Upregulation of immunoreactive angiotensin II release and angiotensinogen mRNA expression by high-frequency preganglionic stimulation at the canine cardiac sympathetic ganglia.

The possible involvement of the local angiotensin system in ganglionic functions was investigated in the canine cardiac sympathetic ganglia. Positive chronotropic responses to preganglionic stellate stimulation at high frequencies, after intravenous administration of pentolinium plus atropine, were inhibited by the nonpeptide angiotensin AT(1) receptor antagonist forasartan or the angiotensin I-converting enzyme inhibitor captopril, whereas the rate increases elicited by the postganglionic stellate stimulation and norepinephrine given intravenously failed to be inhibited by these antagonists. The levels of endogenous immunoreactive angiotensin II, as determined by radioimmunoassay in the incubation medium of the stellate and inferior cervical ganglia, were increased after the high-frequency preganglionic stimulation of the isolated ganglia. The increment of the peptide was also antagonized by the pretreatment with captopril but not by a chymase inhibitor, chymostatin. The expression of angiotensinogen mRNA was observed in the stellate ganglion, adrenal, liver, and lung but not in the ovary and spleen. The expression of the mRNA in the stellate and inferior cervical ganglia increased after high-frequency preganglionic stimulation of the in vivo dogs for a period of 1 hour. These results indicate that an intrinsic angiotensin I-converting enzyme-dependent angiotensin system exists in the cardiac sympathetic ganglia, which is activated by high-frequency preganglionic stimulation.

Antagonism by gamma-aminobutyric acid of the stimulant effect of angiotensin II on cardiac sympathetic ganglia in spinal dogs.

The effects of angiotensin II and neuro-aminoacids administered through the right subclavian artery (i.a.) to the cardiac sympathetic ganglia were investigated in spinal dogs. Angiotensin II (1--8 micrograms) elicited a dose-dependent positive chronotropic effect which was reduced after i.a. injection of saralasin (100 micrograms). The effect of angiotensin II was not reduced after combined treatment with either hexamethonium (10 mg/kg) plus atropine (0.1 mg/kg) or hemicholinium-3 (5 mg/kg) plus preganglionic stimulation. The dose-dependent response to angiotensin II of heart rate was inhibited by GABA (50, 500 micrograms), GABOB (500 micrograms) and muscimol (50, 100 micrograms). The inhibition of the response to angiotensin II by a small dose of GABA (50 micrograms), but not by a high one (500 micrograms), was antagonized by i.a. injection of picrotoxin (2 mg). The positive chronotropism induced by bethanechol (25, 50 micrograms) and a small dose of acetylcholine (25 micrograms) were significantly inhibited by a high dose (500 micrograms) but not by a low dose (50 micrograms) of GABA. These results confirm that angiotensin II stimulates cardiac chronotropism by acting on the angiotensin II receptor located at the cardiac ganglia and show that this stimulant effect is antagonized by GABA.

Possible inhibitory role of endogenous gamma-aminobutyric acid in the nonnicotinic functions of the dog cardiac sympathetic ganglia.

Participation of endogenous gamma-aminobutyric acid (GABA) in the functions of dog cardiac ganglia was investigated. The ganglionic stimulants as well as agents affecting GABA system were given directly into the cardiac sympathetic ganglia through the right subclavian artery (i.a.), unless otherwise mentioned. Inhibition of endogenous GABA degradation by the GABA-transaminase inhibitor, aminooxyacetic acid (AOAA) administered 10 mg/kg i.v. 2 hr before completion of surgical procedures did not alter the positive chronotropic responses to bethanecol (25 and 50 micrograms) and acetylcholine (25, 50 and 100 micrograms) but reduced markedly those to angiotensin II (1 and 2 micrograms). This reduction was antagonized by picrotoxin (5 mg). Diazepam given 10 mg/kg i.v. also inhibited the ganglionic responses to angiotensin II in both untreated and AOAA-pretreated dogs, this inhibition by diazepam being more marked in the AOAA-pretreated than in the untreated dogs. The same dose of diazepam did not affect the responses to acetylcholine but reduced to a certain degree of responses to bethanechol in the AOAA-pretreated dogs. These inhibitions by diazepam were also reversed by picrotoxin. After i.v. treatment with the glutamic acid decarboxylase inhibitors, 3-mercaptopropionic acid (50 mg/kg) or isoniazid (200 mg/kg), the ganglionic responses to angiotensin II were not altered, but inhibitory effects of diazepam on the responses to angiotensin II were eliminated after 3-mercaptopropionic acid but not after isoniazid. These results suggest that endogenous GABA may play an inhibitory role in the nonnicotinic ganglionic pathways and that diazepam probably exerts a ganglionic action through endogenous GABAergic mechanisms.

[Effects of CN-100 (2-(10,11-dihydro-10-oxodibenzo [b,f] thiepin-2-yl) propionic acid) on cardiovascular and autonomic nervous function in the dog and guinea pig].

1) In pentobarbital-anesthetized dogs, intravenous administration of CN-100 at 40 mg/kg exhibited a transient hypotension, accompanied with a slight respiratory excitation and a temporal increase of heart rate followed by slight and gradual decrease at 20 and 40 mg/kg. 2) In isolated guinea pig atria, CN-100 (10(-4), 10(-5) g/ml) decreased the heart rate, without influencing the myocardial contraction. 3) In anesthetized dogs, the vertebral and carotid blood flow slightly and gradually increased at 5-20 mg/kg and decreased at 40 mg/kg. The drug at 20 mg/kg similarly increased the femoral flow. 4) In anesthetized dogs, CN-100 (40 mg/kg) slightly potentiated hypertensive responses to noradrenaline and adrenaline, without affecting heart rate responses to these amines. 5) In anesthetized dogs, CN-100 (40 mg/kg) scarcely had effect on the blood pressure rise and bradycardia induced by respective proximal and distal end stimulation of the severed vagus nerve, but enhanced the hypertension due to the carotid sinus reflex. CN-100 augmented the tachycardia elicited by pre- and postganglionic stellate stimulation in spinal dogs. 6) In isolated guinea pig trachea muscle, CN-100 (3 x 10(-6) g/ml) reduced the resting tone and relaxation response to noradrenaline, but slightly enhanced contractile responses to field stimulation and acetylcholine. 7) These results suggest that CN-100 exerts weak cardiovascular and autonomic nervous actions.

Effects of brovincamine on the autonomic nervous function in the dog and rat.

Effects of brovincamine (BV) on peripheral nerves were studied in dogs and rats. 1) In pentobarbital-anesthetized dogs, BV (6.4 mg/kg) administered i.v. did not affect the changes of blood pressure and heart rate induced by noradrenaline and adrenaline, but slightly inhibited the hypotensive effect of acetylcholine. BV had no effect on the hypertension elicited by carotid sinus reflex, but diminished the bradycardia by vagus nerve stimulation. BV did not influence the tachycardia elicited by stimulation of the postganglionic nerve to stellate ganglion, but slightly inhibited that by the preganglionic stimulation. 2) In spinal dogs, BV (6.4 mg/kg) given i.v. slightly inhibited the increases of blood pressure and heart rate induced by i.v. dimethylphenylpiperazinium (DMPP). When i.v. administered in divided doses of 2 and 4 mg/kg, BV induced a slight but stepwise inhibition of the tachycardia elicited by direct administration of DMPP, bethanechol (BCH) and angiotension II (AT II) to the cardiac sympathetic ganglia via the subclavian artery. 3) In rat isolated diaphragm nerve preparations, BV at 10(-5) and 10(-4) g/ml dose-dependently reduced the twitch response to nerve stimulation. 4) In conclusion, BV does not affect the sympathetic activities but inhibits the cholinergic function in the autonomic nervous system.

In vivo direct effects of cholinergic agents on the inferior mesenteric and cardiac ganglia with relation to their receptors in the dog.

The relative contribution of nicotinic and muscarinic receptors to the cholinergic transmission of the inferior mesenteric ganglion was studied in spinal dogs by recording changes in perfusion pressure of the inferior mesenteric artery as an indicator of ganglionic function. Preganglionic stimulation elicited a frequency (2.5--320 Hz)-dependent rise in the perfusion pressure, which was inhibited by i.v. hexamethonium (C6) (10 mg/kg) or atropine (0.1 mg/kg) administered after C6. Acetylcholine (ACh) (0.1--1000 microgram) administered into the inferior mesenteric artery to reach the mesenteric ganglion induced a dose-dependent rise in perfusion pressure and this dose-response curve was shifted to the right by C6 or atropine. Bethanechol (1--1000 microgram) i.a. produced a dose-dependent rise in the pressure, which was abolished after i.v. atropine. Tetramethylammonium (1--300 microgram) i.a. elicited an increase in the pressure thought the effects were decreased at larger doses, and these effects were strongly inhibited by i.v. C6. ACh (5--100 microgram) administered into the right subclavian artery to reach the cardiac sympathetic ganglia caused a dose-dependent positive chronotropic effect, which was inhibited by i.a. C6 or atropine. The results suggest that the inferior mesenteric ganglion seems to differ from the cardiac ganglia in relative contribution of nicotinic and muscarinic receptors to the cholinergic transmission.

Negative chronotropic effect of catecholamines on adrenergic receptors in cardiac ganglia in the spinal dog.

The effects of catecholamines (CAs) on cardiac chronotropism were investigated in the spinal dog. The CAs were administered through the right subclavian artery (i.a.) to reach the cardiac sympathetic ganglia. Without preganglionic stimulation. CAs administered intra-arterially induced a slight negative chronotropic effect, which was reversed to a positive chronotropic effect after neostigmine (200 microgram, i.a.) in many cases. With preganglionic stimulation, intra-arterial injection of norepinephrine (0.5-25 microgram), epinephrine (0.1-10 microgram), or dopamine (0.1-500 microgram) caused dose-dependent bradycardia. The negative chronotropic effect of dopamine was significantly inhibited intra-arterial phentolamine (2 mg), dihydroergotamine (0.4 mg), apomorphine (0.5 mg), haloperidol (0.5 mg), or chlorpromazine (5 mg) but not by propranolol (0.1 mg) or bulbocapnine (1 mg), whereas the same effect of epinephrine was significantly reduced by alpha-blockade but not by propranolol or the dopamine antagonists. These results suggest that CAs exert a negative chronotropic action by inhibiting cardiac ganglionic transmission and that the receptors for dopamine are alpha-adrenergic and dopamine-specific and those for epinephrine are alpha-adrenergic specific.

Presynaptic facilitation by the new nootropic drug nebracetam, of ganglionic muscarinic transmission in the dog cardiac sympathetic ganglion.

Effects of nebracetam (4-aminomethyl-1-benzylpyrrolidine-2-one hemifumarate, WEB 1881 FU, CAS 118607-07-1), a new nootropic drug, on impulse transmission in the cardiac sympathetic ganglia were studied in spinal dogs by monitoring heart rate as an indicator of the ganglionic function. The ganglionic stimulants were given directly into the cardiac sympathetic ganglia through the right subclavian artery (i.a.). Nebracetam, 5 mg/kg, i.v. caused a slight and temporal increase in heart rate. After nebracetam, the frequency-response curves of heart rate for preganglionic stellate stimulation (0.25-4 Hz) were not altered in the untreated and atropine-pretreated animals, but the curves (2.5-40 Hz) were shifted to the left in the hexamethonium-pretreated animals. The enhancement of ganglionic muscarinic transmission was dose-dependent on nebracetam i.v. at doses ranging from 0.5 to 15 mg/kg, with a maximal effect at 5 mg/kg. This enhanced muscarinic transmission by nebracetam was almost abolished after subsequent administration of pirenzepine 0.5 mg/kg i.v. The enhancement in the muscarinic transmission by nebracetam was also eliminated after depletion of acetylcholine at preganglionic sites caused by treatment with hemicholinium-3 in combination with preganglionic stimulation. Furthermore, nebracetam failed to affect dose-dependent post-ganglionic stimulation by McN-A-343 (1-32 micrograms), 1,1-dimethyl-4-phenylpiperazinium (1-32 micrograms) and angiotensin II (0.1 and 0.2 micrograms) administered i.a. directly to the ganglia. These results suggest that nebracetam facilitates the ganglionic muscarinic transmission through acting on presynaptic sites.

Activation of endogenous thromboxane A2 biosynthesis mediates presynaptic inhibition by endothelin-3 of dog stellate ganglionic transmission.

Effects of endothelin-3 on ganglionic transmission were investigated in dog cardiac sympathetic ganglia. Positive chronotropic responses to preganglionic stellate stimulation were inhibited by endothelin-3 (0.5-2 micrograms) given directly to the ganglia through the artery. To find possible inhibitory effects of the peptide at presynaptic sites, acetylcholine released from the isolated stellate ganglia was determined. The amount of acetylcholine released during preganglionic stimulation was reduced by exposure to endothelin-3 (10(-9) to 10(-6) M). A similar reduction of acetylcholine release was observed after application of a stable thromboxane A2, a thromboxane A2/prostaglandin H2 receptor agonist, U-46619, and prostaglandin E2 at concentrations from 10(-8) to 10(-4) M, but not by the same concentrations of prostaglandins F2 alpha and I2. The reduction elicited by endothelin-3 was unaffected by a phospholipase C inhibitor, neomycin, or a protein kinase C inhibitor, H-7, but was antagonized by pretreatment with phospholipase A2 inhibitors, dexamethasone or methylprednisolone, and by cyclooxygenase inhibitors, aspirin and indomethacin. In addition, the reduction also was antagonized by pretreatment with a thromboxane A2 synthetase inhibitor, OKY-046, and a specific thromboxane A2 receptor antagonist, S-145, but not by a specific prostaglandin E2 receptor antagonist, SC-19220. Furthermore, endothelin-3 (10(-7) M) stimulated the OKY-046- and indomethacin-sensitive formation of thromboxane A2 in the ganglia. These results indicate that endothelin-3 inhibits the sympathetic ganglionic transmission by reducing acetylcholine release at preganglionic terminals and that this inhibition seems to involve activation of endogenous thromboxane A2 production.

Ionotropic mechanisms involved in postsynaptic inhibition by the endothelins of ganglionic transmission in dog cardiac sympathetic ganglia.

We investigated the effects of endothelin-1 and endothelin-3 (ET-1, ET-3) on the ganglionic transmission of cardiac sympathetic ganglia in vivo by the direct administration of agents to the ganglia through the right subclavian artery while monitoring the heart rate (HR) as an indicator of the ganglionic function in spinal dogs. The positive chronotropic responses to dimethylphenylpiperazinium (DMPP) and McN-A-343 administered to the ganglia were similarly inhibited by ET-1 (0.05-0.2 microg) and ET-3 (0.5-2 microg), but ET-1 was approximately 10 times more potent than ET-3. The inhibition induced by ETs was antagonized by endothelin ETA receptor antagonist BQ-123 (20 microg). This inhibition was unaffected by pretreatment with indomethacin given intravenously (i.v.), ruling out the possible involvement of endogenous prostaglandins production. The voltage-sensitive Ca2+ channel antagonist nifedipine had no effect on inhibition. However, the inhibition was antagonized by pretreatment with the low conductance Ca2+-activated potassium channel antagonists, such as apamin (20 microg intraarterially, i.a.), scyllatoxin (10 mug i.a.) and D-tubocurarine (0.6 mg i.a.). On the other hand, the voltage-sensitive K+ channel antagonist 4-aminopyridine (4-AP), ATP-dependent K+ channel antagonist, glibenclamide, and high-conductance Ca2+-activated K+ channel antagonists iberiotoxin and charybdotoxin failed to affect the inhibition by ETs. The results suggest that ETs inhibit the nicotinic and muscarinic ganglionic transmission through the ETA receptor-operated low-conductance Ca2+-activated potassium channel at postganglionic sites.

Increment of calmodulin in proportion to enhancement of non-nicotinic responses after preganglionic stimulation of the dog cardiac sympathetic ganglia.

The possible involvement of calmodulin in ganglionic function was investigated. Drugs were given directly into the cardiac sympathetic ganglia through the right subclavian artery (i.a.), unless otherwise stated. Positive chronotropic responses to angiotensin II (0.1 and 0.2 micrograms) were enhanced after repetitive high frequency preganglionic stimulation to the right stellate ganglion. After the stimulation, positive chronotropic responses to bethanechol (2.5, 5 and 10 micrograms), but not those to dimethylphenylpiperazinium (2.5, 5 and 10 micrograms), also were enhanced. The enhancement of response to angiotensin II was not affected by i.v. pretreatment with hexamethonium (40 mg/kg) plus atropine (1 mg/kg) or nifedipine (1 mg/kg). Responses to angiotensin II were not enhanced by A23187 (0.3 mg). The enhanced response to angiotensin II after the stimulation was reduced by the calmodulin antagonists, trifluoperazine (0.1, 0.2 and 0.4 mg) and by N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (0.5, 1 and 2 mg), but not by promethazine (1 mg) and N-(6-aminohexyl)-1-naphthalenesulfonamide (0.5, 1 and 2 mg). The enhanced response to bethanechol after the stimulation also was inhibited by N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide. Pretreatment with N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide before the stimulation prevented development of the enhancement in responses to the peptide. The inhibition of endogenous protein synthesis by cycloheximide, 2.5 or 5 mg/kg i.v. 6 hr before surgical procedures, strongly inhibited development of the enhancement in responses to angiotensin II.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of brotizolam on cardiovascular functions and autonomic nervous system.

The effects of brotizolam (2-bromo-4-(2-chlorophenyl)-9-methyl-6H-thieno(3,2-fl-1,2,4-triazolo [4,3-a]-1,4-diazepine, We 941, Lendormin), a new thieno-triazolo-diazepine, on the heart, hemodynamic functions and the autonomic nervous system were investigated in rats, guinea pigs, rabbits, cats and dogs: In pentobarbital anesthetized dogs, 1 or 5 mg/kg brotizolam administered intravenously, decreased heart rate, with a frequency-dependent prolongation of the intervals and heightening of the T-waves in the electrocardiogram, depressed respiration, whereas the blood pressure was unaffected. In urethane anesthetized rabbits, 5 or 10 mg/kg brotizolam intravenously had almost no distinct effect on blood pressure and heart rate, though it slightly decreased respiratory rate at 10 mg/kg. In nonanesthetized rabbits, brotizolam exerted similar actions on respiration, blood pressure and heart rate. In isolated guinea pig atria, 1-10 mg/l brotizolam did not show noticeable effects on contractile force but decreased slightly the pulse rate. In pentobarbital anesthetized dogs, vertebral and carotid blood flow remained almost unchanged after 0.05 mg/kg brotizolam intravenously, but were increased following 0.5 mg/kg. Cardiac output and coronary flow were not changed by 0.5 mg/kg brotizolam but slightly decreased accompanied by a decrease in blood pressure and heart rate by 1 mg/kg. Femoral flow was not affected by 0.5 or 1 mg/kg. After 5 mg/kg brotizolam given intravenously in dogs, the pressor effect of epinephrine was significantly enhanced and the positive chronotropic effect increased to a certain degree. Both effects of norepinephrine also tended to be enhanced.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of brotizolam on smooth muscle and other organs.

Effects of brotizolam (2-bromo-4-(2-chlorophenyl)-9-methyl-6H-thieno[3,2-f]-1,2,4-triazolo [4,3-a]-1,4-diazepine, We 941, Lendormin) on smooth muscle and other biological systems were examined. In isolated intestinal preparations, brotizolam in higher concentrations shifted the concentration-contractile response curve after addition of acetylcholine down to the right. However, brotizolam did not affect the intestinal transport. Therefore, even if brotizolam possesses a non-specific inhibitory action on smooth muscle, it would be quite weak. Brotizolam, nitrazepam and estazolam in high doses showed a miotic action. Brotizolam had no effect on the digestive system, that is, gastric secretion, bile secretion and intestinal propulsive activity were not influenced. A depression of salivary secretion, which may be due to an additive action of Eidelberg's mixture, was observed. Brotizolam, nitrazepam and estazolam enhanced the sleeping time induced by ethanol and increased locomotor activity induced by methamphetamine, but did not affect the chewing behavior. There was no indication that continuous administration of brotizolam affected significantly the levels of lipids and sugar in the blood serum.

Cardiovascular effects of 1-(3,4-dimethoxyphenyl)-2-(4-diphenylmethylpiperazinyl) ethanol and possible mechanisms involved.

Cardiovascular effects of NC-1100 (1-(3,4-dimethoxyphenyl)-2-(4-diphenylmethylpiperazinyl)ethanol and possible modes of action were studied in dogs and guinea pigs. 1. In pentobarbital-anesthetized dogs, intravenous administration of NC-1100 (0.05-1.6 mg/kg) induced a dose-dependent fall of blood pressure, a bradycardia followed by temporal tachycardia, a slight and transient stimulation of respiration and a prolongation of the R-R interval with slight augmentations of P, R and T waves in ECG. 2. In pentobarbital-anesthetized dogs, NC-1100 (2.5-80 micrograms/kg) administered to the maxillary and vertebral artery dose-dependently increased the blood flow in the respective artery. 3. Intravenous administration of NC-1100 (0.05-1.6 mg/kg) also exhibited dose-dependent increases of the maxillary and vertebral blood flow, though the increase in maxillary flow was a little reduced at a high dose of 1.6 mg/kg. Intravenous administration of NC-1100 (0.1-1.6 mg/kg) caused a slight increase in the aortic and coronary blood flow, a decrease in renal flow and a slight and transient decrease followed by an increase in femoral flow. 4. In pentobarbital-anesthetized dogs, NC-1100 (1 mg/kg) administered i.v. did not affect responses of blood pressure and heart rate to norepinephrine and isoprenaline (isoproterenol) but slightly inhibited hypotensive responses to acetylcholine. NC-1100 had no effect on hypertension elicited by carotid sinus reflex and on bradycardia by vagus stimulation. NC-1100 slightly inhibited the tachycardia elicited by pre- as well as postganglionic stellate stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

The inhibition of ganglionic transmission via presynaptic dopamine DA1 and postsynaptic DA2 receptor activation in the canine cardiac sympathetic ganglia.

The involvement of dopaminergic mechanisms in modulating ganglionic transmission of the dog cardiac sympathetic ganglia were investigated in both in vivo and in vitro experiments. The positive chronotropic responses to preganglionic stellate stimulation were inhibited by R(+)SK&F38393 and talipexole administered directly to the ganglia through the artery, and the inhibitory effects were antagonized by pretreatment with R(+)SCH23390 and S(-)sulpiride, respectively. McN-A-343 and 1,1-dimethyl-4-phenylpiperazinium iodide given through the artery to reach the ganglia displayed dose-dependent positive chronotropic effects. The positive chronotropic effects were inhibited by (-)quinpirole and talipexole, but not by R(+)SK&F38393. The inhibitions were antagonized by S(-)sulpiride and tended to be antagonized by yohimbine. The acetylcholine output from the isolated stellate ganglia by preganglionic stimulation (5 Hz) was unaffected in the presence of (-)quinpirole and talipexole, but was concentration-dependently reduced in the presence of R(+)SK&F38393, and the reduction was antagonized by R(+)SCH23390. The results thus suggest that the dopamine receptor agonists inhibit the ganglionic transmission by reducting acetylcholine release via preganglionic DA1 receptor stimulation and by inhibiting postganglionic nicotinic and muscarinic activation via postganglionic DA2 receptor stimulation.

Increase of acetylcholine release by nebracetam in dog cardiac sympathetic ganglion.

The effects of nebracetam (4-aminomethyl-1-benzylpyrrolidine-2-one hemifumarate, WEB 1881FU), a potential cognitive enhancer, on acetylcholine release from the preganglionic nerve terminals were investigated in the isolated dog stellate ganglia. Acetylcholine release from the isolated ganglia by preganglionic stimulation (5 Hz) was enhanced in the presence of nebracetam, 10(-7) to 10(-5) M. The release was decreased to a certain extent by bethanechol, 10(-5) M, and this decrease was completely antagonized by AFDX-116 (10(-5) M), a selective M2 muscarinic antagonist, but was unaffected by nebracetam (10(-6) M). Under the depleted condition of acetylcholine induced by pretreatment with hemicholinium-3 (10(-5) M) in combination with prolonged preganglionic stimulation, the release was increased to a degree by nebracetam or choline alone and was markedly increased in the presence of both nebracetam and choline. Nebracetam did not directly act on choline acetyltransferase activity, but acetylcholine formation was stimulated in the isolated ganglion incubated with the agent at 10(-6) M and in the ganglion isolated from the dog to which nebracetam, 5 mg/kg, was previously administered i.v. Uptake of choline in the isolated ganglia was not altered by nebracetam (10(-6) M) but was enhanced under the depleted conditions. These findings suggest that nebracetam enhances acetylcholine release from presynaptic sites of dog stellate ganglia not by blocking presynaptic M2 muscarinic autoreceptors but by accelerating acetylcholine formation, and by increasing choline uptake when acetylcholine is depleted.

Contribution of nitric oxide to the presynaptic inhibition by endothelin ETB receptor of the canine stellate ganglionic transmission.

We previously reported that endothelin (ET) 3 inhibited presynaptically the dog stellate ganglionic transmission. Here, we report the investigation of the possible involvement of nitric oxide pathway in the endothelin-induced inhibition of the ganglionic transmission. The amount of acetylcholine released by preganglionic stimulation for 10 min was concentration-dependently inhibited after exposure to ET-3 (10(-9)-10(-6) M) or IRL-1620, endothelin ET(B) receptor agonist (10(-8)-10(-5) M). The inhibition was antagonized by pretreatment with a nonselective endothelin receptors antagonist (bosentan) and an ET(B) receptor antagonist (BQ-788) or a neuronal nitric oxide synthase inhibitor, 3-bromo-7-nitroindazole, but was not inhibited by a selective ET(A) receptor antagonist, BQ-123. The reduction induced by ET-3 was also antagonized by treatment with a selective inhibitor of soluble guanylyl cyclase, 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalin-1-one. In addition, similar reductions were also mimicked by exposure to cGMP analog, 8-bromoguanosine-3, 5-cyclic monophosphate and nitric oxide donor, S-nitroso-N-acetylpenicillamine. Exposure to ET-3 or IRL-1620 for a 30-min period increased the levels of total nitric oxide (NO), nitrite plus nitrate NO(x) concentration in the incubation medium, with the increase in NO(x) also being antagonized by BQ-788 at the same concentration. The ET-3-induced increase in NO(x) was antagonized by treatment with the same concentration of 3-bromo-7-nitroindazole or a selective inhibitor of receptor-mediated Ca(2+) entry, 1-[b-[3-(4-methoxyphenyl) propoxy]-4-methoxyphenethyl]-1H-imidazole (10(-5) M), and with a calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide. These results indicate that ET(B) receptor activation inhibits the sympathetic ganglionic transmission via reducing acetylcholine release from presynaptic nerve terminals, although this inhibition also seems to involve the ET(B) receptor-operated Ca(2+)-calmodulin-dependent activation of endogenous nitric oxide production.

[Effect of a new bronchodilator, S-1540 (Bitolterol) and S-1541 on the tracheo-bronchial and cardiovascular system].

The actions on the bronchial smooth muscle and cardiovascular system S-1540 (Bitolterol) (Shionogi Pharmaceuticals), a new bronchodilator which is chemically related to isoprenaline, and S-1541 which is the active metabolite of S-1540 were studied in comparison with the action of isoprenaline (isoproterenol) and orciprenaline (metaproterenol). 1) The relaxing effect on isolated guinea-pig tracheal muscle constricted previously with histamine BaCl2 or acetylcholine was highest with S-1541, followed by isoprenaline and orciprenaline, in that order, and lowest with S-1540. The relaxing effect of S-1541 on acetylcholine-induced tracheal constriction was reduced and that of S-1540 was completely abolished by a previous treatment with propranolol. The relaxing actions of those drugs on bronchial spasms induced by histamine in vivo were highest with S-1541, followed by isoprenaline, and lowest with S-1540. 2) All these drugs exhibited the depressor and positive chronotropic actions in guinea-pigs. The potencies of the actions were found to be in the following order; isoprenaline was most potent, followed by S-1541 with a little less intensity, orciprenaline much weaker, and S-1540 still weaker with a positive chronotropic action of about 1/1000 of S-1541 and depressor action about 1/500. In the open chest guinea-pig, positive inotropic and chronotropic actions of S-1541 were about the same or slightly more potent than those of isoprenaline; S-1540 had a very weak action, being only about 1/1000 as active as S-1541. These actions of S-1540 were completely eliminated by propranolol pretreatment. S-1540 induced to remarkable changes in the electrocardiogram wave forms even in high doses. 3) Those drugs elicited the depressor, positive chronotropic and inotropic actions in rabbits and dogs. In rabbits, isoprenaline was most potent; S-1541 was similar to or a little weaker than isoprenaline; and S-1540 was extremely weak. In the dog, isoprenaline showed the highest of the above effect, followed by S-1541, orciprenaline and S-1540 in that order, with S-1540 having an extremely low activity. 4) The actions of S-1541 and isoprenaline appeared very rapidly but were of short duration, the duration of orciprenaline was moderate, and the actions of S-1540 rapidly appeared and were of an extremely long duration. It is suggested that S-1540 itself has pharmacological activities in vivo and the active metabolites such as S-1541 also have the activities. S-1540 can be administered by the oral route, is of long duration, and is thus considered to be a bronchodilator with a relative high specificity.