J. R. Garrett

Secretory responses in granular ducts and acini of submandibular glands in vivo to parasympathetic or sympathetic nerve stimulation in rats.

SummaryThe roles of sympathetic and parasympathetic nerves in the secretion of saliva from submandibular glands of rats have been tested by electrical stimulation of either nerve for 1 h unilaterally in separate animals. The flows of saliva thereby induced and their protein content were monitored. Structural changes in each gland were assessed by light- and electron microscopy and compared with the unstimulated contralateral control gland, and the extent of the changes was determined morphometrically. Sympathetic nerve stimulation induced a relatively low flow of saliva that was rich in protein and was accompanied by extensive degranulation from both acinar and granular duct cells. In contrast parasympathetic nerve stimulation induced a considerable flow of saliva that had a low protein content and no detectable degranulation occurred from the secretory cells. It is possible, therefore, that some protein in parasympathetic saliva may have arisen from a non-granular pathway.

Changes in parotid acinar cells accompanying salivary secretion in rats on sympathetic or parasympathetic nerve stimulation

SummaryMorphological and secretory effects of stimulating autonomic nerves have been studied in parotid glands of rats. Sympathetic stimulation evoked a slow flow of saliva which had a high concentration of amylase. After long term sympathetic stimulation secretory granules were heavily depleted from the parotid acinar cells. Parasympathetic stimulation evoked a copious flow of saliva with a low concentration of amylase. However, at high frequency stimulation the total amount of amylase secreted on parasympathetic stimulation was as great or even greater than on sympathetic stimulation, nevertheless, any loss of secretory granules from the acinar cells was very small.It is concluded that secretion of parotid acinar granules in the rat is principally a sympathetic function. Secretion of fluid is more effectively produced by parasympathetic stimulation and much of the amylase in such saliva appears to have arisen from sources other than the secretory granules.

Neural control of salivary myoepithelial cells

1. The pressures in the ducts of the submaxillary, parotid and sublingual glands were recorded in cats under chloralose anaesthesia. A single stimulus applied to the parasympathetic glandular nerve caused a pressure rise, the size of which increased with the initial pressure. This response was abolished by a small dose of atropine.

The innervation of normal human submandibular and parotid salivary glands. Demonstrated by cholinesterase histochemistry, catecholamine fluorescence and electron microscopy.

Abstract The nerves in human submandibular and parotid glands were similar in distribution and appearance. No specialized “nerve endings”, nor any axons beneath the parenchymal basement membrane, were detected. Neuro-effector sites are thought to occur where an axon—partially bared of Schwann cell—has its free surface in relatively close approximation to an effector cell. Such sites were seen frequently in association with acini, myoepithelia, intercalary ducts and muscular blood vessels, somewhat less often in association with striated ducts and rarely by collecting ducts. The principal parenchymal innervation was cholinergic but many adrenergic nerves were also present. No specialized sensory structures were observed.

The influence of nerves on the secretion of immunoglobulin A into submandibular saliva in rats

1 The influence of sympathetic and parasympathetic nerve stimulations on salivary secretion of immunoglobulin A (IgA) was studied in the submandibular glands of anaesthetized rats by stimulating the nerve supplies with bipolar electrodes. 2 Although the flow of saliva from sympathetically stimulated glands was only 23 % of that from parasympathetically stimulated glands the output of IgA was over 2‐fold greater. This difference was attributable to influences of the nerves on IgA secretion through the epithelial cell polymeric immunoglobulin receptor‐mediated pathway, as Western blotting with specific antibodies to IgA and secretory component revealed that secretory IgA (SIgA) dominated in all saliva samples. 3 Study of saliva secreted in sequential periods of nerve stimulation or following rest pauses suggested that SIgA secretion occurred in the absence of stimulation but this was upregulated 2.6‐ and 6‐fold by parasympathetic and sympathetic nerve stimulations, respectively, compared with the calculated unstimulated rate. 4 The IgA content of extensively stimulated glands was 77 % of levels in unstimulated contralateral control glands despite a secretion into saliva equivalent to almost 90 % of the glandular IgA content. The IgA may be synthesized and secreted by glandular plasma cells at a rate which exceeds demand and/or such synthesis may be upregulated by nerve impulses. 5 The results indicate that salivary secretion of SIgA is upregulated by nerve impulses and that sympathetic nerves induce a greater effect than parasympathetic nerves.

Nitric oxide-related vasodilator responses to parasympathetic stimulation of the submandibular gland in the cat.

1. The extent to which parasympathetic vasodilator responses, in the submandibular gland of the cat, depend upon release of nitric oxide related (NO chi) or endothelium‐derived relaxing factor (EDRF) within the gland has been investigated in anesthetized cats given N omega‐nitro‐L‐arginine methyl ester (L‐NAME) which specifically blocks the synthesis of EDRF from arginine. 2. Close intra‐arterial infusions of L‐NAME (> or = 100 mg kg‐1) produced a steady and significant rise in mean aortic pressure together with a steady increase in basal submandibular vascular resistance over the next 20‐30 min, which persisted thereafter. 3. In cats pretreated with propranolol, to block beta‐adrenoceptor‐mediated vasodilatation, salivation and vasodilatation in response to stimulation of the chorda‐lingual nerve were reduced but not abolished by L‐NAME (> or = 100 mg kg‐1, I.A.). Subsequent administration of atropine (> or = 1 mg kg‐1 I.V.) completely suppressed the secretory response and virtually eliminated the vascular response. 4. In cats pretreated with atropine (> or = 1.0 mg kg‐1 I.V.) administration of L‐NAME (> or = 100 mg kg‐1 I.A.) effectively suppressed the vasodilator response to chorda‐lingual stimulation at 2 Hz continuously, or at 20 Hz for 1 s at 10 s intervals. 5. Administration of L‐NAME (> or = 100 mg kg‐1 I.A.) effectively suppressed the submandibular vasodilator response to infusions of VIP (10 and 20 ng I.A.) and significantly reduced, but did not abolish that to acetylcholine (100 ng min‐1 I.A.). 6. These results provide further support for the view that both acetylcholine and vasoactive intestinal polypeptide‐like immunoreactivity (VIP) are released from the postganglionic parasympathetic nerve terminals and produce effects on the blood vessels in submandibular glands of the cat. They also provide evidence for a direct vascular action of acetylcholine, independent of NO chi, but VIP appears to act indirectly via NO chi formation.

Mucocele formation in cats by glandular duct ligation.

Abstract Complete ductal obstruction has largely been disregarded as a possible factor in mucocele production, since duct ligation of rodent salivary glands has always produced atrophy and never mucoceles. In the present study, duct ligation of the sublingual gland, avoiding the nerves, in 23 cats from 1 day to 1 yr produced mucous extravasation in 13 glands, with mucocele formation in 6 of these, and marked atrophy in only 8 glands. This suggests that complete ductal obstruction should not be disregarded as a possible aetiological factor in mucocele formation.

Alkaline-phosphatase and adenosine-triphosphatase histochemical reactions in the salivary glands of cat, dog and man, with particular reference to the myoepithelial cells

SummarySalivary myoepithelial cells were demonstrated by alkaline-phosphatase techniques in cat, but not in man or dog, and by an adenosine-triphosphatase technique in man, but not in cat or dog.Electron-microscopical cytochemistry showed that the reaction product from the respective techniques in cat and man was associated with the myoepithelial plasma membrane and that it was most constant and usually strongest at the plasma membrane adjacent to the acinar cells.In the dog, the reaction product from the adenosine-triphosphatase technique was found lining the canaliculi and lumina of the acini of the parotid gland, and of the non-mucous acini of the submandibular and sublingual glands. Alkaline-phosphatase reaction product was found lining the canaliculi and lumina in the sublingual gland.These remarkable species differences indicate that neither technique can be regarded as a universal marker of salivary myoepithelial cells. Inconsistencies in activity were found within the myoepithelium of individual glands and suggest that even the appropriate technique may not be relied upon to demonstrate all the myoepithelial cells present in a tissue section.ZusammenfassungMyoepithelzellen der Speicheldrüsen lassen sich bei der Katze — nicht jedoch bei Mensch und Hund — mittels der alkalischen Phosphatase-Reaktion darstellen. Der Nachweis für Adenosintriphosphatase fällt in diesen Zellen beim Menschen, nicht bei Katze und Hund, positiv aus.Elektronenmikroskopisch-cytochemisch zeigt sich, daß das Reaktionsprodukt der jeweiligen Methode bei der Katze und beim Menschen an den Plasmamembranen der Myoepithelzellen auftritt und zwar am regelmäßigsten und meistens am stärksten in der Nachbarschaft der Azinuszellen.Beim Hund fällt in der Ohrspeicheldrüse sowie den nicht-mukösen Acini der Glandulae submandibularis und sublingualis das Reaktionsprodukt der Adenosintriphosphatase-Reaktion an der Begrenzung der Azinuskanälchen und der Lumenoberfläche aus. Alkalische Phosphatase ist in der Glandula sublingualis in den Wänden der Kanälchen und an den Lumina lokalisiert.Diese bemerkenswerten Unterschiede zwischen den verschiedenen Tierarten zeigen, daß keine der verwendeten Methoden zur Universalmarkierung von Myoepithelzellen der Speicheldrüsen geeignet ist. Außerdem ist die Aktivität des Myoepithels bei den einzelnen Drüsen uneinheitlich. Dies legt die Vermutung nahe, daß man sich selbst bei Anwendung der richtigen Methode nicht darauf verlassen kann, alle in einem Gewebsschnitt vorhandenen Myoepithelzellen zu erfassen.

Secretory activity and the myoepithelial cells of salivary glands after duct ligation in cats

Abstract Submandibular and parotid ducts were tied unilaterally in cats for periods from 12 to 81 days. Secretion has been tested in the glands on supramaximal nerve stimulation. Duct ligation caused a large reduction in secretory capacity but a small amount of secretion could always be obtained, even from very atrophic glands. Pressure changes were tested in the ducts resulting from nerve stimulation and from certain drugs administered intravenously. Responses attributable to myoepithelial contraction, which could be distinguished from secretion, were found on parasympathetic nerve stimulation, with parasympathomimetic drugs and also with kallidin and bradykinin. An increased sensitivity to the kinins was found in ligated glands. Histological and ultrastructural studies showed that the extent of the acinar atrophy paralleled the diminution in secretion. Myoepithelial cells persisted, but often showed an abnormal architecture, especially where underlying acinar atrophy had occurred, and in such sites they were associated with a grossly thickened basement membrane. The work supports the concept that salivary myoepithelial cells in the cat have a motor parasympathetic innervation.

Effects of nerve stimulation and denervation on secretory material in submandibular striated duct cells of cats, and the possible role of these cells in the secretion of salivary kallikrein

SummaryStriated ducts in cats after 24 hours starvation normally contained glycogen, especially in the basal regions. They also contained neutral mucin and tryptophan in apical parts of “light” cells and small irregular “secretory” granules were found in a similar distribution by electron microscopy.—Parasympathetic nerve stimulation caused a loss of glycogen but no apparent change in the apical secretory material, despite a copious secretion.—Sympathetic stimulation caused a loss of glycogen and an extensive depletion of apical secretory material, although the salivary flow was small.—Parasympathetic denervation caused progressive atrophy of striated ducts and oedematous degeneration of some cells occurred. Persisting “light” cells tended to contain few basal infoldings, few mitochondria and little apical secretory material.—Sympathetic denervation caused a loss of apical secretory material between 2–4 days, which may have been due to “degeneration activation”. Thereafter little change was evident but some ductal atrophy had occurred by 32 days.— These changes in ductal secretory material correspond more closely than acinar changes to the alterations in glandular and salivary kallikrein resulting from similar experiments by other workers. It therefore seems likely that submandibular salivary kallikrein in the cat is present in the secretory material of striated ducts.