Pharmacological analysis of sympathetic function in the embryonic chick heart

Sympathetic nerve cells enter the embryonic chick heart on the fifth day in ovo, but it is uncertain when these nerves become functional. Using pharmacological probes known to affect the embryonic circulation, sympathetic nerve function was examined at various stages of development. Exogenous norepinephrine elicited cardioacceleration in the hearts of embryos with intact extraembryonic circulation both before (stage 20-24) and after (stage 28-32) sympathetic innervation of the heart, and this acceleration could be inhibited by propranolol and practolol. In contrast, ganglionic stimulation with 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP) elicited cardioacceleration only after stages 27-28 (i.e., after sympathetic innervation), producing a 25-30% increase in heart rate over the predrug levels of 148.7 +/- 1.8 beats/min. DMPP-elicited positive chronotropy was reduced by beta-receptor antagonists, hexamethonium, guanethidine (GuE), and tetrodotoxin. In preparations of the embryonic thorax in which the innervated heart was separated from brain and adrenal influences, DMPP elicited a GuE-sensitive cardioacceleration. It is concluded that during chick embryonic development, no more than a 1-day interval exists between the appearance of sympathetic nerves in the heart and the onset of neuronal function in that organ.

Actions of cholecystokinin octapeptide on smooth muscle of isolated dog intestine

Adult dogs were anesthetized and segments of small intestine were isolated and perfused via a mesenteric artery with Krebs-bicarbonate solution. Muscle responses along the circular and longitudinal axes were monitored with extraluminal strain gauge transducers. Agonists were administered as intraarterial bolus injections in volumes not exceeding 0.1 ml. Antagonists were dissolved in the Krebs perfusion solution. The C-terminal octapeptide of cholecystokinin (CCK-OP) produced dose-related tonic and phasic contractions of smooth muscle along the transverse axis and tonic and phasic relaxations along the longitudinal axis of the muscle segments. Smooth muscle responses to CCK-OP were reduced by atropine sulfate (0.1 mug/ml) and minimally affected by hexamethonium (10 mug/ml) perfusion. Tetrodotoxin (TTX, 5 ng/ml) selectively reduced muscle responses to dimethylphenylpiperazinium (0.5 mug) and CCK-OP (0.2 mug) but failed to alter responses to bethanechol (BeCh, 5 mug). Higher concentrations of TTX (10 ng/ml) abolished responses to CCK-OP. Depolarizing doses of nicotine (500 mug) selectively antagonized responses to 5-hydroxytryptamine (5HT, 5 mug) and CCK-OP (0.2 mug) but did not alter responses to BeCh (5 mug). Perfusion with tetraethylammonium (1 mg/ml) reduced muscle responses to depolarizing doses of nicotine and abolished the nicotine-induced antagonism of 5HT and CCK-OP. The intestinal smooth muscle response to CCK-OP in the dog is mediated through a neurogenic mechanism. CCK-OP interacts with a nonnicotinic receptor on postganglionic cholinergic neural elements in this preparation.

Effects of halothane on ganglionic discharges

The effects of halothane on ganglionic transmission were studied by recording extracellular potentials from the postganglionic nerve of the isolated hamster stellate ganglion. Halothane, at concentrations greater than 0.1 mM, decreased the potentials evoked by preganglionic stimuli at 0.2 Hz. Halothane also blocked discharges elicited by 1,1-dimethyl-4-phenylpiperazinium, a selective nicotinic agonist, and discharges elicited by the nicotinic actions of exogenous acetylcholine. Repetitive preganglionic stimulation (30 Hz, 5 seconds) in the presence of nicotine (10(-3) M), or hexamethonium (10(-3) M), evoked asynchronous discharges in the postganglionic nerve. These discharges were suppressed by low concentrations of atropine, and were probably due to the muscarinic actions of neurotransmitter. Halothane depressed these discharges at approximately the same concentration that it depressed the compound action potential elicited by low frequency preganglionic stimulation in the untreated ganglion. Halothane had no effect on the discharges elicited by 4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride (McN-A-343), a selective muscarinic agonist, or the discharges elicited by the muscarinic actions of acetylcholine. These results are most readily explained by hypothesizing that halothane acts at two sites in the ganglion. It appears to depress the postsynaptic response to the nicotinic actions of the neurotransmitter, acetylcholine. Also, it probably depresses transmitter release from the presynaptic nerve endings during repetitive stimulation.

Presence of muscarinic inhibitory and absence of nicotinic excitatory receptors at the terminal sympathetic nerves of chicken hearts

Nicotine (2 X 10(-4) M) or acetylcholine (5.5 X 10(-4) M) in the presence of 3 X 10(-6) M atropine did not increase the rate or amplitude of contraction in isolated atria or ventricular strips of the chicken heart; both drugs also did not cause an output of noradrenaline or adrenaline and did not evoke antidromic discharges in the right sympathetic nerves of isolated perfused chicken hearts. In contrast, "high K+-solutions" evoked an output of noradrenaline and adrenaline and caused a burst of antidromic discharges. Dimethylphenylpiperazine (DMPP; 3.1 X 10(-4) M), by a tyramine-like action, elicited a small output of noradrenaline and increased rate and amplitude of contraction" but did not evoke antidromic discharges. The noradrenaline output caused by DMPP was not reduced by lowering the extracellular Ca2+ concentration from 1;8 to 0.1125 mM.-Acetyl-choline (10(-5) and 10(-4) M)inhibited the noradrenaline and adrenaline outputs evoked by electrical stimulation of the right sympathetic nerves (3 HZ, 1 ms, 30 V); the inhibition was blocked by 3 X 10(-6) M atropine.-It is concluded that the terminal parts of sympathetic nerves of the chicken heart possess muscarinic inhibitory receptors but lack nicotinic excitatory receptors. Thus prejunctional nicotinic receptors are not an integral part of the terminal sympathetic neurone otherwise they would be present at this neurone in all species.

Tricyclic antidepressant drugs as antagonists of muscarinic receptors in sympathetic ganglia

Close arterial injection of McN-A-343 into the superior cervical ganglion of the cat resulted in contractions of the nictitating membrane. The ganglionic effects of McN-A-343 but not those of DMPP were antagonized in a dose-related manner by 2-10 mug of desipramine, imipramine, chlorimpramine, iprindole and viloxazine. No correlation was found between the dose of each drug which blocked the effects of McN-A-343 and that required to potentiate the responses of the nictitating membrane to intra-arterial administration of noradrenaline. It is concluded that clinically effective antidepressant agents can block muscarinic receptors in neural tissue, even if they do not do so in smooth muscle and gland cells.

Reversible adrenergic alpha-receptor blocking action of 2,4'-dimethyl-3-piperidino-propiophenone (tolperisone)

The vascular action of 2,4'-dimethyl-3-piperidino-propiophenone hydrochloride (tolperisone hydrochloride), a centrally acting muscle relaxant, was investigated in pentobarbital anesthetized dogs. Tolperisone given intravenously produced a transient hypotension, tachycardia, and hyperventilation. The drug increased the femoral arterial flow, and decreased the superior mesenteric arterial flow following an initial transient increase. When injected directly into femoral and mesenteric arteries, tolperisone caused a rapid increase in both arterial flow (vasodilatation). However, femoral vessels were about 90 times as sensitive as mesenteric vessels to tolperisone. These results indicate that tolperisone shifts the blood volume from mesenteric (visceral) vessels to femoral (skeltal) ones. The femoral vasodilatation produced by i.a. tolperisone was not depressed by the pretreatment with i.a. propranolol, atropine or chlorphenylamine. Tolperisone decreased the contractile force in an isolated and cross-circulated papillary muscle. Tolperisone produced adrenaline reversal and antagonized the pressor response to noradrenaline. Moreover, femoral vasoconstriction caused by i.a. adrenaline was converted to vasodilatation and that caused by i.a. noradrenaline was depressed during an i.a. infusion of tolperisone. These results indicate that tolperisone blocks adrenergic alpha-receptors. The blocking action was rapid in onset, short-lived, and in addition, competitive.

Distribution of excitatory vagal fibers in canine gastric wall to control motility

The distribution of cholinergic excitatory neurones in the canine gastric wall was studied by recording electrical and mechanical responses to electrical stimulation of the nerves of Latarjet and close intraarterial perfusions of drugs which stimulate nerve and muscle. Electrical stimulation of the anterior nerve of Latarjet produced contractile activity on the anterior side, followed rapidly by activity on the posterior side and vice versa, indicating that the axons of the neurones from each side crossed over to the other. This was not due to the propagation or conduction of electrical response activity, because electrical response activity and contractions induced locally by acetylcholine given into a small artery supplying a segment of stomach did not propagate. The cross-over innervation and the direct innervation were both segmental, in that the response to nerve stimulation dropped out in segments as the branches of the nerves of Latarjet were cut successively. Mainly, preganglionic axons crossed over from the anterior side to the posterior side, but both pre- and postganglionic axons crossed over from the posterior side. This was demonstrated by observing the spread of electrical and mechanical responses, or lack of it, in response to local injections of acetylcholine and dimethylpeprazinium. The study shows that there is a segmental distribution of excitatory neurones in the gastric wall which is appropriate to produce a ring of contraction to control gastric emptying and mixing.

Inhibition of catecholamine release from the adrenal medulla by halothane. Site and mechanism of action

In isolated bovine adrenals perfused with Locke solution in a retrograde fashion we investigated the effects of halothane on the catecholamine release evoked by various secretagogues. 1. The catecholamine release induced by activation of the nicotinic receptors on the chromaffin cells with 1,1-dimethyl-4-phenylpiperazinium was almost completely inhibited (by about 90%) by 1.4 X 10(-3) M halothane. 2. It was shown by means of cumulative concentration-response curves of acetylcholine for its stimulating effect on catecholamine release (pD2 = 4.04) that halothane was a non-competitive antagonist (pD'2 = 3.17). 3. Halothane (1.4 X 10(-3) and 4.3 X 10(-3) M) did not decrease the catecholamine secretion in response to pilocarpine or histamine. 4. The 5-hydroxytryptamine-induced catecholamine release was not impaired by 1.4 X 10(-3) M halothane, but was significantly inhibited (by 44%) by 4.3 X 10(-3) M halothane. 5. At 1.4 X 10(-3) M halothane the catecholamine release induced by gamma-aminobutyric acid (GABA) was inhibited by 40%. 4.3 X 10(-3) M halothane completely blocked the secretion induced by GABA. 6. The catecholamine secretion in response to 56 mM KCl or to introduction of CaCl2 after perfusion with Locke solution deficient in CaCl2 was not reduced by halothane (1.4 X 10(-3) and 1.4 X 10(-2) M). 7. Halothane (1.4 X 10(-3) M) did not inhibit the catecholamine release evoked by acetaldehyde or tyramine from glands perfused with Ca2+ -free Locke solution throughout the experiments. It is concluded that the site of action of halothane is the cell membrane of the chromaffin cell. The anaesthetic does not impair the permeability of the membrane to calcium ions. Halothane may cause a conformational change of membrane proteins, particularly of the nicotinic receptor (and at higher concentrations of GABA and 5-hydroxytryptamine receptors); thus, stimulation may be prevented by an inhibition of agonist-receptor interaction.

Supersensitivity induced by the toxin of Brazilian scorpion venom (Tityus serrulatus Lutz e Mello)

The purified toxin of the Brazilian scorpion venom (TsTX) enhances the pharmacological actions of directly and indirectly acting substances on several preparations. The enhancing action of TsTX is more pronounced for the indirectly acting drugs, which is highly suggestive of a prejunctional site of action. Secondarily, TsTX does also produce an unspecific increase of sensitivity at the level of the pharmacological receptor itself. The mechanism by which these changes are brought about remains to be determined.

Inhibition by ethanol of noradrenaline output from peripheral sympathetic nerves: possible interaction of ethanol with neuronal receptors

The sympathetic nerve terminals of the isolated rabbit heart perfused with Tyrode solution were used to study the action of ethanol on the noradrenaline uptake and release. The uptake of exogenous noradrenaline (10 ng/ml) into the sympathetic nerve endings, the noradrenaline output evoked by raising the concentration of potassium ions in the perfusion fluid, and the release in response to electrical stimulation of the nerve axons were inhibited only by lethal concentrations of the alcohol; the concentrations which caused 50% inhibition (IC50) amounted to 760 mM, 830mM, and 1150 mM respectively. However, ethanol at concentrations compatible with moderate intoxication reduced the noradrenaline release in response to activation of the nicotine receptors on the nerve terminals by dimethylphenylpiperazine; the threshold concentration was 36 mM and the IC50 was 129 mM. It is suggested that this effect is due to hydrophobic interaction of the alcohol with receptor proteins, thus inhibiting stimulus formation.

Mechanism of the indirect sympathomimetic effect of 5-hydroxytrypt-amine on the isolated heart of the rabbit

1 Rabbit isolated hearts, perfused by the Langendorff technique, were used to investigate the indirect sympathomimetic effects of 5-hydroxytryptamine (5-HT). Comparisons were made with noradrenaline and with two indirectly acting sympathomimetic agents with entirely different mechanisms of action, tyramine and dimethylphenylpiperazinium (DMPP). 2 The cardiac stimulant effects of 5-HT, tyramine and DMPP were inhibited by propranolol and practolol and the pA2 values obtained were similar to those obtained with noradrenaline as the agonist. 3 Responses to 5-HT, tyramine and DMPP were greatly reduced on hearts from rabbits pretreated with 6-hydroxydopamine. Such hearts had less than 7% of their normal catecholamine concentration and no fluorescence characteristic of noradrenaline in the cardiac sympathetic nerves could be demonstrated. 4 Rapid, reversible and selective tachyphylaxis to 5-HT was demonstrated during perfusion with 5-HT. In hearts desensitized to DMPP by perfusion with DMPP, responses to 5-HT were also reduced. 5 Perfusion of hearts with colchicine inhibited stimulant responses to 5-HT and DMPP but had little effect on responses to noradrenaline or tyramine. 6 Desmethylimipramine enhanced cardiac stimulant responses to noradrenaline and to a lesser extent, those to 5-HT and DMPP. Responses to tyramine were consistently inhibited by desmethylimipramine. 7 Tetrodotoxin abolished responses of the heart to electrical nerve stimulation but left responses to noradrenaline, 5-HT and DMPP unaffected. 8 5-HT, tyramine and DMPP evoked 3H-release from hearts whose neuronal noradrenaline stores had been labelled by perfusion with [3H]-(-)-noradrenaline. The pattern of release evoked by 5-HT was similar to that of DMPP but differed from that of tyramine. 9 Reducing the calcium concentration in the Tyrode solution from 3.6 to 0.2 mEq/1 did not affect 3H-overflow after tyramine but greatly inhibited that evoked by 5-HT and DMPP. 10 The results confirm that the stimulatn effects of 5-HT on the rabbit isolated heart are the result of noradrenaline release. They further suggest that the site of the release is the terminal sympathetic nerve network. The mechanism of release shows more similarities to that of DMPP (calcium-dependent depolarization and exocytosis) than to that of tyramine (neuronal uptake and stoichiometric displacement).

Onset of chronotropic effects of nicotinic drugs and tyramine on the sinoatrial pacemaker in chick embryo heart: relationship to the development of autonomic neuroeffector transmission

Spontaneous electrical activity, recorded extracellularly from the sinoatriial pacemaker region in the isolated chick embryo heart, was inhibited by nicotine (10(-5)M) on the 11th incubation day and thereafter. Blockade of the inhibitory effects of nicotine hexamethonium, tetroditoxin and atropine supported the conclusion that nicotine initiated propagated impulses in postganglionic cholinergic nerves and released acetylcholine to act on atropine-sensitive receptors on pacemaker cells. Dimethylphenylpiperazinium, like nicotine, inhibited the sinoatrial pacemaker. The onset of the inhibitory effect of nicotine occurred within 1 day of the appearance of cholinergic neuroeffector transmission. The acceleratory action of tyramine (2.9 X 10(-5)M) increased markedly on the 20th incubation day, that is, within 1 day of the appearance of adrenergic neuroeffector transmission. The positive chronotropic effects of tyramine were opposed by cocaine and by propranolol. Nicotine also evoked pacemaker acceleration that was observed on the 21st incubation day and thereafter. However, the sympathomimetic effect of nicotine required elevation (2 times normal) of the external Ca++ concentration. Ontogenetic and pharmacologic evidence support the conclusion that the drug-induced changes in pacemaker impulse frequency depended upon an interaction with autonomic nerves. The results are consistent with the hypothesis that the gap between morphologic innervation of the heart by autonomic nerves and the appearance of transmission is related, at least in part, to the amount of transmitter available for release.

Influence of sympathetic nerves on development of responsiveness of the chick smooth muscle to drugs

The role of sympathetic nerves in the development of responsiveness of smooth muscle to drugs was investigated using the expansor secondariorum muscle of 2- to 40-day-old chicks. The normal developmental decrease in the responsiveness of the muscle to acetylcholine was prevented by surgical transection of the nerve or chronic treatment with guanethidine, while it was facilitated by chronic treatment with dimethylphenylpiperazinium. Sensitivity of the muscle to noradrenaline, remaining constant during normal development, was increased by nerve section or guanethidine treatment, while it was slightly decreased by dimethylphenylpipe-azinium treatment. These results suggest that sympathetic nerves regulate the development of the responsiveness of the chick expansor secundariorum muscle to drugs, at least the developmental decrease in responsiveness to acetylcholine.

Inhibition of receptor-mediated noradrenaline release from the sympathetic nerves of the isolated rabbit heart by anaesthetics and alcohols in proportion to their hydrophobic property

The actions of anaesthetics (diethyl ether, enflurane, chloroform, methoxyflurane) and alcohols (ethanol, 1-propanol, 1-butanol, 1-pentanol) on the noradrenaline release from (and uptake into) the sympathetic nerve terminals were studied in isolated rabbit hearts perfused with Tyrode solution at constant flow rate. The noradrenaline in the perfusate was assayed spectrofluorimetrically. 1. Ethaonol, 1-propanol, 1-butanol and all anaesthetics (at concentrations which decreased by more than 65% the noradrenaline output in response to activation of the nicotinic receptors) did not significantly affect the spontaneous noradrenaline output. Only 1-pentanol (3.75 X 10(-3) M) caused an increase in spontaneous noradrenaline output. 2. The uptake of exogenous noradrenaline from the perfusion fluid into the sympathetic nerve terminals was not influenced by the anaesthetics and alcohols (at concentrations which decreased by more than 65% the noradrenaline output evoked by stimulation of the nicotinic receptors). 3. All anaesthetics and alcohols caused a concentration-dependent inhibition of the noradrenaline release in response to activation of the nicotinic receptors on the nerve terminals by 1,1-dimethyl-4-phenylpiperazine or acetylcholine in the presence of atropine. The concentrations of the compounds which decreased the noradrenaline output by 50% were as follows: diethyl ether: 5.1 X 10(-3) M; enflurane: 2.9 X 10(-4) M; chloroform: 2.6 X 10(-4) M; methoxyflurane: 3.8 X 10(-5) M; ethanol: 1.5 X 10(-1) M; 1-propanol: 1.9 X 10(-2) M; 1-butanol: 6.0 X 10(-3) M; 1-pentanol: 1.2 X 10(-3) M.

Effects of nicotine on rebound excitation of guinea-pig small intestine

Poststimulus rebound contractions and associated action potentials of the circular muscle layer occurred after termination of transmural electrical stimulation. Low concentrations of nicotine (1 x 10(-6) to 5 x 10(-6) g/ml) either abolished or greatly reduced the poststimulus response. The contractile force and time duration of the response were reduced, and the latency of the response was increased by low concentrations of nicotine. The depressant action of low concentrations of nicotine was reversed by an increase in concentration from 5 x 10(-6) to 1 x 10(-4) g/ml. The effects of low concentrations of nicotine were mimicked by 1,1-dimethyl-4-phenylpiperazinium iodide, and they were prevented by hexamethonium, pentolinium, gallamine and large concentrations of atropine. Gallamine increased myogenic electrical and mechanical activity and potentiated the poststimulus rebound response. Pretreatment with guanethidine produced a small reduction in the inhibitory action of nicotine. Propranolol and phentolamine suppressed the poststimulus response, but the specificity of the action was questionable. The effects of nicotine may be mediated by excitation of intrinsic inhibitory neurons.

Antagonism by propranolol of the ganglion stimulant action of 5-hydroxytryptamine

The effects of racemic propranolol and its constituent isomers were studied on ganglionic stimulation produced in situ by close arterial injection of 5-HT and DMPP to the superior cervical ganglion. Ganglion stimulation was recorded in terms of the resultant contraction of the nictitating membrane. d,l-Propranolol caused a biphasic antagonism of the ganglion stimulant effect of 5-HT. At low doses, 0.5-10 mug, the antagonism was surmountable by increasing the amount of 5-HT. The l-isomer (0.2-4 mug) but not d-propranolol also caused antagonism. At higher doses, 0.1-5 mg, both d,l- and d-propranolol caused a second type of blockade of 5-HT which was not surmountable and resembled that seen with procaine. The ganglion stimulant effects of DMPP and acetylcholine were only antagonised by the higher doses of d- and d,l-propranolol. d,l-Propranolol did not reduce the direct stimulation by 5-HT on the muscle of the nictitating membrane.

Absence of sensitization to epinephrine-induced cardiac arrhythmia and fibrillation in dogs and cats anesthetized with CI 744

Ci 744 (20 mg/kg, given intramuscularly (IM) produced a reliable level of surgical anesthesia in both dogs and cats. Animals anesthetized in this way did not have an increased sensitivity to cardiac fibrillation after they were given epinephrine. Epinephrine-induced ventricular arrhythmia observed in C1 744-anesthetized animals was eliminated in cats and was markedly reduced in dogs by bilateral vagotomy. Myocardial fibrillation was not produced by epinephrine (0.1 to 100 mug/kg, intravenously (IV) in dogs and cats anesthetized with C1 744 alone. Pentobarbital anesthesia, like C1 744 anesthesia, did not sensitize the heart, whereas a significant number of thiamylal-halothane-anesthetized animals died from cardiac fibrillation after they had been given epinephrine. Additional dogs were anesthetized with C1 744 or pentobarbital and given a series of pressor and depressor agents (isoproterenol, epinephrine, tyramine, 1, 1-dimethyl-4-phenylpiperazium iodide (DMPP) plus bilateral carotid occlusion) before and after vagotomy. The responses with either anesthetic were similar with the exception that the reflex bradycardia to pressor agents was more evident in C1 744- than in pentobarbital-anesthetized dogs.

Muscarinic cholinergic regulation of cyclic guanosine 3,5-monophosphate in autonomic ganglia: possible role in synaptic transmission

The effects of acetylcholine, and of agents which selectively mimic or block its nicotinic and muscarinic actions, have been studied on the levels of guanosine 3,5-monophosphate (cyclic GMP) and adenosine 3,5-monophosphate (cyclic AMP) in slices of bovine superior cervical ganglion. Low doses of either acetylcholine or the muscarinic agonist, bethanechol, caused a substantial increase in the level of cyclic GMP, and slightly increased the level of cyclic AMP; the acetylcholine- and the bethanechol-induced increases in cyclic GMP were blocked by atropine, the muscarinic antagonist, but not by hexamethonium, the nicotinic antagonist. The nicotinic agonist N,N-dimethylphenylpiperazinium did not alter the level of either of the cyclic nucleotides. Dopamine increased the level of cyclic AMP and acetylcholine partially prevented this dopamine-induced increase in cyclic AMP. The data are consistent with a model for the ganglion in which muscarinic cholinergic synaptic transmission is mediated by an increase in the level of cyclic GMP in the postganglionic neurons and dopaminergic transmission by an increase in the level of cyclic AMP in these neurons.

The importance of a central adrenergic mechanism in the cardiovascular responses to ouabain

Central administration of ouabain in the ventricular system of vagotomized dogs and cats elicited increases in blood pressure, cardiac contractile force and cardiac rate followed by ventricular arrhythmia. Spinal transection (C2) or hexamethonium treatment abolished the central effects of ouabain. Bilateral stellate ganglionectomy prevented the tachycardia and reduced the pressor response to the lower dose (15 mug) of ouabain; bilateral adrenalectomy only reduced the pressor effect. Neither of the procedures alone was adequate to inhibit the cardiovascular responses following a higher dose (90 mug) of ouabain whereas a combination of both procedures blocked these responses completely. Tachyphylaxis to the cardiovascular effects of very high doses of intracerebroventricularly (i.c.v.)-administered ouabain was shown to be of central origin. Prior depletion of brain catecholamines by Ro 4-1284 or 6-hydroxy -dopamine, and central adrenergic neuron blockade by bretylium prevented the centrogenic effects of ouabain. Similarly, central alpha- or beta-adrenoceptor blockade also prevented the responses to i.c.v. orabain. The results suggest that ouabain causes the release of adrenergic mediator (noradrenaline) in the brain, probably by a depolarization of a primary neuron(s), and that the central adrenergic mechanism is responsible for the genesis of the cardiovascular effects. Both alpha- and beta-adrenoceptors seem to be important in the central control of cardiovascular function. The most sensitive site for ouabain action was found to be the posterior hypothalamus in the vicinity of the third ventricle.

[Pharmacological studies on the cough reflex]

The artificially induced cough reflex in experimental animals should necessarily be similar to the cough which occurs naturally in humans. The curve demonstrated during a cough of each patient with respiratory disease was characteristic. Compared with the curve of a cough-like reflex (CLR) induced by DMPP, the curve of a cough induced by electrical stimulation of the tracheal mucosa was similar to that of a cough in humans. In dogs and cats anesthetized with alpha-chloralose (80 similar to 100 mg/kg i.p.), the number of CLR with DMPP was dose dependent. Tachphylaxis did not occur despite repeated administration of DMPP. DMPP (5 similar to 10 mug/kg i.v.) did not affect airway resistance. CLR with DMPP was depressed not only by morphine, codeine, oxymethebanol, picoperidamine, piclobetol and hexacol but also by hexamethonium. Thus, it appears that the mechanism of CLR with DMPP is different from that in the cough reflex. This CLR may be utilized for determining the physiology of cough reflex and the site of action of antitussives.

Electrical and mechanical activity of the isolated canine stomach perfused with homologous, in vitro, oxygenated blood

Electrical and mechanical activity was recorded from six totally isolated canine stomachs perfused with homologous blood oxygenated in vitro. Reactions to electrical vagal stimulation to cholinergic drugs and to pentagastrin were recorded. Electrical control activity, electrical response activity and mechanical response of isolated stomachs, observed in this in vitro system, were identical to those found in canine-isolated stomachs perfused with cross-circulated blood of living animals. It appears that when a living animal is included in the perfusion system of the isolated stomach, drugs used for gastric stimulation are rapidly metabolized and, due to this physiological clearance, repeated injections of stimulants can be given for several hours. Using the in vitro perfusion system, as in this experiment, injected drugs accumulate in the perfusion blood, as no clearance mechanism is available. Partial or total exchange of perfusion blood is therefore recommended. With these reservations, the in vitro system appears to be an easy method for the study of nonstimulated and stimulated electrical and mechanical activity of the totally isolated canine stomach.