The effect of intra(cerebro)ventricular reserpine on the acetylcholine content of the heart, ileum and hypothalamus of the dog

The effect of injection of reserpine into the cerebral ventricles on the acetylcholine contents of the sino-atrial node, ileum and hypothalamus of the dog was studied in ten dogs. Another group of five dogs served as a control. The effect of intravenous administration of reserpine, in the same dose as given intracerebroventricularly, was also studied on the acetylcholine content of these tissues in five dogs. General sedation, bradycardia, miosis, salivation, emesis and purgation were looked for. Tissues were removed 1 hr after administration of reserpine for estimation of acetylcholine content, which was increased in all the tissues studied. The increase in the peripheral tissues was greater than in the hypothalamus. The increase in the acetylcholine content was not quantitatively related to the other effects of reserpine. The increase in the acetylcholine content of the sino-atrial node and the ileum and also the peripheral effects observed on intracerebroventricular administration of reserpine can be attributed to its central action. With the same dose of reserpine given intravenously the acetylcholine content of the sino-atrial node was significantly increased, while that of the hypothalamus and ileum was not.     

The effect of reserpine on the acetylcholine content of different areas of the central nervous system of the dog

The acetylcholine content of the frontal and temporal lobes, hippocampus, hypothalamus, cerebellum and spinal cord was estimated in 18 dogs 3 hr. after the intravenous administration of reserpine. Another group of 7 dogs served as control. After reserpine (0.5 mg./kg. body weight) there was an increase of acetylcholine in all the areas under study except in the hippocampus. The increase was specially marked in the hypothalamus. In the hippocampus, however, reserpine caused a significant decrease of acetylcholine.     

Blocking effect of McN-A-343 on cardiac slowing produced by vagal stimulation

The effect of McN-A-343 was studied by direct administration into the sinus node artery of dogs vagotomized at the mid-cervical level. McN-A-343 blocked sinus bradycardia caused by electrical stimulation of the right vagus, while bradycardia induced by administration of acetylcholine or nicotine into the sinus node artery was not modified.     

THE EFFECT OF CORTICOSTEROID PRETREATMENT IN VIVO ON THE CONTRACTION OF GUINEA-PIG ILEUM AND DUODENUM

The effects of corticosteroid pretreatment on the contraction caused by acetylcholine or electrical stimulation of guinea-pig ileum and duodenum were studied. The acetylcholine dose-response curves for steroid pretreated ileum but not duodenum were significantly shifted to the right; evidence that pretreated ileum required higher dose of acetylcholine than normal to cause 50% maximal contraction. Naloxone enhanced the contraction of normal ileum caused by acetylcholine given at the dose of ED50, but not that of normal duodenum. The dose of morphine required to abolish electrically induced contraction was higher in steroid pretreated ileum than in normal ileum. Hence, corticosteroid pretreatment may affect intestinal contractility via opioidergic mechanisms which are found in the ileum but not in the duodenum.     

Pertussis toxin-sensitive G-proteins in the sino-atrial node and right atrium of bovine heart

Three apparently distinct pertussis toxin (PTX)-sensitive substrates, with Mrs of 39, 40 and 41 kDa, were identified in membranes prepared from the sino-atrial (SA) node and right atrium of bovine heart. Based on their biochemical characterization, the effects of guanine nucleotides/MgCl2 on their PTX-catalyzed [32P]ADP ribosylation, and the PTX-induced decrease in radiolabelled agonist high-affinity binding to muscarinic acetylcholine receptors present in these membranes, we tentatively identify these proteins as the alpha-subunits of the G0 and Gi subtypes of G-proteins. These results indicate that PTX alters the G-protein modulation of SA nodal and atrial muscarinic acetylcholine receptors by disrupting at least one of a group of PTX-sensitive G-proteins present in these tissues.     

An easy and direct approach to investigate conduction properties of the rabbit sinus node

The sinus node is not only important for the generation of the cardiac impulse but also as conductor of this impulse from the site of origin toward the atrium. An easy method to investigate conduction properties of sinus nodal tissue directly is described. The isolated right atrium of the rabbit was divided--via an incision perpendicular to the crista terminalis--into two halves connected only by a bridge of sinus nodal tissue. By means of two atrial surface electrodes conduction through the sinus node bridge was monitored. It appeared that conduction in the sino-atrial border zone is many times slower than in the atrium and refractory period markedly longer. In the center of the sinus node conduction is again slower and refractory period longer than in the border zone. Validity of the method was tested by reconstruction of the conduction route of stimulated impulses using microelectrode recordings. Applications of the method were demonstrated by studying the effects of rate and rhythm, hypothermia, hypoxia, acetylcholine and norepinephrine as well as verapamil. The model is suitable for investigation of the effects of drugs and other interventions on impulse conduction in sinus nodal tissue.     

EFFECT OF RESERPINE ON CATECHOLAMINE CONTENTS AND MET-ENKEPHALIN AND β-ENDORPHIN LEVELS IN THE HYPOTHALAMUS AND THE PITUITARY

1. The effects of reserpine treatment on the contents of catecholamines and opioid peptides have been studied in the rat hypothalamus and pituitary. 2. Hypothalamic and pituitary catecholamines were drastically depleted following acute reserpine treatment. 3. Reserpine treatment also resulted in a significant decrease in immunoactive met-enkephalin content in both the hypothalamus (25%) and the anterior lobe (50%), but not in the neurointermediate lobe of the pituitary. 4. No changes were observed in immunoactive beta-endorphin levels. 5. These findings suggest that the met-enkephalin contents in the hypothalamus and the anterior pituitary may be under catecholaminergic control. 6. The lack of effect of acute reserpine treatment on immunoactive beta-endorphin contents might be due to the opposing effects of adrenergic and dopaminergic mechanisms.     

Pharmacological mapping of regional effects in the rabbit heart of some new antiarrhythmic drugs

In vitro preparations of rabbit heart were made from which measurements of effective refractory period (ERP), atrio-Hisian (A-H) and His-Purkinje (H-P) conduction times could be obtained, analogous to electrophysiological measurements customarily carried out in vivo. Intracellular potentials also were recorded from the sino-atrial (SA) node, atrium, bundle of His, preterminal Purkinje fibres and papillary muscles. The effects of a range of concentrations of three new antiarrhythmic drugs, melperone, cibenzoline and alinidine were compared, the lower concentrations studied corresponding to clinical levels. At low concentrations the effects of melperone, inducing bradycardia and lengthening ERP, could be attributed to prolongation of action potential duration (APD) in the sinus node and atrial and ventricular tissues. The slope of slow diastolic depolarization was not altered, nor was there any change in A-H or H-P conduction time, or in maximum rate of depolarization (MRD). At higher concentrations melperone had a substantial class 1 action, but there was no negative inotropic effect, or other evidence of restriction of slow inward current. Cibenzoline was primarily a class 1 agent but also lengthened APD to some extent in the SA node and in atrial and ventricular muscle, but not in Purkinje fibres. APD thus became more uniform along the ventricular conducting pathway. Cibenzoline also depressed contractions and increased A-H conduction time, implying restriction of slow inward current. The bradycardia could thus be attributed to a slowing of both depolarization and repolarization in the SA node, without any change in slope of the slow diastolic depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of amnesic doses of reserpine or syrosingopine on mouse brain acetylcholine levels

The effects of reserpine and syrosingopine on mouse whole brain acetylcholine levels were examined. At 2 or 24 hr following injection, the brains were removed and analyzed by mass spectrometry. No differences were found between drug-treated and control mice in the acetylcholine content of the brain at either time interval. The results suggest that whole brain acetylcholine levels do not predict the amnesic effects of either reserpine or syrosingopine.     

Effect of chlorpromazine and reserpine on the catechol amine content of different areas of the central nervous system of the dog

The effects of chlorpromazine and reserpine on the noradrenaline and adrenaline contents of the frontal cortex, the hypothalamus, the hippocampus and the midbrain were studied in the dog. In control dogs, the catechol amine concentrations were highest in the hypothalamus and lowest in the frontal cortex and the hippocampus. Noradrenaline contents were about seven to nine times as high as those of adrenaline in all the areas. Small doses of chlorpromazine raised the catechol amines in all the areas, the rise being maximum with 5 mg/kg. With increase in the dose of chlorpromazine there was a gradual reversal of the effect and, with 25 mg/kg, there was diminution of noradrenaline content in all the areas except in the hypothalamus. In general, chlorpromazine produced a greater rise in adrenaline than it did of noradrenaline content, and the increase of both amines was very high in the midbrain and the hippocampus compared with the other areas. Reserpine, however, depleted the catechol amine contents of all areas. The depletion was greatest for noradrenaline, an effect quite marked in the midbrain and the frontal cortex. It was concluded that the actions of these two tranquillizers on the catechol amines of dog brain differed both as to site and mechanism.     

Electrophysiological effects of alpha-adrenoceptor antagonists in rabbit sino-atrial node,cardiac Purkinje cells and papillary muscles.

The effects of prazosin, labetalol, and medroxalol were studied in the rabbit sino-atrial node, Purkinje cells and papillary muscles. At concentrations producing similar bradycardia, labetalol and medroxalol reduced the maximum rate of depolarization (Vmax) and overshoot potential in the sinus node. Prazosin had no such effects. These large and highly significant reductions in Vmax and overshoot in sinus node cells were observed at concentrations of medroxalol and labetalol which had no negative inotropic effect. If depolarization in the sinus node was due to the second inward current, this would imply that such currents in the sinus node and contracting cardiac muscle are pharmacologically distinct. All three drugs prolonged action potential duration in the sinus node, Purkinje cells and papillary muscles in a dose-related manner. Recovery after 1 h in drug-free solution from the effects of medroxalol and labetalol was only partial in the sinus node, but almost complete in Purkinje cells and papillary muscle. Recovery from prazosin was complete in all tissues. All three drugs depressed Vmax in Purkinje cells and papillary muscles in a dose-related manner, and recovery was complete. It is concluded that all three drugs had class 1 and class 3 antiarrhythmic actions, which could contribute to their protective effects in ischaemia and reperfusion independently of blockade of myocardial alpha-adrenoceptors.     

Effects of α-adrenoceptor-stimulating drugs on baroreceptor reflexes in conscious cats

The action of some α-adrenoceptor stimulating drugs with a central effect (clonidine, α-methyldopa, reserpine) on baroreceptor reflexes was studied in conscious cats (both in the resting condition and when influenced by emotional tension or electrical stimulation of the hypothalamus). The sedative effect of these drugs was observed simultaneously with bradycardia and the increase of baroreceptor reflexes. Clonidine and reserpine (in 6–24 h after injection) lowered blood pressure while α-methyldopa (40 mg/kg) increased it. Confrontation with a dog or electrical hypothalamic stimulation produced hypertensive reactions and diminished the baroreflexes. All drugs reduced the emotional and hypertensive reactions caused by natural stress situations and restored baroreceptor reflexes. On the other hand, neither clonidine nor α-methyldopa changed the decrease of baroreceptor reflexes caused by electrical hypothalamic stimulation. It is supposed that central α-adrenoceptor stimulating drugs do not influence processes of hypothalamic modulation of baroreceptor reflexes. The increase in baroreflex activity after clonidine, α-methyldopa and reserpine appears to be due to a direct effect of the drugs on the central neurones mediating baroreceptor reflexes and to the tranquillizing action of these drugs.     

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.     

Nitrergic modulation of acetylcholine release in the enteric nervous system: differences between guinea-pig and man

The effects of the NO donor, SNAP, and of the NO-synthase inhibitor, L-NNA, on release of acetylcholine and contractions were studied in isolated ileum preparations of man and guinea-pig. Strips were incubated with [³H]choline and superfused with a physiological salt solution. Release of [³H]acetylcholine was elicited by electrical stimulation. In the guinea-pig ileum, SNAP (100 M) increased basal [³H]acetylcholine release and muscle tone, and, in addition, inhibited the electrically-evoked release and contractions. In contrast, SNAP had no effect on basal or evoked [³H]acetylcholine release in the human ileum. L-NNA (300 M) facilitated the evoked release and contractions of the guinea-pig ileum, but had no effect in the human ileum. It is concluded that endogenous NO exerts a tonic inhibitory effect on cholinergic neurotransmission in the guinea-pig ileum which contributes to the relaxant effect of NO. The results do not indicate that NO has a similar function in the human ileum.     

Neurotransmitter control of thyrotropin secretion in the rat

In rats adapted to a +30°C temperature for one week, transfer to a temperature of +4°C increased immunoassayable serum TSH from 150–300 ng/ml 800–2000 ng/ml in 30 min. Since this response, as well as the level of serum TSH without stimulation, were decreased by reserpine, phentolamine, phenoxybenzamine, disulfiram and diethyldithiocarbamate, noradrenaline may be involved in the stimulation of TSH secretion. TRH-induced TSH increase was not blocked by reserpine.

1-Dopa, a noradrenaline precursor, decreased the TSH response to cold; -methyl-p-tyrosine increased the TSH level. Apomorphine decreased the level of serum TSH and inhibited the response to cold. The possibility of a dopaminergic inhibitory factor released from the hypothalamus is discussed. 5-HT has possibly a role in the acetylcholine is involved.     

POSITIVE INOTROPIC ACTION OF GLYCERYL TRINITRATE AS OBSERVED IN THE BLOOD-PEWUSED PAPILLARY MUSCLE PREPARATION OF THE DOG HEART

1. The effects of glyceryl trinitrate on the coronary vasculature and on the contractility of the ventricular myocardium were investigated by the use of papillary muscle preparations of the dog, and that on the sino-atrial node activity by the use of sino-atrial node preparations of the dog. The papillary muscle preparation was cross-circulated through the anterior septal artery and the sino-atrial node preparation through the sinus node artery from a donor dog. The papillary muscles were driven at a rate of 120 beats/min. Drugs were injected close-arterially. 2. Glyceryl trinitrate, in doses of 0.03–100 μg, produced dose-related increases in blood flow and developed tension. An increase in developed tension caused by 100 μg of glyceryl trinitrate amounted to about 24% of the basal developed tension. Large doses of glyceryl trinitrate (100–300 μg) produced a negative inotropic effect after a positive one in some preparations. 3. The positive inotropic effect of glyceryl trinitrate was not modified by propranolol, excluding a possible participation of an adrenergic mechanism. 4. Glyceryl trinitrate in large doses failed to modify the positive inotropic effect of calcium chloride. 5. Glyceryl trinitrate in a wide range of doses (0.03–100 μg) had virtually no effect on sino-atrial node activity.     

The effects of reserpine and 6-hydroxydopamine on the concentrations of some arylakylamines in rat brain.

1 The concentrations of p- and m-tyramine were measured in the caudate nucleus of the rat brain following subcutaneous injection of reserpine or intraventricular injection of 6-hydroxydopamine, beta-Phenylethylamine was analysed in the hypothalamus after reserpine. 2 Endogenous levels of p-tyramine and m-tyramine in the caudate nucleus, and beta-phenylethylamine in the hypothalamus were 8.02, 2.25 and 2.52 ng/g respectively. 3 Tyramine concentrations were reduced to less than 20% of control values one day after a reserpine injection of 1 or 10 mg/kg. A single dose of reserpine (0.4 mg/kg) significantly decreased the content of both tyramines in the caudate nucleus. The effects became apparent as early as 45 min after drug case of m-tyramine. 4 The hypothalamic content of beta-phenylethylamine was unaffected by reserpine. 5 Ten days after an intraventricular injection of 6-hydroxydopamine (250 mug), p- and m-tyramine concentrations in the caudate nucleus were significantly below control levels. 6 The results suggest that p- and m-tyramine may be stored by an intraneuronal reserpine-sensitive storage mechanism. Alternatively, the tyramines may replace some of the catecholamines from their storage granules and then be released as false transmitters by the nervous impulse. The observed changes in tyramine levels might also the fact that these amines may be metabolically related to another amine which is stored in reserpine-sensitive granules.     

Effects of nicorandil on the membrane currents of rabbit sino-atrial node cells

The effects of nicorandil (SG-75) (3-500 micrograms/ml) on the membrane potential and currents of the rabbit sino-atrial node were studied using the voltage clamp technique. Low concentrations of nicorandil (3-10 micrograms/ml) increased the action potential duration (APD) and depolarized the maximum diastolic potential (DMP), but higher concentrations had no such effect and even decreased APD and tended to hyperpolarize MDP. Regardless of these effects, nicorandil decreased the heart rate concentration-dependently. On the current systems of the sino-atrial node, 3 micrograms/ml of nicorandil decreased the outward current (ik), but concentrations of over 10 micrograms/ml increased it. The voltage dependency of the steady-state activation of ik was unchanged. Nicorandil did not affect the inward current activated by hyperpolarization (Ih) and the slow inward current (is). These results suggest that the cardiac effects induced by nicorandil must have been produced by selective change in the conductance of ik.     

Chronotropic effects of angiotensin I,angiotensin II,bradykinin and vasopressin in guinea pig atria

Chronotropic responses to angiotensin I and angiotensin II, vasopressin and bradykinin were measured in guinea pig isolated right atria. Angiotensin II (100–30 000 pg/ml) was slightly more potent than angiotensin I and caused a maximum tachycardia of 30–40 b/min; only 20% of the maximum response to (?)-noradrenaline. Propranolol (1 μM) or reserpine pretreatment (1 mg/kg i.p., 24 h) did not alter the response to angiotensin II or bradykinin. Converting enzyme inhibition by captopril (10 μg/ml) did not affect resting rate nor the response to angiotensin II but shifted the location of the angiotensin I curve by 40 fold to the right. Bradykinin (5–500 ng/ml) caused small increases in rate while vasopressin 1–100 ng/ml was completely without effect. These results suggest that angiotensin II has a small positive chronotropic effect that is not dependent on tissue noradrenaline release or β-adrenoceptors and that tissue converting enzyme is active in right atria. Relatively high concentrations of angiotensin and bradykinin were required to directly stimulate the sino-atrial node compared with plasma levels measured during physiological stimuli. Therefore these effects on atria are probably of little physiological significance for peptide concentrations in plasma but may be important in relation to local tissue generation of angiotensin II.     

The response of isolated rabbit atria to aconitine

The arrhythmias observed in isolated rabbit atria appear to be due to two actions of aconitine. One is an apparent direct stimulant effect on the sino-atrial node and the other is a depressant effect on the processes involved in intra-atrial propagation of impulses. Acetylcholine has either an inhibitory or stimulatory effect on atria pretreated with aconitine because it antagonizes the actions of aconitine both on the sinus node and on conduction. When conduction block is not apparent, acetylcholine depresses the atrial rate. On the other hand, when conduction is markedly depressed, acetylcholine increases the atrial rate.