Effects of the muscarinic agonist McN-A-343 on responses to sympathetic nerve stimulation in the rabbit ear artery

Pharmacological analysis of functional neurovascular transmission in canine splenic arteries: role of neuropeptide Y

1 The effects of neuropeptide Y (NPY) upon the isolated vasculature are reviewed. 2 The vasconstrictor responses to periarterial nerve stimulation (PNS) and neurotransmission by noradrenaline (NA) and ATP are discussed and illustrated using canine isolated perfused splenic artery. 3 Modulation of the vascular responses to PNS by NPY via pre- and post-junctional NPY Y2 and Y1 receptors is discussed. 4 Evidence is presented for different alpha1-adrenoceptor subtypes mediating vasoconstriction to exogenous and endogenously released NA and their different locations in the neurovascular junction and extrajunctional regions. 5 Activation of NPY Y1-receptors potentiates sympathetic nerve activated alpha1-adrenoceptor vasoconstriction. The proposal that the postjunctional alpha1B adrenoceptor may be linked to the NPY Y1-receptor and is responsible for co-operation between sympathetic and NPYergic interactions in the vasculature is discussed.

Skin blood vessels are simultaneously innervated by sensory, sympathetic, and parasympathetic fibers

Despite the known major role of skin blood vessel innervation in blood flow control, particularly in disease, little information on the co-innervation of blood vessels by sensory and autonomic fibers and the relationships of these fibers to one another is available. To fill this gap, we performed a light and electron microscopic analysis of the innervation of skin vessels by sensory and autonomic fibers by using the rat and monkey lower lips as a model. In rats, double-labeling immunocytochemistry revealed that combinations of fibers immunoreactive for substance P (SP) and dopamine-beta-hydroxylase (DbetaH), SP and vesicular acetylcholine transporter (VAChT), as well as DbetaH and VAChT occurred only around blood vessels in the lower dermis. All fiber types travelled in parallel and in close proximity to one another. In the upper dermis, blood vessels were innervated by SP-containing fibers only. Although nerve terminals displayed synaptic vesicles, synaptic specializations were never observed, suggesting that, in this territory, these fibers do not establish synaptic contacts. Quantification of the distance between the various immunoreactive terminals and their presumptive targets (smooth muscle cells and endothelial cells) revealed that both sympathetic and parasympathetic fibers were significantly closer to the endothelial cell layer and smooth muscle cells compared with sensory fibers. In monkeys, double-labeling immunocytochemistry was performed for SP-DbetaH and SP-VAChT only. The results obtained are similar to those found in rats; however, the fiber density was greater in monkeys. Our findings suggest that the regulation of skin microcirculation might be the result of the coordinated functions of sensory and autonomic fibers.

Evidence for facilitatory and inhibitory muscarinic receptors on postganglionic sympathetic nerves in mouse isolated atria

1. McNeil A 343 (10 microM-30 microM) enhanced the fractional stimulation-induced (S-I) outflow of radioactivity from mouse isolated atria which had been incubated with [3H]-noradrenaline. The enhancing effect of McNeil A 343 was not altered by hexamethonium (300 microM) suggesting that it was not due to an action at nicotinic receptors. It is also unlikely that McNeil A 343 enhanced the S-I outflow of radioactivity in mouse atria by blocking neuronal reuptake of noradrenaline since the effect persisted in the presence of cocaine (30 microM). 2. The facilitatory effect of McNeil A 343 on the S-I outflow of radioactivity was attenuated by atropine (0.3 microM), pirenzepine (0.2 microM or 1.0 microM), dicyclomine (1.0 microM) and methoctramine (1.0 microM) and was thus due to activation of muscarinic receptors. 3. In contrast to the effect of McNeil A 343, another muscarinic receptor agonist, carbachol (3.0 microM) significantly decreased the S-I outflow of radioactivity. The receptors through which McNeil A 343 acts to enhance the S-I outflow of radioactivity appear to be distinct from inhibitory prejunctional muscarinic receptors. The relatively M 1-selective antagonist, pirenzepine (0.2 microM), attenuated the facilitatory effect of McNeil A 343 whereas a higher concentration (1.0 microM) was required to block the inhibitory effect of carbachol. Conversely, the relatively M2-selective antagonist, methoctramine (0.1 microM), blocked the inhibitory effect of carbachol but a higher concentration of methoctramine (1.0 microM) was required to block the facilitatory effects of McNeil A 343. These results tentatively ascribe facilitatory muscarinic receptors as belonging to the Ml subtype and inhibitory muscarinic receptors as belonging to the M2 subtype. 4. The non-selective muscarinic receptor antagonist, atropine, enhanced the S-I outflow of radioactivity, suggesting that there was tonic activation of inhibitory prejunctional muscarinic receptors by endogenous acetylcholine released from parasympathetic nerves. However, pirenzepine (0.03 pM-LO microM) did not decrease the S-I outflow of radioactivity, suggesting that under the conditions of the present study, facilitatory muscarinic receptors are not tonically activated by endogenous acetylcholine.

Muscarinic M1- and M2-receptors mediating opposite effects on neuromuscular transmission in rabbit vas deferens

Twitch contractions of the rabbit vas deferens elicited by electrical field stimulation were inhibited by tetrodotoxin, guanethidine, bretylium and alpha,beta-methylene-ATP but were unaffected by hexamethonium, physostigmine, 1,1-dimethyl-4-phenylpiperazinium and prazosin, suggesting that they resulted from ATP released following postganglionic sympathetic nerve stimulation. McN-A-343 inhibited but carbachol and several other muscarinic agonists potentiated the twitch contractions; these effects were not modified by hexamethonium or physostigmine. Muscarinic agonists had no effect on the tension in unstimulated organs whereas contractions elicited by ATP, noradrenaline and KCl were potentiated by carbachol but remained unaffected by McN-A-343. The responses of the twitch contractions to McN-A-343 and carbachol were inhibited to different degrees by antimuscarinic drugs: the affinity (pA2) of atropine, secoverine and himbacine against McN-A-343 and carbachol was similar. However, pirenzepine, telenzepine, trihexyphenidyl, dicyclomine and hexahydro-sila-difenidol displayed preferential antagonism of the responses to McN-A-343 whereas the converse was true for AF-DX 116 and gallamine. The highly significant correlation between the pA2 values obtained for 10 antagonists against carbachol responses in rabbit vas deferens and rat left atrium suggests that the receptors may be similar. The data support the presence of a presynaptic M1-receptor mediating inhibition and a postsynaptic, cardiac-like M2-receptor responsible for enhancing neurogenic contractions in rabbit vas deferens.

Interaction of some muscarinic agonists and antagonists at the prejunctional muscarinic receptor in the rabbit ear artery preparation

The inhibitory effect of several muscarinic agonists on responses to sympathetic nerve stimulation of the isolated perfused ear artery of the rabbit was compared to that of acetylcholine in preparations pretreated with dyflos, cocaine and yohimbine. In general the potency of the agonists was similar to that observed at peripheral muscarinic sites except for arecaidine propargyl ester and 4-(m-chlorophenylcarbamoyloxy)-2-butynyl trimethylammonium chloride (McN-A-343). The inhibitory effect observed with N-benzyl-3-pyrrolidyl acetate methobromide (AHR-602) was not exerted via muscarinic receptors. With carbachol (CCh) as an agonist, the antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) was found to have a pKB value of 7.74 and thus was 19 fold less active as an antagonist of responses to the agonist, than previously reported for guinea-pig ileum. When McN-A-343 was used as the agonist, the slope of the Schild plot with the antagonist was significantly less than unity. It is suggested that an allosteric interaction of 4-DAMP may be involved with this agonist. By use of an allosteric model, a pKB of 8.56 for 4-DAMP was obtained. Secoverine produced similar pKB values with either CCh (8.19) or McN-A-343 (8.13) as the agonist.

Different sensitivity of blocking effects of alpha-adrenoceptor blocking agents on vascular responses to intraluminal norepinephrine and periarterial stimulation in isolated dog arteries

The stainless steel cannula inserting method was used to examine the effects of periarterial electrical nerve stimulation and intraluminal norepinephrine in the isolated and perfused mesenteric artery of the dog. The optimum conditions for inducing an increase in perfusion pressure over 50 mmHg to periarterial electrical stimulation were 3-5 msec duration, 40-50 volts and 10-20 Hz. After the treatment with phentolamine or prazosin, the vasoconstrictor response to norepinephrine was readily inhibited completely at a relative small dose of 0.3-3 micrograms. Periarterial stimulation-induced vasoconstriction was also significantly suppressed by a relatively large dose of 100 micrograms of phentolamine or prazosin in concentrations 30 to 100 times larger than that required for blocking the norepinephrine-induced constriction. Yohimbine in relatively small doses potentiated the stimulation-induced vasoconstriction, but rather suppressed it in a large dose. The constrictor response to periarterial stimulation was significantly suppressed by 1 and 10 micrograms of intraluminal tetrodotoxin. It is concluded that periarterial electrical stimulation in the cannula inserting method is useful for studying autonomic pharmacology and physiology in vasculature with due regard to the characteristics.

The interaction of McN-A-343 with pirenzepine and other selective muscarine receptor antagonists at a prejunctional muscarine receptor

The effect of several muscarine receptor antagonists on responses to carbachol (CCh) and McN-A-343 (McN) were compared in the perfused rabbit ear artery preparation stimulated via noradrenergic nerves at 3 Hz in the presence of cocaine (10 microM) and yohimbine (1 microM). The slope of the dose-response curve to McN was significantly less (P less than 0.05) than that for CCh although both agonists produced up to 100% inhibition of responses to nervous stimulation. All the antagonists investigated produced parallel shifts of the dose-response curve to the agonists and atropine, fenipramide or stercuronium gave a similar pA2 value with either agonist. Pirenzepine was a competitive antagonist when CCh was used, as judged by a slope of 0.96 +/- 0.10 for the Arunlakshana-Schild (A-S) plot (pKB 6.2). Displacement of 3H-(-)QNB binding by pirenzepine gave a pKI value of 6.0 which was not significantly different to the pKB value. When McN was used as the agonist, the dose-ratios obtained with pirenzepine (0.5 microM) were significantly different (P less than 0.01) to those with CCh as agonist and the slope of the A-S plot over the concentration range of 0.1 to 3 microM was significantly less than 1.0 (P less than 0.01), indicating that the inhibition was not a simple competitive interaction. It is suggested that the interaction of McN and pirenzepine may involve an allosteric mechanism.

Dual effect of the muscarinic agonist McN-A-343 on vascular neuroeffector transmission

The site and mechanism of action of McN-A-343 (4-m-chlorophenylcarbamoyloxy)-2-butynyltrime-thylammonium chloride) on sympathetic neuroeffector transmission in the rabbit isolated pulmonary artery was studied. Low concentrations (10(-6) - 3 x 10(-5) M) of McN-A-343 and cocaine enhanced (up to 210 and 236%, respectively) the contractions evoked by electrical-field stimulation, while higher concentrations (10(-4) -3 x 10(-4)M) inhibited them. McN-A-343 (10(-4)M) caused an initial transitory potentiation (222% of control) of the stimulation-evoked contractions followed by an inhibition. In the presence of cocaine (3 x 10(-5)M), the potentiation caused by McN-A-343 was prolonged and the secondary inhibitory phase was thus abolished. Physostigmine (10(-5) - 10(-4)M), hexamethonium (10(-5) M), atropine (3 x 10(-7) M), suprofen (10(-5) M), and 4-aminopyridine did not alter the effect of McN-A-343 (1-(-4)M). Cocaine (3 x 10(-5)M) and (+)-amphetamine (10(-5) M) reversed the McN-A-343-evoked block, while they did not alter the inhibition caused by tetracaine (3.2 x 10(-5) M). Atropine (3 x 10(-7) M) had no effect on the McN-A-343-induced block, while 4-aminopyridine (10(-4) M) caused a partial and transitory reversal. On the aorta McN-A-343 (10(-4)M) did not alter the contractile concentration-response curve of (-)-noradrenaline (10(-9) - 3 x 10(-4)M), while that of serotonin (10(-8) - 3 x 10(-5)M) was moved to the right in a competitive manner. McN-A-343 (10(-4)M) did not alter the contractions evoked by noradrenaline (10(-7) M) during the period corresponding to the stimulation-evoked enhancement and subsequent inhibition. McN-A-343 (10(-4)M) slightly antagonized the contractions caused by tyramine (10(-6) - 10(-3) M) and carbachol (10(-6) - 10(-3) M). It is concluded that McN-A-343 enhances stimulation-evoked transmitter release by a presynaptic facilitatory action mediated via receptors localized on the outer surface of adrenergic neurones and to a lesser extent by inhibition of noradrenaline re-uptake. The enhancement does not involve presynaptic nicotine or muscarine receptors. Furthermore, McN-A-343 inhibits transmitter release by acting as an adrenergic neurone blocking agent at an intraneuronal site. The inhibition does not involve presynaptic muscarine inhibitory receptors and is prostaglandin-independent.

Effects of the muscarinic agonist McN-A-343 on the release by sympathetic nerve stimulation of (3H)-noradrenaline from rabbit isolated ear arteries and guinea-pig atria

1 McN-A-343 (4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride) in concentrations of 10(-5) and 10(-4)M inhibits the stimulation-induced efflux of radioactivity from segments of rabbit ear artery that have previously been incubated with (-)-[(3)H]-noradrenaline, and also decreases the contractile response.2 The inhibitory effects of McN-A-343 (10(-5)M) on the efflux of radioactivity and the contractions induced by low frequencies of stimulation (2 and 5 Hz) are reversed by atropine, but atropine does not modify these effects with high frequencies of stimulation (20 and 50 Hz).3 McN-A-343 (10(-4)M) enhances the stimulation-induced efflux of radioactivity from guinea-pig atria that have previously been incubated with (-)-[(3)H]-noradrenaline, and prolongs the positive inotropic response. These effects are not modified by atropine.4 It is concluded that McN-A-343 has different effects on adrenergic transmitter release in the two tissues. In the artery, it acts as an agonist on muscarinic receptors of adrenergic terminals to inhibit transmitter release at low frequencies of stimulation. In the atria it enhances transmitter efflux from the tissue, largely by inhibiting re-uptake.

Atropine-resistant effects of the muscarinic agonists McN-A-343 and AHR 602 on cardiac performance and the release of noradrenaline from sympathetic nerves of the perfused rabbit heart

1 The effects of 4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride (McN-A-343) and N-benzyl-3-pyrrolidyl acetate methobromide (AHR 602) on cardiac performance and noradrenaline release from terminal sympathetic fibres were measured in isolated perfused hearts of rabbits.2 In the presence of sufficient atropine to block muscarinic receptors, high concentrations of McN-A-343 and AHR 602 caused no cardiac stimulation and there was no increase in the resting output of noradrenaline into the perfusates.3 McN-A-343 and AHR 602 increased both the mechanical responses and the transmitter overflow evoked by electrical stimulation of the sympathetic nerves (SNS) but inhibited both parameters during perfusion with 1,1-dimethyl-4-phenylpiperazinium (DMPP). The effects were atropine-resistant and qualitatively similar to those seen with cocaine. Hexamethonium inhibited DMPP, but affected neither SNS per se nor the facilitatory effects of McN-A-343 and AHR 602 on SNS.4 McN-A-343, cocaine and desipramine (but not AHR 602 or hexamethonium) blocked the net cardiac noradrenaline uptake and increased the positive chronotropic effect of noradrenaline.5 Prior perfusion with concentrations of cocaine and desipramine sufficient to block uptake reduced or abolished the facilitatory effects of both McN-A-343 and AHR 602 on SNS.6 Cocaine, McN-A-343 and AHR 602 displayed local anaesthetic properties on the guinea-pig wheal and frog nerve plexus tests, and their relative potencies in this respect were similar to those for inhibition of DMPP-evoked transmitter overflow. Hexamethonium did not produce local anaesthesia.7 The results indicate that the facilitated release of noradrenaline after SNS and the inhibition of release after DMPP produced by McN-A-343 and AHR 602 are the result of their combined local anaesthetic action and inhibition of amine uptake.

Venous relaxation caused by acetylcholine acting on the sympathetic nerves

Experiments were performed to determine whether acetylcholine affects the sympathetic activation of the cutaneous veins of the dog. Changes in isometric tension of saphenous vein strips were recorded at 37°C in an organ bath. Addition of acetylcholine at 10 -11 to 10 -8 g/ml did not affect basal tension, but larger doses (5 x 10 -8 to 5 x 10 -7 g/ml) caused a contraction of the strips which varied from slight to marked. Acetylcholine at 10 -8 to 10 -7 g/ml caused a further increase in tension when it was added to strips already contracted by norepinephrine, tyramine, KCl, or BaCl 2 ; in contrast, similar doses of acetylcholine caused relaxation of strips contracted by liberation of norepinephrine from the nerve terminals by electrical stimulation (1-10 cps). This relaxation was not influenced by propranolol or hexamethonium but was abolished by atropine (10 -8 g/ml). In intact dogs, the lateral saphenous vein was perfused with autologous blood at constant flow. A sustained venoconstriction was induced either by electrical stimulation of the lumbar sympathetic chain or by a continuous infusion of norepinephrine. An infusion of acetylcholine (10 -7 to 10 -6 g/ml min -1 ) relaxed veins constricted by sympathetic stimulation but not those constricted by norepinephrine. Thus, acetylcholine, in doses smaller than those known to have a direct constrictor effect, causes relaxation of cutaneous veins, probably by inhibiting the release of norepinephrine from nerve terminals.

Comparison of effects of six cholinomimetic drugs on inhibition of uptake of 3 H-( )-noradrenaline by guinea-pig atria

The effects of N,N-dimethyl-N'-phenyl-piperazinium (DMPP), 4-(m-chlorophenyl-carbamoyloxy) - 2 - butynyltrimethylammonium chloride (McN-A-343), pilocarpine, acetylcholine, methacholi-ne and nicotine in inhibiting the uptake of (3)H-(+/-)-noradrenaline by guinea-pig atria were compared. In concentrations of 1 x 10(-4)M, the percentage inhibitions were as follows: DMPP, 89.1%; McN-A-343, 78.7%; pilocarpine 43.5%; acetylcholine, 35.7%; methacholine, 32.9%; nicotine, 21.6%.

Effects of several muscarinic agonists on cardiac performance and the release of noradrenaline from sympathetic nerves of the perfused rabbit heart

1. The effects of several muscarinic agonists on atrial tension development, ventricular rate and noradrenaline release from terminal sympathetic fibres evoked by electrical nerve stimulation (SNS) and 1,1-dimethyl-4-phenylpiperazinium (DMPP) were measured in isolated perfused rabbit hearts.2. Hexamethonium, in a concentration which almost abolished the release of noradrenaline by DMPP, had no effect on the release produced by SNS, confirming that the stimulation was postganglionic.3. The order of potency for inhibition of atrial tension development was N-methyl-1,2,5,6, tetrahydro-nicotinic acid prop-2-yne ester (MH-1)>oxotremorine > acetylcholine > methacholine > carbachol > furtrethonium > pilocarpine>4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride (McN-A-343)>N-benzyl-3-pyrrolidyl acetate methobromide (AHR 602). All effects were abolished by atropine (1.4 x 10(-6)M).4. Each compound was more potent relative to acetylcholine in inhibiting ventricular rate than atrial tension. With the exception of carbachol, the order of potency was the same.5. Both AHR 602 and McN-A-343 facilitated the release of noradrenaline by SNS and inhibited that by DMPP. The effects were atropine-resistant and hence non-muscarinic.6. The muscarinic compounds (except AHR 602 and McN-A-343) each produce atropine-sensitive inhibition of noradrenaline release evoked both by SNS and DMPP although it is likely that furtrethonium and pilocarpine have additional non-muscarinic inhibitory activity against DMPP. The order of potency on both parameters and the potencies relative to acetylcholine were in good agreement with those for inhibition of atrial tension.7. The results suggest that similar muscarinic receptors mediate inhibition of atrial tension development, ventricular rate and neuronal noradrenaline release caused by SNS and DMPP.8. In terms of the two muscarinic sites known to be present in the superior cervical ganglion, the receptors of the terminal fibres mediating inhibition of noradrenaline release are more likely to correspond to those mediating hyperpolarization than to those mediating depolarization, for which AHR 602 and McN-A-343 show specificity.

Effects of McN-A-343 and DMPP on the uptake and release of 3 H-noradrenaline by guinea-pig atria

1. McN-A-343 4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride and DMPP (N,N-dimethyl-N'-phenylpiperazinium iodide) inhibit the uptake of (+/-)-(3)H-noradrenaline by guinea-pig atria, being approximately as potent as cocaine in this respect.2. The inhibition of uptake produced by McN-A-343 or DMPP was not affected by atropine or hexamethonium in concentrations which antagonized actions on muscarinic and nicotinic receptors respectively.3. McN-A-343 in the presence of atropine had a positive inotropic action on atria, but this was not accompanied by efflux of radioactivity from atria previously incubated with (-)-(3)H-noradrenaline.4. In the presence of McN-A-343, responses of atria to noradrenaline were increased and those to tyramine were decreased.5. DMPP had positive inotropic and chronotropic actions on atria, and these effects were accompanied by an increase in efflux of radioactivity from atria previously incubated with (-)-(3)H-noradrenaline.