INHIBITION OF NORADRENALINE UPTAKE BY DRUGS

Reevaluation of the indoleamine hypothesis of depression. Evidence for a reduction of functional activity of central 5-HT systems by antidepressant drugs

The effects of antidepressant drugs on central 5-HT receptor activity were studied in rats and mice. Antidepressant drugs were evaluated for their ability to displace 3H-5-HT and 3H-d-LSD from membrane binding sites in the dorsal neocortex of rats in vitro and for their ability to block 5-HTP and d-LSD induced behavioral effects in mice. The degree of blockade of head-twitches in mice produced by the antidepressants was highly correlated with their affinity for 3H-d-LSD binding sites. A number of antidepressant drugs such as amitriptyline, nortriptyline, mianserine, doxepine, nomifensine and dibenzepine appear to possess marked 5-HT receptor blocking activity at some type of 5-HT receptors in brain. New antidepressant drugs such as zimelidine, which specifically inhibit 5-HT reuptake and do not block 5-HT receptor sites, may after chronic treatment also reduce the functional activity of 5-HT systems by producing adaptive changes in postsynaptic 5-HT mechanisms. Thus, a new indoleamine hypothesis of depression is presented: the therapeutic action of antidepressant drugs may in part be due to a reduced functional acitivity of some central 5-HT systems.

The in vivo binding of [3H]-desipramine and [3H]-chlorpromazine to areas in the rat brain

The distribution of [3H]-desipramine (DMI) and of [3H]-chlorpromazine (CPZ) in rat brain was determined by the incorporation of radioactivity into various regions of the brain and by autoradiography of transverse cryostat sections. The label from [3H]-DMI was rapidly distributed in all brain regions, reaching peak levels within 30 min and considerably decreasing 1--4 h after injection. Following the selective destruction of catecholaminergic nerve terminals by intracerebral administration of 6-hydroxydopamine, a marked reduction in the incorporation of DMI, but not of CPZ, was evident in all brain areas investigated. The autoradiographed sections clearly demonstrated a preferential uptake of both drugs by the caudate nucleus. These findings suggest that DMI might be largely bound to presynaptic dopamine and norepinephrine terminals, while the CPZ binding involves postsynaptic sites.

Effects of tricyclic antidepressants on cardiovascular responses to norepinephrine and phenylephrine during pregnancy

The effects of imipramine and amitriptyline on the responses of the uteroplacental vasculature to norepinephrine and phenylephrine were investigated in the pregnant ewe. Experiments were performed on conscious animals in which electromagnetic flow transducers were chronically implanted on the uterine arteries. Administered alone, the tricyclic antidepressants had no effect on mean arterial pressure (MAP) or estimated uteroplacental vascular conductance (UPVCe). Following intravenous infusion of either imipramine (1 mg. per kilogram) or amitriptyline (2.5 mg. per kilogram), the pressor response to norepinephrine (1 microgram per kilogram) and the duration of that response were significantly increased (p less than 0.05). In addition, both the duration of the norepinephrine-produced decrease in uteroplacental blood flow (UPBF) and the amplitude of the decrease in UPVCe were enhanced. In contrast, responses to phenylephrine (2.5 microgram per kilogram) were unaffected by prior administration of either imipramine or amitriptyline. Of additional interest were findings suggesting differential sensitivities to alpha-agonists of the uteroplacental compared with other vascular beds. These observations bring attention to the possibility of interactions between endogenous or exogenous norepinephrine and the tricyclic antidepressants and suggest that the possibly unique sensitivities of the uteroplacental bed should be considered when prescribing drugs during pregnancy.

Comparison of the responses of single cortical neurones to tyramine and noradrenaline: effects of desipramine

1 The technique of microelectrophoresis was used in order to compare the actions of tyramine and noradrenaline on single neurones in the cerebral cortex of the rat.2 Tyramine could both excite and depress cortical neurones. Each tyramine-sensitive cell was also sensitive to noradrenaline. There was a high correlation between the directions of responses to tyramine and noradrenaline, most cells excited by tyramine being excited by noradrenaline, and most cells depressed by tyramine being depressed by noradrenaline.3 In the case of both excitatory and depressant responses, tyramine appeared to be less potent than noradrenaline.4 Tyramine evoked ;slower' responses than noradrenaline, both the latencies to onset and the recovery times being longer for responses to tyramine than for responses to noradrenaline.5 When the rates of release of tyramine and noradrenaline from micropipettes were measured in vitro, no significant difference could be observed between the transport numbers of the two drugs. Thus the difference in potency between the two drugs, and the difference in the time courses of responses to the two drugs, are presumably of biological origin.6 Desipramine could discriminate between neuronal responses to tyramine and noradrenaline: responses to tyramine were antagonized, while responses to noradrenaline were either potentiated or unaffected. Responses to DL-homocysteic acid were not affected by desipramine.7 The results are consistent with the hypothesis that tyramine is an indirectly acting sympathomimetic amine in the brain, and desipramine acts by blocking the uptake of both tyramine and noradrenaline into presynaptic noradrenergic nerve terminals.

Noradrenaline, depressive illness, and the action of amitriptyline

The tyramine-dose/pressor response test was carried out on a series of patients suffering from primary depressive illness before and during treatment with amitriptyline. The severity of their depression was assessed during the study of the Hamilton Rating Scale (HRS). The decreased tyramine sensitivity induced by the drug, which is related to the inhibition of NA reuptake, correlated significantly with the plasma concentration of nortriptyline. However, contrary to the expectation of the noradrenaline hypothesis of depression, the decreased tyramine sensitivity, i.e., the degree of NA-reuptake blockade, did not show any correlation with clinical improvement following 6 weeks' treatment with amitriptyline.

Effect of carbamazepine on the in vitro uptake and release of norepinephrine in adrenergic nerves of rabbit aorta and in whole brain synaptosomes

The effects of carbamazepine, in vitro, on adrenergic neuronal and whole brain synaptosomal uptake and release of tritiated norepinephrine (3H-NE) were assessed. At 10(-4) M, carbamazepine inhibited 3H-NE uptake by 22% in rabbit thoracic aorta and in brain synaptosomes. At the same concentration, carbamazepine inhibited stimulation-induced release of 3H-NE by 42.6% and inhibited isometric contraction in rabbit ear artery helical strips by 31.6%. At 10(-5) M, carbamazepine exhibited a 17.6% inhibition of 3H-NE uptake in brain synaptosomes in the absence of effects on transmitter release. Cocaine, 10(-4) M, and imipramine, 10(-4) M, inhibited uptake by 88% and 85%, respectively, in aorta, and cocaine, 10(-4) M, inhibited synaptosomal uptake by 67.7%. Since antiepileptic blood levels of carbamazepine range between 1.3 and 3.0 X 10(-5) M, it was concluded that the observed effects of carbamazepine are insufficient to account for the anticonvulsant action of the drug. However, the blockade of 3H-NE uptake by brain synaptosomes at 10(-5) M serves to explain the recently described analeptic activity of this agent.

Effects of several tricyclic antidepressants on the hemodynamics and myocardial contractility of the anesthetized dogs

Cardiovascular effects of several imipramine analogs were investigated in the anesthetized mongrel dogs. Significant reduction in the cardiac output produced by lower doses (2.5 mg/kg, i.v.) of imipramine and 2-OH-DMI was not due to a depression of myocardial contractility. In contrast, 2-OH-imipramine (1.25 mg/kg) and DMI (2.5 mg/kg) significantly reduced contractility within 10 min after i.v. administration; however, significant decrease in the cardiac output did not occur until after 60 min. Higher doses (5 mg/kg) of imipramine, DMI and 2-OH-DMI significantly attenuated cardiac rate, contractility and output within 5 min after i.v. administration. 2-OH-imipramine, 2.5 mg/kg, i.v., depressed contractility and cardiac output to a degree equivalent to that produced by 5 mg/kg of imipramine, DMI and 2-OH-DMI. 3-Chloro-imipramine (5 mg/kg, i.v.) induced decrease in the cardiac output was essentially due to a significant reduction in the heart rate since the effects of this compound on the contractility were transient in nature. 3-Cl-8-OH-metabolite of this compound had no significant effects on the cardiovascular system. The results of this investigation demonstrated that the complex cardiovascular effects of tricyclic antidepressants observed in these studies were perhaps due to a direct and/or autonomically mediated effects on the heart and vasculature. Further, the data support the conclusions that the activity of the parent compounds together with that of the metabolites contributes to overall changes observed. While all the agents are capable of reducing cardiac output, 2-OH-metabolite of imipramine appears to be most toxic on the myocardium and 3-Cl-imipramine possessed only transient effects on the contractile properties.

Antidepressant evaluation and the pharmacological actions of FG4963 in depressive patients

FG4963 a phenylpiperidine derivative and potent 5-HT reuptake inhibitor at neuronal sites was investigated in a group of 10 depressive patients, and its effect was compared with that of amitryptyline in a group of 10 depressive patients treated with amitriptyline. FG4963 was found to be significantly inferior as an antidepressant compared to amitryptyline over a 6-week period. FG4963 did not appear to be anticholinergic as judged by its lack of effect on salivary flow. Its effect (in the dosage used) on the tyramine dose--pressor response and NA dose--pressor response tests were less than those of amitryptyline.

Adrenergic stimulation of the lateral hypothalamic area on sodium and potassium excretion

The effects of adrenergic stimulation of the lateral hypothalamic area on sodium and potassium excretion were studied in rats bearing implanted cannulae. When noradrenaline was injected into several points of the lateral hypothalamic area, a dose-related increase in natriuresis and kaliuresis was observed. Rats previously injected through the same cannulae with alpha (Regitine) or beta (Propranolol) blocking agents showed different natriuretic responses when injected with noradrenaline. It was observed that the normal noradrenaline-induced natriuresis was abolished by the alpha-adrenergic blockers, while beta-adrenergic blockers increased the response. Intrahypothalamic injection of Isoproterenol, and activator of the beta-adrenergic receptor, induced a decrease in natriuresis, kaliuresis and urinary volume. In contrast, injection of Metaraminol, an alpha-adrenergic agonist, caused an increase in sodium and potassium excretion and a reduction of urinary volume. Drugs blocking the destruction of noradrenaline or its reuptake by the presynaptic nerve endings potentiated 2-fold the action of 20 nmol of noradrenaline. These experiments provide good evidence for the existence of an adrenergic mechanism consisting of alpha and beta receptors which works antagonistically on the regulation of sodium and potassium excretion. The excretion on the two electrolytes is stimulated by the alpha-adrenergic system, and inhibited by the beta-adrenergic system.

Interactions between cardioactive drugs and antidepressants

The most important cardiovascular interactions between cardioactive drugs and monoamino-oxidase inhibitors or tricyclic antidepressants are reviewed. Post-ganglion blocking agents (e.g., guanethidine), clonidine, reserpine, and alpha-methyl-dopa should not be used in patients needing antide-present therapy. For hypertension, diuretics, beta-blokkers, and vasodilators should be used. In patients with cardiac disease negative interactions between membrane-stabilizing antiarrhythmic agents and tricyclic antidepressants may be observed. Caution is recommended when using both drugs. On the other hand, the use of digitalis is relatively free of negative interactions. Some of the mechanisms possibly involved are discussed. The practical implications of such effects are presented and some clinically useful guidelines are suggested.

The effect of tricyclic antidepressants and neuroleptics on the peripheral and central action of norepinephrine in reserpine-treated mice

The effect of exogenous norepinephrine on the ptosis induced by reserpine and its modification by tricyclic antidepressants and neuroleptics were studied in reserpine-pretreated mice. S.c injection of norepinephrine (0.3-5 mg/kg) reversed dose-dependently the ptosis induced by reserpine. The maximal effect was obtained 15 min after norepinephrine administration. Tricyclic antidepressants (2.5 and 5 mg/kg i.p.) potentiated the effect of norepinephrine. In contrast neuroleptics (1 and 5 mg/kg i.p.) antagonized it. Intracerebral injection of norepinephrine (5-20 mug) also reversed dose-dependently the ptosis induced by reserpine, and the maximal effect was obtained within 5 min. Tricyclic antidepressants potentiated the effect of norepinephrine, but neuroleptics antagonized it. Among tricyclic antidepressants, the potentiating action of secondary amines was stronger than that of tertiary amines. Chlorpromazine blocked the action of norepinephrine more strongly than did the same dose of haloperidol.

Release of noradrenaline proposed as a mechanisms for the positive inotropic action of dipyridamole

In the arterially blood-perfused canine papillary muscle, i.a. injections of dipyridamole (10-300 mug) produced a dose-dependent increase in developed tension amounting to about 45% of the basal developed tension at 300 mug. The positive inotropic response to dipyridamole was greatly reduced by a prior i.a. injection of propranolol (10 mug) or by pretreatment with reserpine (0.2 mg/kg s.c. for 3 consecutive days) but not affected by a prior i.a. injection of tetrodotoxin (1 mug) or desmethylimipramine (3-10 mug). The positive inotropic response to dipyridamole reduced by pretreatment with reserpine was restored by i.a. infusion of noradrenaline (0.03 mug/min). Dipyridamole did not modify the positive inotropic responses to noradrenaline and tyramine. These results suggest that the positive inotropic response to dipyridamole is largely due to noradrenaline released from adrenergic nerve endings by a mechanism that differs from those operative in the action of tyramine or in liberation of noradrenaline upon excitation.

Further study of the adrenoceptors of the saphenous vein of the dog: influence of factors which interfere with the concentrations of agonists at the receptor level

In the present study the affinities of some sympathomimetic amines for alpha- and beta-adrenoceptors of the dog saphenous vein tissue were determined after all known factors interfering with the concentration of these agonists at the receptor level had been assessed and excluded. It was observed that in control experiments the relative potencies of sympathomimetic agonists for inducing contractions were: adrenaline (1.6) greater than noradrenaline (1.0) greater than phenylephrine (0.38) greater than isoprenaline (0.009). The elimination of neuronal uptake by cocaine, 4 X 10(-6) M, enhanced predominantly the effects of noradrenaline (by a factor of 7.5), whereas block of catechol-O-methyl transferase (COMT) by U-0521, 10(-4) M, only enhanced those of adrenaline (by a factor of 2.6) and block of beta-adrenoceptors by propranolol, 5 X 10(-7) M, enhanced those of isoprenaline (by a factor of 3) and adrenaline (by a factor of 1.8). Block of COMT enhanced the effects of adrenaline approximately as much as did the blockade of neuronal uptake; this seems to indicate that the affinity of adrenaline for extraneuronal and neuronal uptake processes is approximately the same. Regarding the relaxation-inducing capacity of sympathomimetic agents it was observed that isoprenaline, adrenaline and noradrenaline are full agonists, whereas phenylephrine was not able to produce relaxation amounting to more than 5% of the maximum. Denervation did not modify the relaxant effects of isoprenaline. After elimination of all known factors interfering with the concentration of the sympathomimetic agonists in the biophase, the ratios between the ED50's of each amine for alpha- and beta-adrenoceptors were: adrenaline = 34, noradrenaline = 109 and isoprenaline = 0.0041.

Tricyclic antidepressants: effects on the firing rate of brain noradrenergic neurons

The spontaneous activity of the norepinephrine-containing cells of the locus coeruleus was recorded in chloral hydrate-anesthetized rats. The effect of seven tricyclic antidepressants on the firing rate of single cells in the locus coeruleus was studied. All the drugs tested, except iprindole markedly decreased the rate of firing of the noradrenergic cells. Antidepressants having a secondary amine in the side chain, desipramine, nortriptyline and chlordesipramine, were more potent than their respective tertiary amine analogues, imipramine, amitriptyline and chlorimipramine. Alteration of the rate of drug metabolism by pretreatment with SKF-525A or phenobarbital did not change the doses of tertiary antidepressnats required to decrease norepinephrine cell firing. Depletion of the norepinephrine stores by pretreatment with alpha-methyl-p-tyrosine and reserpine markedly increased the dose of desipramine required to depress the norepinephrine cells. The results are in good agreement with previous studies showing that secondary amine antidepressants are more potent than their tertiary amine homologues in blocking the uptake of norepinephrine into brain and peripheral tissues. Despite their lower potency it is concluded that tertiary antidepressants act on noradrenergic neurons in their unchanged form and not via secondary amine metabolites formed during the recording experiments since alterations in liver metabolism did not influence the response. The findings are consistent with the suggestion made from studies on transmitter turnover that antidepressants by inhibiting reuptake of norepinephrine cause a stimulation of postsynaptic receptors which decreases the activity of the presynaptic neurons by a feed-back mechanism. This view is further supported by the finding of an inverse relation between the norepinephrine content of the brain and the dose of desipramine required to decrease the firing rate of the noradrenergic neurons.

Comparative studies of a new 5HT-uptake inhibitor and some tricyclic thymoleptics

The new 5HT-uptake inhibitor, FG 4963, and some tricyclic thymoleptics antagonized p-chloroamphetamine (PCA)-induced hypermotility in rats. FG 4963 was active in about the same s.c. and p.o. doses as chlorimipramine. FG 4963, imipramine and chlorimipramine potentiated hypermotility induced in mice by the 5HT precursor 5HTP, FG 4963 being slighly more active than chlorimipramine. In contrast to the tricyclic thymoleptics FG 4963 did not potentiate the heart rate increasing effect of NA in pithed rats. The peripheral anticholinergic effect of FG 4963 and of desipramine was almost identical while the other imipramine derivatives were more active. All tricyclic thymoleptics were strong peripheral antihistaminics, but FG 4963 was almost devoid of this action. Acute tests for ECG changes in guinea pigs and toxicity in mice and rats showed that FG 4963 and chlorimipramine were less toxic than imipramine and amitriptyline. FG 4963 is presumably a selective 5HT-uptake inhibitor producing much less potentiation of peripheral sympathetic mechanisms than do the tricyclic antidepressants.

Neurochemical and pharmacological studies on a new 5HT-uptake inhibitor, FG4963, with potential antidepressant properties

A new phenylpiperidine derivative, FG4963, and several tricyclic antidepressants were compared in various in vitro and in vivo tests for central 5HT- and NA-uptake inhibition. FG4963 was found to be a 5HT-pump blocker with activity similar to that of chlorimipramine. FG4963 inhibited NA-uptake less than the most potent tricyclic thymoleptics. In contrast to imipramine derivatives FG4963 was a weak inhibitor of peripheral NA-uptake. FG4963 seems to produce central 5HT-potentiation without affecting organ functions regulated by the autonomic nervous system as much as tricyclic antidepressants.

The role of dopamine and noradrenaline in temperature control of normal and reserpine-pretreated mice

Drugs with the common property of stimulating dopamine receptors, have been tested for their effects on core temperature in control and reserpine-pretreated mice. Apomorphine, amantadine, amphetamine, L-dopa and atropine all produced a fall in mouse oesophageal temperature, their efficacy correlating with their ability to activate central dopamine receptors. Amphetamine and L-dopa had a biphasic effect the initial fall being followed by a rise. In reserpine-pretreated mice only amphetamine, apomorphine, L-dopa and D.L-threo-dihydroxyphenyl-serine effectively reversed hypothermia. Amphetamine had the highest efficacy of all the drugs tested. The sum of the effects of apomorphine and D.L-threo-dihydroxyphenylserine was equivalent to the effect of amphetamine alone. It is suggested that in control mice dopaminergic mechanisms mediate the hypothermia and noradrenergic mechanisms the hyperthermia. In reserpine-pretreated mice both systems are involved in the mechanisms restoring body temperature to normal.

Arrhythmias and inhibition of noradrenaline uptake caused by tricyclic antidepressants and chlorpromazine on the isolated perfused rabbit heart

1. Isolated rabbit hearts were perfused with a modified Tyrode solution containing noradrenaline in concentrations increasing stepwise from 5.9 nM to 5.9 muM at 5 min intervals. This dose regime was applied twice before and once 20 min after starting perfusion with one of 9 tricyclic drugs. Ventricular rate and right atrial and ventricular tensions were recorded using the transverse method. 2. Infusions of noradrenaline evoked ventricular arrhythmias in hearts perfused with amitriptyline 4.8 muM, chlorpromazine 5.0 muM, desipramine 5.0 muM, dibenzepine 34.7 muM, doxepin 4.7 muM, imipramine 4.7 muM, noxiptiline 9.1 muM and opipramole 9.2 muM. The incidence of arrhythmias increased with the concentration of noradrenaline applied and the dose of tricyclic drug administered. Whenever arrhythmias had started they continued as long as noradrenaline was infused. Noradrenaline failed to produce arrhythmias in hearts not exposed to drugs and after iprindole 4.7 muM or cocaine 2.9-18 muM. 3. Propranolol 0.1 muM inhibited the incidence of arrhythmias after doxepin 4.7 muM plus noradrenaline 5.9-190 nM. 4. Neuronal uptake of exogenous noradrenaline in the rabbit heart was inhibited by the tricyclic drugs in the following order of declining p potency: doxepin, noxiptiline, amitriptyline, desipramine, chlorpromazine, imipramine, dibenzepine, opipramole and iprindole. 5. Among tricyclic drugs the potency to inhibit amine uptake is related to the incidence of arrhythmias evoked by a submaximal concentration of noradrenaline. It appears, however, that these two parameters are not causally linked. 6. The isolated rabbit heart perfused with noradrenaline might be used as a model for testing the arrhythmogenic actions of tricyclic drugs and the treatment of such arrhythmias.

Effects of imipramine and desipramine on responses of single cortical neurones to noradrenaline and 5-hydroxytryptamine

1 The technique of microelectrophoresis was used in order to study the effects of imipramine and desipramine on single neurones in the somatosensory cortex of the cat, anaesthetized with halothane.2 Imipramine and desipramine, when applied for a brief period, did not affect the firing rate of the vast majority of the neurones tested.3 Both potentiation and antagonism of excitatory responses to noradrenaline could be observed after a brief application of either of the antidepressants. Four drug-interaction patterns could be distinguished: potentiation of immediate onset; potentiation reaching its maximum after a delay; antagonism followed by potentiation; antagonism followed by recovery.4 When different doses of the same antidepressant were applied, it was found that the drug-interaction patterns were related to the dose of antidepressant applied, a lower dose causing potentiation, and a higher dose antagonism of the response.5 Both potentiation and antagonism of depressant responses to noradrenaline could be observed.6 Both excitatory and depressant responses to 5-hydroxytryptamine were modified by imipramine and desipramine: a smaller dose of the antidepressant potentiated, and a higher dose antagonized the responses.7 Excitatory responses to glutamate were not affected by imipramine and desipramine.

Antagonism of noradrenaline and histamine by desipramine in the isolated artery of the rabbit ear

1. The effects of desipramine (DMI) were examined on the vasoconstrictor responses of the isolated perfused artery of the rabbit ear to noradrenaline (NA) and to histamine. Innervated and sympathetically denervated arteries were used.2. In innervated arteries, DMI in concentrations of 1 x 10(-8) to 1 x 10(-7)M enhanced the responses to NA; higher concentrations reduced the responses. In sympathetically denervated arteries, DMI caused only reduction of the responses to NA.3. Responses to histamine were reduced by DMI in both innervated and denervated arteries. DMI was considerably more potent as an antagonist of histamine than of noradrenaline.4. The reduction by DMI of the responses to NA and histamine in both innervated and denervated arteries was associated with a parallel shift to the right of the concentration-response curves of the agonist and a depression of the maximal response. These effects of DMI were reversible.5. Analysis of the data by the method of Arunlakshana & Schild (1959) showed the following: the antagonism of the action of NA by DMI on denervated arteries fulfilled the requirements for competitive antagonism; antagonism of the action of NA on innervated arteries was not competitive; antagonism of the actions of histamine on innervated and denervated arteries was not competitive.6. It is suggested that DMI antagonizes the action of NA and histamine on the perfused artery of the rabbit ear in two ways: (i) reversible specific antagonism which is competitive for NA and not competitive for histamine; (ii) reversible non-specific antagonism which is non-competitive for both agonists.

Distribution theory of resistance of neurogenic vasoconstriction to alpha-receptor blockade in the rabbit

The effects of α-receptor-blocking agents on the contractile responses of isolated rabbit arteries to sympathetic nerve stimulation and exogenous l -norepinephrine ( l -NE) were compared. In the pulmonary artery and aorta, yohimbine, phentolamine, and phenoxybenzamine blocked the response to nerve stimulation less than that to an equipotent dose of l -NE. This resistance of neurogenic response was independent of the frequency and number of stimuli and persisted after inhibition of the nerve l -NE uptake by cocaine. The neurogenically released transmitter l -NE probably forms a high concentration near the adventitia-media junction, whereas the exogenous NE is distributed evenly throughout the thickness of media. Thus higher concentrations of α-receptor-blocking agents would be needed to block the effect of neurogenic l -NE than to block that of exogenous l -NE. This explanation of the resistance was thought to be more appropriate to the large vessels tested than that based on neuroeffector proximity.