Effects of neurokinin A and calcitonin gene-related peptide on mucociliary activity in rabbit maxillary sinus

The Rabbit Maxillary Sinus: A Review of the Effects of Innervation on Mucociliary Activity

The stable bone walls of the maxillary sinus of the rabbit permit undisturbed recordings of the mucociliary activity by a photoelectric technique in vivo. The distribution of peptidergic neurotransmittors in the rabbit maxillary sinus was compared with their mucociliary effects on the same preparation. Nerve fibers containing neuropeptide Y were abundant around blood vessels and glands in the lamina propria. A few nerve fibers were seen just beneath the epithelium. Injections with neuropeptide Y decreased mucociliary wave frequency, the maximum decrease was about 15% for the doses 1.0 and 5.0 μg/kg. Vasoactive intestinal polypeptide (VIP) was found in the subepithelial layer and also distributed close to glands and blood vessels in the lamina propria. Administration of VIP alone did not change the mucociliary activity. However, if the rabbits were challenged with threshold doses of the mucociliary stimulant methacholine, the response to the cholinergic agonist was potentiated by VIP. Substance P (SP)-containing nerve fibers were found in the subepithelial layer, with single varicose endings sometimes penetrating into the epithelium. Challenges with SP produced a prompt increase of the mucociliary activity (the maximum increase was about 50% above baseline level), presumably due to increased chloride flux toward the lumen. Similar effects were produced by neurokinin A, which emanates from the same precursor molecule as SP. Another sensory peptide, calcitonin gene-related peptide was without effect on the mucociliary system. Our data indicate that there is a correlation between the occurrence of nerve fibers just beneath the epithelium and mucociliary effects. A localization close to the epithelium seems a logical prerequisite for epithelial effects.

Calcitonin gene-related peptide in vitro stimulation of ciliary beat in human upper respiratory cilia

Calcitonin gene-related peptide (CGRP) is one of the neuropeptides that is released in the human nasal mucosa after trigeminal nerve stimulation. We investigated the in vitro effect of CGRP on the ciliary beat frequency (CBF) of human upper respiratory cilia. Ciliated epithelium of freshly removed adenoidal tissues was used in all experiments. CBF was measured using a computerized photo-electric method. The results showed that CGRP exerted a significant dose-dependent stimulation on CBF in concentrations of 10(-9)-10(-6) M (n = 10), with a maximum of 23%. Our findings indicate that CGRP in vivo may help to protect the airway epithelium by directly stimulating ciliary beat.

NK1 receptors mediate the increase in mucociliary activity produced by tachykinins

The mucociliary activity of the rabbit maxillary sinus is increased after exposure to airway irritants such as cigarette smoke and capsaicin. This effect is partly due to a cholinergic reflex but involves an atropine-resistant response probably mediated by the release of tachykinins such as substance P or neurokinin A from sensory nerve endings. The aim of the present investigation was to evaluate the type of tachykinin receptor which mediates this increase in mucociliary activity. The mucociliary activity of the rabbit maxillary sinus was studied photoelectrically in vivo. It was found that a selective NK1 receptor agonist, [Sar9,Met(O2)11]substance P, dose dependently stimulated mucociliary activity, the maximum increase being 43.74 +/- 6.07% at a dose of 1 nmol/kg. A selective NK2 receptor agonist, [Nle10]neurokinin A-(4-10), produced a much weaker response, the maximum increase being 15.23 +/- 3.86% at a dose of 10 nmol/kg, whereas an NK3 receptor agonist, [Pro7]neurokinin B, was without effect. When the effects of the selective agonists were compared with the responses elicited by naturally occurring tachykinins at a dose of 1 pmol/kg, the order of the magnitude of the responses was [Sar9,Met(O2)11]substance P > substance P > neurokinin A. At this dosage the NK2 and NK3 receptor agonists did not have a significant effect. Pretreatment with the endopeptidase inhibitor phosphoramidon did not influence the magnitude of the responses but increased their duration. It is concluded that the NK1 receptor is responsible for the increase in mucociliary activity elicited by tachykinins released from sensory afferents in the upper airways.

Neutral endopeptidase inhibitor potentiates the tachykinin-induced increase in ciliary beat frequency in rabbit trachea

We used cultured rabbit tracheal epithelium to determine the effect of mammalian-derived tachykinin on airway ciliary activity and its modulation by neutral endopeptidase EC 3.4.24.11 (NEP). Neurokinin A (NKA) caused dose-dependent increases in ciliary beat frequency (CBF), as measured by a photoelectric method, with the maximal increase from the baseline 15.7 +/- 1.7% (mean +/- SEM, p less than 0.01), whereas substance P (SP) had no effect. The NKA-induced increase in CBF was not inhibited by phentolamine, propranolol, or atropine, but it was abolished by the tachykinin antagonist [D-Pro2, D-Trp7,9]SP. Pretreatment of tissue with thiorphan (10(-5) M), a NEP inhibitor, had little effect on CBF responses to NKA; however, it significantly potentiated the responses to SP (14.9 +/- 3.0%, p less than 0.01). Other peptidase inhibitors, including captopril, bestatin, and leupeptin, did not alter the tachykinin-induced CBF response, suggesting that angiotensin converting enzyme, aminopeptidases, and serine proteinases do not modulate ciliary activity in response to tachykinins. These results suggest that NKA increases CBF by acting directly on tachykinin receptors and that NEP may play a role in modulating the tachykinin-induced stimulatory effects on CBF.

Mucociliary activity and the diving reflex

It has previously been shown that mucociliary activity in the rabbit maxillary sinus is immediately increased after short-term exposure to such airway irritants as cigarette smoke and ammonia vapor. This increase is mediated through the stimulation of capsaicin-sensitive nerve endings. Besides producing the mucociliary effect, these irritants inhibit breathing, a response characteristic of the diving reflex in mammals. Whether an increase in mucociliary activity is part of the diving reflex was investigated by injecting 0.5 mL water into the nasopharynges of anesthetized rabbits. Mucociliary and respiratory responses were compared with the effects of mechanical stimulation (ie, rotating an intranasal catheter until sneezing occurred). Water challenge produced an increase in mucociliary activity of 21.6% +/- 2.4%, a response that began approximately 10 seconds after injection. Mucociliary acceleration was completely blocked by atropine, indicating a cholinergic mechanism, but was unaffected by pretreatment with capsaicin. The respiration rate was inhibited by about 45% after challenge with water. Pretreatment with atropine and capsaicin had no effect on this reduced respiratory rate. Mechanical stimulation of the nasal mucosa accelerated mucociliary activity. This response appeared approximately 4 seconds after stimulation was begun, and occurred simultaneously with the onset of sneezing. The peak increase was 22.0% +/- 2.1%. Sneezing was followed by an increase in the respiration rate of about 40%. Pretreatment with atropine or capsaicin had no effect on respiratory responses, but did inhibit mucociliary acceleration, suggesting that the response is mediated through cholinergic effector neurons after activation of capsaicin-sensitive nerve endings.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic and C-fibre mediated mechanisms in the stimulation of mucociliary activity induced by prostaglandins and histamine

The involvement of cholinergic and C-fibre mediated mechanisms in the stimulation of mucociliary activity induced by prostaglandins and histamine was investigated in vivo in the rabbit maxillary sinus with a photoelectric technique. The prostaglandins E, (PGE,) and F2(2) alpha (PGF2 alpha) in dose of 0.1 microgram/kg and 10 micrograms/kg respectively stimulated the mucociliary activity in a biphasic fashion, with a small initial response during the first 1-2 min and a later maximum response after 3-4 min. These effects were resistant to atropine and to the SP antagonist (D-Pro2, D-Trp7,9)SP. The small initial response was blocked by pretreatment with high doses of capsaicin (13 mg i.a.), while the maximum response was unaffected. This indicates that the mucociliary responses induced by PGE, and PGF2 alpha involve capsaicin-sensitive C-fibres but that neither acetylcholine nor substance P were responsible. Histamine (50 micrograms/kg) stimulated mucociliary activity in the rabbit maxillary sinus and the effect was abolished by pretreatment with high doses of capsaicin and reduced by the SP antagonist (D-Pro2, D-Trp7,9)SP. This indicates that the histamine-induced stimulation of mucociliary activity involves capsaicin-sensitive C-fibres and that the effect might be mediated by substance P.

Capsaicin evokes secretion of nasal fluid and depletes substance P and calcitonin gene-related peptide from the nasal mucosa in the rat

1. The secretion of nasal fluid was studied in anaesthetized rats after topical application of capsaicin, and of calcitonin gene-related peptide (CGRP) alone or CGRP in combination with substance P (SP). The flow of nasal fluid was stimulated and the secretions collected by a filter paper technique. The concentrations of SP and CGRP in nasal biopsies were determined after topical or systemic administration of capsaicin. 2. Capsaicin (single dose administration) stimulated nasal secretion in a dose-dependent manner. The effect was inhibited by hexamethonium, lignocaine, or by the tachykinin antagonist (D-Pro2, D-Trp7,9)-SP, but not by atropine, or by a combination of the histamine H1-receptor antagonist chlorpheniramine and the H2-receptor antagonist ranitidine. 3. When applied cumulatively, capsaicin rapidly produced desensitization. The concentrations of SP and CGRP in the nasal mucosa were reduced by capsaicin 6 days after topical or s.c. administration but not 15 min after topical application of desensitizing doses. 4. CGRP did not stimulate the secretion of nasal fluid and did not alter SP-evoked nasal secretion. 5. The inhibition by hexamethonium of the capsaicin-evoked nasal secretion suggests the involvement of ganglionic reflexes. In addition, the inhibition of the response to capsaicin by (D-Pro2,D-Trp7,9)-SP and lidocaine and the depletion of SP and CGRP after capsaicin indicate the involvement of tachykinin-mediated axon reflexes.

Effects of calcitonin gene-related peptide on airway epithelial functions in dogs

We studied the effects of calcitonin gene-related peptide (CGRP) on ciliary beat frequency (CBF) and electrical properties of canine tracheal epithelium by a photoelectric method and Ussing's short-circuit technique, respectively. CGRP dose dependently increased CBF, an effect that was accompanied by elevation of intracellular cyclic AMP but not affected by blockade of either Ca2+-influx or arachidonic acid metabolism. In contrast, CGRP elicited only a small and transient increase in short-circuit current without significant alterations in transepithelial potential difference or tissue conductance. These results suggest that CGRP may play a role in regulating airway mucociliary transport function.

VIP potentiates cholinergic effects on the mucociliary system in the maxillary sinus

The neuropeptide vasoactive intestinal polypeptide (VIP), which is found in a population of cholinergic parasympathetic neurons in the airways, has no effects per se on mucociliary activity. In order to test the hypothesis that VIP may modulate cholinergic regulation of the mucociliary system, VIP was infused intraarterially (8.4 pmol/kg/min), and the response to challenges with methacholine in the maxillary sinus of rabbits were recorded with a photoelectric technique. Occurrence of VIP-like immunoreactivity in the rabbit maxillary sinus, maxillary nerve, and sphenopalatine ganglion was investigated. Immunoreactivity against VIP was found in nerve fibers in the subepithelial layer of the maxillary sinus and in numerous nerve cell bodies in the sphenopalatine ganglion. Infusion of VIP potentiated the mucociliary increase induced by methacholine. The mucociliary wave frequency change increased from 6.1% +/- 1.7% to 13.3% +/- 3.9% (0.01 micrograms/kg methacholine), from 11.6% +/- 3.6% to 18.8% +/- 2.2% (0.05 micrograms/kg) and from 17.0% +/- 3.0% to 27.4% +/- 3.6% (0.1 micrograms/kg). Both peak responses and response durations increased during infusions. In contrast, the vasodilating agent papaverine sulphate did not influence the mucociliary response to methacholine. The modulating effect of VIP on the mucociliary system, taken together with the morphologic observations, suggest that VIP may have a physiologic role in the regulation of the mucociliary system in the maxillary sinus.

Nasal exposure to airway irritants triggers a mucociliary defence reflex in the rabbit maxillary sinus

The effect on mucociliary (m.c.) activity in the rabbit maxillary sinus of cigarette smoke and ammonia (NH3) vapour delivered through a tracheal cannula or as nasal challenges was investigated by a photo-electric technique, and compared with simultaneously induced changes in the respiratory rate. Neither irritant had any effect on m.c. activity in the sinus after tracheo-bronchial exposure. However, the respiration rate was increased by NH3 vapour (2.5 ml, diluted 1:1 with room air) and neat cigarette smoke (10 ml) by 76.9% and 24.3% respectively (median values). In contrast, nasal challenges with both irritants increased m.c. activity by 24.1% (NH3) and 19.1% (cigarette smoke), and reduced the respiration rate by 31.0% (NH3) and 28.4% (cigarette smoke) (median values). NH3 vapour sometimes produced an apnea proper. Identical results were obtained in laryngectomized rabbits, indicating that laryngeal afferents were not involved in the responses. Moreover, topical application of the C-fibre stimulant capsaicin mimicked the effects produced by the airway irritants. It is concluded that nasal exposure to irritants triggers at least two different protective reflexes. One is the increase of m.c. activity in the upper airways involving sensory C-fibres and the other the apneic reflex of Kratschmer.