Effect of chlorpromazine, reserpine, benactyzine and phenobarbitone on the release of corticotrophin in the rat

A single injection into the rat of chlorpromazine, reserpine, benactyzine or phenobarbitone stimulates the release of corticotrophin. This effect is not seen after the drugs have been injected daily for 5 days, nor when the rats are hypophysectomized or pretreated with hydrocortisone. The stimulant effect of ether on corticotrophin release is not modified by pretreatment with a single injection, nor to any great extent after 5 daily injections of these drugs.

Effects of asarone and beta-asarone on conditioned responses, fighting behaviour and convulsions

In the Ayurvedic system of medicine, the roots and rhizomes of an indigenous Indian plant Acorus calamus are used together with the roots of Rauwolfia serpentina for treating many mental ailments. The influence of asarone and beta-asarone (the trans and cis forms of 2,4,5-trimethoxy-1-propenyl benzene), two active principles of Acorus calamus, when given alone and together with either reserpine or chlorpromazine, has been studied on the conditioned avoidance response of trained rats, on the fighting behaviour of paired mice subjected to mild foot shock and on electro-convulsions. Except for electro-convulsions, asarone in small doses potentiates the effects of reserpine and of chlorpromazine; beta-asarone has no such effect. Estimation of the 5-hydroxytryptamine content of rat brain showed that neither acorus oil nor its active principles increase the concentration of 5-hydroxytryptamine; nor do these compounds cause an additional decrease in the 5-hydroxytryptamine content of the brains of animals treated with reserpine. It is concluded that the potentiating effect of these principles is unrelated to 5-hydroxytryptamine concentration. In experiments using electro-convulsions, asarone increased the percentage mortality of animals treated with chlorpromazine but not of those treated with reserpine.

Stimulation and sensitization of the isolated Venus heart by cerebrospinal fluid

5-Hydroxytryptamine was not detected in animal cerebrospinal fluid after amine oxidase inhibitors, reserpine, or both. Both human and animal cerebrospinal fluid can produce a stimulating effect on the clam heart which is not due to 5-hydroxytryptamine. Cerebrospinal fluid also has the property of increasing the sensitivity of the clam heart to 5-hydroxytryptamine.

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.

An action of 5-hydroxytryptamine on adrenaline receptors

Contractions of isolated strips of cat spleen due to 5-hydroxytryptamine, adrenaline, histamine and acetylcholine were antagonized by phenoxybenzamine. Responses to both 5-hydroxytryptamine and adrenaline were not blocked in strips which were protected by a high concentration of either 5-hydroxytryptamine or adrenaline throughout exposure to phenoxybenzamine. The contraction due to a large dose of 5-hydroxytryptamine lasted less than 1 hr even when the drug was still present. Strips thus desensitized to 5-hydroxytryptamine responded normally to acetylcholine and histamine but did not respond to adrenaline. The actions of 5-hydroxytryptamine and adrenaline were blocked by 2-bromolysergic acid diethylamide or by dihydroergotamine. These results indicated that 5-hydroxytryptamine and adrenaline act on the same receptors. Cocaine potentiated the action of adrenaline but inhibited the action of 5-hydroxytryptamine. The sensitivity to 5-hydroxytryptamine of spleen strips from cats treated 24 hr earlier with reserpine was only one-fiftieth of that of normal strips. Cocaine potentiated the action of 5-hydroxytryptamine on strips from reserpine-treated cats. A high concentration of 5-hydroxytryptamine in spleen strips from reserpine-treated cats and in cocaine-treated strips prevented phenoxybenzamine from blocking the actions of adrenaline. The effects of tyramine on spleen strips almost exactly paralleled the effects of 5-hydroxytryptamine. Strips showing tachyphylaxis to tyramine did not respond to 5-hydroxytryptamine. It is concluded that 5-hydroxytryptamine has a dual action, viz., a major action due to release of stored noradrenaline and a minor direct action of adrenaline receptors.

Cardiac noradrenaline stores

The effects of single doses of reserpine or of guanethidine in increasing the heart rate of the dog heart-lung preparation have been studied. Compared with reserpine, guanethidine increased heart rate more and more rapidly, and the increase lasted longer. When the effects of reserpine had subsided, guanethidine now caused a similar rate of change and maximum increase in heart rate, but recovery was quicker. Guanethidine given alone caused less release of noradrenaline in the right atrium than did reserpine alone, but both drugs together caused greater release than did either alone. Thus liberation of noradrenaline in the right atrium was unrelated to the effectiveness of either drug to increase heart rate. Guanethidine and reserpine did not increase the heart rate of heart-lung preparations from dogs which had received reserpine for 2 days and which contained no noradrenaline. Guanethidine had similar actions on the heart rate of preparations either given a slow intravenous infusion of noradrenaline or a single dose of reserpine. Treatment of a normal heart-lung preparation with noradrenaline increased the atrial noradrenaline content, but subsequent addition of reserpine or of guanethidine changed heart rate in the same manner as for preparations not given noradrenaline. Treatment with reserpine increased the heart's sensitivity to noradrenaline without changing initial heart rate. These results are discussed in relation to the idea that there may be more than one noradrenaline compartment in the heart.

Study of the relationship between the neurotransmitter store and adrenergic nerve block induced by reserpine and guanethidine

The heart rate response to cardioaccelerator nerve stimulation and the corresponding levels of myocardial norepinephrine content were determined and correlated in dogs at various time intervals following the intravenous injection of either 3 mg/kg reserpine, or 10 mg/kg guanethidine. Guanethidine produced complete blockade of the cardiac accelerator response before producing measurable myocardial depletion of norepinephrine. In contrast, reserpine reduced the positive chronotropic response to cardioaccelerator nerve stimulation only after myocardial norepinephrine levels have been reduced to approximately 0.3 µg/g. An infusion of norepinephrine did not restore the heart rate response to cardioaccelerator nerve stimulation in either the reserpine or guanethidine treated dogs. These data suggest that the interference with adrenergic transmission produced by guanethidine is independent of changes in the level of stored adrenergic transmitter. The reserpine-induced blockade of adrenergic transmission may ultimately be dependent upon the mission may ultimately be dependent upon the depletion of adrenergic transmitter, but almost complete depletion of stored adrenergic transmitter must occur before reserpine-induced adrenergic blockade occurs.

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.

CARDIAC AND VASCULAR EFFECTS OF SYMPATHOMIMETIC DRUGS AFTER ADMINISTRATION OF TRI-IODOTHYRONINE AND RESERPINE

In spinal cats treated with tri-iodothyronine, the effects of sympathomimetic drugs on cardiac contraction were diminished. Ouabain failed to restore the effects on the contractile force of the heart. The effects of sympathomimetic drugs on the force of contraction of papillary muscle were not reduced by tri-iodothyronine, but the threshold for induction of automaticity was lowered. There was no evidence that in cats treated with reserpine the sensitivity of peripheral vessels to sympathomimetic agents is decreased and that blood pressure changes are merely secondary to changes in cardiac contraction.

THE EFFECT OF SOME PHENOTHIAZINE TRANQUILLIZERS ON THE OESTROUS CYCLE OF ALBINO MICE

The effects of reserpine and of nine phenothiazine compounds on the oestrous cycle of albino mice were tested. With the exception of promethazine (which is not a tranquillizer) all the phenothiazine compounds and reserpine prolonged the oestrous cycle. The mechanism by which these tranquillizers interfere with the oestrous cycle is discussed.

CIRCADIAN RHYTHM IN PINEAL SEROTONIN: EFFECT OF MONOAMINE OXIDASE INHIBITION AND RESERPINE

The pineal gland of the rat shows a circadian rhythm in its serotonin content, the amount of serotonin decreasing at night. This decrease can be prevented by inhibiting the action of monoamine oxidase. Reserpine abolishes the circadian rhythm in pineal serotonin in the same manner as does interruption of the sympathetic nervous connections of the central nervous system and the pineal gland. These observations suggest that circadian changes in release and binding of serotonin may occur in the pineal gland, and that a central mechanism in which monoamines participate may control the circadian pineal-serotonin rhythm.

EFFECTS OF SMALL ORAL DOSES OF RESERPINE ON VASCULAR RESPONSES TO TYRAMINE AND NOREPINEPHRINE IN MAN

Experiments were done to see if reserpine, in small oral doses, alters the responses to tyramine and norepinephrine in man. Each of seven normotensive subjects was studied on three occasions. The first and third sessions served as pre- and post-treatment control sessions; the second session was held after oral administration of reserpine (0.25 to 1 mg. per day) for 2 weeks. Blood pressure was measured with a sphygmomanometer, and forearm blood flow was measured with a water plethysmograph. Reserpine reduced resting blood pressure and heart rate but forearm blood flow did not change. The pressor, forearm vasoconstrictor, and bradycrotic actions of intravenous tyramine were suppressed by reserpine, but the pressor, vasoconstrictor, and bradycrotic actions of three intravenous doses of norepinephrine were not augmented significantly. The results indicate that oral administration of small doses of reserpine may cause depletion of endogenous catecholamines in man as suggested by the suppressed response to tyramine. The decreased response to tyramine was not accompanied by hypersensitivity to exogenous norepinephrine. In equipressor doses norepinephrine produced greater forearm vasoconstriction and more reflex bradycardia than did tyramine.

SOME OBSERVATIONS ON THE PHARMACOLOGY OF ALPHA-METHYLDOPA

alpha-Methyldopa in high concentrations impaired the responses of rabbit isolated ileum and guinea-pig isolated vas deferens to stimulation of the sympathetic nerves and to noradrenaline, but these preparations taken from animals previously treated with alpha-methyldopa showed no sign of impairment. Contractions of the cat nictitating membrane were reduced but not abolished by alpha-methyldopa. In cats, dogs and rats, pressor responses to noradrenaline were usually slightly increased by alpha-methyldopa. Pressor responses to tyramine were not affected consistently. alpha-Methyldopa, alpha-methyldopamine and alpha-methylnoradrenaline behaved like dopa, dopamine and noradrenaline respectively in restoring the responses of tissues from reserpine-treated animals to stimulation of the sympathetic nerves to the rabbit ileum, the guinea-pig vas deferens and the cat nictitating membrane and in restoring responses to tyramine of the cat blood pressure and nictitating membrane, and the rat blood pressure. The potency of alpha-methylnoradrenaline relative to noradrenaline ranged from one-half to one-ninth on various preparations. The results are discussed in relation to the antihypertensive action of alpha-methyldopa.

VENOUS AND ARTERIAL RESPONSES TO NOREPINEPHRINE IN DOGS TREATED WITH RESERPINE

Experiments were done to see if the effects of norepinephrine upon veins, arteries, and small vessels are augmented in dogs after treatment with reserpine. With intra-arterial injection of increasing doses of norepinephrine into the perfused foreleg there were progressive increments in total, arterial, small vessel, and venous resistances. In animals treated with reserpine the increments in total and small vessel resistances were greatly augmented while increments in segmental arterial resistance were increased only slightly. The venous responses in these treated dogs were not augmented. Similar effects on segmental resistances were noted with infusion of norepinephrine into a systemic vein. The vasoconstrictor effect of tyramine was reduced in treated dogs and was restored after intra-arterial and intravenous norepinephrine. The results indicate that veins do not participate in the increased vascular responsiveness to norepinephrine which occurs in forelegs of dogs after treatment with reserpine.

THE INFLAMMATORY RESPONSE TO IMPLANTATION OF COTTON PELLETS IN THE RAT

The subcutaneous implantation of a cotton pellet in the rat evokes a short-lasting phase of increased capillary permeability lasting some 20 min. after implantation followed by a more sustained phase which occurs after 2·5–3 hr. The early increase is antagonised by lysergic acid diethylamide, reserpine and 5-HT. The peak granuloma weight is reached at 2 days, and then falls rapidly. Antagonism of oedema and granulation tissue by hydrocortisone and reserpine can be demonstrated at 2 days after implantation.

MECHANISM FOR CARDIAC STIMULATION DURING HYPOXIA

In isolated guinea pig atria, hypoxia was induced by bubbling nitrogen through Tyrode solution. A significant increase in both the amplitude and frequency of the contractions occurred, followed by a decrease. Average rate in 11 control atria was 138 ± 9.2 contractions/min and increased during hypoxia by an average value of 12.7 ± 2.3 contractions/min ( P < 0.001). Amplitude of shortening increased by an average of 10.5 ± 2.12% ( P <0.001). In 19 preparations pretreatment with reserpine blocked the transient stimulant effect of hypoxia on both amplitude and frequency of contractions. Isometric contractions were recorded from 30 isolated cat papillary muscles. The developed isometric tension increased during hypoxia by an average of 17.3 ± 2.8% ( P < 0.001). Later, a decrease in contractile force was observed. Pretreatment of the animals with guanethidine and chronic cardiac sympathectomy blocked and pretreatment with reserpine decreased the stimulant effect of hypoxia on the cat papillary muscle. The transient stimulant effect of hypoxia was compared to the staircase phenomenon. Both chronic cardiac sympathectomy and pretreatment with reserpine blocked the increase in force induced by a change in rate from 60 to 120.