A comparison of the effects of vasoactive intestinal polypeptide on secretion from the submaxillary gland of the sheep and pig

Transcriptome analysis reveals potential immune function-related regulatory genes/pathways of female Lubo goat submandibular glands at different developmental stages

Background

The submandibular glands, as major salivary glands, participate in rumen digestion in goats. Sialic acid, lysozyme, immunoglobulin A (IgA), lactoferrin and other biologically active substances secreted in the submandibular glands were reported in succession, which suggests that the submandibular gland may have immune functions in addition to participating in digestion. The aim of this study was to map the expression profile of differentially expressed genes (DEGs) at three different stages by transcriptome sequencing, screen immune-related genes and pathways by bioinformatics methods, and predict the immune function of submandibular glands at different developmental stages.

Methods

Nine submandibular gland tissue samples were collected from groups of 1-month-old kids, 12-month-old adolescent goats and 24-month-old adult goats (3 samples from each group), and high-throughput transcriptome sequencing was conducted on these samples. The DEGs among the three stages were screened and analysed. Key genes and signalling pathways were selected via protein-protein interaction (PPI) network analysis.

Results

The results revealed 2,706, 2,525 and 52 DEGs between 1-month-old and 12-month-old goats, between 1-month-old and 24-month-old goats, and between 12-month-old and 24-month-old goats, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses indicated that most of the DEGs were enriched in immune- related GO terms and pathways. Based on functional enrichment analysis and network analysis, 10 genes (PTPRC, CD28, SELL, LCP2, MYC, LCK, ZAP70, ITGB2, SYK and CCR7), two signalling pathways (the T cell receptor signalling pathway and the NF-κβ signalling pathway) and eight GO terms (T cell receptor signalling pathway, neutrophil mediated immunity, B cell mediated immunity, regulation of alpha-beta T cell activation, positive regulation of T cell proliferation, regulation of leukocyte differentiation, positive regulation of antigen receptor-mediated signalling pathway, positive regulation of lymphocyte proliferation) that may play key roles in the immune functions of the goat submandibular glands at different developmental stages were identified. Moreover, we found that eight antibacterial peptide-encoding genes were downregulated in the tuberculosis and salivary secretion pathways, while all immunoglobulins were upregulated in 10 immune system pathways. These findings indicate that the submandibular glands may be important immunological organs during the growth process of goats and that the immune function of these glands gradually weakens with age up to 12 months but remains relatively stable after 12 months of age. Overall, this study will improve our understanding of transcriptional regulation related to goat submandibular gland immune function.

Effect of the neuropeptides vasoactive intestinal peptide, peptide histidine methionine and substance P on human major salivary gland secretion

OBJECTIVE

The parasympathetic transmitters vasoactive intestinal peptide (VIP) and substance P (SP) are secretagogues in salivary glands of animals. Currently, we hypothesise that in human salivary glands, these neuropeptides and the VIP-related peptide histidine methionine (PHM) also exert secretory actions, reflected morphologically by exocytosis of acinar protein/glycoprotein-storing granules.

MATERIALS AND METHODS

Submandibular and parotid gland tissues, exposed in vitro to VIP and PHM, and SP, respectively, were examined by light and transmission electron microscopy. For comparison, the response to in vitro stimulation of isoproterenol, phenylephrine and carbachol was examined. Moreover, the peptidergic innervation of the glands was examined by immunohistochemistry.

RESULTS

Vasoactive intestinal peptide- and PHM-immunoreactive nerves were in close proximity to acini and ducts in the two glands, while these elements lacked a SP-positive innervation. While no morphological changes occurred in response to SP (parotid glands), VIP and PHM administration (submandibular glands) caused conspicuous acinar degranulation accompanied by luminal space broadening. In the two glands, both α1 - and β-adrenergic receptor stimulation and muscarinic receptor stimulation caused similar changes as to VIP/PHM, although to varying extent.

CONCLUSIONS

Vasoactive intestinal peptide and PHM, but not SP, are likely transmitters in the parasympathetic control of salivary (protein) secretion in humans.

Characterization of Prejunctional Muscarinic Receptors: Effects on the Release of VIP and Functional Responses and Receptor Expression in the Ovine Submandibular Gland

In the in vivo experiments on anaesthetized sheep, it was presently examined whether muscarinic receptor antagonists with diverse selectivity affect the release of VIP in response to electrical stimulation of the parasympathetic chorda tympanic nerve differently, and if the changes in the release could be associated to altered secretory and vasodilator responses. The location of the muscarinic receptor subtypes was examined also. In the experiments, blood was collected out of the submandibular venous drainage before and during electrical stimulation of chorda tympani nerve in the absence and presence either of pirenzepine or methoctramine. While metchoctramine increased the output of protein, pirenzepine inhibited flow of saliva and increased protein output, vasodilatation, and VIP output. In morphological examinations, the inhibitory muscarinic M4 receptor occurred interacinarily in the gland. It is concluded that prejunctional muscarinic receptors, most likely of the M4 subtype, exert inhibitory modulation of the parasympathetic release of VIP in the ovine submandibular gland.

Distribution and function of muscarinic receptor subtypes in the ovine submandibular gland

The effects of muscarinic receptor antagonists on responses to electrical stimulation of the chorda-lingual nerve were determined in pentobarbitone-anesthetized sheep and correlated to the morphology of tissue specimens. Stimulation at 2 Hz continuously, or in bursts of 1 s at 20 Hz every 10 s, for 10 min induced similar submandibular fluid responses (19 ± 3 vs. 21 ± 3 μl·min−1·g gland−1), whereas vasodilatation was greater during stimulation in bursts (−52 ± 4 vs. −43 ± 5%; P < 0.01). Continuous stimulation at 8 Hz induced substantially greater responses (66 ± 9 μl·min−1·g gland−1 and −77 ± 3%). While atropine (0.5 mg/kg iv) abolished the secretory response at 2 and 20 Hz (1:10 s), a small response persisted at 8 Hz (<5%). The “M1-selective” antagonist pirenzepine (40 μg/kg iv) reduced the fluid response at all frequencies tested ( P < 0.05–0.01), most conspicuously at 2 Hz (reduced by 69%). Methoctramine (“M2/M4-selective”; 100 μg/kg iv; n = 5) had no effect on fluid or the vascular responses but increased the protein output at 2 (+90%, P < 0.05) and 8 Hz (+45%, P < 0.05). The immunoblotting showed distinct bands for muscarinic M1, M3, M4, and M5 receptors, and immunohistochemistry showed muscarinic M1 and M3 receptors to occur in the parenchyma. Thus muscarinic M1 receptors contribute to the secretory response to parasympathetic stimulation but have little effect on the vasodilatation in the ovine submandibular gland. Increased transmitter release caused by blockade of neuronal inhibitory receptors of the M4 subtype would explain the increase in protein output.

Submandibular responses to stimulation of the parasympathetic innervation in anesthetized sheep

Submandibular secretory and vascular responses to stimulation of the parasympathetic innervation and the output of vasoactive intestinal peptide (VIP) were investigated in anaesthetized sheep in the presence and absence of atropine (>/=0.5 mg/kg). In the absence of atropine, parasympathetic stimulation caused an increase in the flow of saliva and a decrease in submandibular vascular resistance; the latter response persisted after the administration of atropine and was then significantly reduced at the lowest but not at the higher frequencies tested. The output of VIP from the gland was frequency dependent over the range of 10-20 Hz (continuously) and significantly increased after atropine (P < 0.02). Furthermore, the fall in vascular resistance was linearly related to log VIP output after total muscarinic blockade. Intracarotid infusions of synthetic VIP produced dose-dependent falls in submandibular vascular resistance, together with a corresponding increase in submandibular blood flow. It is concluded that the atropine-resistant vasodilatation that occurs in this gland during parasympathetic stimulation is likely to be due largely, if not entirely, to the release of VIP.

The effect of parasympathetic postganglionic denervation on parotid salivary protein secretion in anaesthetized sheep

Effects of unilateral parasympathetic denervation of ovine parotid glands were examined in anaesthetized sheep 21-28 days after nerve section. Parasympathetic denervation reduced the mass of the ipsilateral gland while increasing that of the contralateral gland to the extent that total gland mass was greater than in sheep with normally innervated glands. The spontaneous secretion (8.8 +/- 1.1 microl min(-1) g gland(-1)) was significantly less from denervated than from innervated glands of normal control animals (26.0 +/- 2.7 microl min(-1) g gland(-1); P< 0.01) and contained more protein. Rates of flow, and the outputs of sodium and potassium, in response to sympathetic stimulation, were similar from normally innervated and chronically denervated glands, when allowance was made for the discrepancy in weights, whereas the output of protein was significantly enhanced following parasympathetic denervation (innervated--31.4 +/- 7.3 microg g gland(-1), denervated--83.4 +/- 26.6 microg g gland(-1); P< 0.05). Intra-arterial infusions of acetylcholine (130 pmol min(-1) kg(-1)) elicited a flow of parotid saliva, the protein content of which was significantly enhanced by prior parasympathetic denervation. Intra-arterial infusions of vasoactive intestinal peptide (VIP; 2.5 pmol min(-1) kg(-1)) produced a small but statistically significant (P< 0.05) increase in the flow of parotid saliva from the contralateral, innervated but not from denervated glands. It also caused a small increase in protein output, which was significantly enhanced by prior denervation. VIP had no synergistic effect on the parotid responses to acetylcholine. The results show that the parasympathetic innervation to the parotid gland of the sheep exerts important trophic effects on the gland. Interaction of adrenergic and cholinergic receptors makes an important contribution to stimulation of the secretion of protein and prior denervation potentiates the protein responses to both acetylcholine and VIP.

Effects of endothelin on submandibular salivary responses to parasympathetic stimulation in anaesthetized sheep

Submandibular responses to stimulation of the parasympathetic chorda tympani nerve have been investigated in anaesthetized sheep before, during and after an intracarotid infusion of endothelin, which reduced the blood flow through the gland by 56+/-5%. Stimulation of the peripheral end of the chorda tympani nerve produced a frequency-dependent increase in the flow of submandibular saliva, and in sodium, potassium and protein output. The reduction in submandibular blood flow, which occurred in response to endothelin, was associated with a decrease in the flow of saliva at all frequencies tested amounting on average to 44+/-6% (P<0.01). The flow of saliva was linearly related to the blood flow before and after endothelin. Both parameters were also linearly related during the infusion of endothelin and the regression lines were parallel. Salivary sodium concentration was significantly increased at the lower frequencies (1 and 2 Hz). Protein output was generally reduced but the difference only achieved statistical significance during stimulation at 1 Hz (P<0.01). Thus, submandibular secretory responses to parasympathetic stimulation are significantly attenuated by reducing the blood flow through the gland in this way.

VIP- and PACAP-induced salivary chromogranin A secretion in the isolated perfused submandibular gland of rats

In the study reported in this paper, sensitive ELISA for rat CgA was developed using synthetic rat CgA(359-389) as antigen, N alpha-biotinylated glycylglycyl rat CgA(359-389), and antirat CgA(359-389) serum for the measurement of CgA-LI in rat saliva. CgA-LI in rat submandibular tissues and saliva was characterized by both immunohistochemical and immunochemical methods. Using isolated perfused rat submandibular gland. VIP at 0.1-1.0 nM in the presence of 0.1 microM ACh was found to cause CgA-LI secretion, whereas neither PACAP-27 nor PACAP-38 showed any effect on CgA secretion.

Expression of vasoactive intestinal polypeptide receptor mRNA and secretory regulation by vasoactive intestinal polypeptide in rat submandibular and sublingual salivary glands

Vasoactive intestinal polypeptide (VIP)-receptor mRNA was strongly expressed in the acinar cells in the submandibular gland but not in the sublingual gland. VIP-containing nerve fibres were richly distributed around acini in the submandibular gland but were rare around acini of the sublingual gland. In the submandibular gland, the chorda was stimulated at various frequencies (1-40 Hz) together with an infusion of (N-Ac-Tyr1, D-Phe2)-GRF(1-29)-NH2 (109 M), VIP antagonist, which reduced salivary flow from the submandibular gland only at high-frequency stimulation (> 20 Hz), and more markedly reduced the salivary protein concentration. When the chorda was continuously stimulated the antagonist reduced the salivary flow only during the initial 5 min. Exogenous VIP 10(-12) - 10(-8) M) infusion at the same time as chorda stimulation caused no increase in salivary flow, but the salivary protein concentration was increased in a dose-dependent manner. In the sublingual gland, neither VIP nor the VIP antagonist affected chorda-evoked salivary flow and protein concentration. Thus, endogenous VIP may play a part in the regulation of both fluid and protein secretion, especially of protein, evoked by chorda stimulation at high frequency in the submandibular gland. These phenomena occurred only in the initial phase of secretion. In the sublingual gland, it seems likely that VIP plays no part in the regulatory mechanism, at least with regard to salivary fluid secretion in the acinar cells.

Parasympathetic NANC-secretion of saliva in the mink, and effects of substance P and VIP

In both parotid and submandibular glands a parasympathetic non-adrenergic, non-cholinergic (NANC) nerve-evoked secretion of saliva was demonstrated. Saliva evoked by exogenous substance P was poor in protein, while saliva evoked by VIP was protein-rich. In a subthreshold dose for fluid secretion VIP released protein and potentiated the responses elicited by substance P, particularly regarding the output of protein. The two neuropeptides may contribute to the parasympathetic NANC secretion of saliva in the mink. Further, agonists responsible for the secretory NANC response are also likely to contribute to the secretory response of the glands to parasympathetic stimulation in the absence of autonomic receptor blockade in this species.

Evidence against the involvement of vasoactive intestinal peptide in ovine parotid secretion and blood flow

1. The proposition that stimulation of the secretomotor nerve to the ovine parotid gland might involve co-release of vasoactive intestinal peptide (VIP) was tested by studying responses to infusion of VIP directly into the gland's arterial blood supply and by assay of VIP in parotid venous blood. 2. In unstimulated glands, an arterial blood concentration of 1.5 - 2.5 X 10(-9) mol/L VIP did not evoke fluid secretion but it increased K+ and phosphate secretion and glandular blood flow. The same blood concentration of VIP potentiated the stimulation of salivary flow rate caused by intraarterial infusion of bethanechol but nerve stimulation was not potentiated. VIP increased glandular blood flow in both conditions of stimulation. 3. Atropine blocked neurally stimulated salivary secretion but an increase in glandular blood flow was still detectable. There was therefore no evidence for a non-cholinergic neural mechanism for salivary secretion. 4. Furthermore, VIP concentrations in glandular venous blood were not increased by nerve stimulation. 5. The results indicate that exogenous VIP can affect the flow and composition of ovine parotid secretion but was not involved in the response to secretomotor nerve stimulation.

Protein secretion in salivary glands of cats in vivo and in vitro in response to vasoactive intestinal peptide

In anaesthetized cats exogenous vasoactive intestinal peptide failed to elicit any secretion of saliva from the submandibular and parotid glands. However, protein release from both glands occurred in response to VIP in the presence of alpha- and beta-adrenoceptor blocking agents and was dose-dependent. This response was revealed by means of a subsequent washout flow of saliva evoked by intravenous injections of methacholine or stimulations of the parasympathetic innervation. The submandibular glands responded to vasoactive intestinal peptide at a lower dose than the parotid glands. In the presence of atropine (but in the absence of adrenoceptor blockers), stimulation of the parasympathetic chorda-lingual nerve, which of itself elicited no secretion of saliva, contributed to the release of protein within the submandibular gland, since the output of protein in response to a subsequent stimulation of the sympathetic innervation was increased. Vasoactive intestinal peptide administered in combination with methacholine or during ongoing parasympathetic nerve-induced salivary secretion revealed positive interactions, particularly with respect to protein release. In-vitro protein release in response to vasoactive intestinal peptide was also demonstrated by perfusing small pieces of the two glands in the presence of muscarinic and adrenoceptor blockers. As in vivo, submandibular tissue responded at a lower concentration of vasoactive intestinal peptide than the parotid tissue. One to two weeks after combined parasympathetic and sympathetic denervation of the parotid glands, the glands were sensitized to vasoactive intestinal peptide when tested in vitro. It is concluded that vasoactive intestinal peptide or a structurally related peptide is a potential transmitter in the parasympathetic control of protein secretion in salivary glands of cats.

VIP-containing nerve fibres in the submandibular gland of the dog and protein secretion in vitro in response to VIP

Previously, administration of VIP has been shown to elicit no flow of saliva from the submandibular gland of the dog. However, in the present study we found VIP to cause release of protein in vitro from canine submandibular gland tissue. Furthermore, VIP-containing nerve fibres were demonstrated in large numbers in association with acini. Thus, VIP may be involved in the nervous regulation of salivary protein secretion in the dog.

The influence of vasoactive intestinal peptide receptors in dispersed acini from rat submandibular gland on cyclic AMP production and mucin release

Vasoactive intestinal peptide has been identified as an important regulator of submandibular salivary gland function, consistent with its localization with acetylcholine in parasympathetic neurones innervating this gland. Enzymatically dispersed acini from rat submandibular gland are a useful system in which to study gland regulation at the cellular level. Here, three aspects of vasoactive intestinal peptide interactions with acini were examined: inhibition of binding of [125I]-vasoactive intestinal peptide, stimulation of cyclic AMP production and enhancement of mucin release. Vasoactive intestinal peptide and peptide histidineisoleucineamide inhibited [125I]-vasoactive intestinal peptide binding to intact acini, with IC50 values of 16 +/- 3 and 46 +/- 17 nM, respectively. This rank order of potency agrees with that observed previously in assays using rat submandibular gland membranes and is similar to values obtained in assays measuring increases in cyclic AMP production in which the ED50 values for vasoactive intestinal peptide and peptide histidineisoleucineamide were 3.1 +/- 1.8 and 29 +/- 13 nM, respectively. Although vasoactive intestinal peptide stimulation of cyclic AMP production was only about 10% of that seen in response to isoproterenol, the levels of mucin release induced by the two agents were more similar. The ED50 for vasoactive intestinal peptide-stimulated mucin release was 0.12 +/- 0.05 nM, thus suggesting an activation anomaly in the vasoactive intestinal peptide receptor-coupled signal transduction pathway at a point between cyclic AMP production and mucin release.

Secretion of protein from salivary glands in the ferret in response to vasoactive intestinal peptide

1. Secretory responses of ferret parotid and submandibular glands were investigated in the presence of muscarinic, alpha- and beta-adrenoceptor blocking agents. 2. In pentobarbitone-anaesthetized animals I.V. doses of vasoactive intestinal peptide (VIP) failed to elicit overt secretion of saliva from either gland. 3. However, an occult secretion of protein occurred in response to VIP from both types of gland. This was revealed by means of a subsequent I.V. wash-out injection of substance P, which is a potent secretagogue in ferrets. This effect of VIP was much more marked in the submandibular than in the parotid gland. 4. Electrical stimulation of the chorda-lingual nerve gave rise to protein secretion in the submandibular gland at subthreshold frequencies for overt non-cholinergic, non-adrenergic secretion of saliva, as revealed by subsequent wash-out I.V. injection of substance P. 5. Protein secretion in response to VIP was also demonstrated in vitro by perifusing small pieces of the two glands. The sensitivity of submandibular tissue to VIP greatly exceeded that of the parotid tissue. 6. It is concluded that VIP, or a structurally related peptide, may be involved in the non-cholinergic, non-adrenergic secretory response of ferret salivary glands evoked by parasympathetic nerve stimulation.