Uptake and Retention of 14C-Bretylium in Degenerating Postganglionic Sympathetic Nerves of the Rat

Abstract The uptake and retention of ¹⁴C-bretylium was studied in rat salivary glands and irides in vivo at different time intervals after sympathetic denervation or decentralization. The uptake of bretylium was increased on the denervated side during a time period which precedes the degeneration release of sympathetic transmitter, but was later on reduced. On the other hand, the retention of bretylium on the denervated side was already markedly reduced during the time period preceding the onset of the degeneration transmitter release. In experiments with chronically denervated salivary glands, or glands atrophied by means of excretory duct ligation, a pronounced extraneuronal accumulation was observed. The extraneuronal accumulation of bretylium may partly mask the changes in disposition of the drug induced by the sympathetic denervation. The results are in accordance with the hypothesis that bretylium must be associated with special sites at the adrenergic nerve terminals in order to exert its degeneration delaying effect.     

On the disposition of [3H]metaraminol in the rat salivary gland

The left salivary glands of rats were sympathetically denervated or decentralized. In some experiments the excretory ducts of the left submaxillary and sublingual glands were ligated to produce atrophy of the acinar cells. The rats received [³H]metaraminol (³H-MA) intravenously and were killed at various time intervals thereafter. The amount of ³H-MA in the salivary glands was determined. ³H-MA was taken up and retained in the intact gland, but disappeared rapidly from the denervated one, indicating that ³H-MA is taken up and stored in the adrenergic neuron. Decentralization resulted in a decreased turnover of the amine, especially during the first 18 hr, which supports the view that metaraminol is released by nerve activity. The ability of the salivary gland to take up ³H-MA was diminished by glandular atrophy, and the disappearance of the ³H-MA so taken up was delayed.     

Cocaine-like effect of ketamine on vascular adrenergic neurones

The influence of ketamine on adrenergic and cholinergic responses was studied in the rabbit pulmonary artery in vitro. Ketamine and cocaine potentiated smooth muscle contractions elicited by nonadrenaline, adrenaline and transmural electrical stimulation of adrenergic neurone terminals. Arterial contractions elicited by tyramine were enhanced by ketamine, while cocaine blocked them. Ketamine moved the concentration-response curve of carbachol slightly to the right. Nicotine-induced contractions were blocked by ketamine and cocaine. The adrenergic neurone blocking effect of bretylium and dimethylphenylpiperazinium on the response to transmural stimulation was prevented by ketamine. The uptake of ³H-noradrenaline by rabbit isolated aorta was inhibited by ketamine and cocaine. It is concluded that ketamine inhibits the membrane amine pump in the terminals of postganglionic adrenergic neurones in a cocaine-like manner.     

The effect of corticosterone on extraneuronal amine uptake and effector response in rat salivary glands

The effect of corticosterone on effector cell response to noradrenaline in vivo and on extraneuronal amine uptake in vitro has been investigated in rat submaxillary glands. When tissue slices were incubated with [³H]noradrenaline the level of extraneuronally retained radioactive material was found to be markedly reduced at a concentration of 10 μg ml^?1 of corticosterone after inhibition of neuronal uptake by protriptyline. Corticosterone in a dose of 10 mg kg^?1 was found to markedly potentiate the secretory response to noradrenaline in vivo, when the neuronal uptake of noradrenaline was blocked by protriptyline (10 mg kg^?1, i.p.). Inhibition of neuronal uptake alone by protriptyline or of the extraneuronal uptake alone by corticosterone in the doses used here did not affect the dose-response curve for noradrenaline, at least not in its lower part. The data thus clearly show that the extraneuronal amine uptake of rat salivary glands is blocked by corticosterone and that this extraneuronal uptake might be regarded as a mechanism of importance for the inactivation of the adrenergic transmitter.     

THE EFFECT OF COCAINE AND DESIPRAMINE ON NEURONAL UPTAKE OF [3H]-NORADRENALINE AND SENSITIVITY TO NORADRENALINE OF RAT MESENTERIC RESISTANCE ARTERIES

1. The effects of cocaine and desipramine (DMI) on neuronal uptake (uptake₁) of [³H]-noradrenaline (NA) and isometric tension development to exogenous NA were assessed in mesenteric resistance arteries of Wistar rats. 2. Both drugs concentration-dependently inhibited [³H]-NA uptake₁, DMI being more potent than cocaine. The maximum inhibition produced by each drug was the same as that produced by denervation with 6-hydroxydopamine. In denervated vessels there was no effect of cocaine on [³H]-NA uptakel. 3. Cocaine, in the same concentration range which caused inhibition of uptakel, increased the sensitivity to NA, while DMI, in a concentration range which inhibited uptake₁, did not increase the sensitivity to NA and at high concentrations reduced the sensitivity and maximal response to NA. Since DMI affected responses to NA but not responses to vasopressin and potassium its effect is probably related to blockade of α₁-adrenoceptors. 4. We conclude that the effect of cocaine on the sensitivity to NA reflects inhibition of uptakel in rat resistance arteries, while DMI cannot be used to assess the functional effect of uptakel in this preparation.     

Cocaine and neuronal uptake in the canine saphenous vein

Summary This study was designed to investigate the effects of the neuronal uptake inhibitor, cocaine on the adrenergic neuroeffector interaction in the canine saphenous vein. Tissues were incubated with ³H-noradrenaline in control solution or in presence of the cocaine. The tissue content of ³H-noradrenaline and its metabolites was determined after the incubation. As the concentration of cocaine in the incubation medium increased gradually less ³H-noradrenaline and DOPEG were detected in the tissue, while the content of DOMA, NMN, MOPEG and, in particular that of VMA increased; comparable results were obtained with high concentrations of cocaine and desmethylimipramine (DMI). Helical strips of canine saphenous veins were incubated with ³H-noradrenaline and mounted for isometric tension recording and for measurement of the efflux of labelled transmitter and its metabolites. Cocaine, but not DMI, slightly increased the spontaneous efflux of DOPEG, suggesting that cocaine enters the nerve terminals and displaces noradrenaline from its storage sites. During electrical stimulation, cocaine at 3×10^–5 mol/l increased the contractile response and the overflow of ³H-noradrenaline, DOMA, NMN and MOPEG and decreased the appearance of DOPEG. Similar results were obtained with DMI (10^–6 mol/l) except that it did not increase the overflow of DOMA and MOPEG. During electrical stimulation in presence of DMI, cocaine did not affect the contractile response and decreased the appearance of intact labelled transmitter. Electrical stimulation, cocaine and DMI did not affect the overflow of VMA. The present experiments indicate that in the canine saphenous vein: (1) DOPEG is formed intraneuronally, but DOMA, MOPEG, NMN and VMA extraneuronally; (2) VMA is retained in the tissue much longer than the other metabolites; (3) determination of total ³H-content after incubation with ³H-noradrenaline in presence of inhibitors of neuronal uptake underestimates the degree of inhibition of the neuronal amine carrier; and (4) the quantification of the effect of cocaine on the neuronal uptake of released transmitter is complicated by several other actions of the drug (local anesthetic properties, displacement of stored transmitter, activation of effector cells) and that of the effect of DMI by its inhibitory effect on monoamine oxidase, in particular at extraneuronal sites.Supported in part by grant HL 05883 from the National Institutes of Health     

Influence of cocaine and sodium on bretylium uptake by reserpine-treated guinea-pig left atrium.

1 The effects of cocaine and sodium on bretylium uptake into sympathetic nerve terminals were investigated in the reserpine-treated guinea-pig left atrium. The ability of bretylium pretreatment to increase the retention of noradrenaline was used as an index of bretylium uptake. Such increased retention has been assessed both by direct measurement and by the ability of tyramine to produce an inotropic response. 2 The restoration of the response to tyramine after incubation with noradrenaline was abolished when the atrium was pretreated with bretylium in the presence of cocaine. When bretylium was added before cocaine, or when alpha-methyl-noradrenaline (not a substrate for monoamine oxidase) was used for incubation, the responses to tyramine were restored in the normal way. 3 Bretylium greatly enhanced the retention of [3-H]-noradrenaline; when bretylium was added in the presence of cocaine, [3-H]-noradrenaline retention was severely impaired. 4 Pretreatment with bretylium in a low-sodium (25 mM) or sodium-free medium significantly decreased the retention of [3-H]-noradrenaline, as compared with the control. 5 Potassium deprivation did not modify the enhanced retention of [3-H]-noradrenaline induced by bretylium pretreatment. 6 Bretylium was released from the nerve terminals by exposure of the preparation to a sodium-free medium or to a solution containing calcium 50 mM, leading to a considerable decrease in [3-H]-noradrenaline retention. 7 The results are consistent with the view that both cocaine and sodium deprivation block the uptake of bretylium by the adrenergic nerve terminals, and that bretylium is probably taken up by a mechanism similar to or identical with the uptake system for noradrenaline and other amines.     

The release of 3H-dopamine from the isolated rabbit ileum

1. Segments of rabbit ileum incubated with ³H-DOPA or ³H-dopamine and perfused with McEwen solution spontaneously release ³H-dopamine; this basal release is doubled when the sympathetic nerves are stimulated. Evidence is presented to show that the release is probably from the sympathetic nerve terminals.

2. Both cocaine and bretylium reduce the spontaneous release of ³H-dopamine as well as the increased release resulting from sympathetic nerve stimulation. Guanethidine depresses the release during nerve stimulation but increases the spontaneous release of the amine. Phenoxybenzamine potentiates both the spontaneous release and that during nerve stimulation.

3. Tyramine releases ³H-dopamine from the preparation but tachyphylaxis to the drug rapidly develops.

4. It is concluded that the release of ³H-dopamine from the sympathetic nerves of the isolated perfused rabbit ileum possesses many of the characteristics of that of noradrenaline from other sympathetically innervated structures.

     

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.     

Inhibition of the Uptake of 3H-Dopamine and 14C-5-Hydroxytryptamine in Mouse Striatum Slices

Abstract: The inhibitory activities of a number of compounds on the simultaneous uptake of ³H-dopamine (³H-DA) and ¹⁴C-5-hydroxytryptamine (¹⁴C-5-HT) in the same slices of the mouse striatum were examined. Experiments with inactive DA and 5-HT demonstrated that the uptake of the two amines occurs at different sites. In vitro (+)-amphetamine was 2.7 times more potent than the (-)-isomer whereas in vivo this difference was about 6 times. (+)-Amphetamine was also significantly more active than the (-)-enantiomer on the ³H-DA uptake in striatal slices from the rat. The methylester group in cocaine is essential for the inhibitory activity of cocaine, which had similar potencies on the two uptake mechanisms. Benztropine was much more active on the ³H-DA uptake than on the ¹⁴C-5-HT uptake. In vivo the amphetamine derivatives including prolintane and methylphenidate were the most active compounds on the ³H-DA uptake, but the 4-substituted amphetamines were more active on the ¹⁴C-5-HT uptake. Among other compounds benztropine was as active as (+)-amphetamine on the ³H-DA uptake. None of the compounds tested seem to be useful as model compounds for the selective inhibition of the DA uptake, since they have other pharmacological effects at lower doses.     

The accumulation of [3H]noradrenaline in the adrenergic nerve fibres of reserpine-treated mice

Mice, pretreated with reserpine, were given [³H]noradrenaline (³H-NA) intravenously and were killed 30 min later. Only small amounts of ³H-NA were recovered from the hearts. The monoamine oxidase inhibitor nialamide in a dose of 10 mg/kg increased the ³H-NA recovered from the hearts of reserpine-treated animals severalfold. In higher doses, however, this effect of nialamide was no longer observed. When ³H-NA was replaced by [³H]α-methylnoradrenaline, nialamide only reduced the amount of amine recovered from the hearts. The balance between the opposing actions of nialamide depended on dosage, time interval and temperature in a manner suggesting that the inhibitory influence was due to accumulation of endogenous amines in the adrenergic nerve fibres. Bretylium and harmaline also preserved ³H-NA in reserpine-treated animals whereas iproniazid, pheniprazine, pargyline and tranylcypromine did not do this. Moreover, pargyline blocked the ability of nialamide to enhance ³H-NA accumulation. The uptake of ³H-NA observed after monoamine oxidase inhibition in the hearts of reserpine-treated mice was almost completely blocked by pretreatment with desipramine or protriptyline, potent blockers of amine uptake by adrenergic nerve fibres.     

Interactions of inhibitors of noradrenaline uptake and angiotensin on the sympathetic nerves of the isolated rabbit heart

1. The interaction of angiotensin and several inhibitors of the uptake of noradrenaline across the neuronal membrane (cocaine, desipramine, protriptyline. and pronethalol) on the output of noradrenaline produced by sympathetic nerve stimulation has been studied in the isolated perfused rabbit heart.2. Most of these drugs increased noradrenaline outflow-angiotensin, for example, by 175%. Cocaine (10(-4)M) did not change the amine overflow, probably because this very high concentration inhibited not only the re-uptake but also the liberation of noradrenaline.3. Desipramine, protriptyline, and pronethalol, although infused in concentrations which enhanced the noradrenaline output, were not able to impair the angiotensin-induced increase of transmitter overflow. In the presence of cocaine (10(-4)M) the increase elicited by angiotensin was slightly reduced, though lower concentrations of cocaine, as previously described, do not interfere with the effect of angiotensin.4. In contrast to the interaction between uptake inhibitors and angiotensin, the augmented output of noradrenaline caused by an uptake inhibitor could not be increased further by infusion of a second uptake inhibitor.5. It is concluded that the increase of the outflow of noradrenaline during sympathetic nerve stimulation by small doses of angiotensin is not caused by an inhibition of re-uptake. On the contrary, the transmitter liberation seems to be facilitated. This is a novel principle of drug action on the sympathetic nerve terminals.     

Comparison between the effects produced by chronic denervation and by cocaine on the sensitivity to,and on the disposition of,noradrenaline in isolated spleen strips

Summary A comparison was made between the effects of cocaine and denervation on the sensitivity to, on the rate of inactivation of, and on the roles played by iproniazid and tropolone in the inactivation of noradrenaline by cat spleen strips. For studying the rate of inactivation of noradrenaline the oil immersion technique was used. Cocaine was used in four different concentrations. In all concentrations did it enhance the sensitivity to noradrenaline. When cocaine was used in concentrations of 10 and 50×10^–6 M, the enhancement was significantly higher than that caused by denervation (11.61 and 14.81 vs. 6.42, respectively: p<0.001). Since denervation produces an enhancement of the effect of noradrenaline which is smaller than that caused by cocaine, the blockade of neuronal uptake cannot fully account for all supersensitivity induced by cocaine. On the other hand, cocaine produces no further enhancement of the effect of noradrenaline in denervated strips. It is assumed that cocaine acts in normal (control) preparations by two mechanisms: 1. blockade of neuronal uptake accounting for an enhancement like that caused by denervation (about 6 times); 2. facilitation of the action of noradrenaline by interference with a hypothetical postjunctional structure which depends on the presence of intact adrenergic nerves and which accounts for the remaining degree of enhancement (about 2 times).Strips treated with cocaine (50×10^–6 M) required for half-relaxation 7.42 times the time of the controls, whereas denervated strips only required 4.84 times the control time. On the other hand in denervated strips cocaine (50×10^–6 M) produced a further 1.55-fold prolongation of the half-relaxation time. Thus, the effect of cocaine on this parameter is concluded to be due primarily to blockade of neuronal uptake and secondarily to another factor, which could be related to uptake₂.The influence of cocaine and denervation on the role played by iproniazid and tropolone on the inactivation of noradrenaline was not significantly different; apparently, in this preparation, the monoamine oxidase involved in terminating the action of noradrenaline is predominantly if not entirely situated intraneuronally, whereas catechol-O-methyltransferase seems to be situated intra- and extraneuronally almost in equal proportions.     

Autoradiography of 14C-choline uptake in endplates and skeletal muscle of mice

Summary The uptake of ¹⁴C-choline into the axonal part of the motor endplate and muscle of mouse diaphragms was investigated by autoradiography. With i. v. doses of 0.1 g/g choline chloride, the uptake into the nerve endings is fast (<2 min) and into muscle slower (>2 min). With higher doses (1.0 g/g) the uptake into muscle tissue is accelerated.The radioactivity in the endplates decreases with a halflife time of 20 min and remains constant in the muscle fibres over 60 min. Denervation by cutting the phrenic nerve reduces the uptake into endplates by 40% within 14 h, but probably induces uptake into regenerating Schwann cells during 30 days. Some compounds with choline-like structure (hemicholinium-3, decamethylen-dicholine, triethyl-choline) reduce the high-affinity uptake of choline into the nerve endings with sublethal doses, whereas tetraethylammonium and N-hydroxyethyl-4-(1-naphthylvinyl)-pyridinium, an inhibitor of cholinacetyltransferase, are less active. Half lethal doses of cocaine, imipramine and reserpine have no significant action on uptake of choline into the endplates. Chlorpromazine slightly diminishes the uptake into endplates. Chlorpromazine and imipramine reduce uptake into the muscle fibres.     

Studies on the distinction between uptake inhibition and release of [3H]dopamine in rat brain tissue slices

There exists some confusion over the classification of drugs as either uptake inhibitors or releasing agents for biogenic amines. We have evaluated this problem with rat brain tissue slices (neostriatum and cortex), using [³H]dopamine and the following compounds: potassium chloride, tyramine, d-and l-amphetamine, cocaine, amantacline, desipramine. amitriptyline, nortriptyline and protriptyline. Additional experiments were performed with l-dopa and [³H]serotonin in slices from whole rat brain. Potassium chloride and tyramine. both strong releasing agents, diminished the accumulation of [³H]dopamine during uptake studies. l-Dopa also caused release of [³H]serotonin and an inhibition of [³H]serotonin accumulation. Whenever a releasing action was observed, there was always a diminution in the amount of [³H]amine accumulation and this action (expressed as a per cent effect) was at least equal in magnitude to the per cent released. On the other hand, cocaine was an example of a pure uptake inhibitor; it did not evoke a releasing action at concentrations where a powerful uptake inhibition was seen. From these data, it was possible to conclude that, in the tissue slice system, an experimentally observed release was real (that is. not materially affected by blockade of reuptake), whereas a releasing action evoked an apparent inhibition of uptake equal in magnitude to the releasing action. Before a drug can be designated as an uptake inhibitor, the dose-response curve for inhibition of [³H]amine accumulation should be distinctly to the left of the dose-response curve for release. Our data indicate that, in the neostriatum, all of the drugs studied except cocaine were pure releasing agents and that drugs previously designated as uptake inhibitors were releasing agents. In the cortex, strong inhibition of uptake without significant releasing action was evident for many of the drugs.     

The inhibition of 3H-biogenic amine uptake by 5,6-dihydroxytryptamine: A comparison with the effects of 6-hydroxydopamine

5,6-Dihydroxytryptamine was a competitive inhibitor of both ³H-serotonin and ³H-dopamine uptake into rat brain tissue slices. In contrast, 6-hydroxydopamine inhibited ³H-dopamine uptake but did not inhibit ³H-serotonin uptake even at a 6-Hydroxydopamine concentration of 10^?4 M. In these experiments, catalase was present in the incubation medium to decompose hydrogen peroxide which is a product of the autoxidation of 6-hydroxydopamine and an inhibitor of biogenic amine uptake systems. These above data may help to explain the relative specificity of 6-hydroxydopamine for adrenergic nerve terminals in contrast to the effects of 5,6-dihydroxytryptamine on both adrenergic and serotonergic nerve terminals. Kinetic analyses showed that 5,6-dihydroxytryptamine had almost the same affinity for the ³H-serotonin transport system as did ³H-serotonin itself. In contrast, 5,6-dihydroxytryptamine had an affinity for the ³H-dopamine transport system approximately 1/30 that of ³H-dopamine.     

Doxepin: Effects on transport of biogenic amines in man

A new tricyclic antidepressant, doxepin, was evaluated for its ability to block the amine uptake mechanism of the peripheral adrenergic neuron and blood platelet in man. At low doses, there was no evidence of inhibition of the amine pump. However, at moderate doses (200–300 mg/day), necessary for effective antidepressant activity, doxepin was found to inhibit the pressor responses to tyramine and to reduce platelet 5-HT. These studies indicate that doxepin is a less potent inhibitor of the amine pump in the peripheral adrenergic neuron and blood platelet than is DMI or protriptyline. Doxepin, at the antidepressant dose level does alter biogenic amine uptake, an effect consistent with the biogenic amine hypothesis of depression. However, at 300 mg/day, a dose which blocks the pressor response to tyramine, antagonism of the antihypertensive effects of guanethidine and related drugs was demonstrated.This investigation was supported in part by Public Health Service Grant Numbers: MH 11468; 2 T01 HE 05545; 1 P11 GM 15431; 5 R01 HE 10842; 5 M01 RR 00095-10; RR 95.Dr. Oates is a Burroughs-Wellcome Scholar in Clinical Pharmacology.     

Inhibition of amine uptake in the mouse heart by some new "thymoleptic" drugs

A number of new and established thymoleptic drugs were given to mice. Their inhibitory action on the uptake of [³H]metaraminol and [³H]noradrenaline in the heart was investigated. Among the compounds tested a monomethylamino-derivative was in general 2–3 times more potent than the corresponding dimethyl-amino-derivative. The phthalan derivative 3,3-dimethyl-1-(3-methylaminopropyl)-1-phenylphthalan (Lu 3–010) was as efficient as protriptyline in all the tests performed. Changes in the substitution of the phthalan skeleton influenced the activity critically. As it is devoid of anticholinergic activity Lu 3–010 appears to be the most specific inhibitor of the amine transport mechanism of the adrenergic cell membrane found so far.     

The distribution of some quaternary ammonium salts in the peripheral nervous system of cats in relation to the adrenergic blocking action of bretylium

The concentrations of bretylium in the peripheral nervous system of cats after subcutaneous dosage have been compared with those drugs bearing either chemical or pharmacological resemblance to bretylium. o-Bromobenzyltrimethylammonium iodide (383C57), a chemical homologue of bretylium with feeble adrenergic blocking activity, selectively accumulated in adrenergic neurones to attain concentrations comparable with those found for bretylium, but it did not persist in the neurones. {2-(4-Benzoyl-2,6-dimethylphenoxy)ethyl}trimethylammonium, the 4-benzoyl derivative of 2,6-xylyl choline ether (172C58), a pharmacological analogue of bretylium but with little chemical resemblance, had a less marked selective affinity for adrenergic neurones and the concentrations after an effective dose were much lower than found for bretylium. Pentacynium {N¹-5-cyano-5,5-diphenylpentyl)-N¹N¹N²-trimethylethylene-1-ammonium-2-morpholinium di-iodide}, a bis-quaternary ammonium-type ganglion blocking agent, had no selective affinity for adrenergic neurones. Bretylium was not displaced from adrenergic neurones by a subsequent dose of 172C58. The potency and duration of local anaesthetic action of bretylium, 383C57 and 172C58 were roughly parallel to the potency and duration of their adrenergic blocking action. The results are discussed in relation to the role of selective accumulation in adrenergic neurones by bretylium in its adrenergic blocking activity.     

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 2.5×10^–8 M had very little effect on 5-hydroxytryptamine uptake. Neither tricyclic antidepressant had any marked effect on dopamine uptake.A. T. was supported by a grant from the Mental Health Research Fund.