Vasoactive intestinal polypeptide and acetylcholine stimulate exocrine secretion of epidermal growth factor from the rat submandibular gland

A comparison between intratracheal and inhalation delivery of Aspergillus fumigatus conidia in the development of fungal allergic asthma in C57BL/6 mice

Allergic asthma is a debilitating disease of the airways characterized by airway hyperresponsiveness, eosinophilic inflammation, goblet cell metaplasia with associated mucus hypersecretion, and airway wall remodelling events, particularly subepithelial fibrosis and smooth muscle cell hyperplasia. Animal models that accurately mimic these hallmarks of allergic airways disease are critical for studying mechanisms associated with the cellular and structural changes that lead to disease pathogenesis. Aspergillus fumigatus, is a common aeroallergen of human asthmatics. The intratracheal (IT) delivery of A. fumigatus conidia into the airways of sensitized mice has been described as a model of allergic disease. Here, we compared the IT model with a newly developed inhalation (IH) challenge model. The IH model allowed multiple fungal exposures, which resulted in an exacerbation to the allergic asthma phenotype. Increased recruitment of eosinophils and lymphocytes, the hallmark leukocytes of asthma, was noted with the IH model as compared to the IT model in which macrophages and neutrophils were more prominent. Immunoglobulin E (IgE) production was significantly greater after IH challenge, while that of IgG(2a) was higher after IT challenge. Airway wall remodelling was pronounced in IH-treated mice, particularly after multiple allergen challenges. Although the IT model may be appropriate for the examination of the played by innate cells in the acute response to fungus, it fails to consistently reproduce the chronic remodelling hallmarks of allergic asthma. The ability of the IH challenge to mimic these characteristics recommends it as a model suited to study these important events.

Diminished epidermal growth factor levels in infants with necrotizing enterocolitis

BACKGROUND/PURPOSE

Because epidermal growth factor (EGF) is trophic to the intestinal mucosa, and neonatal necrotizing enterocolitis (NEC) is associated with a disrupted intestinal mucosal barrier, the authors sought to determine whether diminished levels of EGF were present in infants with NEC.

METHODS

Saliva, serum, and urine specimens were obtained from infants with NEC during a 3-year period (February 1995 to May 1998). Control patients without NEC were chosen based on similar postnatal age and birthweight. EGF levels were determined by enzyme-linked immunosorbent assay (ELISA). Differences between groups were compared using Mann-Whitney Rank sum test with P less than .05 considered significant. Results are presented as mean values +/-SEM.

RESULTS

Twenty-five infants with NEC were compared with 19 control patients. Birth weight (1,616+/-238 g control v. 1,271+/-124 g NEC) and postnatal age (23+/-6 days control v. 22+/-3 days NEC) were similar. Infants with NEC had significantly lower levels of EGF in both saliva (590+/-80 pg/mL control v. 239+/-41 pg/mL NEC; P<.001) and serum (35+/-8 pg/mL control v. 5.6+/-1.9 pg/mL NEC; P<.001). Urinary EGF was also lower in the NEC group, but was not statistically significant.

CONCLUSIONS

Premature infants with NEC have significantly diminished levels of salivary and serum EGF. Reduced levels of this growth factor may distinguish infants at risk for NEC and play a pivotal role in the pathogenesis of the perturbed intestinal mucosal barrier that is central to this condition.

The distribution of endogenous epidermal growth factor after small bowel resection suggests increased intestinal utilization during adaptation

BACKGROUND/PURPOSE

Although exogenous epidermal growth factor (EGF) amplifies adaptation after massive small bowel resection (SBR), the role for endogenous EGF is unclear. The authors sought to determine whether SBR was associated with changes in the levels of EGF in the serum, saliva, or urine and EGF receptor (EGF-R) signaling in the ileum.

METHODS

Male ICR mice underwent 50% proximal SBR or sham surgery bowel transection/reanastomosis). After 3 days, levels of EGF were measured by enzyme-linked immunosorbent assay (ELISA) in the serum, saliva, and urine. EGF-R activation was measured in isolated ileal enterocytes by probing an EGF-R immunoprecipitate with an antibody to phosphotyrosine.

RESULTS

When compared with sham, SBR resulted in no change in serum, increased salivary (2209+/-266 nmol SBR v 1183+/-119 nmol sham, P<.05) and decreased urinary (417+/-58 nmol SBR v 940+/-143 nmol sham; P<.05) EGF levels. EGF-R activation increased 2.5-fold after SBR.

CONCLUSIONS

Increased salivary and reduced urinary EGF linked with enhanced EGF-R activation suggests increased ileal utilization of EGF during adaptation. This observation, along with the known beneficial effects of exogenous EGF, infers a crucial role for endogenous EGF in the pathogenesis of intestinal adaptation after SBR.

Protein secretion from rat submandibular acini and granular ducts: effects of exogenous VIP and substance P during parasympathetic nerve stimulation

The influences of exogenous vasoactive intestinal peptide (VIP) and substance P on the release of peroxidase from acini and true tissue kallikrein (rK1) from granular ducts of the rat submandibular gland were studied during continuous parasympathetic stimulation. Parasympathetic nerve impulses caused a moderate flow of saliva (mean +/- SD, 108+/-26 microl/g tissue/min) that had a low protein concentration (174+/-88 microg/ml). The outputs of peroxidase and rK1 were minimal (14.3+/-11.8 pmol DCF/g tissue/min and 6.5+/-3.4 nmol AFC/g tissue/min, respectively). When administered intravenously, VIP had no apparent effect on the overall flow rate, but caused a significant increase in the output of peroxidase; 450% at 1 microg/kg and a further 10-fold increase at 10 microg/kg. In contrast, substance P (1 microg/kg) evoked a marked increase in flow rate (68%), and peroxidase secretion increased only 3-fold. The output of rK1 was unaffected by either VIP or substance P. Our results support the hypothesis that acinar, but not granular duct, protein secretion is evoked by non-adrenergic, non-cholinergic peptides released from parasympathetic nerve terminals.

Elevation of intracellular cAMP by noradrenaline and vasoactive intestinal peptide in striated ducts isolated from the rabbit mandibular salivary gland

Salivary gland intralobular ducts are responsible for the modification of the electrolyte composition of the primary fluid secreted by the acini. However, the intracellular messengers that regulate this and other intralobular duct cell processes have not been fully characterized. To investigate the possibility that cAMP-mobilizing agonists may be involved, intralobular (striated) ducts were isolated from the rabbit mandibular salivary gland by tissue dissociation and microdissection and maintained in tissue culture overnight. Individual duct fragments were stimulated with the secretory agonists noradrenaline, vasoactive intestinal peptide (VIP) and substance P and their cAMP content measured by acetylated radioimmunoassay. Both noradrenaline and VIP elevated intracellular cAMP content concentration dependently, but substance P did not. The response to noradrenaline was blocked by the beta-adrenoceptor antagonist propranolol, but not by the alpha-adrenoceptor antagonist prazosin. Application of the VIP analogue [D-p-Cl-Phe6, Leu17]-VIP decreased the VIP-induced cAMP response. These results demonstrate that striated intralobular duct cells possess beta-adrenoceptors and peptidergic receptors that are coupled to adenylate cyclase and activated by noradrenaline and VIP, respectively. By elevating ductal cAMP content, these agonists may regulate both the electrolyte content of the primary saliva and the secretion of protein(s) from the ducts.

Effects of vasoactive intestinal peptide and its homologues on the acetylcholine-mediated secretion of fluid and protein from the rat submandibular gland

1. Acetylcholine-mediated (ACh-mediated) secretion of fluid and protein from rat submandibular glands was enhanced by intravenous injection of vasoactive intestinal peptide (VIP) and of secretin but not of peptide histidine isoleucine (PHI) or gastric inhibitory peptide (GIP). 2. When VIP and ACh were administered together, the enhancement of fluid secretion was inhibited by pretreatment with atropine or 4-DAMP and the enhancement of protein secretion was inhibited by pretreatment with atropine or phentolamine. 3. The enhancement of the ACh-induced secretion of fluid by secretin was strongly inhibited by pretreatment with atropine, and it was weakly inhibited by pretreatment with phentolamine or haloperidol. 4. These results suggest that the synergistic effects of VIP, PHI, secretin and GIP on the ACh-mediated secretion of fluid and protein from the rat submandibular gland do not reflect the extent of the structural homology of each peptide to VIP.

Effects of vasoactive intestinal peptide and its homologues on the noradrenaline-mediated secretion of fluid and protein from the rat submandibular gland

1. Noradrenaline-mediated secretion of fluid and protein from rat submandibular glands was enhanced by vasoactive intestinal peptide (VIP) and secretin but not by peptide histidine isoleucine (PHI) or gastric inhibitory peptide (GIP). 2. The synergistic effect of the combination of VIP with noradrenaline (NA) was antagonized by pretreatment with prazosin or phentolamine but not by pretreatment with yohimbine or propranolol. 3. These results suggest that VIP and secretin but not PHI and GIP can significantly enhance the secretion of fluid and protein that is mediated by NA in rat submandibular gland and that the synergistic effect of VIP and NA involves both alpha 1-adrenergic receptors and receptors for VIP.

Effects of vasoactive intestinal peptide and its homologues on the substance P-mediated secretion of fluid and protein from the rat submandibular gland

1. Vasoactive intestinal peptide (VIP) and secretin elicited slight secretion of saliva but peptide histidine isoleucine (PHI) and gastric inhibitory peptide (GIP) failed to elicit secretion of saliva from rat submandibular glands. 2. Substance P (SP)-mediated secretion of fluid and protein were enhanced by VIP and secretin but not by PHI or GIP. 3. These results suggest that the effects of VIP, PHI, secretin and GIP on the secretion of fluid from rat submandibular glands and the synergistic effects of VIP and its homologues on the SP-mediated secretion of fluid and protein do not correspond to the extent of the structural homology of each analogue to VIP.

Effects of sialoadenectomy and exogenous EGF on molar drift and orthodontic tooth movement in rats

Effects on bone remodeling have been attributed to epidermal growth factor (EGF). Sialoadenectomy (SX) removes the major source of EGF in rodents and decreases both salivary and serum EGF levels. EGF effects on rat alveolar bone remodeling manifested by molar drift (MD) and orthodontic tooth movement (OTM) were examined using the following two approaches: 1) EGF depletion by SX and replacement by orally administered EGF (50 micrograms.animal-1.day-1); 2) sham rats supplemented with matching amounts of EGF. MD and OTM were measured using cephalometric radiographs; bone formation was measured histomorphometrically using tetracycline labeling. Normal MD was not detected after SX, and alveolar bone formation was significantly reduced both around the tooth and in nondental sites. Replacement EGF given to SX rats and supplemental EGF administered to sham rats changed the direction and enhanced the rate of MD. A mesially directed orthodontic force applied to the molars of SX animals increased bone formation on the distal aspect of the tooth roots. Supplemental EGF did not significantly affect OTM. EGF affects alveolar bone remodeling, as manifested clinically by alterations in normal maxillary MD.

Processing of epidermal growth factor in the rat submandibular gland by Kallikrein-like enzymes

Epidermal growth factor (EGF) is synthesized as a precursor which is processed intracellularly to a 6 kDa EGF in the rat submandibular gland. This gland contains very high amounts of kallikrein-like enzymes, and the purpose of the present study was to examine whether any of five such enzymes, rK1, rK2, rK7, rK9 or rK10, can process the rat EGF precursor. Molecular weight forms of EGF, that were N- or C-terminally extended compared to submandibular gland EGF were obtained from rat urine. These extended forms of EGF were incubated with each of the enzymes for 24 h at 37 degrees C. Two enzymes, rK7 and rK10, were able to cleave N- and C-terminally extended EGF, releasing a form of EGF which eluted similarly to submandibular gland EGF upon gel filtration, and which was recognized both by antibodies against rat EGF and by the EGF receptor. One enzyme, rK1, cleaved C- but not N-terminally extended EGF. Neither rK2, nor rK9 cleaved the extended forms of EGF. In previous immunohistochemical studies rK1, rK7 and rK10 have all been demonstrated in the EGF containing cells of the rat submandibular gland. EGF and rK1 are also synthesized in the rat kidney but the present study demonstrated that EGF and rK1 are not colocalized in this organ. Based on the cleavage of the extended forms of rat EGF by rK1, rK7 and rK10 and on the fact that the enzymes are abundant and colocalized with EGF in the rat submandibular gland, we suggest that rK1, rK7 and rK10 can be involved in the processing of the EGF precursor in the rat submandibular gland.

Control of intracellular Ca2+ by adrenergic and muscarinic agonists in mouse mandibular ducts and end-pieces

The changes in free Ca2+ ([Ca2+]i) in the cells of the secretory end-pieces and intralobular ducts of mouse mandibular glands exposed to adrenergic or cholinergic agonists were measured using fluorescence imaging techniques. [Ca2+]i in both cell types increased in a dose-dependent manner during both adrenergic and cholinergic stimulation. The duct cells responded to noradrenaline and to acetylcholine over the same concentration range (30 nmol/l to 3 mumol/l) although the maximum increase in [Ca2+]i above resting levels evoked by noradrenaline (ca. 137 nmol/l) was about twice that evoked by acetylcholine. The response to acetylcholine was blocked by atropine (0.1 mumol/l) and the response to noradrenaline was blocked by the alpha 1-adrenergic antagonist, prazosin (0.1 mumol/l), but not by the alpha 2-adrenergic antagonist, yohimbine. The alpha-adrenergic agonist, phenylephrine, mimicked the action of noradrenaline but the beta-adrenergic agonist, isoproterenol, had no effect. In contrast to the duct cells, the end-piece cells responded to acetylcholine at much lower concentrations (threshold << 1 nmol/l) than to noradrenaline (threshold ca. 300 nmol/l) and the size of the increase in [Ca2+]i above resting levels evoked by acetylcholine (216 nmol/l) was nearly 5-times greater than for noradrenaline. VIP and substance P failed to evoked a Ca2+ response in either end-piece or duct cells.

Release and binding of epidermal growth factor in the pancreas of rats

Previous studies showed that EGF is produced by salivary and duodenal glands and released in saliva and duodenal secretion. Using specific radioimmunoassay of EGF, this study showed that the salivary glands and duodenal mucosa contain high levels of EGF, reaching, respectively, about 38 and 4 micrograms/g of tissue weight. EGF immunoreactivity was also found in high amounts in the pancreatic tissue (20 micrograms/g) and the pancreatic juice (32 ng/mL), where the content of EGF was found to increase in response to feeding, cholecystokinin, or bombesin and to decrease after the administration of atropine and somatostatin. Studies on the binding of EGF revealed that pancreatic acinar membranes possess the specific and saturable EGF receptors with a high affinity sites with Kd of about 4.3 nM and binding capacity of about 62 fmol/mg of protein, and with low affinity sites with Kd of 21 nM and binding capacity of about 180 fmol/mg of protein. The observed high content of immunoreactive EGF in the pancreatic tissue and the presence of high and low affinity binding sites for EGF in the pancreatic acinar membranes, as well as the high EGF output in the pancreatic juice and its alterations in response to hormonal and postprandial stimulation, suggest an important role of EGF in pancreatic physiology.

Identification of functional receptors for vasoactive intestinal peptide and neurotensin in the human submandibular gland duct cell line, HSG-PA

The HSG-PA human submandibular gland adenocarcinoma cell line has attracted attention recently as a potentially useful cell culture model for studies of salivary duct cell function and regulation. These cells possess a variety of morphological and biochemical markers found in salivary duct cells. Recently, muscarinic cholinergic receptors coupled to inositol intracellular Ca2+ mobilization (He et al., Eur. J. Physiol., 413 (1989) 505-510) and K+ fluxes (Ship et al., Am. J. Physiol., 259 (1990) C340-C348) have been identified in HSG-PA cells. In this study, we report the presence in these cells of functional receptors for two neuropeptides, vasoactive intestinal peptide (VIP) and neurotensin. Receptors for both peptides were labeled in intact cell radioligand binding studies and exhibited pharmacological profiles similar to receptors found in other tissues. There was close agreement between binding Ki values and the ED50 values for stimulation of second messenger production and modulation of K+ efflux, with all values between 1 and 5 nM. Whereas neurotensin stimulated K+ efflux dramatically, VIP alone had no effect but enhanced the response to neurotensin. These studies thus represent the initial documentation of functional receptors for VIP and neurotensin in a cell line of salivary duct cell origin.

Vasoactive intestinal peptide interacts with alpha-adrenergic-, cholinergic-, and substance-P-mediated responses in rat parotid and submandibular glands

Secretory dose-response curves were obtained with both acetylcholine and phenylephrine treatment in rat parotid and submandibular glands. Vasoactive intestinal peptide (VIP), which produced relatively low volumes of protein-rich saliva in rat salivary glands, also enhanced acetylcholine-, phenylephrine-, and substance-P-mediated fluid and protein secretion when administered in combination with these agents. The specific mechanisms involved in the synergistic actions of VIP with substances such as acetylcholine, phenylephrine, and substance P, which are primarily linked to the production of fluid secretion in rat salivary glands, have yet to be determined.

Human salivary epidermal growth factor, haptocorrin and amylase before and after prolonged exercise

The concentration of epidermal growth factor (EGF), amylase, haptocorrin, total protein, sodium and potassium was studied in mixed saliva collected from 25 individuals before and after a 2 h-long cross-country race. The concentration was higher following the run for all components studied. The concentrations obtained before and after the run, given as extreme values and median, are 0.2-1.3 (0.4), 0.3-1.5 (0.8) nmol/l for EGF, 15-72 (25), 23-162 (58) nmol/l for haptocorrin and 24-502 (120), 155-5,030 (1,200) kU/l for amylase. The increased concentration of the components studied is most probably caused by an increased adrenergic and VIP'ergic tonus of the individuals after the run.