OBSERVATIONS ON AN ISOLATED, INNERVATED PREPARATION OF RAT URINARY BLADDER

The birth and postnatal development of purinergic signalling

The purinergic signalling system is one of the most ancient and arguably the most widespread intercellular signalling system in living tissues. In this review we present a detailed account of the early developments and current status of purinergic signalling. We summarize the current knowledge on purinoceptors, their distribution and role in signal transduction in various tissues in physiological and pathophysiological conditions.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

The role of cholinesterases in rat urinary bladder contractility

This study examines the effects of inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) on acetylcholine (ACh)-induced contraction in rat urinary bladder smooth muscle. Neostigmine, a non-selective ChE inhibitor, caused concentration-dependent contractions in rat urinary bladder strips, whereas tetraisopropylpyrophosphoramide (iso-OMPA; a BuChE inhibitor) failed to affect the resting tone of the preparations. Neostigmine (1 microM) markedly augmented the contractile responses to ACh. Although iso-OMPA (10 microM) also potentiated ACh-induced contraction, the effect was less than that evoked by neostigmine. The activities of AChE in rat urinary bladder strips were significantly (P<0.05) higher than those of BuChE. These results indicated that AChE, rather than BuChE, plays an important role in controlling ACh-induced contractions of rat urinary bladder.

Tachykinin receptors of the NK2 type involved in the acetylcholine release by nicotine in guinea-pig bladder

1. The effects of guanethidine and tachykinins on nicotine- and electrical stimulation-induced cholinoceptor responses were studied in isolated urinary bladder from the guinea-pig. 2. Acetylcholine release and the contractile response stimulated by nicotine were partially reduced by a sympathetic nerve blocker, guanethidine. Neurokinin A (but not substance P methyl ester or senktide) enhanced both acetylcholine release and contraction by nicotine in the presence of guanethidine. 3. Frequency-contraction curves (1 to 50 Hz) for electrical field stimulation (EFS) were partially reduced by atropine (1 microM), and after desensitization to alpha,beta-methylene adenosine 5'-triphosphate, the atropine-resistant contraction to EFS was completely abolished. Guanethidine, the tachykinin antagonist [D-Arg1, D-Pro2, Trp7,9, Leu11]-substance P and application of neurokinin A or substance P did not change the contractile response to EFS. Preganglionic nerve stimulation (5 Hz and 20 Hz) also evoked a similar response to EFS and was not influenced at all by guanethidine or neurokinin A. 4. We conclude that the ability of nicotine to release acetylcholine is enhanced both by endogenous tachykinins (probably released from sympathetic nerves) and by exogenously applied tachykinins as a result of interaction with NK2 receptors in the urinary bladder.

Omega conotoxin and prejunctional modulation of the biphasic response of the rat isolated urinary bladder to single pulse electrical field stimulation

1. Single pulse electrical field stimulation (EFS) produces a biphasic response of muscle strips of the rat isolated urinary bladder consisting of an early and a late contraction which were atropine-resistant and atropine-sensitive, respectively. Repeated application of desensitizing doses of the P2 purinoceptor agonist, alpha, beta-methylene ATP (mATP) inhibited the early response while leaving unaffected the late component. 2. Omega conotoxin (CTX, 0.1 microM) inhibited both the early and the late response either in control conditions or after enhancement by physostigmine (0.1 microM). The effect of CTX was, in both cases, more pronounced on the late than the early response to EFS. CTX (0.1 microM) failed to affect contraction produced by ATP or acetylcholine at concentrations (0.3 mM and 0.5 microM) which produced a response similar to that to EFS. 3. The effect of physostigmine was more intense for the late than the early response and was abolished by atropine. In the presence of CTX, physostigmine enhanced both the early and the late components of the mechanical response to EFS. 4. Nifedipine (0.1-1 microM) reduced to a similar extent both the early and late responses. Bay K 8644 (1 microM) produced a marked enhancement of the response to EFS, which, however, did not have a distinct late peak. In the presence of Bay K 8644, either atropine (3 microM) or tetrodotoxin (1 microM) had minor inhibitory effects indicating the myogenic origin of the response. 5. Neurokinin A (0.1-1 nM) enhanced both the early and late responses to EFS without affecting the contraction produced by exogenous acetylcholine or ATP. A consistent potentiation was evident also in the presence of CTX and for the early response, in the presence of atropine. Clonidine (3 microM) inhibited the response to EFS either in the absence or the presence of physostigmine. The inhibitory effect of clonidine, shown previously to depend upon activation of prejunctional alpha 2-adrenoceptors, was still observed in presence of CTX or atropine. 6. It is concluded that CTX-sensitive voltage dependent calcium channels play a more important role in determining the cholinergic rather than the non-cholinergic, putatively purinergic, component of the biphasic response of the rat bladder to single pulse EFS. The action of CTX is likely to be exerted on N-type rather than L-type (dihydropyridine-sensitive) calcium channels. Prejunctional modulation (enhancement by neurokinin A, inhibition by clonidine) occurs even in the presence of CTX-sensitive channels blockade.

Effects of omega-conotoxin GVIA on autonomic neuroeffector transmission in various tissues

1. The effects of omega-conotoxin GVIA (conotoxin), a potent inhibitor of neuronal N-type Ca2+ channels, have been examined on responses to stimulation of noradrenergic, cholinergic and non-adrenergic, non-cholinergic (NANC) nerves in a range of isolated tissues to investigate the role of conotoxin-sensitive Ca2+ channels in neurotransmission. 2. Contractions elicited by field stimulation of noradrenergic nerves in rat and mouse anococcygeus muscles, rabbit ear artery and rat vas deferens (epididymal portion) were inhibited by conotoxin. Responses to noradrenaline, and to adenosine triphosphate in the vas deferens, were not affected. 3. Positive chronotropic responses to field stimulation of noradrenergic nerves were inhibited by conotoxin in rat and mouse atria, but responses to noradrenaline and tyramine were not affected. 4. The stimulation-induced release of noradrenaline was inhibited by conotoxin in the rabbit ear artery and in rat and mouse atria. 5. Relaxations in response to stimulation of the noradrenergic perivascular mesenteric nerves were reduced or abolished by conotoxin in rat and rabbit jejunum. The response to noradrenaline in rat jejunum was not affected. 6. Contractions elicited by stimulation of cholinergic nerves were inhibited by conotoxin in rat jejunum and mouse ileum (perivascular mesenteric nerves), and in guinea-pig taenia caeci (field stimulation). Responses to acetylcholine in rat jejunum and mouse ileum were not affected. 7. Contractions elicited by stimulation of the cholinergic plus NANC pelvic nerves were inhibited by conotoxin in rabbit colon, and to a lesser extent in guinea-pig colon. The stimulation-induced contraction of the guinea-pig colon was inhibited by conotoxin by a greater proportion in the presence than in the absence of atropine. Responses to acetylcholine were not affected in the rabbit colon but were slightly reduced in the guinea-pig colon. 8. Relaxations in response to field stimulation of NANC nerves were inhibited by conotoxin in guinea-pig taenia caeci and rat gastric fundus strips, and in rat anococcygeus muscle when the tone was raised by guanethidine but not when it was raised by carbachol. The relaxations produced by sodium nitroprusside in the rat gastric fundus and anococcygeus were not affected. 9. Contractions of the rat bladder elicited by stimulation of the peri-urethral nerves, which are NANC- and cholinergically mediated, were relatively insensitive to inhibition by conotoxin. The response were almost completely abolished by tetrodotoxin. 10. The conotoxin-induced inhibitions of responses to nerve stimulation developed slowly and persisted after removal of conotoxin. The responses were almost completely abolished by tetrodotoxin. 10. The conotoxin-induced inhibitions of responses to nerve stimulation developed slowly and persisted after removal of conotoxin. 11. The inhibitory effect of conotoxin was inversely proportional to the frequency of stimulation (in several preparations) and to the Ca2+ concentration in the bathing solution (in rat vas deferens). These observations suggest that the inhibition by conotoxin of the Ca2+ influx required for excitation-secretion coupling in autonomic nerve terminals is not absolute, and can be overcome by repeated stimulation or by raising the Ca2 + concentration.

A study of bladder dysfunction during streptozotocin-induced diabetes in the rat using an in vitro whole bladder preparation

An in vitro whole bladder preparation has been used in this study to examine the effects of eight and 16 week streptozotocin-induced diabetes on detrusor function in the rat. In eight week animals cystometric recordings showed an increase in bladder capacity associated with a decrease in intraluminal pressure. Concentration-response curves revealed a significant increase in sensitivity of the detrusor to beta,gamma-methylene ATP, a potent purinergic agonist, and a trend towards subsensitivity to acetylcholine in bladders from eight week diabetic rats when compared to controls. The atropine-resistant (purinergic) response to neurogenic stimulation was increased over the frequency range two to 30 Hz and was significantly greater at two Hz. In 16 week animals the cystometrogram had partially recovered; capacity had decreased compared to eight week diabetics and intraluminal pressure was within the normal range. Concentration-response curves revealed no significant difference in the response to acetylcholine and a greatly reduced response to beta,gamma-methylene ATP in the 16 week diabetics compared to controls. The atropine-resistant neurogenic response was slightly, but not significantly reduced. The results are discussed in relation to clinical urodynamic measurements of human detrusor dysfunction in diabetes.

Blockade and recovery of cholinergic transmission in rats treated with hemicholinium 3

Nerve-induced responses of parotid gland and gastrocnemius muscle were reduced by HC-3 (1 mg kg-1) in proportion to the number of stimuli. Contractions by somatic muscle at 100 Hz were abolished after 6.0 X 10(3) stimuli while 14 X 10(3) were applied at 20 Hz before secretion was blocked. As stimulus rate was decreased, blockade of secretion resulted from fewer stimuli but no difference in ACh content was found between stimulated and unstimulated glands. When stimuli were withheld for 1.5 h transmission recovered temporarily; initial secretory flow rate was only 50% of that in untreated controls when stimulation resumed. In both organs, the time during which responses were sustained, however, was much shorter than when the preparations were stimulated initially. After choline, recovery of transmission was dose-dependent: 150 mg kg-1 were required to restore responsiveness to the muscle and the gland comparable to that in HC-3-treated rats stimulated for the first time. Resting recovery, when stimuli are withheld, probably depends upon stored transmitter becoming mobilized rather than on de novo transmitter synthesis because the endogenous choline in plasma is only 1/1000 of that following exogenous choline.

An atropine-like inhibitory effect of DMPP on rat isolated urinary bladder

DMPP inhibits the nerve-mediated contractions of the rat isolated bladder, its effect being greater in preparations from newborn (2 day old) than adult animals. This effect of DMPP was unaffected by hexamethonium. In preparations from adult animals the effect of DMPP increased with frequency of stimulation and was fully prevented by the presence of atropine. In bladders from newborn rats low concentrations of furthrethonium (FHR) (10 nM) activated a series of rhythmic contractions which were unaffected by tetrodotoxin and abolished by DMPP through an hexamethonium-insensitive action. On the other hand DMPP did not affect rhythmic contractions produced by a low concentration of eledoisin (60 nM). In bladders from adult rats FHR (10 microM) and KCI (30 mM) produced contractures of comparable magnitude. DMPP inhibited, in concentration-related manner the FHR-induced tonic contraction but had little effect on that produced by KCI. These findings indicate that in the rat bladder, DMPP antagonizes selectivity cholinergically-mediated contractions through a mechanism which is unaffected by hexamethonium or tetrodotoxin. An "atropine-like' activity of DMPP should be considered.

Micturition in naive and morphine-dependent rats

Voiding responses were recorded in conscious water-loaded rats. Morphine sulphate (5 mg kg-1) elevated the volume threshold for micturition (MV); the group mean MV of 16 rats after morphine was 40% larger than control. Micturition was nevertheless complete since no urine remained in the bladder afterwards. The implantation of 2 or 4 morphine-base pellets (150 or 300 mg morphine) elevated for 12 days the MV in water-loaded rats. On the 3rd to the 10th day following implantation the group mean was approximately twice that of untreated controls. After micturition was over no residual urine was found in the bladder. Within 3 days the rats became tolerant to the antinociceptive action of the morphine-base pellets but little apparent tolerance developed to their action on micturition. On the 1st day after the pellets were removed, the mean MV was reduced. When withdrawal was precipitated by the administration of naloxone the MV was often too small to measure. This component of a withdrawal syndrome could be elicited in the rats throughout the 12 days of morphine pellet implantation. The administration of 20 mg kg-1 morphine sulphate to anaesthetized rats did not decrease the contractions of the urinary bladder to repetitive stimulation of its motor nerves at 1 and 20 Hz.

The postganglionic excitatory innervation of the mouse urinary bladder and its modulation by prejunctional GABAB receptors

Field stimulation produced reproducible contractions of the mouse isolated urinary bladder whose amplitude was frequency-related. These contractions were partially sensitive to atropine (3 microM), unaffected by hexamethonium (10 microM) and almost abolished by tetrodotoxin (0.5 microM). Atropine (3 microM) suppressed contractions produced by exogenous acetylcholine thereby indicating atropine-resistance of the nerve-mediated contractions. Nerve-mediated contractions of the mouse urinary bladder were enhanced by physostigmine (0.1-0.5 microM) and inhibited by hemicholinium-3 (0.5 mM) thus confirming the presence of a cholinergic component in the excitatory postganglionic innervation. Atropine (3 microM) inhibition of the nerve-mediated contractions increased with increasing duration and strength of the train of stimulation. The nerve-mediated contractions of the mouse bladder were unaffected by phentolamine (0.2 microM), propranolol (0.3 microM) or indomethacin (5 microM). ATP (1mM) the major candidate for the role of nonadrenergic-noncholinegic (NANC) excitatory neurotransmitter in the mammalian urinary bladder produced a contraction of the mouse isolated bladder. Exposure to the stable ATP analogue alpha, beta-methylene ATP (APCPP) or beta, gamma-methylene ATP (APPCP) produced a partial desensitization of the nerve-mediated response which, for APCPP, was greater in the presence than in the absence of atropine (3 microM). In the presence of atropine (3 microM) and after APCPP desensitization the amplitude of the response to field stimulation amounted to about 20% of the original response and was sensitive to tetrodotoxin, indicating that it is nerve-mediated. GABA (0.001-0.3 mM) inhibited the amplitude of field stimulation induced contractions of mouse urinary bladder. This effect was mimicked by the selective GABAB receptor agonist, (+/-)-baclofen, but not by the selective GABAA receptor agonist, homotaurine. GABA and (+/-)-baclofen exhibited cross-desensitization. The GABA-or (+/-)-baclofen-induced inhibition of the nerve-mediated contractions were reduced by previous exposure to homotaurine (1 mM) or to 5-aminovaleric acid (2 mM), two GABAB receptor antagonists. On the other hand the inhibitory effects of GABA or (+/-)-baclofen were unaffected by picrotoxin (0.1 mM), a selective GABAA receptor antagonist. The inhibitory effect of GABA on nerve-mediated contractions was reduced in the presence of atropine or hemicholinium-3 as well as following desensitization of P2-purinoreceptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacological evidence for the existence of two components in the twitch response to field stimulation of detrusor strips from the rat urinary bladder

Isolated strips from the anterior dome of the rat urinary bladder respond to single pulse field stimulation with a contraction. Two distinct components of this contraction ("early' and "late') could be observed, both of which were unaffected by hexamethonium (10 microM) and almost abolished by tetrodotoxin (1 microM) indicating their dependence on neurotransmitter release from postganglionic nerve endings. Atropine (3 microM) inhibited the "late' component (over 60%) to a significantly greater extent than the "early' component (less than 10%) Amplitude of the "early' component was usually greater than that of the "late' component. There was almost no difference between the "early' and "late' component in respect of their relationship to stimulus strength and pulse duration. Physostigmine (0.03 microM) enhanced both components of the nerve-mediated contraction, although enhancement of the "late' component was much greater than that of the "early' one. Tetraethylammonium (TEA, 0.5-5 mM) enhanced, in a concentration-related manner, both "early' and "late' components of the nerve-mediated contraction. Following exposure to physostigmine or TEA (5 mM) both "early' and "late' components of contraction were almost completely inhibited by tetrodotoxin. Atropine inhibition was more evident on the "late' as compared to "early' component of contraction. These findings demonstrate the presence, in the twitch response of rat isolated urinary bladder to field stimulation, of two nerve-mediated components which exhibit a different susceptibility to atropine and physostigmine.

Possible involvement of adenine nucleotides in the neurotransmission of the mouse urinary bladder

The urinary bladder of the mouse contracts to several agonists, namely acetylcholine, noradrenaline, adrenaline, histamine, angiotensin, serotonin, purine nucleotides and prostaglandin F2 alpha. Atropine partially reduced the contraction induced by electrical stimulation, whereas propranolol and tolazoline were ineffective. The atropine resistant component of the neurogenic response was reduced by indomethacin. Methysergide and diphenhydramine were ineffective. Desensitization of the bladder by alpha,beta-methylene ATP abolished the response to ATP and greatly reduced the non-adrenergic non-cholinergic component of the neurogenic response. The results suggest that ATP could be the transmitter responsible for the non-cholinergic non-adrenergic contraction of the mouse urinary bladder.

Neuropeptide action on the guinea-pig bladder; a comparison with the effects of field stimulation and ATP

A comparison was made between the effects of several neuropeptides and ATP as possible mediators of the non-adrenergic, non-cholinergic excitatory response in detrusor strips from the guinea-pig urinary bladder. Both substance P and vasoactive intestinal polypeptide produced contractions of the guinea-pig bladder, but the form of the atropine-resistant neurogenic excitation was mimicked more precisely by ATP. Neither methionine enkephalin nor leucine enkephalin had a prominent direct action on the smooth muscle (up to 100 microM) and did not significantly modify the cholinergic or non-cholinergic components of the response elicited by field stimulation. A proteolytic enzyme, chymotrypsin (10 U/ml), antagonised the excitatory effect of substance P, but not that of the non-adrenergic, non-cholinergic excitatory response or ATP. The slow excitation elicited by a high concentration of vasoactive intestinal polypeptide (10 microM), in contrast to responses elicited by ATP or field stimulation, was attenuated by preincubation with the structurally related polypeptide PHI, which was itself inactive (up to 10 microM). The present observations argue against a role for the peptides studied as neuromuscular transmitters in the detrusor but do not preclude such a role for ATP.

The effects of nicotine on spontaneous contractions of cat urinary bladder in situ

Nicotine and dimethyl-phenylpiperazinium (DMPP) increased intravesicular pressure and then transiently depressed the spontaneous activity of the urinary bladder in chloralose anaesthetized cats. Adrenaline (5-10 micrograms kg-1), noradrenaline (5-20 micrograms kg-1) and isoprenaline (40-50 micrograms kg-1) which depressed spontaneous urinary bladder activity, were antagonized by the beta-receptor blocking agent propranolol (1 mg kg-1). Phenylephrine (10-30 micrograms kg-1) was ineffective on the urinary bladder though it increased the systemic blood pressure. This latter effect was blocked by the alpha-receptor blocking agent phentolamine (2 mg kg-1). Acetylcholine (2-8 micrograms kg-1) caused a marked fall in systemic blood pressure, which was potentiated by physostigmine, but failed to produce any response on the intravesicular pressure even after physostigmine (50-100 micrograms kg-1) treatment. ATP (2 mg kg-1) produced an increase in intravesicular pressure accompanied by a fall in systemic blood pressure. The increased intravesicular pressure was antagonized by quinidine (20 mg kg-1); however, the fall in blood pressure remained unaltered. The increased intravesicular pressure induced by nicotine (20-40 micrograms kg-1) or DMPP (50-100 micrograms kg-1) was not affected by phentolamine (2 mg kg-1), propranolol (1 mg kg-1) or guanethidine (15-20 mg kg-1). Physostigmine (50-100 micrograms kg-1), hemicholinium 3 (2 mg kg-1) or atropine (1 mg kg-1) were also unable to affect the response to nicotine. Hexamethonium (1 mg kg-1), reduced the amplitude of spontaneous bladder contractions and quinidine (20 mg kg-1) abolished the effect of nicotine. 7 Bilateral sectioning of the cervical sympathetic or hypogastric nerves did not alter the effect of nicotine or DMPP. Higher spinal cord transection (Cl-C2) blocked the spontaneous, as well as the nicotine- and DMPP-induced, contractions of the bladder. 8 It is concluded that the increase in intravesicular pressure induced by nicotine is atropineresistant and is not mediated either through adrenergic or cholinergic mechanisms. It is probable that a purinergic mechanism is involved, via the activation of P2-receptors present in the urinary bladder.

The effects of parasympathetic blocking agents on bladder electromyograms and function in conscious and anaesthetized cats

Voiding induced in conscious cats by infusion of sterile saline into the bladder via a chronically implanted bladder catheter was stable over many months. Artefact-free recordings of electrical activity obtained from the bladder neck and dome of these preparations during bladder filling and voiding showed characteristic voiding electromyograms but did not permit a functional differentiation. Both voiding and the associated electromyogram were abolished by the ganglion blocking agent, pentolinium. Hyoscine or methyl atropine did not affect the electromyogram but impaired the ability of cats to empty their bladders completely. In anaesthetized cats, ganglion blocking agents prevented a rise in bladder pressure during sacral ventral root stimulation but a hyoscine-sensitive bladder contraction was seen following the period of stimulation. Further stimulation during this post-stimulus rise in intravesical pressure revealed a hyoscine-sensitive stimulus-bound relaxation. Sacral ventral root stimulation relaxed the bladder neck/proximal urethra particularly in the presence of sympathetic tone.

The effects of purified botulinum neurotoxin type A on cholinergic, adrenergic and non-adrenergic, atropine-resistant autonomic neuromuscular transmission

The twitch response observed during low frequency electrical stimulation of postganglionic cholinergic neurones supplying the longitudinal smooth muscle of the guinea-pig ileum was markedly reduced by incubation with an homogeneous preparation of botulinum type A neurotoxin (4.3-8.6 nM). This intoxication of the autonomic cholinergic neurones was long-lasting, irreversible by washing, but readily reversed by 4-aminopyridine (50-1000 microM). The noradrenergic motor response of the rat anococcygeus following field stimulation was partially antagonised by the neurotoxin. The non-adrenergic inhibitory response of the guinea-pig taenia coli, elicited by field stimulation, was not antagonised by botulinum toxin, suggesting that a source of a non-adrenergic inhibitory transmitter exists, other than intramural cholinergic neurones. However, the neurogenic excitatory responses of the guinea-pig bladder, elicited by field stimulation in the presence of atropine and guanethidine, were virtually abolished by botulinum toxin. It is suggested that the parasympathetic neurones which supply the smooth muscle of the guinea-pig urinary bladder co-release acetylcholine and a non-cholinergic excitatory transmitter; ATP or polypeptides are possible candidates.

Lack of correlation between ultrastructural and pharmacological types of non-adrenergic autonomic nerves

In order to test the premise that non-adrenergic, non-cholinergic (NANC) autonomic nerves have a distinctive ultrastructural appearance, clearly different from that of cholinergic nerves, a detailed quantitative ultrastructural analysis has been made of the non-adrenergic innervation of 15 tissues thought from pharmacological evidence to be innervated by NANC nerves (rat and rabbit anococcygeus muscles; rabbit hepatic portal vein; extrinsically denervated toad lung); cholinergic nerves (atria of rat, rabbit, guinea-pig and toad); or both (guinea-pig cervical and thoracic trachealis muscle; rabbit rectococcygeus muscle; urinary bladder of rat, rabbit, guinea-pig and toad) in addition to their adrenergic supply. Following fixation with a modified chromaffin procedure allowing identification of adrenergic nerves, large, randomly selected samples of non-adrenergic nerve profiles from each tissue were analysed with respect to numbers, relative proportions, and size frequency distributions of different vesicle classes within the profiles. The neuromuscular relationships within each tissue were also analysed. On the basis of these analyses, it is clear that there are no consistent ultrastructural differences between cholinergic and NANC autonomic nerves: neither proportions nor sizes of the vesicles provide any clue as to the transmitter used by a particular nerve. The great majority of nerve profiles, whether cholinergic or NANC, contain predominantly small clear "synaptic" vesicles. Large filled "peptidergic" vesicles are no more common in most NANC

Resistance of adrenergic neurotransmission in the toad heart to adrenoceptor blockade

Stimulation of sympathetic nerves to the toad heart produced increases in both the rate and force of cardiac beat. Although these responses were abolished by treatment with bretylium (10-6 mol.1-1) or 6-hydroxydopamine (100 mg.kg-1), and surgical sympathetic denervation, they were not abolished by treatment with propranolol (10-6 mol-1-1) and phentolamine (3 X 10-6 mol.1-1), either alone or in combination. The responses remaining after adrenoceptor blockade could not be ascribed to the effects of neurally released dopamine, ATP, adenosine, histamine or a variety of neuropeptides, although the participation of an as yet unidentified co-transmitter cannot be ruled out. Quantitative analysis of the interactions between propranolol and adrenaline on cardiac adrenoceptors, after blockade of alpha-receptors and amine uptake mechanisms, revealed that these interactions do not comply with the conditions for simple competitivity. Therefore, in addition to its action on beta-receptors, adrenaline seems to be producing excitation of the toad heart by acting on adrenoceptors which cannot be classified as either alpha- or beta-receptors. These results, together with the existence of close neuromuscular gaps (less than 50 nm) in the toad heart, are consistent with the hypothesis that sympathetic excitation of the toad heart is mediated by both "extra-junctional" beta-adrenoceptors, and "junctional" adrenoceptors which are neither alpha- nor beta-receptors.

Pharmacological characterization of the excitatory innervation to the guinea-pig urinary bladder in vitro: evidence for both cholinergic and non-adrenergic-non-cholinergic neurotransmission

1 Field stimulation of strips of guinea-pig isolated urinary bladder with 5 s trains at 0.1 to 15 Hz resulted in frequency-dependent, reproducible contractions. 2 At concentrations of 1 and 4 x 10(-7) M and 1 x 10(-6) M, atropine produced a variable, partial inhibition of contractions at all frequencies but was most effective at frequencies of 3 Hz or more. 3 Tetrodotoxin (TTX), 5 x 10(-7) M, inhibited contractions at all frequencies by 80 to 90%. 4 Physostigmine, 2 x 10(-6) M, significantly enhanced the contractile response to frequencies of less than 10 Hz but did not enhance responses resistant to inhibition by atropine. Hexamethonium, 1 x 10(-4) M, slightly enhanced the contractile response to frequencies of 4 Hz or greater. 5 (+/-)-Propranolol (5 x 10(-6)M), guanethidine (1 x 10(-6)M), phentolamine (5 x 10(-6)M) and clonidine (3 x 10(-8)M) each enhanced the contractile response to field stimulation. 6 Contractile responses obtained in the presence of atropine (4 x 10(-7) M) and guanethidine (1 x 10(-6) M) increased with time and were inhibited 60 to 80% by TTX (5 x 10(-7)M. 7 It is concluded that the cholinergic nervous system contributes, in part, to electrically-induced excitatory contractions of the isolated urinary bladder of the guinea-pig. Concomitant sympathetic stimulation appears to serve an inhibitory role. In addition, a major portion of the contractile response appears to be due to a non-cholinergic non-adrenergic, as yet unidentified, substance.

Atropine and micturition responses by rats with intact and partially innervated bladder

1 Micturition responses by a group of 17 rats wee recorded during a water diuresis. During a 2 h period, uniform volumes of urine were passes at regular intervals; the mean of the voiding responses by each animal was consistent from one water loading period to another. Residual urine volumes were physiologically insignificant. 2 Atropine treatment did not compromise seriously micturition by water-loaded rats. Treated animals micturated more frequently; the mean volume was 68% of control. The residual urine volume was equal to that of controls. 3 Several week after the surgical removal of half the motor innervation of the bladder, there was no significant effect on micturition. Mean voiding volumes were not different from those of controls; residual urine volumes were the same as before denervation. 4 After half the innervation of the bladder had been destroyed. The effect of atropine on micturition was enhanced. Volumes passes were 50% of control; large residual volumes remained when micturition was over. Only in this group could bladder distension be found. 5 It is concluded that functional responses of the rat urinary bladder are not only resistant to atropine but also to the sizeable reduction in the number of neuroeffector units in the bladder itself. The functional reserve of the rat bladder musculature is remarkably high when assessed by its ability to empty adequately.

Purine antagonists in the identification of adenosine-receptors in guinea-pig trachea and the role of purines in non-adrenergic inhibitory neurotransmission

1 To test the possibility that adenosine receptors exist within the trachea of the guinea-pig, an attempt has been made to identify a compound with adenosine antagonist activity in this tissue.2 Quinidine, phentolamine, phenoxybenzamine, 2-2'-pyridylisatogen tosylate (PIT) and caffeine were tested for antagonism of spasmolytic responses to adenosine, adenosine 5'-triphosphate (ATP) and adenine on the guinea-pig isolated trachea.3 Quinidine (10 and 25 mug/ml), phentolamine (10 and 30 mug/ml) and phenoxybenzamine (10 mug/ml) had little or no effect on response to adenosine, ATP and adenine. PIT (21 mug/ml) potentiated responses to adenosine, ATP and adenine by an unexplained mechanism.4 Caffeine (25 mug/ml) partially relaxed the trachea and inhibited spasmolytic responses to both adenosine and ATP, but not to adenine, isoprenaline, aminophylline or prostaglandin E(2) (PGE(2)).5 A number of compounds related to caffeine (xanthine, hypoxanthine, theophylline and theobromine) were tested for adenosine antagonist activity. Xanthine (300 mug/ml) and hypoxanthine (300 mug/ml) did not relax the trachea or antagonize spasmolytic responses to adenosine. Both theophylline (10 mug/ml) and theobromine (30 mug/ml) partially relaxed the trachea; theophylline, but not theobromine, antagonized spasmolytic responses to adenosine.6 pA(2) values for caffeine and theophylline as antagonists of adenosine were 4.3 and 4.7 respectively. However, the slopes of the Schild plot regressions were significantly less than 1.0 for both compounds.7 Four compounds, adenine, AH 8883, M30966 and ICI 63197, which like caffeine and theophylline, have phosphodiesterase inhibitory activity were tested for adenosine antagonist activity in the trachea. Adenine and AH 8883 had no effect and M30966 and ICI 63197 caused significant potentiation.8 The effects of caffeine and theophylline were also investigated on the non-adrenergic inhibitory response to nerve stimulation (NAIR). Both caffeine (100 mug/ml, n = 4) and theophylline (30 mug/ml, n = 4) enhanced the NAIR (20 Hz) while virtually abolishing matched responses to exogenous adenosine.9 The results support the existence of adenosine receptors in the guinea-pig trachea.

Autonomic innervation of the muscles in the wall of the bladder and proximal urethra of male rats

The muscular coat of the body of the rat bladder is innervated almost exclusively by cholinergic endings:adrenergic endings are rare. In the inner longitudinal muscle layer of the proximal urethra, 53% of 310 autonomic nerve endings observed in close relation to the smooth muscle cells were adrenergic and the remaining 47% cholinergic. The middle circular muscle layer of the proximal urethra was innervated predominantly by adrenergic endings: in this layer 86% of the total of 335 endings examined wre regarded as adrenergic. A similar predominantly adrenergic innervation was noted in the outer longitudinal layer of the proximal urethra. A number of striated muscle fibres arose from the outermost striated muscle layer of the proximal urethra and intruded deeply into the outer and middle smooth muscle layers. These intruding striated muscle fibres also received direct autonomic (mostly adrenergic) innervation. The significance of these findings in relation to the physiology of the lower urinary tracts is discussed.

Effects of adenosine 5'-triphosphate (ATP) and beta-gamma-methylene ATP on the rat urinary bladder

1 High concentrations of adenosine 5'-triphosphate (ATP, 100 to 1000 micrometer) were required to cause contraction of the rat urinary bladder, while adenosine and adenosine 5'monophosphate (AMP, 1 to 50 micrometer) produced relaxation. 2 One hundred fold lower concentrations of beta-gamma-methylene ATP, which is resistant to degradation to AMP and adenosine, caused dose-dependent, phasic contractions which mimicked atropine-resistant responses to nerve stimulation. 3 Adenosine and AMP caused dose-dependent inhibition of carbachol-induced contractions; theophylline competitively antagonized this inhibition but not the contractile responses to beta-gamma-methylene ATP, ATP or atropine-resistant nerve stimulation. 4 These results suggest that the insensitivity of the rat bladder to ATP is due to its rapid degradation to AMP and adenosine and support the hypothesis that the bladder receives a purinergic excitatory innervation.

Purinergic innervation of the guinea-pig urinary bladder

1 A number of criteria for considering adenosine 5'-triphosphate (ATP) as a neurotransmitter in the guinea-pig urinary bladder have been examined. In addition, the effect of tachyphylaxis to ATP on the response to non-adrenergic, non-cholinergic nerve stimulation has been re-examined.2 Quinacrine fluorescence histochemistry revealed a population of nerve fibres, ganglion cells, and nerve bundles in the bladder which were not seen in either the iris or vas deferens, where adrenergic and cholinergic nerves predominate. The distribution and morphology of the quinacrine-positive nerves in the bladder were different from those observed with catecholamine fluorescence and cholinesterase histochemistry, and were unaffected by chemical sympathectomy.3 Release of ATP from the bladder during stimulation of intramural excitatory nerves, in the presence of atropine and guanethidine increased to 3-12 times prestimulation levels. Tetrodotoxin abolished both the contractile response and the increase in ATP release resulting from intramural nerve stimulation. There was no increase in ATP release during contraction resulting from direct muscle stimulation following nerve paralysis with tetrodotoxin.4 Sympathectomy with 6-hydroxydopamine did not affect release of ATP in response to intramural nerve stimulation.5 Release of ATP was dependent on the concentration of calcium ion in the medium.6 Contractions in response to non-adrenergic, non-cholinergic intramural nerve stimulation were closely mimicked by ATP, but not by acetylcholine or histamine.7 Adenosine and dipyridamole reduced the contractions to both ATP and non-cholinergic nerve stimulation.8 2-2'-Pyridylisatogen was not a specific blocker of either ATP or intramural nerve stimulation in the guinea-pig bladder. 2-Substituted imidazolines initiated spontaneous activity making it impossible to assess any blocking action that they may have had.9 Prostaglandins (E(1), E(2) and F(2alpha)) gave weak, slow contractions and an increase in spontaneous activity. Both the response to ATP and non-adrenergic, non-cholinergic nerve stimulation were greatly potentiated in the presence of prostaglandins.10 In the presence of indomethacin the response to non-adrenergic, non-cholinergic nerve stimulation was virtually abolished following desensitization to ATP.

Neurogenic vasodilation of cat cerebral arteries

Transmural nerve stimulation (TNS) with 0.3-msec pulses between 1 and 25 Hz dilated cat cerebral artery segments in the presence of active muscle tone. Maximum vasodilatation occurred at 8 Hz. The dilator response to exogenous acetylcholine, but not to TNS, was abolished by atropine. Neither physostigmine nor hemicholinium affected the dilator response to TNS, which persisted after administration of guanethidine, phenoxybenzamine, propranolol, reserpine, and chronic sympathectomy. However, it was abolished by tetrodotoxin and cold storage. When examined histochemically, cat and rabbit cerebral arteries exhibited a rich plexiform distribution of acetylcholinesterase which was not affected appreciably by sympathetic denervation. These results suggest that vasodilation is not mediated through modification of sympathetic activity. They also indicate the existence of a nonadrenergic, possibly noncholinergic, vasodilator innervation in cat cerebral arteries. Preliminary studies suggest that the transmitter is not histamine, ATP, prostaglandins, gamma-aminobutyric acid, dopamine, or serotonin. The cat cerebral artery segments contrast with the isolated rabbit cerebral arteries which predominantly constrict in response to TNS and show a small dilator response.

Sensitivity changes in guinea-pig atria and ileum following subacute administration of dyflos

1. Subacute administration of dyflos to guinea-pigs (1.2 mg/kg, s.c., daily for 10 days) led to the development of subsensitivity to carbachol in the ileum but not in the electrically stimulated left atrium. 2. Atria from dyflos-pretreated animals became supersensitive to acetylcholine but the ileum became subsensitive to this agonist despite marked inhibition of cholinesterases. The degree of subsensitivity was less than that for carbachol. 3. Subsensitivity also developed to histamine and was of a similar order to that observed for carbachol supporting the suggestion that subsensitivity is a nonspecific post-receptor mechanism. 4. Other changes which occurred in the ileum, together with the increase in the EC50 value to agonists were an increase in tissue mass, an increase in the slope of the concentration-response curve to agonists and an increase in the maximal response to agonists.

Atropine resistance and muscarinic receptors in the rat urinary bladder

The action of an anticholinesterase and an antimuscarinic drug upon nerve-induced contractions of the rat urinary bladder were examined during transmural stimulation at 20 Hz. Responses were graded in magnitude by limiting the duration of the stimulus trains. 2 Responses of low magnitude produced by short stimulus trains were unchanged by atropine; however, maximal responses resulting from long stimulus trains were diminished in magnitude and shortened in duration. 3 Responses of small magnitude elicited by short stimulus trains involve muscarinic receptors in close proximity to the neuroeffector junction and are resistant to atropine. 4 Maximal responses elicited by long stimulus trains involve 'junctional' muscarinic receptors as well as receptors located at the periphery of the junction; the 'extrajunctional' receptors are blocked by atropine. 5 Responses of low magnitude produced by short stimulus trains were unaffected by echothiophate; however, the duration of maximal responses resulting from the long stimulus trains was extended. 6 The inhibition of cholinesterase did not increase the occupation of muscarinic receptors by the transmitter; however, after large quantities of transmitter were released by the long stimulus trains the association between the receptors and acetylcholine was prolonged.

Innervation of the muscle of the bladder in the rat

A quantitative ultrastructural analysis of the organisation and terminal density of the nerves associated with the muscle of the body of the bladder was undertaken in the rat. The results obtained were suggestive of the organisation of the intramuscular plexuses into 2 separate and possibly functionally distinct networks. The nerves ramifying within the muscle fascicles mostly contained between 1 and 3 axons and on the basis of counts made in 12 animals, appeared to provide the muscle with only a moderate level of innervation. Although adrenergic terminals were frequently seen in the perivascular plexuses, they were rarely encountered in the nerves within the muscle fascicles. The majority of the terminals in the intrafascicular nerves were similar to those normally classified as cholinergic and, in many, the exposed parts of the axonal membrane were closely related to that of adjacent muscle cells. In addition to clear vesicles and large dense-cored vesicles, many of these terminals contained scattered small dense-cored vesicles. It was suggested that the involvement of the material present in the small dense-cored vesicles with acetylcholine in impulse transmission might account for the atypical features of such transmission in the bladder and in particular its resistance to blockade by atropine. The nerves forming the interfascicular networks contained few axons with cholinergic terminals, and were characterised by much larger numbers of a morphologically distinctive type of terminal. Some of these were indistinguishable from those recently defined as the terminals of purinergic axons but their distribution in the nerves suggests that they represent the terminals of afferent axons and is consistent with the concept that, together with those observed in other tissues, such axons are involved in pain perception.

Effect of sympathomimetic drugs on canine bladder: surgical model for assessment of regional differences

A surgical procedure is described in which the canine bladder was divided into body and base. The two-chambered bladder thus formed was used to assess the effect of sympathomimetic drugs in situ. Stimulation of either alpha- or beta-receptors produced a change in pressure in both chambers. The bladder base showed a greater sensitivity to alpha-receptor stimulation than did the body of the bladder. No difference in sensitivity to beta-receptor stimulation was noted between body and base.

Atropine resistant excitation of the urinary bladder: the possibility of transmission via nerves releasing a purine nucleotide

1. The possibility that a purine nucleotide is involved in excitatory transmission to the urinary bladder has been tested. All the purine compounds tested which contained a pyrophosphate bond produced contraction, adenosine triphosphate (ATP) being the most potent. Adenosine and adenosine monophosphate caused relaxation.2. The response to ATP closely mimicked the nerve-mediated contraction, both being characterized by a rapid contraction which was not maintained. A lack of sensitivity to ATP was noted in some preparations of the rat urinary bladder.3. Both nerve-mediated contractions and contractions caused by ATP were blocked by quinidine, while the response to acetylcholine persisted.4. Nerve-mediated responses were depressed during tachyphylaxis produced by high concentrations of ATP. Tachyphylaxis did not occur when low concentrations were used. Possible explanations for these results are discussed.5. The results are consistent with the hypothesis that non-cholinergic excitatory nerves to the guinea-pig bladder release a purine nucleotide, but do not provide critical evidence for it.

Non-cholinergic transmission by post-ganglionic motor neurones in the mammalian bladder

1. In mucosa-free preparations of the detrusor muscle electrical stimulation with 0.1 msec pulses has been utilized to reveal the non-cholinergic nature of most, if not all, of the post-ganglionic motor neurones in the guinea-pig bladder.2. The twitches elicited by 0.1 msec pulses were abolished by tetrodotoxin, but were not reduced by dimethyltubocurarine or by hexamethonium. Hexamethonium was nevertheless present in all the experiments in order to restrict acetylcholine action to ;muscarinic' receptors in the muscle fibres.3. There was little or no diminution in the twitches after prolonged exposure to atropine, 10(-8)-10(-5) g/ml., although the twitch-matching dose of acetylcholine was raised 1000-2500 times. Hence, there was no anomalous refractoriness to atropine in these ;muscarinic' receptors.4. Despite massive atropinization, the recruitment of unoccupied transmitter-receptors by means of extra pulses remained unaffected.5. Eserine failed to potentiate the atropine-resistant twitches.6. The twitches were not depressed by morphine.7. Noradrenaline produced relaxation and twitch reduction. The twitches persisted after alpha + beta adrenoceptor blockade with phentolamine + pronethalol and were unaffected by the monoamine oxidase and catecholamine-O-methyl transferase inhibitors, tranylcypromine and pyrogallol.8. Rapid contractions were elicited by 5-HT and by histamine but the twitches remained unaltered after antagonism of 5-HT by methysergide and of histamine by mepyramine.9. The twitches could be mimicked by injections of ATP, but after desensitization of the preparation to ATP the response to electrical stimulation remained unaltered.10. Prostaglandins E(2) and F(2alpha), only in large doses, produced delayed, sluggish contractions which persisted after the wash; these contractions were quite different from the responses to electrical stimulation, which were immediate, sharp and brief.11. The non-cholinergic nature of the post-ganglionic motor neurones was confirmed in the bladder of two other species, the cat and the rabbit.

Effects of some drugs on the responses of the rat isolated, innervated urinary bladder to indirect electrical stimulation

1. The effects of some drugs known to inhibit transmission in the superior cervical ganglion and at the neuromuscular junction were investigated on the cholinergic nerve-smooth muscle junction, using the rat isolated innervated urinary bladder preparation.2. HC-3 and Win 4981 inhibited the indirectly evoked contractions; the block was typically slow in onset, depended on the rate of stimulation and was partially reversed by choline. The moderate coincident inhibition of acetylcholine-responses disappeared after washing the tissue, while the block of the neuronally evoked contractions persisted.3. Morphine, methylpentynol carbamate, chloral hydrate and strychnine inhibited indirectly evoked contractions without inhibiting the responses to acetylcholine. Paraldehyde inhibited both types of response.4. Hexamethonium, mecamylamine and tubocurarine had no effect on either type of response. Tetraethylammonium augmented both types of response; the augmentation due to lower concentration was followed by a moderate block of the neuronally evoked contractions.5. Small concentrations of procaine markedly inhibited responses to acetylcholine and produced a partial block of the neuronally evoked contractions.6. None of the drugs affected conduction in the isolated phrenic nerve.7. All the drugs other than paraldehyde and procaine appeared to act at the nerve terminals. The results are generally consistent with the view that HC-3 and Win 4981 act by limiting transport of choline across nerve membrane and that the other drugs act by inhibiting the release of acetylcholine. A reduction in sensitivity of the effector cell membrane may account, wholly or in part, for the action of paraldehyde and procaine.

The interaction of hemicholinium-3 and oxotremorine in isolated organ preparations

On isolated ileum preparations of the rat and guinea-pig, hemicholinium-3 antagonizes contractions elicited by acetylcholine and oxotremorine to the same extent. Hemicholinium-3 was a mild antagonist to acetylcholine but a stronger one to oxotremorine and carbachol on the ileum of the rabbit. Whereas hemicholinium-3 has no anti-acetylcholine activity on the isolated urinary bladder of the rat, it antagonizes the contractions elicited by oxotremorine and carbachol, and acetylcholine after eserine. Morphine has an anti-oxotremorine activity on this organ. Increasing concentrations of oxotremorine release increasing amounts of acetylcholine from the rat isolated intestine.

Comparison of effect of morphine-like analgesics on transmurally stimulated guinea-pig ileum

1. Morphine-like analgesic drugs caused depression of twitches of the isolated guinea-pig ileum in response to transmural electrical stimulation. The drugs tested were the narcotic analgesics codeine, diamorphine, fentanyl, morphine, morphine-N-oxide, normorphine, oxymorphone, pethidine, phenazocine and phenoperidine and the analgesic narcotic antagonists nalorphine and pentazocine.2. With the first application of one of these drugs the extent of depression of twitches was proportional to concentration. Except in the case of pethidine, there was no further depression when additional drug was added to the organ bath. With the second application of a drug after washing out the first dose, the depressant effect was less; that is, tolerance developed. With pethidine, the depression of twitches was proportional to concentration and tolerance could not be observed.3. When tolerance had been produced by cumulative addition of these drugs, a concentration was reached at which further addition resulted in increased activity of the ileum.4. With codeine, morphine and normorphine, the twitches were increased in height and regular.5. With diamorphine, fentanyl, oxymorphone, pentazocine, phenazocine and phenoperidine there were increased but irregular responses to transmural stimulation.6. Having reached the concentration at which these effects were observed, washout of the drug resulted in reduction of activity; the twitches became smaller or the irregular responses ceased.7. Readministration of a drug after activity of the ileum had been depressed by withdrawal of that drug resulted in restoration of activity, the ileum being dependent on the presence of the drug for its activity.8. Codeine and nalorphine did not produce as great an increase in activity on readministration to a dependent ileum as did morphine: they seem to act as partial agonists in producing this effect.9. In similar experiments with the isolated urinary bladder of the rat and guinea-pig, morphine was less active in depressing responses to stimulation than it was on the ileum, and tolerance to the drug and dependence on it did not occur.10. These observations have been discussed in relation to analgesic activity, tolerance and dependence in man.

The pharmacological nature of the response of the reserinized guinea-pig vas deferens to postganglionic nerve stimulation

1. Intracellular recordings from single smooth muscle cells of the guinea-pig vas deferens have been made after depletion of neuronal stores of noradrenaline by chronic reserpine treatment.2. Junctional responses to postganglionic hypogastric nerve stimulation were depressed, but large excitatory junction potentials (EJPs) and action potentials could still be evoked by stimulation at 1-2 c/s.3. These junctional responses were not reduced by the presence of hyoscine (5 x 10(-7) g/ml.), but were greatly depressed by the presence of bretylium (2 x 10(-6) g/ml.).4. Even in the presence of bretylium, junctional responses leading to action potentials could still be evoked by using high voltages of stimulation.5. It is concluded that when neuronal noradrenaline stores have been depleted by reserpine some noradrenaline is still available for release by nerve stimulation.6. It is further concluded that if the non-adrenergic component of the response of the guinea-pig vas deferens to nerve stimulation is cholinergic, this component is resistant to blockade by hyoscine.

Dual vasoconstrictor and vasodilator innervation of the uterine arterial supply in the guinea pig

The innervation of the extrinsic uterine arterial supply of the guinea pig has been studied using an isolated perfused preparation. The preparation was normally at minimal tone and responded to periarterial stimulation by a vaso-constriction which was mimicked by norepinephrine and abolished by bretylium. Constrictor responses both to stimulation and to norepinephrine were similar in both pregnant and non-pregnant states. In pregnant preparations, raising the tone of the vessels with norepinephrine revealed a powerful dilator response to periarterial stimulation. This response was mimicked by acetylcholine, potentiated by anticholinesterases, reduced by hyoscine, and abolished by-local anesthetic treatment. In contrast, virgin preparations showed only a weak dilator response to stimulation, while the response to acetylcholine even at high concentrations was usually negligible. Histochemical examination of the vessels revealed a dense plexus of fine nerve fibers exhibiting high acetylcholinesterase activity along the main uterine artery. The fibers lay in close apposition to the vascular muscle layer. Nerve fibers exhibited fluorescence for catecholamines were also abundant, but were distributed along the secondary as well as the main arteries. It is concluded that the uterine arterial supply of the guinea pig is innervated by both adrenergic constrictor and cholinergic dilator fibers. The dilator fibers appear to be functional only during pregnancy. The possibility of a noncholinergic dilator innervation is also discussed.

Acetylcholine in extracts and perfusates of urinary bladder

Tissue extracts of the urinary bladder of the rat, cat and guinea-pig contain an acetylcholine-like substance which is considered to be stored predominantly in post-ganglionic nerve fibres. An acetylcholine-like substance was liberated into the fluid bathing the isolated bladder of the guinea-pig and its output was increased 200-fold after transmural stimulation. The acetylcholine-like substance, both from bladder extracts (rat, cat and guinea-pig) and perfusates (rat), was found at the same Rf value as acetylcholine chloride when separated by paper chromatography in three solvent systems. It is concluded that the substance was acetylcholine.

The inhibitory nerve fibres in the vagal supply to the guinea-pig stomach

1. A comparison was made between the inhibitory responses of the isolated atropinized guinea-pig stomach to stimulation of the vagus and to stimulation of the perivascular nerves.2. When low frequencies of stimulation were used, the vagi were more effective than the perivascular nerves in causing relaxation of the stomach.3. The responses to vagal stimulation were faster in onset than were the responses to perivascular nerve stimulation.4. Responses to perivascular nerve stimulation were abolished by low concentrations of bretylium, whereas responses to vagal stimulation were only slight reduced. Vagal responses were strongly reduced by higher concentrations of bretylium.5. Amphetamine relieved the blockade of perivascular nerve responses which was caused by bretylium, but never relieved the reduction of the vagal responses.6. It is argued that the vagal inhibitory fibres are not susceptible to ;adrenergic neurone blockade', the observed reduction of the responses being due to some other action of bretylium.7. These differences between the vagal and perivascular inhibitory innervations of the stomach suggest that the post-ganglionic fibres in the vagal pathway and the intramural inhibitory nerves described in the guinea-pig caecum are similar.