Presence Of Guanethidine Research Articles

Vagally mediated gastric motor and emetic reflexes evoked by stimulation of the antral mucosa in anaesthetized ferrets.

1. In the urethane-anaesthetized ferret chemical (NaCl, NaOH or HCl) or mechanical (stroking) stimulation of the gastric antral mucosa evoked a decrease in corpus pressure and inhibition of contractions in the presence of guanethidine, adrenalectomy and sectioned greater splanchnic nerves. 2. The fall in corpus pressure was present following administration of atropine but was abolished by vagotomy. 3. Preliminary evidence, using 100 mM-NaOH as the stimulus, is presented that the effects on corpus motility are due to simultaneous activation of the vagal efferents supplying the intramural non-adrenergic non-cholinergic inhibitory neurones and inhibition of those supplying the intramural cholinergic neurones. 4. The possible roles of this antro-corpus vago-vagal reflex in the regulation of gastric emptying and in the prodromal phase of vomiting are discussed.

The effect of reserpine on sympathetic, purinergic neurotransmission in the isolated mesenteric artery of the dog: a pharmacological study.

Electrical transmural stimulation evoked a transient contraction in the isolated mesenteric artery of the dog. This contraction was abolished by guanethidine or tetrodotoxin and was partially inhibited by prazosin. Noradrenaline was competitively antagonized by prazosin. Similarly, in the reserpine-treated artery, electrical transmural stimulation produced a transient contraction which was abolished by guanethidine or tetrodotoxin. However, prazosin failed to inhibit this contraction. The contraction to noradrenaline was not significantly different from the response it produced in control vessels. Tyramine (10(-5) M), which acts on sympathetic nerves to release noradrenaline, evoked a tonic contraction in the untreated artery. This contraction was abolished or markedly attenuated by prazosin or guanethidine. The response was not observed in the reserpine-treated artery, indicating that reserpine had depleted the nerves of noradrenaline. In the control vessel alpha,beta-methylene-ATP produced a transient contraction which was followed by a complete relaxation to the basal level. This contractile response was not significantly different in the presence of guanethidine or prazosin or in the reserpine-treated artery. After desensitization of the vessel to alpha,beta-methylene ATP (5 X 10(-6) M) the prazosin-resistant contractions induced by electrical transmural stimulation were abolished both in reserpine-treated and untreated arteries. Also the contractile responses to ATP and alpha-beta-methylene-ATP were abolished but the responses to tyramine (control vessels), noradrenaline and KCl were not affected. 8-Phenyltheophylline (10(-5) M) showed no inhibitory effect on the contractile responses to electrical transmural stimulation, tyramine, ATP or alpha,beta-methylene-ATP. 7. Neuropeptide Y, peptide YY, vasoactive intestinal polypeptide, bombesin and substance P (10-7 and 10-6 M for each peptide) caused no contractile response in the dog mesenteric artery. 8. These experiments provide further evidence that the sympathetic contraction of the isolated mesenteric artery of the dog induced by electrical transmural stimulation consists ofan adrenergic and a purinergic component and that the latter component is mediated through postsynaptic P2- purinoceptors.

Autonomic innervation of the canine penile artery and vein in relation to neural mechanisms involved in erection.

Neural control of the penile artery and vein of dogs was investigated using isometric tension recording and microelectrode methods. Field stimulation evoked twitch-like contractions of these two vessels and these contractions were blocked by guanethidine. In the artery, twitch-like contractions were more effectively blocked by yohimbine than by prazosin. During high tone of arterial and venous tissues evoked by noradrenaline (NA) in the presence of guanethidine, field stimulation evoked muscle relaxation that was not affected by atropine but was abolished by tetrodotoxin. In parallel to the mechanical responses, field stimulation evoked excitatory junction potentials (EJPs) in both arterial and venous smooth muscle cells. In the case of the artery, an action potential was superimposed on the EJP. The NA-induced contraction was suppressed by vasoactive intestinal polypeptide (VIP), dose-dependently. On the other hand, alpha, beta-methylene-ATP did not affect the muscle relaxation induced by field stimulation. These results indicate that the penile artery and vein of the dog are innervated by adrenergic excitatory nerves and non-adrenergic, non-cholinergic inhibitory nerves. The transmitter possibly involved in the latter is discussed.

Distribution and properties of excitatory and inhibitory junction potentials in circular muscle of the guinea-pig stomach.

In the presence of guanethidine (10(-6)-5 X 10(-6) M), transmural nerve stimulation evoked an excitatory junction potential (e.j.p.) in the fundus region and an inhibitory junction potential (i.j.p.) in the antrum region of the circular muscle of the guinea-pig stomach. The e.j.p. was blocked by atropine (over 2 X 10(-7) M) while the i.j.p. was blocked by apamin (10(-7) M) but not by adrenergic or cholinergic receptor antagonists. Therefore the i.j.p. may be non-adrenergic and non-cholinergic in nature. In the presence of atropine, nerve stimulation evoked the non-adrenergic, non-cholinergic i.j.p. in both regions of the stomach. In the antrum region, single stimuli enhanced the subsequent slow wave by 1.1-1.3 times, in comparison with that before the stimuli, and this effect was blocked by atropine (over 2 X 10(-7) M). The reversal potential for the e.j.p. was about -18 mV, while that for the i.j.p. was -87 mV in the atropinized fundus and -89 mV in the antrum region. In the fundus region, a pair of nerve stimulations with short intervals (1-4 s) reduced (depression) and with long intervals (5-20 s) enhanced (facilitation) the second e.j.p. or the i.j.p. After inhibition of acetylcholine esterase (AChE) by physostigmine or neostigmine, nerve stimulation evoked an enhanced e.j.p., and then produced a sustained depolarization with a duration of 3-5 s in the fundus region, while the amplitude of slow waves after nerve stimulation was further enhanced in the antrum region. These effects of anticholinesterases were blocked by atropine. Exogenously applied acetylcholine (ACh) depolarized the smooth muscle membrane; the threshold concentration of ACh was about 1000 times higher in the antrum region (10(-6) M) than in the fundus region (10(-9) M). It is concluded that in the guinea-pig stomach, regional differences in junction potentials may be due to different sensitivities of ACh receptor, and that nerve stimulation evokes a cholinergic e.j.p. in a high-sensitivity region (fundus) and a non-adrenergic, non-cholinergic i.j.p. in a low-sensitivity region (antrum).

POSSIBLE INVOLVEMENT OF SUBSTANCE P IN THE CONTRACTION PRODUCED BY PERIARTERIAL NERVE STIMULATION IN THE RAT ILEUM

The effect of substance P (SP) on the contractile responses produced by periarterial (mesenteric) nerve stimulation was studied in the rat isolated ileum. Periarterial nerve stimulation at 1-50 Hz, with 10 V (maximum) and 0.2 msec pulse duration, for 15-20 sec, produced frequency-dependent contractions in the rat ileum. In the presence of guanethidine (10 microM) and 6-hydroxydopamine (1 microM), to block noradrenergic responses, periarterial nerve stimulation at 1-20 Hz still produced small contractions which were reduced by atropine (1 microM) and morphine (1 microM). In the presence of atropine, morphine, guanethidine and 6-hydroxydopamine, the contraction produced by periarterial nerve stimulation was readily abolished by tetrodotoxin (1 microM), capsaicin (3.3 microM) and an SP-antagonist (SPA1, 10 microM). SP in low concentrations (0.01-1.0 microM) potentiated the contractions produced by periarterial nerve stimulation at 1-2 Hz by 20-30%. High concentrations of SP (1.0-10.0 microM) reduced the contractile response by 40-50%. Indomethacin (2.8 microM) amd mepyramine (1 microM) had no effect on these responses. When the mesenteric nerve supply to the gut was cut, periarterial nerve stimulation produced no contraction in the rat ileum. However, SP in low concentrations, still produced small contractions which were abolished by an SP-antagonist but not by tetrodotoxin. SP in low concentrations, slightly increased the contractions produced by ACh (0.5-50 microM) or TEA (2.4-12 mM). High concentrations of SP significantly reduced the ACh and TEA-induced contractions in the rat ileum.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory junction potentials of the guinea-pig duodenum in the treatment with catecholamines.

The inhibitory junction potentials (IJPs) in response to single and repetitive stimulation were recorded from the smooth muscle cells of the guinea-pig duodenum intracellularly. In adrenaline and noradrenaline (10(-8)-10(-5) g/ml), the IJP could be evoked in spite of a hyperpolarization of the cell membrane. The amplitude of the IJP was slightly changed in these agents but not abolished. Similar results were obtained in isoprenaline (10(-5) g/ml) and phenylephrine (10(-5) g/ml). The IJPs evoked by single and repetitive stimulation were not blocked by phentolamine (10(-7) g/ml) and propranolol (10(-5) g/ml). In propranolol (10(-7)-10(-5)/g/ml), the membrane was depolarized and the amplitude and the rate of hyperpolarization in the IJP were decreased. The membrane potential was decreased and the amplitude of the IJP was slightly increased in the presence of guanethidine (10(-5) g/ml). The amplitude of the IJP was increased with increasing the concentration of tyramine (10(-6)-10(-5) g/ml). These results suggest that the transmitter released from the intramural inhibitory nerve in the duodenum is nonadrenergic and this type of inhibition seems to be independent from adrenergic inhibition.

Effects of goniopora toxin on non‐adrenergic, non‐cholinergic response and purine nucleotide release in guinea‐pig taenia coli

1. Effects of goniopora toxin (GPT) on non-adrenergic, non-cholinergic inhibitory responses were examined in isolated guinea-pig taenia coli and the transmission mechanism was analysed.2. GPT (20-50 nM) gradually augmented the relaxation and rebound contraction induced by electrical transmural stimulation in the presence of guanethidine and atropine. These effects were abolished by tetrodotoxin.3. The resting tension and the response to exogenously applied ATP were little affected by GPT.4. The action potentials and the electrotonic potentials recorded by a double sucrose-gap method were little affected by GPT.5. These results indicate that the augmentation is elicited by a direct action of GPT on the non-adrenergic, non-cholinergic neurones, rather than on the smooth muscles per se.6. GPT augmented the amplitude of the inhibitory junction potential (i.j.p.) recorded in the presence of guanethidine and atropine. GPT also enhanced the (3)H efflux in response to electrical transmural stimulation of preparations pre-loaded with [(3)H] adenosine. Tetrodotoxin markedly inhibited or abolished the i.j.p. and (3)H efflux.7. These results would suggest that augmentation of the non-adrenergic, non-cholinergic responses is due to increased transmitter release from the nerve. Under conditions in which the transmitter release was augmented, the non-adrenergic, non-cholinergic response showed an essentially similar pattern to that obtained under normal conditions; therefore the inhibitory response is probably due to a putative transmitter, possibly ATP or a related nucleotide.

Effect of various drugs and extrinsic denervation on the non-adrenergic inhibitory neurons in the rat stomach.

The effects of various drugs and extrinsic denervation on the non-adrenergic inhibitory nerves in the rat stomach were examined. Stimulation of the intramural nerves supplying the longitudinal smooth muscle strips taken from the rat stomach produced responses consisting initial contractions followed by relaxations in the presence of guanethidine in case of the tone of the preparation maintained with serotonin. After scopolamine treatment, transmural nerve stimulation (TMS) caused a relaxation or a relaxation followed by a transient after-contraction. All of these responses were abolished reversibly with tetrodotoxin. After cold storage of rat stomach strips for 5 d at 4 degrees C, the TMS-induced response was not observed, but noradrenaline still relaxed these strips. The TMS-induced relaxation reached a maximum amplitude at 2-5 Hz, and was entirely independent of alpha- and beta-blockers, or a combination of them. It was not affected by treatment of 6-hydroxydopamine and reserpine. These results strongly suggested that the relaxation was not myogenic, but neurogenic, and was not elicited by stimulation of adrenergic neurons. Strychnine and poly-L-lysine inhibited the relaxation elicited by TMS even in normal and transection-treated rats. Histochemical studies showed degenerative changes due to the dissection at the axons of a ganglion in the Auerbach's plexuses by transection. The effect of various drugs and extrinsic denervation on the response to TMS in relation to non-adrenergic inhibitory nerves in the rat stomach is discussed.

Physiological and pharmacological characteristics of the baboon (Papio anubis) oviduct.

The pharmacological and electrophysiological characteristics of the oviduct of the preovulatory baboon (Papio anubis) have been investigated. The longitudinal and circular muscle of both isthmus and ampulla contract upon transmural stimulation, and this effect is completely blocked by phentolamine, guanethidine, and tetrodotoxin, suggesting that contractions are mediated by norepinephrine released from adrenergic nerves acting on α-receptors on the smooth muscle. In circular preparations of the isthmus and in ampulla, nonadrenergic, noncholinergic inhibitory nerves could be demonstrated in the presence of guanethidine. Pharmacologically, the oviductal smooth muscle is contracted by norepinephrine, histamine, acetylcholine, Substance P, 5-hydroxytryptamine, ATP, adenosine, PGF2α, U44069, and U46619 and is inhibited by PGE2 and isoproterenol. Extracellular recording of electrical activity of the ampulla determined that electrical impulses traveled at a velocity of 2–5 mm/sec, that there was a reduction in conduction velocity towards ovulation, and that following ovulation the duration of the electrical bursts increased.

The mechanism of the motor response to periarterial nerve stimulation in the small intestine of the rabbit.

In the presence of guanethidine, periarterial nerve stimulation caused a frequency-dependent motor response in the rabbit isolated ileum. Tachyphylaxis to capsaicin greatly diminished the effect of periarterial stimulation; the remaining portion of the contractile response was susceptible to hexamethonium. The motor effect of periarterial stimulation is mediated by two different mechanisms: one via parasympathetic preganglionic nerves and the other sensitive to capsaicin.

Facilitation of sympathetic neurotransmission in the rat anococcygeus muscle by prostaglandins D2 and F2 alpha.

1 Investigations were made into the effects of prostaglandins D2 (PGD2) and F2 alpha (PGF2 alpha) on the responses of the rat anococcygeus muscle to field stimulation of intrinsic motor (sympathetic) and inhibitory nerves, and to exogenous noradrenaline. 2 PGD2 (2.8 X 10(-6) mol/1) substantially increased the motor responses to field stimulation at all frequencies tested (2 to 32 Hz), and caused a smaller increase in the responses to noradrenaline. 3 PGF2 alpha (2.8 X 10(-6) mol/1) strongly potentiated the motor responses to field stimulation (2 to 32 Hz) and also to noradrenaline. This prostaglandin had quantitatively similar effects on the responses to both types of stimulus. 4 PGD2 was without effect on the inhibitory responses evoked by field stimulation in the presence of guanethidine. PGF2 alpha seemed to reduce the inhibitory responses to low frequencies of stimulation (0.5 to 1.5 Hz), but this effect was marginal. 5 The results suggest that PGD2 facilitates sympathetic neurotransmission in this tissue by both pre- and post-junctional actions. The effect of PGF2 alpha seems likely to be mediated predominantly post-junctionally.

COMPARATIVE PHARMACOLOGICAL AND HISTOCHEMICAL EVIDENCE FOR PURINERGIC INHIBITORY INNERVATION OF THE PORTAL VEIN OF THE RABBIT, BUT NOT GUINEA‐PIG

1 Intramural nerve stimulation elicited a powerful relaxation of the longitudinal muscle of the rabbit portal vein in the presence of atropine and guanethidine, but not of the guinea-pig portal vein.2 Intramural nerve stimulation of the rabbit portal vein produced a 13 fold increase in release of (3)H-adenyl compounds after preloading with [(3)H]-adenosine. About 50% of this release was abolished by guanethidine. All release was abolished by tetrodotoxin. No significant release of radioactive compounds was observed during intramural nerve stimulation of the guinea-pig portal vein in the presence of guanethidine, although there was a 6 fold increase in release of radioactivity in the absence of drugs.3 Histochemical studies using quinacrine, which binds ATP showed a fine fluorescent nerve plexus, nerve bundles, and ganglion cells in the rabbit portal vein, but not in the guinea-pig portal vein. This plexus was still present after chemical sympathectomy with 6-hydroxydopamine.4 Adenosine 5'-triphosphate (ATP) relaxed the rabbit portal vein, but usually produced a biphasic response, consisting of a contraction followed by a relaxation, of the guinea-pig portal vein.5 Prostaglandins E(1) and E(2) caused contraction of the rabbit portal vein. Indomethacin, a prostaglandin synthesis inhibitor, potentiated the relaxations of the rabbit portal vein produced by both non-adrenergic, non-cholinergic nerve stimulation and ATP.6 High concentrations of antazoline and phentolamine, which antagonize purinergic responses in the guinea-pig taenia coli, caused a loss of basal tone so that it was not possible to assess their effects on the responses of the portal vein to either non-adrenergic, non-cholinergic nerve stimulation, or ATP.7 Comparison of the results on the portal vein of the rabbit and guinea-pig provides support for the view that: (i) quinacrine fluorescence can be used to localize purinergic nerves and that the rabbit portal vein is supplied by these nerves; (ii) ATP is released from adrenergic nerve fibres, although, based on histochemical analysis, about 3 to 7 times less than is released from purinergic nerve fibres.

Some electrical properties of the rabbit anococcygeus muscle and a comparison of the effects of inhibitory nerve stimulation in the rat and rabbit.

1. Simultaneous recordings of mechanical activity and membrane potential of individual smooth muscle cells have been made in the rabbit anococcygeus muscle and the effect of field stimulation on these examined.2. In the absence of tone the mean resting membrane potential was - 48 mV. In the stretched muscle spontaneous tone and rhythmic activity quite frequently appeared and this was associated with depolarization of the muscle cells.3. The response to field stimulation depended on the frequency of stimulation, the level of membrane potential and the presence of myogenic tone. The usual response to single pulses or low frequency stimulation was a hyperpolarization of up to 30 mV (mean 14+/-6.8 mV) after a latency of 185 msec and accompanied by muscle relaxation. Higher frequencies (over 8 Hz) produced an initial depolarization often with a spike potential and followed by hyperpolarization. The mechanical response in these instances was contraction or contraction followed by relaxation. At all frequencies rebound depolarization and an associated contraction followed the end of stimulation).4. Phentolamine (5x10(-6)M) and guanethidine (10(-6)M) blocked the initial depolarization and contraction but had no effect on hyperpolarization, muscle relaxation or rebound depolarization and contraction.5. The effect of field stimulation in the presence of guanethidine (4x10(-5)M) was re-examined in the rat anococcygeus. Single pulses were ineffective, repetitive stimulation produced muscle relaxation but no hyperpolarization comparable to the rabbit. Any oscillations in membrane potential were damped during field stimulation and sometimes a small hyperpolarization was produced with a maximum amplitude of 13 mV and a mean of 1.9+/-1.2 mV.6. The transmembrane potential at the peak of hyperpolarization in the rabbit was rarely more than -70 mV. Passive displacement of the membrane potential by current pulses altered the amplitude of the hyperpolarization and suggested that there was a reversal potential at between -80 and -90 mV.7. No change in input resistance could be measured during inhibitory nerve stimulation in either the rabbit or the rat but measurements based on electrotonic potentials indicated a reducation in membrane resistance, small in the rat but greater in the rabbit.8. These experiments suggest that in both species muscle relaxation is associated with an increase in ionic permeability and a move, at least in the rabbit muscle, towards an equilibrium potential of -80 to -90 mV. In view of the much smaller effect in the rat it is not clear whether this is the cause or at least the sole cause of the muscle relaxation.

Partial reversal of guanethidine-induced adrenergic neuron blockade by acetaldehyde

Acetaldehyde (5 m m) partially restores responses to transmural stimulation in the isolated rat vas deferens blocked by 30-min exposure to guanethidine (4 × 10 −6 m). Added after blockade and in the presence or absence of guanethidine, the sympathomimetics, dextroamphetamine (7.3 × 10 −6 m), or tyramine (2.9 × 10 −5 m), produce gradual and complete recovery of contractile responses to transmural stimulation. Acetaldehyde produced a 41% recovery at 20 min which was not maintained in the presence of guanethidine. When the Tyrode solution was replaced once after blockade by guanethidine, acetaldehyde produced a 49% recovery of responses at 1 hr. Guanethidine tissue content was assayed spectrofluorometrically under all experimental conditions and found to be unchanged. Neither reserpine pretreatment (5 mg/kg/day × 2) nor denervation of vas deferens altered guanethidine tissue content. These findings suggest that a small portion of guanethidine is accumulated and bound within nerve endings at a site important for norepinephrine release. Sympathomimetics appear to release guanethidine from this specific site in rat vas deferens and cause a shift to nonspecific tissue compartments.

The effect of catecholamines and ATP on the smooth muscle cell membrane of the guinea-pig taenia coli

A comparative study was made of the effects of some catecholamines and purine-like compounds on the smooth muscle cell membrane of the guinea-pig taenia coli, using the double sucrose-gap method. The inhibitory junction potential (IJP) might be mediated by purinergic or adrenergic nerves. Therefore, the effects of these compounds on the membrane resistance and the membrane potential and also on the IJP were measured in the presence of guanethidine and atropine. The potency of the catecholamines tested to mimic the IJP with regard to membrane hyperpolarization and decrease of membrane resistance suggested an action on α-adrenoceptors: adrenaline > noradrenaline ⪢ isoprenaline. Equipotent concentrations of adrenaline and adenosine triphosphate (ATP) were found to exert the same hyperpolarization of the smooth muscle membrane in both the presence and absence of chloride. From the effects observed with phentolamine and tolazoline it is concluded that the IJP is not mediated by adrenergic nerves, for the adrenaline response was abolished, whereas the IJP was unaffected. Furthermore, the ATP-blocking potencies of phentolamine and imidazole could not be demonstrated. On the other hand, the palallelism observed between the responses obtained with ATP and with transmural stimulation is in favor of the hypothesis that the IJP is mediated by purinergic nerves.

Transmission from intramural inhibitory nerves to the smooth muscle of the guinea-pig taenia coli.

1. Membrane potential changes of smooth muscle cells were recorded during stimulation of the intramural inhibitory nerves to the taenia coli.2. Stimulation across the taenia coli with single pulses of 200 musec duration excites the intramural nerves and not the muscle directly.3. The membrane potential changes due to stimulation of the intramural inhibitory nerves were different from those produced by perivascular inhibitory nerve stimulation in the following ways: hyperpolarizations (i.j.p.'s) of up to 25 mV were produced in response to single pulses; the latency, i.e. the time taken for the membrane to hyperpolarize after a stimulus of maximal strength, was as short as 80 msec; when the nerves were stimulated repetitively the membrane was hyperpolarized by up to 35 mV and all spontaneous activity was abolished; the mean hyperpolarization due to repetitive stimulation increased with the frequency of stimulation up to 10 pulses/sec and then remained constant; the hyperpolarization due to stimulation at frequencies greater than 5 pulses/sec was not maintained but decreased after 3-5 sec of stimulation; and finally when stimulation had ceased action potentials commenced firing at frequencies greater than normal.4. The amplitude and rate of hyperpolarization of the i.j.p. increased with increasing strength of stimulation until a maximum amplitude and rate of hyperpolarization was reached. The recovery or depolarizing phase of the i.j.p. was exponential with a time constant which varied from about 250 msec to 500 msec and could not therefore be due to the discharge of the membrane capacitance. In some cases there was an inflexion on this depolarizing phase and in these cases recovery led directly into an action potential.5. Spontaneous hyperpolarizations of the membrane were seen in some cells, and these hyperpolarizations were similar to those recorded on submaximal stimulation of the intramural nerves.6. There were no changes in the characteristics of the i.j.p. in the presence of guanethidine or bretylium.