Effect Upon the Analgesic Action of Reserpine of Central Nervous System Stimulants and Drugs Affecting the Metabolism of Catechol- and Indole-Amines

The effect upon the analgesic action of reserpine of central nervous system stimulants and of drugs affecting the metabolism of catechol-and indole-amines as measured in mice by a hot-plate method has been analysed. The analgesic effect, which has a maximal intensity 48 hr. after injection of the alkaloid, is partially or totally counteracted by MAO inhibitors, LSD-25 and 5-hydroxytryptophan. Central nervous system stimulants given to reserpinised mice before each test were effective in reducing the reaction time to the heat stimulation only 24 and 48 hr. after reserpine. DOPA showed no significant ability to reduce the analgesic effect of reserpine. In the light of these findings a suggestion has been made that 5-hydroxytryptamine rather than catecholamines would be involved in the mechanism of the analgesic effect due to reserpine and since central nervous system stimulants are able to reduce this action initially but are ineffective later, part of the effect is thought to be due to sedation of the animals, the participation of the stimulants being confined to a direct antagonism against the sedation. The lasting analgesic effect is supposed to correspond to a lack of 5-hydroxytryptamine in the cerebral structures.

The action of reserpine and α-methyl-m-tyrosine on the analgesic effect of morphine in rats and mice

The actions of α-methyl-m-tyrosine (mmt) and reserpine upon the analgesic effect of morphine has been studied in rats and mice. In rats, reserpine antagonised the effect of morphine, while mmt did not cause any appreciable change of the effect of morphine, injected either 2 or 24 hr after mmt. Reserpine also produced its antagonistic action to morphine in rats which were previously (24 hr) treated with mmt. Both mmt and reserpine potentiated the effect of morphine in rats pretreated (24 hr previously) with iproniazid. In mice, both mmt and reserpine antagonised the effect of morphine. Reserpine failed to do so in mmt pretreated animals. The effect of morphine was restored 24 hr after the injection of mmt. It is suggested that the inhibitory action of reserpine upon the analgesic effect of morphine is due to the antagonistic action of brain 5-ht, which is activated after being released from its stores by reserpine. The pattern of reserpine—mmt—morphine interactions in rats probably differs from that in mice.

THE INFLUENCE OF β-TETRAHYDRONAPHTHYLAMINE AND A DERIVATIVE ON THE CENTRAL EFFECTS OF 5-HYDROXYTRYPTAMINE, RESERPINE AND IPRONIAZID

N-Methyl-N-propyl-β-tetrahydromphthylamine, a specific antagonist of 5-hydroxytryptamine on the isolated rat uterus preparation, fails to inhibit 5-hydroxytryptamine potentiation of the hypnotic action of hexobarbitone in mice. The potentiating actions of reserpine and iproniazid are likewise unaffected. The action of β-tetrahydronaphthylamine as an antagonist of the potentiating action of 5-hydroxytryptamine on hexobarbitone sleeping time in mice has been confirmed, and it has also been shown to be an effective antagonist of the sleep prolonging effects of reserpine. β-Tetrahydronaphthylamine also shows a partial antagonism to iproniazid potentiation of hexobarbitone hypnosis. These results provide an example of the lack of parallelism between the central and smooth muscle actions of 5-hydroxytryptamine antagonists.

The effects of reserpine and other agents upon leptazol convulsions in mice

Reserpine and tetrabenazine reduced the survival time of mice infused with leptazol. This effect was antagonized by pretreatment with iproniazid. The survival time of iproniazid-treated mice was prolonged by 5-hydroxytryptophan but not by 3:4-dihydroxyphenylalanine. These findings suggest a relation between leptazol sensitivity and brain levels of 5-hydroxytryptamine.

Increase of 5-hydroxytryptamine in the rat brain by raunescine

The Rauwolfia alkaloid raunescine (5 mg./kg., intraperitoneally) increased the concentration of 5-hydroxytryptamine in the brains of rats after iproniazid pre-treatment. This was evident 3 to 4 hr. after raunescine administration. There was no general increase in the noradrenaline content of the brains. In the intestine, raunescine depleted the 5-hydroxytryptamine content by about 50% within 3 to 4 hr. if the animals had been pre-treated with iproniazid. Iproniazid did not increase the content of noradrenaline in the intestine.

Mechanism of action of reserpine in producing gastric haemorrhage and erosion in the mouse

Gastric haemorrhage was produced regularly in mice within 6 hours of the subcutaneous injection of a large dose (2 to 10 mg./kg.) of reserpine or of deserpidine. Rescinnamine, syrosingopine (SU-3118), and tetrabenazine (Ro 1-9569) were less active. Gastric haemorrhage was also produced within 6 hours when 5-hydroxytryptamine (10 mg./kg.) was injected every half-hour. Neither reserpine nor 5-hydroxytryptamine produced gastric haemorrhage in mice which had been vagotomized by tying the oesophagus at the cardio-oesophageal junction or which had been pre-treated with iproniazid. Amphetamine was less effective than iproniazid in preventing gastric haemorrhage after reserpine, and the following drugs were ineffective: cocaine, methyl phenidate (Ritalin), amarin, caffeine, nikethamide, lysergic acid diethylamide and its 2-bromo derivative (BOL148). Gastric haemorrhage was not observed in mice which had been given substantial doses of atropine or of hexamethonium before reserpine. The incidence of haemorrhage was substantially reduced by treatment with an antacid mixture. It is concluded that reserpine-like drugs cause gastric haemorrhage by a mechanism which has an important central component and which involves the liberation of 5-hydroxytryptamine.

Effect of alpha-alkylated tryptamine derivatives on 5-hydroxytryptamine metabolism in vivo

In rats, three alpha-alkylated tryptamine derivatives (alpha-methyl, alpha-ethyl, and alphaalpha-dimethyltryptamine) caused alterations of 5-hydroxytryptamine metabolism typical of monoamine-oxidase inhibitors with short duration of action, viz., an increase of endogenous 5-hydroxytryptamine in brain, enhancement of the increase of 5-hydroxytryptamine in brain and heart after 5-hydroxytryptophan administration, an inhibition of the decrease in 5-hydroxytryptamine in brain induced by a benzoquinolizine derivative and of the increase induced by iproniazid. The increase after iproniazid was antagonized to the same extent by all the tryptamine derivatives and by harmaline, whereas dexamphetamine showed less effect. In the other experiments with brain, the tryptamine derivatives were less potent than harmaline, but somewhat more active than dexamphetamine. alpha-Methyltryptamine and alpha-ethyltryptamine were relatively more effective in the heart than in the brain. Among the tryptamine derivatives alphaalpha-dimethyltryptamine had the weakest activity in brain and in heart.

Relative activity of some inhibitors of mono-amine oxidase in potentiating the action of tryptamine in vitro and in vivo

Several known inhibitors of mono-amine oxidase (iproniazid, isocarboxazid, nialamide, phenelzine, pheniprazine and tranylcypromine) were tested for their ability to (i) inhibit the mono-amine oxidase activity of a rat brain mitochondrial preparation in vitro; (ii) potentiate the action of tryptamine on the isolated rat fundal strip preparation; and (iii) potentiate the acute toxicity of tryptamine in mice. There was some correlation between the order of potency of the drugs in the three tests, particularly in inhibiting the enzyme activity in the Warburg and in the tryptamine toxicity test in mice. Exceptions to this were isocarboxazid which had unexpectedly high activity on the rat fundal strip preparation, and tranylcypromine which was devoid of tryptamine-potentiation action on the rat fundus preparation although it inhibited rat brain mono-amine oxidase in vitro and potentiated the action of tryptamine in vivo. Tranylcypromine was considerably less active in inhibiting the mono-amine oxidase of rat fundus than rat brain tissue in vitro, while iproniazid and isocarboxazid had about the same potency on the enzyme from the two tissues.

The effect of enzyme inhibitors on histamine catabolism in man

The catabolism of histamine was studied in three female psychiatric patients by analysis of the [(14)C]-labelled metabolic products occurring in the urine after a subcutaneous injection of [(14)C]histamine. Each patient was studied before and during treatment with aminoguanidine or iproniazid.Without treatment the patients had a normal histamine catabolism. Aminoguanidine and iproniazid inhibited the oxidation of histamine to imidazoleacetic acid; iproniazid produed a 50% inhibition of the oxidation of methylhistamine to methylimidazoleacetic acid. After iproniazid a large proportion of the injected [C(14)]histamine was excreted as methyl [(14)C]histamine.

Noradrenaline content in the heart and spleen of the mouse under normal conditions and after administration of some drugs

The noradrenaline content of the heart and spleen was investigated in normal mice and in mice treated with drugs. A modification of the methods of Bertler, Carlsson & Rosengren (1958) was used for extraction, and of v. Euler & Floding (1955) for fluorimetric estimation of the amine. In normal mice the mean noradrenaline content of the heart was 0.55 mug/g and that of the spleen 0.26 mug/g fresh tissue. Iproniazid (100 mg/kg), nicotine (0.1 mg/kg) and histamine (0.5 mg/kg), given 1 and 3 hr before killing the mice, did not significantly change the concentration of noradrenaline in the heart. Neither did nicotine and histamine, administered 1 hr before death, significantly alter the noradrenaline content of the spleen. The rapid changes in the catechol amine content of mouse tissues reported with these drugs by De Schaepdryver & Preziosi (1959) were not observed. In contrast, reserpine (2.5 mg/kg), methyl reserpate methyl ether (1 mg/kg), and methyl 18-epireserpate methyl ether (2 mg/kg) caused severe depletion of noradrenaline from the heart and spleen of the mice.

Effect of antisympathomimetic drugs on the plasma concentrations of catechol amines

Intravenous injection of phenoxybenzamine, choline 2,6-xylyl ether bromide (xylocholine, TM 10), piperoxane or dihydroergotamine increases the vasopressor activity of blood plasma, collected from cats under chloralose anaesthesia. The increased vasopressor activity that follows the administration of piperoxane is due to an increase of adrenaline and noradrenaline in the plasma. Cross-circulation experiments show that catechol amines are liberated from the spleen by piperoxane.

The formation of an isoprenaline-like substance from adrenaline

Intravenous injections of adrenaline, but not those of noradrenaline, caused the appearance of a substance which resembled isoprenaline in R(F) value and pharmacological activity in blood withdrawn from the lower abdominal aortae of chloralosed cats rested after acute adrenalectomy and induction of lasting block in autonomic ganglia with hexamethonium. The formation of the isoprenaline-like compound was prevented by pretreatment with pyrogallol but not by pretreatment with reserpine, cocaine, phentolamine, dibenamine, harmaline, or iproniazid. The liver proved a main site of the origin of this isoprenaline-like substance.

Morphological and pharmacological effects of reserpine, given alone or after iproniazid, on the catechol amines of the adrenal glands of the rat

Adrenomedullary cells, after fixation with OsO(4), are filled with well formed granules which are considered to represent their catechol amine content. The submicroscopic appearance of these cells was studied in reserpine-treated rats during the late phase of catechol amine depletion and during the period of its restoration. At 3 days after the beginning of reserpine treatment, the granules appeared to be emptied of their content and small vesicles containing scattered, dense deposits of, presumably, catechol amines began to be seen. At 9 days after the beginning of treatment, these deposits had already become granules and the cells had attained a completely normal appearance. The submicroscopic structure of the adrenomedullary cells of rats pretreated with iproniazid (before reserpine), in which a complete inhibition of monoamine oxidase activity had thus been obtained, was similar to that seen in non-treated animals. In numerous cases, however, some characteristic features were noted: the sacs which usually contained a dense granule of catechol amines appeared swollen and many fine granules could be seen around them; the latter were dispersed in a way suggesting that they may represent a partial breakdown of the large granules which, under the inhibitory action of iproniazid, do not release the catechol amines contained within them.

Drug-induced changes in brain acetylcholine

In rats, drug-induced depression of the central nervous system has been shown generally to be associated with an elevation in level of total acetylcholine in the brain. This generalization held true for a wide variety of depressant drugs with one notable exception: the subacute administration of reserpine, with which there was an increase in cerebral acetylcholine after the first dose, but a return to normal levels after subsequent doses, despite continued depression of the animals. Reduction in the level of total acetylcholine in the brain followed the administration of certain convulsants (pentylenetetrazole and 3,5-dimethylbutylethylbarbiturate); but no change was seen after the administration of several mildly exciting agents. The notable exceptions to this generalization were atropine and scopolamine, which significantly lowered brain acetylcholine in doses producing mild excitation in only some of the animals and no gross manifestations in the rest.

THE CONVERSION OF PYRIDOXINE PHOSPHATE INTO PYRIDOXAL PHOSPHATE IN ESCHERICHIA COLI

1. Evidence is presented for the presence of pyridoxine phosphate oxidase in aqueous extracts of Escherichia coli. Some comparison is made with pyridoxamine phosphate oxidase. 2. Isoniazid and iproniazid were found to combine with pyridoxal phosphate, but isoniazid did not combine with either pyridoxamine phosphate or pyridoxine phosphate. Both oxidase activities were somewhat inhibited by benzylamine and putrescine, but not by phenethylamine or cadaverine. 3. The significance of pyridoxine phosphate oxidase in cell metabolism is discussed.

MONOAMINE OXIDASE INHIBITORS: AUGMENTATION OF PRESSOR EFFECTS OF PERORAL TYRAMINE

Monoamine oxidase inhibitors markedly enhance the oral pressor potency of tyramine by preventing it from being destroyed by the monoamine oxidase normally present in liver and intestine. Since certain types of cheese contain high concentrations of tyramine, they should not be eaten by patients during treatment with a monoamine oxidase inhibitor.

THE 5-HYDROXYTRYPTAMINE CONTENT OF THE PLACENTA AND FOETUS DURING PREGNANCY IN MICE

5-Hydroxytryptamine (5HT) levels were measured in blood and tissues from pregnant mice. Blood levels remained constant during pregnancy and were the same as those in nonpregnant female mice. Placental levels of 5HT increased throughout pregnancy as did the foetal levels. The maternal blood volume of the placenta also increased with advancing gestation. 5HT levels were measured after treatment of the mother with 5HT, and the critical placental level of 5HT observed at about the time of death of the foetus was determined. The levels of 5HT in the placenta and foetus after treatment of the mother with several monoamine oxidase inhibitors were measured, and found to show no significant increase above the normal levels in these tissues. Treatment with cyproheptadine, a 5HT antagonist, did not delay parturition.

EFFECTS OF CHLORPROMAZINE AND BROMOLYSERGIC ACID DIETHYLAMIDE ON GASTRIC SECRETION OF ACID INDUCED BY HISTAMINE IN RATS

In anaesthetized rats in which the lumen of the stomach was perfused with 0.001 to 0.00025 N-sodium hydroxide solution and the pH of effluent fluid was recorded continuously, intravenous administration of chlorpromazine caused transient inhibition of acid secretion. After acid secretion had returned to the control level the responses to histamine were greater than those before chlorpromazine was given. Aminoguanidine, iproniazid and bromolysergic acid diethylamide also potentiated the effect of histamine on acid secretion but the initial inhibition was absent. Indirect evidence from experiments in which mixtures of aminoguanidine with chlorpromazine or bromolysergic acid diethylamide and of iproniazid with chlorpromazine or bromolysergic acid diethylamide were given, suggests that chlorpromazine and bromolysergic acid diethylamide enhance responses to histamine by inhibition of imidazole-N-methyl transferase.