more potent than 5-HT, N-omega-methyl 5-HT was about equipotent, and alpha-methyl 5-HT was much less potent. Exogenous noradrenaline did not reduce the effect of 5-HT, although it reduced the response of the tissue to ES. The maximum increase in tissue tension evoked by 5-HT was unaltered by phentolamine (1 microM) or bretylium (25 microM). These results show that 5-HT did not act on the bladder by inhibiting the release of catecholamines from intrinsic nerves. The effect of 5-HT proved very resistant to attempts to block it with conventional 5-HT antagonists. Several antagonists were studied including ketanserin, methysergide, methiothepin, and MDL 72222 but even at concentrations as high as 1 microM none of them exhibited any marked inhibitory effect against the action of 5-HT. At 10 microM some compounds showed activity, but none abolished the effect except methiothepin - and its action was not surmountable by increasing the concentration of 5-HT. Thus the effect of 5-HT on the bladder was not mediated by 5-HT receptors of types 'M', 'D' or 5-HT2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

The effect of kininase II inhibitors on the response of feline cerebral arteries to bradykinin and angiotensin.

Bradykinin (BK) produced concentration-related relaxations of cat middle cerebral arteries and was ineffective on cat basilar arteries in vitro under resting tension and when contracted with 5-hydroxy-tryptamine (5-HT). Angiotensin I and II (AI, AII) produced concentration-related contraction on both arteries, AII being approximately 10 times more potent than AI. The angiotensin-converting-enzyme inhibitors, SQ, 14225, BPP5a and BPP9a had no effect on the concentration effect curves to BK, AII or 5-HT but responses to AI were inhibited. These results suggest that angiotensin-converting-enzyme is present in both preparations and is important for the conversion of AI to AII but apparently not for the degradation of BK.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1987

Modulation of the vestibulo-ocular reflex by serotonin in the rat.

The effects of intraventricular injection of serotonin (5-HT) and its agonists and antagonists on the amplitude of the vestibulo-ocular reflex were studied in chronic implanted rats. 5-HT (10(-5) M) triggers an increase of the amplitude of the reflex which lasts 30 min. Similar results are obtained when N,N-dimethyl-5-methoxytryptamine (10(-3) M) is introduced into the ventricular cannula. The increasing effects observed both with 5-HT and N,N-dimethyl-5-methoxy-tryptamine are abolished by methiothepin, a potent antagonist of 5-HT receptors. Injection of indirect agonists like pargyline, a monoamine oxidase inhibitor, or fluoxetine, a potent inhibitor of 5-HT reuptake, is followed by an increase of the amplitude of the vestibulo-ocular reflex. These results indicate that 5-HT can modulate the activity of the vestibulo-ocular pathway and muscular tone of extraocular muscles. Location and involvement of various modulating 5-HT sites are discussed.

Animals↗