Augmentation of respiratory mast cell secretion of histamine caused by vagus nerve stimulation during antigen challenge

We studied the effect of vagus nerve stimulation on the mast cell secretion of histamine after intraarterial (i.a.) administration of Ascaris suum antigen (AA) into the bronchial circulation of 10 randomly selected, natively allergic dogs in vivo. Respiratory mast cell response was measured as the arteriovenous difference (AVd) in histamine concentration across the bronchus. Plasma histamine concentration was determined simultaneously from right atrium, right ventricle, and femoral artery 60 and 15 sec before and 15, 30, 45, 60, 75, and 90 sec after i.a. injection of sham (Kreb-Henseleit) diluent, 1:100, and 1:30 concentrations of AA. The mean AVd in plasma histamine for five parasympathetically blocked animals (neural blockade with hexamethonium and beta-adrenergic blockade with propranolol) was 1.28 +/- 0.61 ng/ml (sham), 5.16 +/- 19.7 ng/ml (1:100 AA), and 36.6 +/- 11.1 ng/ml (1:30 AA). Substantial augmentation was obtained when AA was administered during parasympathetic stimulation in five other animals (beta-adrenergic blockade, no neural blockade), which was caused by continuous bilateral electrical stimulation of the vagus nerves. A mean AVd in plasma histamine of 110 +/- 27.6 ng/ml was obtained after 1:100 AA (p less than 0.001 vs parasympathetic blockade) and 166 +/- 32.4 ng/ml for 1:30 AA (p less than 0.001 vs parasympathetic blockade). Parasympathetic stimulation alone did not cause secretion of histamine. In contrast to the AVd response, parasympathetic stimulation did not augment nonrespiratory mast cell secretion after AA challenge. We conclude that vagus nerve stimulation augments secretion of histamine from respiratory mast cells during antigen challenge. We demonstrate that parasympathetic stimulation may potentiate the response to antigen challenge in central airways through augmented mast cell secretion of mediator.     

α7-cholinergic receptor mediates vagal induction of splenic norepinephrine

Classically, sympathetic and parasympathetic systems act in opposition to maintain the physiological homeostasis. In this article, we report that both systems work together to restrain systemic inflammation in life-threatening conditions such as sepsis. This study indicates that vagus nerve and cholinergic agonists activate the sympathetic noradrenergic splenic nerve to control systemic inflammation. Unlike adrenalectomy, splenectomy and splenic neurectomy prevent the anti-inflammatory potential of both the vagus nerve and cholinergic agonists, and abrogate their potential to induce splenic and plasma norepinephrine. Splenic nerve stimulation mimics vagal and cholinergic induction of norepinephrine and re-establishes neuromodulation in α7 nicotinic acetylcholine receptor (α7nAChR)-deficient animals. Thus, vagus nerve and cholinergic agonists inhibit systemic inflammation by activating the noradrenergic splenic nerve via the α7nAChR nicotinic receptors. α7nAChR represents a unique molecular link between the parasympathetic and sympathetic system to control inflammation.     

Chloride concentration of rat parotid saliva evoked by electrical stimulation of parasympathetic or sympathetic nerves with or without antagonists

Chloride (Cl) of saliva evoked by electrical stimulation of the parasympathetic nerve to parotid gland was from two to seven times higher than that elicited with sympathetic nerve stimulation; [Cl] remained elevated (125-135 mEq/liter) for 60 min of parasympathetic nerve stimulation, whereas Cl of sympathetically evoked saliva decreased from high levels of 58 to 15 to 20 mEq/liter. The administration of propranolol, the beta-adrenergic antagonist, 20 min prior to initiation of sympathetic nerve stimulation resulted in saliva with Cl of 100 mEq/liter; when phentolamine, the alpha-adrenergic antagonist was administered prior to sympathetic nerve stimulation, [Cl] was 48-35 mEq/liter. Values with the beta-agonist, isoproterenol, were about 35 mEq/liter, whereas phenylephrine, an alpha-adrenergic agonist, evoked saliva with Cl ranging from 113 to 85 mEq/liter. Flow rate was very high with parasympathetic nerve stimulation and low with sympathetic nerve stimulation, but [Cl] with beta-blockade was not flow dependent: flow was very low but Cl high. Cl secretion is principally regulated by activation of cholinergic and alpha-adrenergic receptors.     

The sphincter of the efferent filament artery in teleost gills: I. Structure and parasympathetic innervation

Previous studies have shown the existence of a sphincter in the efferent filament artery of the teleost gill and its constrictory response to acetylcholine (ACH) and vagal stimulation. This study deals with the muscular organization of this sphincter and the distribution of its innervation as elucidated by degeneration methods and cytochemistry. The sphincter innervation is supplied by the protrematic vagus nerves. Nerve endings filled with cholinergic-type vesicles are located in close association with the adventitial smooth muscle cells and display a strong acetylcholinesterase (ACHE) activity. Section of the protrematic vagus nerve induces a nearly complete degeneration of the sphincter innervation. ACHE-positive nerve cell bodies are present both in the sphincter area and in the protrematic vagus nerve. These results suggest that innervation of the sphincter in the efferent filament artery is cholinergic through the activity of postganglionic axons of the parasympathetic system.     

Fade of the responses of the isolated, blood-perfused dog atrium to cholinergic interventions

In the isolated, blood-perfused, canine right atrium, intramural parasympathetic nerve stimulation and intra-arterial infusions of acetylcholine induced substantial negative chronotropic and inotropic responses. The responses to parasympathetic stimulation reached their maximum values quickly, and then usually faded back toward control levels over the next 1 or 2 min of stimulation. The fade of the responses at high stimulation frequencies (greater than or equal to 30 Hz) was significantly greater than that at lower frequencies. The inotropic responses to acetylcholine infusion (1 microgram/min) faded slightly but significantly, whereas the chronotropic responses did not fade at all. These results suggest that the fade of the cardiac responses to parasympathetic stimulation is mainly ascribable to a progressive reduction in the rate of acetylcholine release from the nerve endings, especially at higher stimulation frequencies. The fade of the inotropic responses was more pronounced and had a longer time course than that of the chronotropic responses. Furthermore, the fade of the inotropic responses diminished significantly as the response magnitude was augmented by an increase in stimulation voltage. Conversely, the fade of chronotropic responses was not significantly affected by this intervention. These differences in the inotropic and chronotropic responses to neural stimulation, and the occurrence of a slight fade of the inotropic response to acetylcholine infusion, suggest that in addition to the predominant prejunctional mechanism, a postjunctional phenomenon may also be partly responsible for the fade of the inotropic response to cholinergic interventions.     

The structural dynamics of vagus influence on the heart rhythm in exposures directed at altering the acting acetylcholine concentration]

In 29 experiments on anaesthetized cats burst stimulation of peripheral cut end of right vagus nerve leads to synchronization of heart and vagus rhythm. Influence of proserine, pilocarpine and prolonged vagus stimulation upon extent of vagus chronotropic effect and its components--tonic and synchronizing--was investigated. In all cases changes of vagus chronotropic effect during this actions were caused by unidirectional shifts of tonic component. Extent of synchronizing vagus chronotropic influences did not depend on the changes of acetylcholine concentration.     

Hepatic Branch Vagus Nerve Plays a Critical Role in the Recovery of Post-Ischemic Glucose Intolerance and Mediates a Neuroprotective Effect by Hypothalamic Orexin-A

Orexin-A (a neuropeptide in the hypothalamus) plays an important role in many physiological functions, including the regulation of glucose metabolism. We have previously found that the development of post-ischemic glucose intolerance is one of the triggers of ischemic neuronal damage, which is suppressed by hypothalamic orexin-A. Other reports have shown that the communication system between brain and peripheral tissues through the autonomic nervous system (sympathetic, parasympathetic and vagus nerve) is important for maintaining glucose and energy metabolism. The aim of this study was to determine the involvement of the hepatic vagus nerve on hypothalamic orexin-A-mediated suppression of post-ischemic glucose intolerance development and ischemic neuronal damage. Male ddY mice were subjected to middle cerebral artery occlusion (MCAO) for 2 h. Intrahypothalamic orexin-A (5 pmol/mouse) administration significantly suppressed the development of post-ischemic glucose intolerance and neuronal damage on day 1 and 3, respectively after MCAO. MCAO-induced decrease of hepatic insulin receptors and increase of hepatic gluconeogenic enzymes on day 1 after was reversed to control levels by orexin-A. This effect was reversed by intramedullary administration of the orexin-1 receptor antagonist, SB334867, or hepatic vagotomy. In the medulla oblongata, orexin-A induced the co-localization of cholin acetyltransferase (cholinergic neuronal marker used for the vagus nerve) with orexin-1 receptor and c-Fos (activated neural cells marker). These results suggest that the hepatic branch vagus nerve projecting from the medulla oblongata plays an important role in the recovery of post-ischemic glucose intolerance and mediates a neuroprotective effect by hypothalamic orexin-A.     

Vagus nerve is involved in lack of blood reflow into sinusoids after rat hepatic ischemia

Although recovery of microcirculation is an important determinant for ischemia-reperfusion injury, little information is available about hepatic blood flow after ischemia. To examine regulatory mechanisms of postischemic hepatic microcirculation, we studied the sinusoidal blood flow after portal triad clamping of rat livers for 5, 15, or 30 min. Hepatic tissue blood flow and erythrocyte blood flow in sinusoids were measured using a laser-Doppler flowmeter and an intravital microspectroscope, respectively. There was a time of no blood flow (lag time) in sinusoids after declamping, dependent on the ischemic time. Cholinergic blockade agents eliminated the lag time, whereas nerve stimulation at the hiatus esophagus or on the hepatoduodenal ligament during reperfusion prolonged it. Chemical denervation with 10% phenol or surgical denervation on the hepatoduodenal ligament eliminated the lag time. The prolongation of lag time by nerve stimulation was completely abrogated by truncal vagotomy. These results suggest that the cholinergic vagus nerve is involved in causing the lag time of sinusoidal blood flow in hepatic ischemia-reperfusion.     

Inspiratory rhythm in airway smooth muscle tone

In anesthetized paralyzed open-chested cats ventilated with low tidal volumes at high frequency, we recorded phrenic nerve activity, transpulmonary pressure (TPP), and either the tension in an upper tracheal segment or the impulse activity in a pulmonary branch of the vagus nerve. The TPP and upper tracheal segment tension fluctuated with respiration, with peak pressure and tension paralleling phrenic nerve activity. Increased end-tidal CO2 or stimulation of the carotid chemoreceptors with sodium cyanide increased both TPP and tracheal segment tension during the increased activity of the phrenic nerve. Lowering end-tidal CO2 or hyperinflating the lungs to achieve neural apnea (lack of phrenic activity) caused a decrease in TPP and tracheal segment tension and abolished the inspiratory fluctuations. During neural apnea produced by lowering end-tidal CO2, lung inflation caused no further decrease in tracheal segment tension and TPP. Likewise, stimulation of the cervical sympathetics, which caused a reduction in TPP and tracheal segment tension during normal breathing, caused no further reduction in these parameters when the stimulation occurred during neural apnea. During neural apnea the tracheal segment tension and TPP were the same as those following the transection of the vagi or the administration of atropine (0.5 mg/kg). Numerous fibers in the pulmonary branch of the vagus nerve fired in synchrony with the phrenic nerve. Only these fibers had activity which paralleled changes in TPP and tracheal tension. We propose that the major excitatory input to airway smooth muscle arises from cholinergic nerves that fire during inspiration, which have preganglionic cell bodies in the ventral respiratory group in the region of the nucleus ambiguus and are driven by the same pattern generators that drive the phrenic and inspiratory intercostal motoneurons.     

Sympathoadrenal system in neuroendocrine control of glucose: mechanisms involved in the liver, pancreas, and adrenal gland under hemorrhagic and hypoglycemic stress.

Glucose homeostasis is maintained by complex neuroendocrine control mechanisms, involving three peripheral organs: the liver, pancreas, and adrenal gland, all of which are under control of the autonomic nervous system. During the past decade, abundant results from various studies on neuroendocrine control of glucose have been accumulated. The principal objective of this review is to provide overviews of basic adrenergic mechanisms closely related to glucose control in the three peripheral organs, and then to discuss the integrated glucoregulatory mechanisms in hemorrhage-induced hypotension and insulin-induced hypoglycemia with special reference to sympathoadrenal control mechanisms. The liver is richly innervated by sympathetic and parasympathetic nerves. The functional implication in glucoregulation of sympathetic nerves has been well-documented, while that of parasympathetic nerves remains less understood. More recently, hepatic glucoreceptors have been postulated to be coupled with capsaicin-sensitive afferent nerves, conveying sensory signals of blood glucose concentration to the central nervous system. The pancreas is also richly supplied by the autonomic nervous system. Besides the well documented adrenergic and cholinergic mechanisms, the potential implication of peptidergic neurotransmission by neuropeptide Y and neuromodulation by galanin has recently been postulated in the endocrine secretory function. Presynaptic interactions of these putative peptidergic neurotransmitters with the classic transmitters, noradrenaline and acetylcholine, in the pancreas remain to be clarified. It may be of particular interest that it was vagus nerve stimulation that caused a dominant release of neuropeptide Y over that caused by sympathetic nerve stimulation in the pig pancreas. The adrenal medulla receives its main nerve supply from the greater and lesser splanchnic nerves. Adrenal medullary catecholamine secretion appears to be regulated by three distinct local mechanisms: adrenoceptor-mediated, dihydropyridine-sensitive Ca2+ channel-mediated, and capsaicin-sensitive sensory nerve-mediated mechanisms. In response to hemorrhagic hypotension and insulin-induced hypoglycemia, the sympathoadrenal system is activated resulting in increases of adrenal catecholamine and pancreatic glucagon secretions, both of which are significantly implicated in glucoregulatory mechanisms. An increase in sympathetic nerve activity occurs in the liver during hemorrhagic hypotension and is also likely to occur in the pancreas in response to insulin-induced hypoglycemia. The functional implication of hepatic and central glucoreceptors has been suggested in the increased secretion of glucose counterregulatory hormones, particularly catecholamines and glucagon.     

Role of depolarization and calcium in contractions of canine trachealis from endogenous or exogenous acetylcholine

The relationships of the electrical to the mechanical responses of the canine trachealis muscle during stimulation of its cholinergic nerves or exposure to exogenous acetylcholine were recorded in the single or the double sucrose gap. At 27 degrees C, the responses to a train of stimuli consisted of a transient depolarization excitatory junction potential of 10-30 mV followed by fading oscillations and contractions. When stimulus parameters were varied in the single sucrose gap, contractions were more closely associated with the occurrence of and varied in duration with the oscillations rather than with the amplitude of the EJP. Acetylcholine superfused at a concentration of 10(-6) M for 30 s caused a prolonged depolarization of 10-20 mV, but a much larger contraction than could be elicited by nerve stimulation. None of the responses to acetylcholine was significantly affected by the Ca channel antagonists, nifedipine, nitrendipine, or verapamil in Ca channel blocking concentrations. When tissues were exposed to a Ca-free medium, the excitatory junction potentials and oscillations rapidly disappeared, but the electrical and mechanical responses to acetylcholine persisted and only gradually disappeared with repetitive exposures. Furthermore, in a medium with normal Ca2+ in the double sucrose gap, depolarization by 10-15 mV with an applied current caused no contraction, and repolarization to the normal membrane potential during acetylcholine-induced contraction caused no relaxation. Tetraethylammonium ion (20 mM) depolarized the membrane, increased membrane resistance, and enhanced the secondary oscillations and contractions after field stimulation. No other K(+)-channel blocker tested (Ba2+, apamin, 4-aminopyridine, glibenclamide, charybdotoxin) had the effect of prolonging secondary oscillations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prejunctional beta 1-adrenoceptors inhibit cholinergic transmission in canine bronchi

The aim of the present study was to determine in canine bronchi the effects produced by norepinephrine (released from adrenergic nerve terminals) on cholinergic neurotransmission. Electrical stimulation of canine bronchi activates cholinergic and adrenergic nerve fibers. The adrenergic neuronal blocker, bretylium tosylate, inhibited the increase in [3H]norepinephrine overflow evoked by electrical stimulation but did not prevent that caused by the indirect sympathomimetic tyramine. During blockade of the exocytotic release of norepinephrine with bretylium, the pharmacological displacement of the sympathetic neurotransmitter by tyramine significantly decreased the contractions evoked by electrical stimulation but did not affect contractions caused by exogenous acetylcholine. Metoprolol, a beta 1-adrenergic antagonist, abolished and propranolol significantly reduced the effect of tyramine during electrical stimulation. alpha 2-Adrenergic blockade, beta 2-adrenergic blockade, or removal of the epithelium did not significantly affect the response to tyramine. These results suggest that norepinephrine when released from sympathetic nerve endings can activate prejunctional inhibitory beta 1-adrenoceptors to depress cholinergic neurotransmission in the bronchial wall.     

Effect of electrical stimulation of the autonomic nerves on the levels and synthesis of cyclic nucleotides in the rat salivary glands: relationship to enhanced growth.

Electrical stimulation of either the parasympathetic or the sympathetic nerve supply to the parotid and submaxillary glands increases the intracellular level of cyclic GMP and the rate of DNA synthesis and cell division while only sympathetic stimulation raises cyclic AMP levels. The periods of electrical stimulation inducing hyperplasia also raise the cyclic GMP concentration but there is no similar correlation with changes in cyclic AMP levels. However, the extent of hyperplasia induced by parasympathetic and sympathetic stimulation is not directly related to the size of the increase in cyclic GMP concentration that these treatments produce. Changes in cyclic AMP levels are reflected in altered in vitro adenylate cyclase activity. This activity is raised after 2 min sympathetic stimulation and markedly decreased with 30 min sympathetic or parasympathetic stimulation. Guanylate cyclase activity shows no such changes with nerve stimulation.     

Parasympathetic control of coronary blood flow

Active parasympathetic coronary vasodilation in excess of any changes in myocardial metabolism has been observed in a number of circumstances. Electrical stimulation of the cardiac end of the cut vagus nerve produces a cholinergic coronary vasodilation that is blocked by atropine. Activation of carotid body chemoreceptors, carotid sinus baroreceptors, or left ventricular receptors elicits reflex parasympathetic coronary vasodilation. The coronary vasodilation produced by these reflexes can be prevented by vagotomy or atropine. The relative importance of parasympathetic coronary control in relation to sympathetic and local metabolic coronary control awaits further research.     

The sphincter of the efferent filament artery in teleost gills: II. Sympathetic innervation

In addition to the cholinergic innervation described in the sphincter of the efferent filament arteries (Bailly and Dunel-Erb, ′86), an aminergic component has been demonstrated by specific techniques. The Falck fluorescence technique reveals a network of nerve fibers displaying a green fluorescence characteristic of catecholamines. At the ultrastructural level two types of fibers are present, one with clear vesicles and another with densecored vesicles. Axo-axonal synaptic relationships exist between the two types. Results of 5- and 6-OHDA (hydroxydopamine) treatments confirm the presence of an aminergic component. These observations support the notion of a dual innervation: cholinergic and adrenergic of, respectively, parasympathetic and sympathetic origin. The presence of presynaptic modulation is suggested. The aminergic component could inhibit or reduce the release of acetylcholine from cholinergic nerve endings. These results suggest that the sympathetic innervation modulates the vasoconstriction effect of the parasympathetic component.     

Effects of vagus nerve stimulation and vagotomy on systemic and pulmonary inflammation in a two-hit model in rats

Pulmonary inflammation contributes to ventilator-induced lung injury. Sepsis-induced pulmonary inflammation (first hit) may be potentiated by mechanical ventilation (MV, second hit). Electrical stimulation of the vagus nerve has been shown to attenuate inflammation in various animal models through the cholinergic anti-inflammatory pathway. We determined the effects of vagotomy (VGX) and vagus nerve stimulation (VNS) on systemic and pulmonary inflammation in a two-hit model. Male Sprague-Dawley rats were i.v. administered lipopolysaccharide (LPS) and subsequently underwent VGX, VNS or a sham operation. 1 hour following LPS, MV with low (8 mL/kg) or moderate (15 mL/kg) tidal volumes was initiated, or animals were left breathing spontaneously (SP). After 4 hours of MV or SP, rats were sacrificed. Cytokine and blood gas analysis was performed. MV with 15, but not 8 mL/kg, potentiated the LPS-induced pulmonary pro-inflammatory cytokine response (TNF-α, IL-6, KC: p<0.05 compared to LPS-SP), but did not affect systemic inflammation or impair oxygenation. VGX enhanced the LPS-induced pulmonary, but not systemic pro-inflammatory cytokine response in spontaneously breathing, but not in MV animals (TNF-α, IL-6, KC: p<0.05 compared to SHAM), and resulted in decreased pO(2) (p<0.05 compared to sham-operated animals). VNS did not affect any of the studied parameters in both SP and MV animals. In conclusion, MV with moderate tidal volumes potentiates the pulmonary inflammatory response elicited by systemic LPS administration. No beneficial effects of vagus nerve stimulation performed following LPS administration were found. These results questions the clinical applicability of stimulation of the cholinergic anti-inflammatory pathway in systemically inflamed patients admitted to the ICU where MV is initiated.     

电刺激家兔迷走神经中枢端诱导的黑-伯反射中的非联合型学习现象

本文旨在研究电刺激家兔迷走神经诱导的黑-伯（Hering-Breuer,HB）反射中的学习和记忆现象。选择性电刺激家兔迷走神经中枢端（频率10～100Hz,强度20～60μA,波宽0．3ms,持续60s）,观察对膈神经放电的影响。以不同频率电刺激家兔迷走神经可模拟HB反射的两种成分,即类似肺容积增大所致抑制吸气的肺扩张反射和类似肺容积缩小所致加强吸气的肺萎陷反射。（1）长时高频（≥40Hz,60s）电刺激迷走神经可模拟呼吸频率减慢,呼气时程延长的肺扩张反射。随着刺激时间的延长,膈神经放电抑制的程度逐渐衰减,表现为呼吸频率的减慢（主要由呼气时程延长所致）在刺激过程中逐渐减弱或消失,显示为适应性或“习惯化”的现象;刺激结束时呼吸运动呈现反跳性增强,表现为一过性的呼气时程缩短,呼吸频率加快,然后才逐渐恢复正常。长时低频（〈40Hz,60s）电刺激迷走神经可模拟呼吸频率加快、呼气时程缩短的肺萎陷反射。随着刺激时间的延长,膈神经放电增强的程度逐渐衰减,同样表现出“习惯化”现象;刺激结束后,膈神经放电不是突然降低,而是继续衰减,表现为呼气时程逐渐延长,呼吸频率逐渐减慢,直至恢复到前对照水平,表现了刺激后的短时增强效应。（2）HB反射的适应性或“习惯化”程度反向依赖于刺激强度和刺激频率,表现为随着刺激强度和频率的增加,膈神经放电越远离正常基线水平,即爿惯化程度减弱。结果表明,家兔HB反射具有“习惯化”这一非联合型学习现象,反映与其有关的呼吸神经元网络具有突触功能的可翅性,呼吸的中枢调控反射具有一定的适应性。     

Mechanisms of the inhibitory effect of the stellate ganglion on cardiac activity

The mechanisms of cardiac activity inhibition caused by stimulation of the stellate ganglion were studied in acute experiments on 28 dogs and 37 cats and chronic experiments on 12 cats. It was shown that inhibition of cardiac activity is caused by stimulation of the parasympathetic fibers of the vagus, anastomozing with stellate ganglion branches and ingoing as part of these fibers to the heart. The hypothesis of change over of the sympathetic nerve fibers to the intracardial cholinergic neurons and the hypothesis of the cholinergic component in the mechanism of catecholamine release by the sympathetic nerve terminals was not confirmed. Therefore, the known Dale's principle as to that one neuron exerts its efferent effect with the aid of one transmitter is quite just. alpha-Adrenoreceptors does not produce any noticeable effect on cardiac activity.     

Autonomic nervous control of gastric somatostatin secretion from the perfused rat stomach

The effect of parasympathetic and sympathetic nerve stimulation on the secretion of gastric somatostatin and gastrin has been studied in an isolated perfused rat stomach preparation. Stimulation of the vagus nerve inhibited somatostatin secretion and increased gastrin release. Splanchnic nerve stimulation increased somatostatin release during simultaneous atropine perfusion, but not in its absence, whereas gastrin secretion was unchanged. The secretory activity of the gastric D-cell was therefore reciprocally influenced by the sympathetic and parasympathetic nerves but sympathetic stimulation was only effective during muscarinic blockade.     

VIP and noncholinergic vasodilatation in rabbit submandibular gland

The effect of parasympathetic nerve activation on rabbit submandibular gland (SMG) blood flow and saliva secretion were studied before and after systemic administration of atropine or hexamethonium. The parasympathetic fibers were stimulated electrically (2 and 15 Hz, 10 V, 1 msec) at the plexus around the submandibular salivary duct or at the chorda lingual nerve. In untreated animals, stimulation of parasympathetic fibers caused a frequency-dependent increase of salivary secretion and blood flow in the SMG. Atropine treatment completely abolished saliva secretion at 2 Hz and 15 Hz and the increase in SMG blood flow during stimulation at 2 Hz. Although atropine significantly reduced the vasodilatory response at 15 Hz, the highest blood flow measured under such circumstances was still about 2.5 times the prestimulation value. After hexamethonium administration no blood flow increase or saliva secretion was seen upon chorda lingual stimulation. The concentration of vasoactive intestinal polypeptide (VIP)-like immunoreactivity in the venous effluent of the SMG increased during nerve stimulation. Atropine significantly reduced, and hexamethonium abolished this VIP-output elicited by parasympathetic nerve stimulation. Local infusion of VIP, peptide histidine isoleucine (PHI) and substance P all caused atropine-resistant vasodilation but no salivation. The present data suggest that VIP and possibly PHI play a role in the atropine-resistant vasodilatation in rabbit submandibular gland elicited by parasympathetic nerve stimulation. The contribution of sensory mediators such as substance P released by stimulation of afferent nerves in the chorda lingual nerve to the salivary and vasodilatory responses seems to be of minor importance in the rabbit submandibular gland.