Neuromodulatory effects of acetylcholine and serotonin on the sensitivity of leech mechanoreceptors.

1. Each segmental ganglion of the leech Hirudo medicinalis contains 6 touch (T) cells, 4 pressure (P) cells and 4 nociceptive (N) cells. The receptive terminals of these cells innervate the skin in discrete areas. These cells are known to have extrasynaptic receptors. 2. We tested the effect of transmitter substances present in leech CNS on the sensitivity of T and P cells to mechanical stimuli. Substances tested included octopamine, FMRFamide, proctolin, substance P, glutamate, GABA, acetylcholine and serotonin. 3. Only acetylcholine and serotonin had consistent effects. Serotonin (1 x 10(-3) M) increased the number of action potentials of T cells elicited by a standard stimulus. Serotonin (1 x 10(-4) M) and acetylcholine (1 x 10(-3) M) increased the number and frequency of action potentials in P cells.     

Substance P-induced contraction of rabbit airways: mechanism of action.

The mechanism by which substance P induces contraction of airway smooth muscle has been the subject of numerous reports. It has been suggested that in rabbit airways the action of substance P is indirect, via the release of endogenous acetylcholine, whereas this is not so in other species. The present detailed study investigated whether substance P-induced contraction in rabbit isolated bronchus and trachea is due to the release of endogenous acetylcholine or in bronchus is due to histamine release and whether substance P is metabolized by the enzymes enkephalinase and acetylcholinesterase. Isometric contraction to cumulative addition of substance P was measured in the presence of 10(-6) and 10(-4) M atropine, 10(-6) M pyrilamine, 10(-5) M phosphoramidon, or 3 x 10(-7) M neostigmine. Neither atropine nor pyrilamine had any effect on the substance P responses. Phosphoramidon, however, produced a 12-fold shift to the left in the response curve with a decrease in the 50% effective concentration from 7.0 x 10(-8) to 6.1 x 10(-9) M (n = 4 control and 5 treated; P less than 0.05). In contrast, neostigmine at a concentration that produced a sixfold shift to the left in the acetylcholine response curve had no effect on substance P responses. We conclude that, in rabbit airways in vitro, substance P-induced contraction is not mediated by release of endogenous acetylcholine or histamine. In addition, endogenous enkephalinase but not acetylcholinesterase may be involved in the degradation of substance P. Our results show that, in contrast to previous studies in rabbits, the mechanism of action of substance P may resemble that described in humans.     

Species differences in the negative inotropic effect of acetylcholine and soman in rat, guinea pig, and rabbit hearts.

1. Acetylcholine reduced atrial contractions by 82.5% in guinea pig, 50.8% in rat, and 41.5% in rabbit. 2. The EC50 values for the negative inotropic effect of acetylcholine were 3.3 x 10(-7) M in rat and guinea pig atria and 4.1 x 10(-6) M in rabbit atria. 3. There was no correlation between the species differences in the negative inotropic effect of acetylcholine in atria and the density or affinity of acetylcholinesterase or muscarinic receptors. 4. Inhibition of atrial acetylcholinesterase with soman reduced the EC50 of acetylcholine three-fold in all species, but did not change the maximal inotropic effect of acetylcholine. 5. Species differences in the negative inotropic effect of acetylcholine may be caused by differences in the coupling between myocardial muscarinic receptors and the ion channels that mediate negative inotropy.     

Adenosine selectively inhibits noncholinergic transmission in guinea pig bronchi

The neuromodulatory action of adenosine and ATP was investigated in isolated guinea pig bronchial strip chain preparations contracted with electrical field stimulation. The tissues were placed in organ baths containing physiological salt solution and stimulated at 8-Hz frequency, 0.5-ms pulse duration, and 30 V (approximately 100 mA) for 5 s. Electrical field stimulation evoked a biphasic contraction of bronchial muscle, consisting of an initial contraction followed by a sustained contraction, which was mediated by intramural cholinergic and noncholinergic nerve stimulations, respectively. Adenosine, at concentrations greater than M, caused a concentration-dependent inhibition in the height of the noncholinergically mediated contraction, accompanied by a very weak inhibition on the cholinergically mediated response. ATP (10(-5) to 3 x 10(-3) M) also produced a similar inhibitory effect on the noncholinergically mediated contraction, but the inhibitory potency was less than that of adenosine. The inhibitory response to adenosine was enhanced by the pretreatment with dipyridamole (2 x 10(-6) M) but antagonized with aminophylline (10(-5) M). Contractions of bronchial muscle evoked by exogenous acetylcholine (2 x 10(-6) M) or substance P (2 x 10(-7) M) were significantly inhibited by the adenosine (3 x 10(-4) M) pretreatment. These data suggest that in isolated guinea pig bronchi adenosine selectively inhibits noncholinergic neurotransmission through prejunctional P1-purinoceptors.     

Stimulatory effect of PG-KII, an NK3 tachykinin receptor agonist, on isolated pancreatic acini: species-related differences

More information is needed on the physiological role of the tachykinins (TKs), especially neurokinin3-receptor (NK3) agonists, in the pancreas. In this paper we investigated and compared the effect of PG-KII (10(-9) to 10(-6) M), a natural NK3-receptor agonist, with that of the known secretagogues substance P (10(-9) to 10(-6)M), caerulein (10(-11) to 10(-8) M) and carbachol (10(-8) to 10(-5) M), on amylase secretion from dispersed pancreatic acini of the guinea pig and rat. PG-KII (10(-7) M) significantly increased basal amylase release from guinea pig pancreatic acini (from 5.4+/-0.9% to 11.3+/-0.5%, P < 0.05) but left basal release in the rat unchanged (6.5+/-0.5%). The stimulant effect of PG-KII on guinea pig acini was significantly reduced by the NK3-receptor antagonist, SR 142801 (5 x 10(-7) M), and left unchanged by the NK1-receptor antagonist, SR 140333 (5 x 10(-7) M). Conversely, substance P (10(-7) M) significantly stimulated amylase secretion from rat and guinea pig acini (12.6+/-0.6% and 12.1+/-0.7%, P < 0.05). This stimulated effect of substance P was antagonized by the NK1--receptor antagonist (5 x 10(-7) M), but not by the NK3-receptor antagonist (5 x 10(-7) M). The PG-KII- and substance P-evoked maximal responses were lower than those evoked by caerulein (10(-9) M) (guinea pig, 19.1+/-1.3%; rat, 1802+/-0.9%, P < 0.01) and carbachol (10(-5) M) (guinea pig, 23.3+/-1.2%; rat, 24.0+/-1.1%, P < 0.01). The inhibitors of phospholipase C U-73122 (10(-5) M), phospholipase A2 quinacrine (10(-5)M), and protein tyrosine kinase genistein (10(-4) M), partly but significantly inhibited PG-KII, as well as carbachol-stimulated amylase release. Coincubation of PG-KII 10(-7) M with submaximal doses of caerulein (10(-11) to 10(-10) M) and carbachol (10(-7) to 10(-6) M) had an additive effect on amylase release. Pre-incubation with PG-KII (10(-7) M) for 30 min significantly reduced the subsequent amylase response to PG-KII, whereas pre-incubation with caerulein 10(-10) M or carbachol 10(-6) M did not. These findings suggest that PG-KII directly contributes to pancreatic exocrine secretion by interacting with acinar NK3 receptors of the guinea pig but not of the rat. PG-KII signal transduction involves the intracellular phospholipase C, phospholipase A2 and protein tyrosine kinase pathways. The NK3 receptor system cooperates with the other known secretagogues in regulating guinea pig exocrine pancreatic secretion and undergoes rapid homologous desensitization.     

Bombesin potentiates the effect of acetylcholine on isolated strips of fish stomach.

The interaction between bombesin and acetylcholine acting on smooth muscle of the stomach wall was investigated in two species of teleost fish. Oncorhynchus mykiss (rainbow trout) and Gadus morhua (Atlantic cod). Acetylcholine or bombesin alone has an excitatory effect on the stomach muscle. The effect on contraction amplitude of acetylcholine (10(-6)-10(-5) M) alone is about 10-times greater than the effect of bombesin (10(-9)-10(-7) M). In molar terms however, bombesin is more potent than acetylcholine. Bombesin (10(-8)-10(-7) M) added 0.5-3 min prior to acetylcholine potentiates the effect of acetylcholine in a dose-dependent manner. The potentiation is most pronounced in circular muscle preparations, but is present also in longitudinal muscle preparations. Bombesin affects the response to carbachol (10(-6) M) with a similar potentiation, indicating that the potentiation is not caused by inhibition of choline esterase activity. Atropine (10(-6)-10(-5) M) abolishes the response to bombesin plus acetylcholine as well as the response to acetylcholine alone. Tetrodotoxin (10(-6) M) does not block the effect of acetylcholine, bombesin or the combination acetylcholine plus bombesin. Substance P (10(-9)-10(-7) M) which has a similar excitatory effect on the stomach muscle as bombesin, does not potentiate the effect of acetylcholine. Immunohistochemistry has shown the presence of strong bombesin-like immunoreactivity in stomach nerves of the cod and weak bombesin-like immunoreactivity in rainbow trout nerves. In addition, bombesin-like immunoreactivity was demonstrated in endocrine cells in the gastric and intestinal mucosa of both species. It is concluded that bombesin, contained either in nerve fibres or in mucosal endocrine cells, specifically potentiates the effect of acetylcholine in the fish stomach.     

Correlation of Na,K-ATPase activity and protein synthesis in nerve cell membranes exposed to acetylcholine]

Acetylcholine (10(-6)--10(-3) M) added to the rat brain homogenate increased that activity of microsomal Na, K-ATPase and (14C)-amino acid incorporation in microsomal proteins. Actinomicin D (5.10(-5) M) eliminated the effect of acetylcholine. It is concluded that acetylcholine induced the synthesis of either Na, K-ATPase itself or some other proteins involved in the enzyme activity regulation.     

Modulation of cholinergic neurotransmission by vasoactive intestinal peptide in ferret trachea

We studied the effect of vasoactive intestinal peptide (VIP) on the contractile responses to electrical field stimulation (EFS) in isolated ferret tracheal segments. VIP did not change resting tension up to 2 X 10(-7) M, but it showed a biphasic effect on the responses to EFS. In concentrations up to 10(-9) M, VIP potentiated the response; at higher concentrations VIP reduced responses. Thus, at a concentration of 10(-9) M, VIP decreased the mean (+/- SE) log EFS frequency, producing 50% of maximum contraction significantly from a control value of 0.476 +/- 0.062 to 0.214 +/- 0.057 Hz (P less than 0.01); at a concentration of 2 X 10(-7) M VIP increased the half-maximal frequency from a control value of 0.513 +/- 0.086 to 0.752 +/- 0.053 Hz (P less than 0.05). The potentiating effect of VIP (10(-9) M) was not inhibited by hexamethonium, indomethacin, pyrilamine, methysergide, or [D-Pro2,D-Trp7,9] substance P. The inhibitory effect of VIP (2 X 10(-7) M) was also not inhibited by hexamethonium, indomethacin, or naloxone. In contrast to EFS-induced contraction, contractions produced by acetylcholine (10(-9) to 10(-3) M) were not affected by VIP at concentrations of 10(-9) and 2 X 10(-7) M. These results suggest that VIP modulates contractions produced by EFS via presynaptic cholinergic mechanisms and probably through a specific VIP receptor.     

Influenza infection causes airway hyperresponsiveness by decreasing enkephalinase

Ferret tracheal segments were infected with human influenza virus A/Taiwan/86 (H1N1) in vitro. After 4 days, the smooth muscle contractile responses to acetylcholine and to substance P were measured. The response to substance P was markedly accentuated, with a threefold increase in force of contraction at a substance P concentration of 10(-5) M, the highest concentration tested. In contrast, the response to acetylcholine was not affected by viral infection. Histological examination of tissues revealed extensive epithelial desquamation. Activity of enkephalinase (neutral metallo-endopeptidase, EC.3.4.24.11), an enzyme that degrades substance P, was decreased by 50% in infected tissues. Inhibiting enkephalinase activity by pretreating with thiorphan (10(-5) M) increased the response to substance P to the same final level in both infected and control tissues. Inhibiting other substance P-degrading enzymes including kininase II (angiotensin-converting enzyme), serine proteases, and aminopeptidases did not affect the response to substance P. Inhibiting cyclooxygenase and lipoxygenase activity using indomethacin and BW 755c did not affect hyperresponsiveness to substance P. Pretreating tissues with antagonists of alpha-adrenoceptors, beta-adrenoceptors, and H1 histamine receptors (phentolamine 10(-5) M, propranolol 5 X 10(-6) M, and pyrilamine 10(-5) M, respectively) had no effect on substance P-induced contraction. These results demonstrate that infection of ferret airway tissues with influenza virus increases the contractile response of airway smooth muscle to substance P. This effect is caused by decreased enkephalinase activity in infected tissues.     

Direct and Continuous Detection of ATP Secretion from Primary Monolayer Cultures of Bovine Adrenal Chromaffin Cells

A method was developed for direct and continuous detection of secretion of ATP from primary monolayer cultures of bovine adrenal chromaffin cells. ATP, which is costored with catecholamines within adrenal chromaffin cells, was released into the incubation medium, where it reacted with firefly luciferin-luciferase producing light detected by a photomultiplier located directly below the culture well. Acetylcholine, nicotine, the Ca2+ ionophore A23187, BaCl2, and KCl induced release of ATP. Induction of release of ATP by acetylcholine was dose dependent, with a threshold at 10(-7) M and a maximum at 10(-4) M. The dose-response curve for nicotine was bell shaped, with a threshold at 10(-7) M, a maximum at 10(-5) M, and diminished release at higher concentrations, an observation indicative of desensitization. Investigation of the initial rates of ATP secretion revealed that 10(-4) M nicotine actually induced release of ATP at a faster rate than 10(-5) M nicotine. However, the rate of ATP release evoked by 10(-4) M nicotine began to decline by 6 s, a result indicating the onset of receptor desensitization, whereas release induced by 10(-5) M nicotine continued unabated. Induction of release of ATP by acetylcholine or nicotine was biphasic, with a rapid, initial phase of release followed by a plateau at 0.5-1.5 min and a second phase of release beginning at 1.5-2 min, reaching a maximum by 2-3 min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of the involvement of nitric oxide and substance P in reducing baroreflex gain in the genetically hypertensive (GH) rat

The attenuation of baroreflex gain associated with hereditary hypertension could involve abnormal signalling by nitric oxide or substance P. Baroreflex gain was measured in age-matched male genetically hypertensive (GH) and nonnotensive (N) anaesthetised rats from heart rate changes in response to i.v. phenylephrine or sodium nitroprusside. In subgroups of these animals, nitric oxide synthesis was inhibited using NG-nitro-L-arginine methyl ester (L-NAME, 30 mg x kg(-1) i.v.), substance P transmission was blocked using the antagonist SR 140333 (360 nmoles x kg(-1) i.v.) or substance P release was inhibited with resiniferatoxin (4 doses of 0.3 microg x kg(-1) i.v. at 4 min intervals). Baroreflex gain was markedly reduced in GH compared to N animals (N -0.37 +/- 0.04 beat x min(-1) x mm Hg(-1), GH -0.17 +/- 0.02 beat x min(-1) x mm Hg(-1), p < 0.0001). Inhibition of nitric oxide synthase increased baroreflex gain in each strain, but the inter-strain difference in gain persisted (post-treatment N -0.57 +/- 0.07 beat x min(-1) x mm Hg(-1), GH -0.24 +/- 0.05 beat x min(-1) x mm Hg(-1) (p < 0.001). Blockade of receptors or inhibition of substance P release did not affect gain in either strain. Nitric oxide, but not substance P, appears to play an inhibitory role in the rat arterial baroreflex. Impairment of baroreflex gain in GH rats is not secondary to altered nitric oxide signaling.     

Role of M1, M3, and M5 muscarinic acetylcholine receptors in cholinergic dilation of small arteries studied with gene-targeted mice

Acetylcholine regulates perfusion of numerous organs via changes in local blood flow involving muscarinic receptor-induced release of vasorelaxing agents from the endothelium. The purpose of the present study was to determine the role of M?, M?, and M? muscarinic acetylcholine receptors in vasodilation of small arteries using gene-targeted mice deficient in either of the three receptor subtypes (M1R(-/-), M3R(-/-), or M5R(-/-) mice, respectively). Muscarinic receptor gene expression was determined in murine cutaneous, skeletal muscle, and renal interlobar arteries using real-time PCR. Moreover, respective arteries from M1R(-/-), M3R(-/-), M5R(-/-), and wild-type mice were isolated, cannulated with micropipettes, and pressurized. Luminal diameter was measured using video microscopy. mRNA for all five muscarinic receptor subtypes was detected in all three vascular preparations from wild-type mice. However, M(3) receptor mRNA was found to be most abundant. Acetylcholine produced dose-dependent dilation in all three vascular preparations from M1R(-/-), M5R(-/-), and wild-type mice. In contrast, cholinergic dilation was virtually abolished in arteries from M3R(-/-) mice. Deletion of either M?, M?, or M? receptor genes did not affect responses to nonmuscarinic vasodilators, such as substance P and nitroprusside. These findings provide the first direct evidence that M? receptors mediate cholinergic vasodilation in cutaneous, skeletal muscle, and renal interlobar arteries. In contrast, neither M? nor M? receptors appear to be involved in cholinergic responses of the three vascular preparations tested.     

alpha-Bungarotoxin interacts with the rat brain tachykinin receptors

alpha-Bungarotoxin (alpha Bgt) was shown to inhibit the binding of the 125I-labeled substance P (SP) and eledoisin (EL) to the rat brain membranes with Kl values of 8.0 +/- 5.0 x 10(-8) and 1.1 +/- 0.5 x 10(-6) M, respectively. Lower inhibitory activity was manifested by several other postsynaptically acting snake venom neurotoxins. The alpha Bgt inhibition of SP binding with a Kl value of 8.5 +/- 5.5 x 10(-8) M to solubilized preparations of the rat brain membranes was demonstrated. The capacity to displace SP was found for d-tubocurarine and phencyclidine, although at concentrations considerably higher than those affecting the nicotinic acetylcholine receptors (AChRs). The results obtained suggest that some of the alpha Bgt-binding polypeptides, distinct from neuronal AChRs, may be functionally associated with the tachykinin receptors (TchR).     

Autoantibodies enhance agonist action and binding to cardiac muscarinic receptors in chronic Chagas' disease

Chronic Chagasic patient immunoglobulins (CChP-IgGs) recognize an acidic amino acid cluster at the second extracellular loop (el2) of cardiac M(2)-muscarinic acetylcholine receptors (M(2)AChRs). These residues correspond to a common binding site for various allosteric agents. We characterized the nature of the M(2)AChR/CChP-IgG interaction in functional and radioligand binding experiments applying the same mainstream strategies previously used for the characterization of other allosteric agents. Dose-response curves of acetylcholine effect on heart rate were constructed with data from isolated heart experiments in the presence of CChP or normal blood donor (NBD) sera. In these experiments, CChP sera but not NBD sera increased the efficacy of agonist action by augmenting the onset of bradyarrhythmias and inducing a Hill slope of 2.5. This effect was blocked by gallamine, an M(2)AChR allosteric antagonist. Correspondingly, CChP-IgGs increased acetylcholine affinity twofold and showed negative cooperativity for [(3)H]-N-methyl scopolamine ([(3)H]-NMS) in allosterism binding assays. A peptide corresponding to the M(2)AChR-el2 blocked this effect. Furthermore, dissociation assays showed that the effect of gallamine on the [(3)H]-NMS off-rate was reverted by CChP-IgGs. Finally, concentration-effect curves for the allosteric delay of W84 on [(3)H]-NMS dissociation right shifted from an IC(50) of 33 nmol/L to 78 nmol/L, 992 nmol/L, and 1670 nmol/L in the presence of 6.7 x 10(- 8), 1.33 x 10(- 7), and 2.0 x 10(- 7) mol/L of anti-el2 affinity-purified CChP-IgGs. Taken together, these findings confirmed a competitive interplay of these ligands at the common allosteric site and revealed the novel allosteric nature of the interaction of CChP-IgGs at the M(2)AChRs as a positive cooperativity effect on acetylcholine action.     

Cholinergic regulation of the corpora allata in adult male loreyi leafworm Mythimna loreyi

The direct effect of acetylcholine on the activation of the corpora allata (CA) was investigated in the adult male loreyi leafworm, Mythimna loreyi. Acetylcholine, in the presence of the choline esterase inhibitor physostigmine (50 microM), elicited a stimulatory effect on juvenile hormone acids (JHAs) release from the CA. Maximum effect was obtained at concentrations of 10 and 50 microM. Repeated administration of 10 microM acetylcholine on the same CA did not elicit similar stimulatory effect. Since JHA release can be significantly activated by carbachol and not by nicotine, this cholinergic effect is likely to belong to the muscarinic type. The effect of acetylcholine was significantly antagonized by gallamine triethiodide (M(2) antagonist) and 4-DAMP (M(3) antagonist), pirenzepine (M(1) antagonist), and tropicamide (M(4) antagonist) were ineffective. It is concluded that in the adult male M. loreyi, the cholinergic regulation of CA is most likely via M(2) and M(3) muscarinic receptors.     

Acetylcholine does not stimulate the release of growth hormone from perifused rat adenohypophyses.

Acetylcholine (1 micromol/L--1 mmol/L) has been reported to stimulate growth hormone release from perifused bovine pituitary slices. We have carried out studies using the perifused pars distalis of the rat adenohypophysis to see whether a similar response is observed. Neither acetylcholine, acetylcholine with eserine, nor carbamylcholine, at concentrations of 10(-9), 10(-6), and 10(-3) M. stimulated the release of growth hormone. Thus we could not demonstrate a similar reponse to acetylcholine in the pars distalis of the rat adenohypophysis as reported in the bovine gland.     

Effects of Substance P on the Binding of Agonists to the Nicotinic Acetylcholine Receptor of Torpedo Electroplaque

Abstract: Abstract: The effect of the neuropeptide substance P on the binding of the cholinergic ligands to the nicotinic acetylcholine receptor of Torpedo electroplaque membranes was examined at a physiological concentration of NaCl (150 m M ). Substance P had no effect on the initial rate of ¹²⁵I-α-bungarotoxin binding at concentrations of <100 μ M . The peptide did not bind to the high-affinity local anesthetic site but allosterically modulated [³H]phencyclidine binding, positively in the absence of agonist and negatively in the presence of agonist. Substance P increased the apparent affinity of the cholinergic agonists carbamylcholine and acetylcholine at equilibrium. The effect of substance P on the equilibrium binding of [³H]acetylcholine was examined directly, and the peptide appeared to increase the affinity of the binding of the second molecule of agonist, with no effect on the binding of the first. This indicates that substance P can affect the cooperative interactions between agonist binding sites. Substance P appeared to increase the rate of carbamylcholine-induced desensitization; however, the data are also consistent with an allosteric mechanism that does not involve the desensitized state. To attempt to differentiate between these mechanisms, the rates of recovery were determined after exposure to peptide and/or agonist. The kinetics of recovery are consistent with stabilization of the desensitized state by substance P if the peptide remains bound long enough to allow rapid recovery to the low-affinity state. However, an allosteric modulation of agonist binding that does not involve the desensitized state cannot be ruled out.     

Acute and chronic studies on functional aspects of coexistence

Autoinhibition of acetylcholine release by the coexisting peptide galanin in the septal afferents to the hippocampus of the rat was examined in tissue slices from the hippocampus. Galanin inhibits the evoked release of the coexisting neurotransmitter, acetylcholine, in the ventral hippocampus, providing an example of autoinhibition of release of a neurotransmitter by one of the coexisting neurotransmitters. The galanin mediated inhibition of the acetylcholine release is a complement to the well known strong cholinergic autoinhibition. The effects of the coexisting galanin and acetylcholine on several second messenger systems were also examined: acetylcholine acting at muscarinic receptors depresses cyclic adenosine 3',5'-monophosphate and stimulates elevation of cyclic guanosine 3',5'-monophosphate levels, whereas neither cyclic adenosine 3',5'-monophosphate nor cyclic guanosine 3',5'-monophosphate levels were affected by galanin (1 microM). Galanin however inhibited partly the muscarinic stimulation of phosphoinositide breakdown, suggesting that inositol phosphate(s) or diacylglycerol may act as second messenger(s) of the galanin action in the hippocampus. The effects of chronic changes in firing rate on the coexisting neurotransmitters in the rat ventral spinal cord containing serotonin, thyrotropin releasing hormone, substance P and substance K were examined. The tissue levels of the coexisting transmitters were studied in rats chronically treated with imipramine (14 days; 2 x 10 mumoles/kg/day) and zimelidine (14 days; 2 x 10 mumoles/kg/day). Upon treatment with zimelidine the tissue levels of the serotonin metabolite 5-hydroxyindoleacetic acid fall by 32% while thyrotropin releasing hormone levels seem to increase 35% and substance P/substance K levels also increase 48 and 72% respectively. Imipramine treatment resulted in similar although less pronounced changes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of acetylcholine on coordination of spontaneous activities registered from different areas of uterus in rats

Spontaneous electrical activities of uterine corpus, periuterine part of horn and uterine cervix in response to intravenous injections of different concentrations of acetylcholine were observed. The changes of frequency and amplitude characteristics of rhythmogenesis in these conditions, both separately and with their co-active state were analysed. Acetylcholine in concentration of 10(-3) M in the blood of the animal creates the optimal conditions for synchronization and coordination of electrical activities in the above areas of the uterus.     

Eosinophil-induced release of acetylcholine from differentiated cholinergic nerve cells

One immunological component of asthma is believed to be the interaction of eosinophils with parasympathetic cholinergic nerves and a consequent inhibition of acetylcholine muscarinic M2 receptor activity, leading to enhanced acetylcholine release and bronchoconstriction. Here we have used an in vitro model of cholinergic nerve function, the human IMR32 cell line, to study this interaction. IMR32 cells, differentiated in culture for 7 days, expressed M2 receptors. Cells were radiolabeled with [3H]choline and electrically stimulated. The stimulation-induced release of acetylcholine was prevented by the removal of Ca2+. The muscarinic M1/M2 receptor agonist arecaidine reduced the release of acetylcholine after stimulation (to 82 +/- 2% of control at 10(-7) M), and the M2 receptor antagonist AF-DX 116 increased it (to 175 +/- 23% of control at 10(-5) M), indicating the presence of a functional M2 receptor that modulated acetylcholine release. When human eosinophils were added to IMR32 cells, they enhanced acetylcholine release by 36 +/- 10%. This effect was prevented by inhibitors of adhesion of the eosinophils to the IMR32 cells. Pretreatment of IMR32 cells with 10 mM carbachol, to desensitize acetylcholine receptors, prevented the potentiation of acetylcholine release by eosinophils or AF-DX 116. Acetylcholine release was similarly potentiated (by up to 45 +/- 7%) by degranulation products from eosinophils that had been treated with N-formyl-methionyl-leucyl-phenylalanine or that had been in contact with IMR32 cells. Contact between eosinophils and IMR32 cells led to an initial increase in expression of M2 receptors, whereas prolonged exposure reduced M2 receptor expression.