The effects of vasoactive intestinal polypeptide on cholinergic neurotransmission in an isolated innervated guinea pig tracheal preparation

Action of propranolol in the reaction of smooth musculature of tracheal rings induced with acetylcholine, histamine, serotonin (5-HT) and prostaglandin (PGF2-alfa) in vitro and in vivo

Actions of acetylcholine (ACh), histamines, serotonins (5-HT) and prostaglandins (PGF2-alfa) in concentrations of 10(-4), 10(-3), 10(-2) and 10(-1) mol/dm(3) were analyzed in vitro conditions in isolated specimens of tracheas of 24 pigs, 7 guinea pigs, and dead persons for different reasons (8), in the presence and without presence of propranolol. Whilst, research regarding actions of aerosolized histamines (10 mg, 1%, 2 min), in the presence and without the presence of aerosolized propranolol (20 mg, 2%, 2 min) was done in vivo in 6 healthy persons. Study results show that propranolol does not emphasize contraction of the airways smooth musculature as induced by ACh, histamine, 5-HT and PGF2-alfa in vitro conditions (p>0,1). Also, in vivo we found a non-significance of tracheal smooth musculature constriction (p>0,1).

Morphological and quantitative study of ganglionated plexus of Calomys callosus trachea

Calomys callosus is a wild, native forest rodent found in South America. In Brazil, this species has been reported to harbour the parasitic protozoan Trypanosoma cruzi. The ganglionated plexus of this species was studied using whole-mount preparations of trachea that were stained using histological and histochemical methods. The histological methods were used to determine the position of the ganglia with respect to the trachea muscle and to determine the presence of elastic and collagen fibers. The histochemical method of NADH-diaphorase was used for morphometric evaluations of the plexus. The tracheal plexus lies exclusively over the muscular part of the organ, dorsal to the muscle itself. It varies in pattern and extent between animals. The average number of neurons was 279 and the cellular profile area ranged from 38.37 microm2 to 805.89 microm2. Acetylcholinesterase (AChE) histochemistry verified that both ganglia and single neurons lie along nerve trunks and are reciprocally interconnected with the plexus. Intensely AChE-reactive neurons were found to be intermingled with poorly reactive ones. Two longitudinal AChE-positive nerve trunks were also observed and there was a diverse number of ganglia along the intricate network of nerves interconnecting the trunks. A ganglion capsule of collagen and elastic fibers surrounding the neurons was observed. Under polarized light, the capsule appeared to be formed by Type I collagen fibers.

Bronchodilating properties of the VIP receptor agonist Ro 25-1553 compared to those of formoterol on the guinea-pig isolated trachea

Ro 25-1553 is a 31-amino acid analogue of vasoactive intestinal peptide (VIP) and has recently been shown to be highly selective for the VPAC(2)-receptor. The bronchodilating property of this compound was evaluated in vitro on preparations of guinea-pig trachea, with the long-acting beta(2)-adrenoceptor selective agonist, formoterol, as a reference. In strip-preparations precontracted with carbachol, Ro 25-1553 caused a concentration-dependent and complete relaxation of the tracheal smooth muscle. Ro 25-1553 was 3-7 times less potent than formoterol on a molar basis, but the efficacy was comparable with that of formoterol. Both compounds showed a rapid onset of action and a similar durability of effect. Ro 25-1553 appeared to interact with formoterol as well as with salmeterol in an additive way. In vagus nerve-trachea tube preparations, when added to the external medium, Ro 25-1553 concentration-dependently and completely inhibited nerve-induced contractions. This occurred in the same concentration range as needed for relaxation of precontracted strips. Ro 25-1553 was active also when administered into the tracheal lumen albeit the concentration had to be increased. The present study supports and extends previous results suggesting that Ro 25-1553 may be a powerful alternative to the beta(2)-adrenoceptor agonists which prevail today.

Parasympathetic neurotransmission in rabbit isolated bronchus is modulated at prejunctional sites via endothelinB receptor stimulation

OBJECTIVE

The aim of this study was to investigate the mechanism involved in endothelin-induced potentiation of the response to parasympathetic nerve stimulation.

METHODOLOGY

We used autoradiographic and functional studies in rabbit isolated bronchi.

RESULTS

Autoradiography revealed dense binding sites for radiolabelled endothelin-3 over bronchial parasympathetic ganglia. The contractile response of the bronchus to electrical field stimulation was significantly potentiated by endothelin-3, endothelin-1, sarafotoxin S6c and BQ-3020 to 326+/-53%, 293+/-63%, 514+/-119% and 655+/-178%, respectively, of control values. The endothelin-3-induced potentiation of neurally evoked responses was not affected by the presence of propranolol, phentolamine or hexamethonium. The potentiation was also unaltered by pretreatment with the endothelinA receptor antagonist BQ-123 (3 micromol/L), but was significantly reduced in the presence of the combined endothelinA/endothelinB receptor antagonist PD 145065, indicating that the potentiation was mediated via endothelinB receptors. Confirmation of endothelinB receptor involvement in the neuropotentiation was obtained by demonstration of a significant amelioration of the potentiation in the presence of the endothelinB receptor selective antagonist BQ-788, and after endothelinB receptor desensitization by the endothelin, receptor selective agonist sarafotoxin S6b.

CONCLUSIONS

These results suggest that the endothelin-induced potentiation of parasympathetic neural responses in the rabbit bronchus is mediated via endothelinB receptor activation.

Neuroregulation by vasoactive intestinal peptide (VIP) of mucus secretion in ferret trachea: activation of BK(Ca) channels and inhibition of neurotransmitter release

1. The aims of this study were to determine: (1) whether vasoactive intestinal peptide (VIP) regulates cholinergic and 'sensory-efferent' (tachykininergic) 35SO4 labelled mucus output in ferret trachea in vitro, using a VIP antibody, (2) the class of potassium (K+) channel involved in VIP-regulation of cholinergic neural secretion using glibenclamide (an ATP-sensitive K+ (K(ATP)) channel inhibitor), iberiotoxin (a large conductance calcium activated K+ (BK(ca)) channel blocker), and apamin (a small conductance K(ca) (SK(ca)) channel blocker), and (3) the effect of VIP on cholinergic neurotransmission using [3H]-choline overflow as a marker for acetylcholine (ACh) release. 2. Exogenous VIP (1 and 10 microM) alone increased 35SO4 output by up to 53% above baseline, but suppressed (by up to 80% at 1 microM) cholinergic and tachykininergic neural secretion without altering secretion induced by ACh or substance P (1 microM each). Endogenous VIP accounted for the minor increase in non-adrenergic, non-cholinergic (NANC), non-tachykininergic neural secretion, which was compatible with the secretory response of exogenous VIP. 3. Iberiotoxin (3 microM), but not apamin (1 microM) or glibenclamide (0.1 microM), reversed the inhibition by VIP (10 nM) of cholinergic neural secretion. 4. Both endogenous VIP (by use of the VIP antibody; 1:500 dilution) and exogenous VIP (0.1 microM), the latter by 34%, inhibited ACh release from cholinergic nerve terminals and this suppression was completely reversed by iberiotoxin (0.1 microM). 5. We conclude that, in ferret trachea in vitro, endogenous VIP has dual activity whereby its small direct stimulatory action on mucus secretion is secondary to its marked regulation of cholinergic and tachykininergic neurogenic mucus secretion. Regulation is via inhibition of neurotransmitter release, consequent upon opening of BK(Ca) channels. In the context of neurogenic mucus secretion, we propose that VIP joins NO as a neurotransmitter of i-NANC nerves in ferret trachea.

NANC neural control of airway smooth muscle tone

1. This review addresses the functional role of the nonadrenergic, noncholinergic (NANC) neural response in the control of airway smooth muscle tone. 2. Functional data from guinea pig airways in vitro indicate that the level of basal smooth muscle tone determines the direction and magnitude of the NANC neural response such that it can stabilise tone. 3. The NANC stabilising effect on tone is adjustable through variation in impulse frequency and the NANC stabilising effect is also powerful; it can abolish near-maximum differences in tone. 4. Cholinergic activation increases the level towards which the NANC responses tend to adjust tone. 5. Adrenergic activation reduces the level towards which the NANC responses tend to adjust tone via beta-adrenoceptors. 6. NANC neural activation, with or without simultaneous adrenergic or cholinergic activation, can stabilise tone at low, intermediate or high levels with a high degree of accuracy. 7. Evidence from other investigators on effects of putative NANC neurotransmitters supports the idea of functional interactions within the NANC system in the airways. 8. It remains to be confirmed whether or not NANC responses play a stabilising role in the control of airway smooth muscle tone in vivo and in higher mammals.

Endogenous vasoactive intestinal peptide and nitric oxide modulate cholinergic neurotransmission in guinea-pig trachea

Guinea-pig tracheal smooth muscle possesses an inhibitory non-adrenergic, non-cholinergic (i-NANC) innervation and the neurotransmitters involved in this response may be vasoactive intestinal peptide (VIP) and nitric oxide (NO). Since i-NANC mechanisms may co-exist with cholinergic nerves we have investigated whether endogenous VIP and NO modulate cholinergic neurotransmission. alpha-Chymotrypsin enhanced the cholinergic contractile responses to electrical field stimulation (EFS at 4 Hz by 38.6 +/- 4.8% (P < 0.05, n = 6) but did not produce a shift in the concentration-response curve to acetylcholine (ACh). L-NG-Nitro-arginine methyl ester (L-NAME) and L-NG-monomethyl arginine (L-NMMA) produced a concentration-dependent enhancement of cholinergic responses to EFS (4 Hz) (at 100 microM, 40.9 +/- 6.6 and 30.2 +/- 5.8%, P < 0.01) with no effect on response curves to ACh. This enhancement was reversed by L-arginine but not D-arginine (1 mM). D-NAME and D-NMMA and L-arginine had no effect on cholinergic neurotransmission. alpha-Chymotrypsin and L-NAME had no effect on excitatory NANC (e-NANC) neural responses in guinea-pig bronchi. These results suggest that endogenous NO and VIP may modulate cholinergic neurotransmission by either functional antagonism at the level of the airway smooth muscle or via a pre-junctional inhibition of ACh release from cholinergic nerve terminals or by both mechanisms.

Influence of vasoactive intestinal polypeptide and NG-nitro-L-arginine methyl ester on cholinergic neurotransmission in the rat gastric fundus

The possible modulating effect of vasoactive intestinal polypeptide (VIP) and nitric oxide (NO), on cholinergic neurotransmission was assessed in longitudinal muscle strips of rat gastric fundus. VIP and NO are the putative co-transmitters of the inhibitory non-adrenergic non-cholinergic (NANC) neurones in this tissue. VIP concentration dependently inhibited cholinergic contractions induced by 2-min transmural stimulation, relaxed tissues, the tone of which was continuously raised by transmural stimulation, and shifted to the right the frequency-response curves for contraction induced by transmural stimulation with a cumulative increase of frequency. The same effect was found when contractions were induced with methacholine, suggesting that only functional antagonism at the postsynaptic smooth muscle cell level is involved. On 30-min incubations, 3 x 10(-4) M NG-nitro-L-arginine methyl ester (L-NAME) potentiated cholinergic responses to 20-s transmural stimulation, while not influencing contractions of similar amplitude evoked by methacholine; the cholinergic responses to 2-min transmural stimulation were also not influenced. The potentiating effect of L-NAME was prevented by L-arginine but not D-arginine. These results suggest that endogenous NO released from the inhibitory NANC neurones during short trains of transmural stimulation interferes with cholinergic neurotransmission either by functional antagonism of acetylcholine at the postsynaptic level or by presynaptic inhibition of acetylcholine release.

Modulation of neural bronchoconstrictor responses in the guinea pig respiratory tract by vasoactive intestinal peptide

Vasoactive intestinal peptide (VIP) is localised to cholinergic nerves in airways. We have investigated the effects of VIP on both cholinergic and non-adrenergic, non-cholinergic (NANC) neuronal bronchoconstrictor responses to electrical field stimulation (EFS) in guinea pig airways and on cholinergic neurotransmission following sensory nerve depletion. VIP significantly attenuated the cholinergic bronchoconstrictor responses to EFS in trachea (EC50 values in upper and lower trachea of 3.7 +/- 0.2 x 10(-9) M and 8.6 +/- 0.3 x 10(-9) M, respectively) and bronchi (31.2 +/- 1.6% inhibition in main and 15.1 +/- 3.3% in hilar bronchi at 10(-7) M VIP) and the NANC bronchoconstrictor responses to EFS in bronchi (with maximum inhibitions of 93.1 +/- 1.8% at 3 x 10(-8) M VIP in main and 40.2 +/- 5.3% at 10(-8) M in hilar bronchi). VIP at 10(-7) M, but not at 10(-10) M, significantly attenuated the contractile responses to exogenously applied ACh in trachea (EC50 values of 4.9 +/- 0.2 x 10(-6) M in the absence and 8.4 +/- 0.4 x 10(-5) M in the presence of VIP 10(-7) M VIP) to SP in main bronchi (EC50 values of 5.7 +/- 0.2 x 10(-8) M in the absence vs. 7.3 +/- 0.3 x 10(-7) M in the presence of 10(-7) M VIP). Since the inhibition of these neural responses is greater than the inhibition of the equivalent responses elicited by the exogenous transmitters, this indicates that VIP may modulate release of acetylcholine from cholinergic nerves and of neuropeptides from sensory nerves, in addition to a post-junctional functional antagonist action.