Action of bretylium on the isolated guinea-pig ileum

Bretylium inhibits the contractions of the longitudinal muscle caused by histamine and, to a lesser extent, those by acetylcholine, carbachol and nicotine. It is a very weak antagonist of 5-hydroxytryptamine and in concentrations of up to 190 mug/ml. does not inhibit the actions of bradykinin and substance P on the longitudinal muscle. The inhibitory effect of bretylium on the emptying phase of the peristaltic reflex is similar to that of ganglion blocking agents, while the much less pronounced effect on the contraction of the longitudinal muscle during the preparatory phase is assumed to be due to a weak atropine-like action.

Stress-induced block of milk ejection

A simple method has been described by which the action of drugs on the stress-induced block in milk ejection can be investigated on lactating guinea-pigs. Reserpine, meprobamate and chlorpromazine when administered to the lactating mother at various periods before suckling reduced the block in milk ejection caused by the stress. Dibenamine and dichloroisoprenaline did not affect in any way the stress-induced block. It is suggested that the stress-induced block in milk ejection is probably a nervous block and not mediated through adrenaline.

Comparative effect of heparin and other agents on traumatic shock in the rat

The effect of heparin and Aureomycin on Noble-Collip drum shock in rats was compared with that of autonomic blocking agents. Intravenous Dibenzyline (0.5 and 1.0 mg/kg) and Mecamylamine (2 mg/kg) notably reduced mortality when given 15–30 minutes prior to drumming. Heparin (2.5–10 mg/kg) and Aureomycin by mouth (150 mg/kg/day for 3 days) had no effect on mortality. Repeated sublethal trauma induced marked protection against drum shock. Concurrent administration of Dibenzyline did not prevent the development of this resistance. Repeated nonspecific stress and exercise failed to protect rats against drum shock suggesting that the development of ‘induced resistance’ is not related to elevated plasma catechol amines. The increased mortality of rats to drum shock incident to reticulo-endothelial blockade was mitigated if Dibenzyline was injected before blockade although not if given after.

An adrenergic basis for bulbar inhibition

Evidence has been obtained showing that intravenous infusion of Diebenzyline in cats anesthetized with Nembutal will consistently and completely abolish inhibition of the patellar reflex induced by direct stimulation of the bulbar reticular formation. The inhibition can always be restored by subsequent infusion of epinephrine. Parallel vasopressor effects can also be observed. Various techniques, including direct injection of Dibenzyline and epinephrine into the medulla through hollow electrodes, provided evidence that these drugs exerted depressant and enhancing effects, respectively, on the thresholds for bulbar inhibition. There appear to be regional differences in epinephrine sensitivity in the medulla. The area corresponding to the nucleus reticularis gigantocellularis appears to be more sensitive to epinephrine than surrounding reticular nuclei. The results suggest that locally released epinephrine activates the gigantocellularis nucleus which, in turn, develops a pattern of discharges leading to an inhibitory effect mediated by spinal projections. This mechanism may explain immobilization which frequently occurs in highly emotional situations.

Effect of sympathomimetic amines on the blocking action of guanethidine, bretylium and xylocholine

Experiments were carried out in which the adrenergic neurone blocking activity of xylocholine, bretylium and guanethidine was studied by the use of the inhibitory responses of the isolated rabbit ileum to lumbar sympathetic nerve stimulation, and the contractions of the nictitating membrane of the anaesthetized cat in response to stimulation of the cervical sympathetic nerves. In both these preparations, after blockade of the effects of sympathetic nerve stimulation had been produced with xylocholine, bretylium or guanethicdine, the sympathomimetic amines, dexamphetamine, mephentermine, hydroxyamphetamine, ephedrine and phenethylamine, reversed the blockade; if these amines were given first, then the adrenergic neurone blocking agents were ineffective. Tyramine and dopamine were effective on the isolated rabbit ileum but not on the cat's nictitating membrane. Effective antagonism of the adrenergic neurone blocking drugs was also shown by some substances which inhibit mono-amine oxidase but only those which in addition possess sympathomimetic effects. Thus phenelzine, pheniprazine and tranylcypromine were effective whereas iproniazid and nialamide were not. Since xylocholine, bretylium and guanethidine were all antagonized by the same agents, it seems likely that they all produce sympathetic blockade by a similar mechanism. The possibility is discussed that the sympathomimetic amines which antagonize the adrenergic neurone blocking drugs are competing with these substances for the same receptor sites.

The action of antisympathomimetic drugs on the urinary excretion of adrenaline and noradrenaline

In cats anaesthetized with pentobarbitone sodium, phenoxybenzamine, dibenamine, phentolamine, and piperoxane reduced the blood pressure and increased the urinary excretion of noradrenaline. When the fall of blood pressure after phenoxybenzamine was prevented by repeated injections of vasopressin, the urinary excretion of noradrenaline did not rise. Hydergine and hydrallazine reduced the blood pressure without raising the urinary excretion of noradrenaline. In dogs, the infusion of small amounts of noradrenaline led to a significantly higher urinary recovery of the amine after phenoxybenzamine than before. It is concluded that antisympathomimetic drugs interfere with the destruction in the body of noradrenaline, whether released reflexly in hypotension or injected.

Interaction between histamine and dichloroisoproterenol, hexamethonium, pempidine, and diphenhydramine, in normal and reserpine-treated heart preparations

Histamine stimulated the isolated auricles and heart of the guinea-pig. The effect was best seen in auricles which had been previously depressed by treatment with reserpine. Ganglionic blocking drugs (hexamethonium and pempidine), applied to auricles which had been previously treated with reserpine, abolished the diphasic effect of nicotine, but did not alter the response to histamine. Dichloroisoproterenol did not modify the stimulant action of histamine in isolated auricles, either before or after treatment with reserpine; nor did it alter the response of the isolated heart. Diphenhydramine reduced or blocked the stimulant action of histamine in auricles which had been previously treated with reserpine. The results support the hypothesis that histamine stimulates the myocardium by a direct action on specific receptors.

Comparison of bretylium and guanethidine: tolerance, and effects on adrenergic nerve function and responses to sympathomimetic amines

Bretylium depresses the slope of regression lines relating frequency of sympathetic nerve stimulation to magnitude of contractions of the cat nictitating membrane. In contrast, guanethidine and reserpine preferentially abolish responses to low rates of nerve stimulation and cause a roughly parallel shift of the regression lines. The hypersensitivity of the nictitating membranes of cats to intravenous adrenaline or noradrenaline is far greater after a series of small daily doses of bretylium or guanethidine than after single large doses. The maximal sensitivity produced was similar to that after postganglionic sympathetic nerve section and exceeded that produced by ganglion blockade. The development of hypersensitivity to catechol amines is accompanied by some return of responses of the nictitating membranes to sympathetic nerve stimulation despite continued daily administration of bretylium or guanethidine. In cats given bretylium daily, responses to low rates of nerve stimulation become greater than in controls unless the dose of bretylium given subcutaneously is 50 mg/kg or more. When marked hypersensitivity to catechol amines has been produced by giving bretylium or guanethidine daily for 7 or 14 days, the sympathomimetic effects of these compounds are greater. Responses to intravenous dimethylphenylpiperazinium are also increased and the results suggest that even large daily doses of adrenergic neurone blocking agents do not appreciably impair the functioning of the adrenal medulla. The pressor effects of intravenous adrenaline, noradrenaline and dimethylphenylpiperazinium iodide increase less than the corresponding nictitating membrane responses. These results are discussed in relation to tolerance to adrenergic neurone blockade, and differences between the effects of bretylium and guanethidine found in man. Bretylium and guanethidine depress the slopes of the dose-response curves for the pressor and nictitating membrane contracting effects of tyramine. When single doses or a short series of daily doses were given, guanethidine caused more depression of the slopes than did bretylium, but nevertheless large depressions of slope were found after giving bretylium daily for several weeks. The magnitude of the responses can be greater or less than in controls depending on the dose of the sympathomimetic amine, the dose of the adrenergic neurone blocking agent and the duration of its administration. The results suggest that injection of tyramine produces a progressively smaller release of adrenaline or noradrenaline during the daily administration of bretylium (or guanethidine) but that in some test situations this is more than compensated for by the development of hypersensitivity to the catechol amine released. Some corresponding changes in responses to amphetamine and ephedrine are also described.

Diuresis in rats: effects of sympathomimetic and sympathetic blocking agents

Dopamine and tyramine possess diuretic properties resembling but weaker than those of noradrenaline in the rat. These three amines produce a relatively smaller loss of sodium than does adrenaline. Bretylium shows a diuretic action which is apparently associated with its sympathomimetic properties and which is antagonized by phenoxybenzamine. However, bretylium causes a relatively greater loss of potassium and chloride than do the sympathomimetic amines. A slight antidiuretic action is shown by bretylium after its diuretic effect has subsided and a similar effect is produced by BW 172C58, which has relatively weak sympathomimetic properties. In contrast to these adrenergic neurone blocking agents, phenoxybenzamine and a ganglion blocking agent (pentacynium) show powerful antidiuretic effects. These observations are consistent with the view that the adrenal medulla has an important role in facilitating water diuresis in rats.

Intestinal ischemia shock in normal and Dibenzyline-protected dogs

An experimental model was developed to facilitate study of the intestinal-hepatic complex in shock. Shock was produced by ischemic injury to the intestine by temporary (4-hr) ligation of the superior mesenteric artery (SMA shock). Protection against shock was induced by Dibenzyline injected into the portal vein. Blood samples before, during, and after arterial occlusion were taken from the femoral, portal, and hepatic veins for hemoglobin, hematocrit, plasma proteins, bacterial culture, endotoxin detoxifying component (EDC), and vasotropic assays (rat mesoappendix). Liver biopsies were taken for carbon distribution in the Kupffer cells. Blood pressure and tissue temperatures were monitored. The data indicate that these parameters of SMA shock are predictable and typical of other types of experimental shock and can be attenuated by Dibenzyline. Bacterial organisms and polysaccharides (EDC) were not present in irreversible shock. Vasotropic assays demonstrated vasodepressor (epinephrine inhibiting) materials, in the peripheral blood. Vasodepressor responses were abolished by the action of Dibenzyline on hepatic function, possibly by sustaining hepatic reticuloendothelial system activity.

The actions of bretylium: adrenergic neurone blocking and other effects

Bretylium caused a specific and lasting depression of many excitatory and inhibitory responses evoked by electrical stimulation of the peripheral sympathetic nervous system, probably by impairing conduction of impulses in adrenergic neurones with consequent failure of noradrenaline and adrenaline release. This effect, which will be referred to as the adrenergic neurone blocking action, was preceded by weak sympathomimetic effects. In the presence of bretylium the effects of adrenaline and noradrenaline were increased, as after sympathectomy. Concentrations producing blocking of adrenergic neurones did not prevent the release of adrenaline and noradrenaline from the adrenal medulla by splanchnic nerve stimulation or by the injection of dimethylphenylpiperazinium iodide, nor did they cause antiparasympathetic or parasympathomimetic effects. No action on the central nervous system has been detected. Curare-like neuromuscular block occurred with 10 to 30 times the amount required to block the response to adrenergic nerve stimulation alone and was accompanied by signs of temporary synaptic block in autonomic ganglia. Adrenergic nerve trunks and sensory nerves in the skin were readily blocked for long periods by topical application of bretylium, whereas the phrenic nerve of the rat was not. Bretylium had little effect on gastrointestinal propulsion or on the sensitivity of smooth muscle to acetylcholine, 5-hydroxytryptamine, adrenaline, or noradrenaline, but moderate amounts depressed the peristaltic reflex and the sensitivity of the guinea-pig ileum to histamine. Bretylium caused postural hypotension in the cat in doses which had little effect on the supine blood pressure. Experiments on the nictitating membrane indicated that compensation for the effects of bretylium on low rates of stimulation of postganglionic sympathetic nerves could be attained by a small increase in the rate of stimulation, whereas compensation for its effects on high rates required an increase in the rate of stimulation beyond physiological limits.

Interactions of sympathomimetic drugs and their antagonists on the isolated atrium

In the isolated guinea-pig atrium, phenoxybenzamine and other antagonists of sympathomimetic drugs and the adrenergic nerve blocking agent guanethidine inhibited the action of butyrylcholine and tyramine and potentiated the action of noradrenaline. Also in the isolated guinea-pig atrium, phenoxybenzamine and cocaine abolished the parasympathetic, and potentiated the sympathetic, effects of vagus stimulation.

The action of sympathetic blocking agents on isolated and innervated atria and vessels

A preparation is described of isolated rabbit atria with both vagus and sympathetic nerves. The action on it of bretylium and of choline 2,6-xylyl ether bromide (TM10) was studied. A concentration of breylium sufficient to abolish the response to sympathetic stimulation also depressed the response to vagal stimulation. The effect was reversible, though more easily with choline xylyl ether. Both drugs abolished the accelerating action of acetylcholine in the presence of atropine, but they augmented the action of tyramine, and did not reduce that of amphetamine. In the vessels of the perfused rabbit ear they abolished the constrictor effect of nervous stimulation and of acetylcholine, but increased that of tyramine.

Effect of dibenzyline on the metabolic actions of epinephrine and thyroxine

Several investigators have attempted to use Dibenzyline to block the metabolic effect of thyroxine as a test of the "epinephrine hypothesis" of thyroxine function. The assumption underlying the use of the drug is that it blocks the hypermetabolism which follows epinephrine administration. This has been tested experimentally and found not to be justified. Dibenzyline does not block specifically the metabolic rate response as measured at 30 C to epinephrine, thyroxine, or a combination of the two hormones. Dibenzyline, thyroxine, and epinephrine show numerous interactions on rate of metabolism, blood glucose, and rectal and surface temperatures, but the Dibenzyline experiments are probably not meaningful in elucidating the role of epinephrine in the peripheral effects of thyroxine.