Morphological changes in salivary glands after treatment with sialagogues. An electronmicroscopical study

A large-scale quantitative EM study on activation of olfactory glands shows no effect of cholinergic agents

Little is known about olfactory glands' regulation despite their presumed importance for normal functioning of the cilia of olfactory neurons. The aim of this study was to establish an assay for olfactory gland activation by using large-scale quantitative electron microscopy (EM). In addition we wanted to test the hypothesis that cholinergic drugs activate the olfactory glands, by using our newly established EM assay. In total, over 70 000 secretory gland vesicles were quantified in over 3000 cells. Olfactory gland cell size (40.8 µm² ± 2.0 SD), vesicle diameter (812 nm ± 57 SD) and vesicles per cell (21.6 ± 4.2 SD) were also quantified. The vesicle percentage of the cell area varied between 24% and 30%. In a blinded study we found no significant effects of cholinergic agents on parameters of vesicle number or vesicle diameter. Unexpectedly, pilocarpine treatment increased olfactory gland size, probably by inducing cell swelling. In conclusion, we have established a quantitative EM assay for olfactory gland activation and provided new data on basic olfactory gland cell characteristics. By using the EM assay, olfactory glands are shown not to be activated by cholinergic agents, which indicates an alternative regulation pathway or constitutive secretion from olfactory glands.

Mechanisms underlying the structural alterations of the rat submandibular gland induced by Tityus serrulatus tityustoxin

As the mechanisms underlying the structural changes induced in rat submandibular glands by Tityus serrulatus tityustoxin have not been reported, the present study was undertaken to investigate the participation of adrenergic and muscarinic cholinergic receptors in these alterations. Most of the stimulatory effects of the toxin are observed in the secretory cells of the acini and granular convoluted tubules (GCT). We evaluated the ability of the toxin to induce morphological changes in acinar and GCT cells after adrenoreceptor and cholino receptor blockage. The influence of tityustoxin-induced adrenal discharge on the acinar and GCT cells was also investigated after bilateral adrenalectomy. We show that the intense cytoplasmic vacuolation of the acinar cells induced by tityustoxin was prevented by prazosin (alpha(1) adenoreceptor blockade) and atropine (muscarinic cholinoreceptor blockade). The decrease of GCT cell granules following tityustoxin injection was completely blocked by prasozin and partially by propranolol. These results indicate that acinar vacuolation, degranulation of GCT cells, reduction of GCT diameter and height of its epithelium depends on tityustoxin induced adrenergic and cholinergic mechanisms. In contrast, tityustoxin induced acinar cell degranulation was not modified by atropine, prasozin or propranolol (beta(1)-beta(2) adenoreceptor blockade). Thus, acinar degranulation seems to be due to a direct action of tityustoxin on of the rat submandibular glands. The degranulation of the GCT cells and the acinar vacuolation was also prevented by bilateral adrenalectomy, suggesting that these effects are mostly due to catecholamines released from the adrenal glands.

Prophylactic effects of pilocarpine hydrochloride on xerostomia models induced by X-ray irradiation in rats

1. In the present study, we investigated the prophylactic effects of pilocarpine hydrochloride on xerostomia models induced by either single (15 Gy) or repeated (8.6 Gy x3 days) X-ray irradiation in rats. Pilocarpine hydrochloride was administered orally 90 min before each irradiation session. Then, 7 days later, salivary volume, amylase activity and protein concentration in the saliva secreted from the right parotid gland were measured before and after a subsequent administration of pilocarpine hydrochloride (intraduodenal). 2. In irradiated no-pretreatment rats, irradiation induced a significant reduction in both spontaneous and pilocarpine hydrochloride-stimulated secretion (both total salivary volume and flow rate), regardless of the protocol used for X-ray exposure. In irradiated, pilocarpine hydrochloride-pretreated rats, salivary secretion was increased after stimulation by pilocarpine hydrochloride (intraduodenal) to a degree that depended on the pretreatment dose of pilocarpine hydrochloride (p.o.) in both xerostomia models. 3. There were no differences in amylase or protein concentrations between irradiated rats pretreated with pilocarpine hydrochloride and irradiated no-pretreatment control rats. 4. A decrease in the weight of the parotid gland was observed in rats exposed to either the single dose or repeated irradiation protocols. Changes in the submandibular gland were less marked than those in the parotid gland. These changes in gland weight were not affected by pilocarpine hydrochloride pretreatment. 5. The responsiveness of the parotid gland to subsequent stimulation with pilocarpine hydrochloride was apparently preserved in both xerostomia models by pretreatment with pilocarpine hydrochloride, which itself increased salivary secretion. This suggests that pilocarpine hydrochloride may exert functional protective effects against xerostomia that occurs following irradiation therapy through a stimulation of salivary secretion.

Significance of saliva for the denture-wearing population

This paper summarises a series of studies already published in German and presents new data related to the aetiology of the 'dry mouth' and its associated problems.

AIMS

To study factors affecting mucous and serous salivary gland secretion, the aetiology of the 'dry mouth' and its associated problems, causative factors for hyposalivation and it's treatment.

SETTING

Two university dental hospitals.

SUBJECTS

587 denture wearers and 521 control subjects, and autopsy material.

INTERVENTIONS

Exercise, chewing, water, oestrogen, pilocarpine, and anetholtrithion therapy, biopsy of the minor glands.

MAIN OUTCOME MEASURES

Palatal secretion (PAL, microL/cm2/min) and parotid salivary flow (PAR), subjective complaints and clinical findings.

RESULTS

Resting flow rates for PAL between 0 and 65 microliters/cm2/min were seen in every age group. The flow rates of PAR (0 to 3.7 ml/10 min) were not correlated with PAL. Most patients with a resting flow rate of PAL < or = 6.0 microliters/cm2 suffer from a 'dry mouth' and Burning Mouth Syndrome (BMS) or oral dysaesthesia (OD) with or without chronic lesions of the oral mucosa. Etiological factors for the incidence of reduced PAL and associated problems include xerostomic drugs, oestrogen deficiency, radiotherapy, thyroid dysfunction, smoking or continuous wearing of complete upper dentures. PAL also correlated with the retention of upper complete dentures. PAL was correlated with the water content of epithelial tissues. PAL and PAR were both increased by drinking ample fluid, improving their circulation by physical exercises, chewing intensively, or taking oestrogens, pilocarpine, anetholtrithion.

CONCLUSIONS

Variation in palatal salivary secretion occurs and is clinically important.

Effects of crude venom, tityustoxin and toxin Ts-gamma from Tityus serrulatus scorpion on secretion and structure of the rat submandibular gland

Changes in the rat submandibular glands after intravenous injections of Tityus serrulatus scorpion venom, tityustoxin or toxin Ts-gamma were studied histologically and morphometrically. The acini and the granular convoluted tubules presented the most prominent changes. The following variables were measured: (a) relative volume occupied by the glandular structures; (b) diameter of the granular convoluted tubules and thickness of their epithelium; (c) diameter of the acini. The cytoplasm of the acinar cells was extensively occupied by large confluent vacuoles and had a reduced number of secretory granules after intravenous injections of venom or toxins. The morphological changes caused by toxin Ts-gamma were greater than those evoked by tityustoxin or crude venom injections. In spite of the changes in acinar cells, acinar diameter showed no significant alterations after venom or toxin injections. Reduction of diameter and depletion of the cytoplasmic secretory granules were observed in the granular convoluted tubules 2 h after intravenous injections of crude venom, or after 1 h with tityustoxin or toxin Ts-gamma. The intravenous injection of crude venom did not induce any visible change in the granular convoluted tubules after 1 h. These structural changes could explain the concomitant intense sialagogue effect elicited by crude venom, tityustoxin and toxin Ts-gamma. The sialagogue effect induced by toxin Ts-gamma was larger than those induced by crude venom or tityustoXin.

Protection against irradiation-induced damage to salivary glands by adrenergic agonist administration

PURPOSE

Irradiation [IR]-induced damage to major salivary glands is an entity first described at the beginning of our century, yet its underlying mechanism is still enigmatic. Exposure of the salivary glands to IR is often inevitable when delivering radiotherapy for malignancies of the head and neck region. Frequently, this results in rapidly developing, life-long severe xerostomia for which no adequate prevention or treatment is available. The purpose of this study was to examine the role of secretion granules in serous cells of the parotid (P) and submandibular (SM) glands as mediators in the IR-induced salivary damage. Functional parameters (flow rate and gland weight), and total body weight were examined at both early term (4 days) and extended term (2 months) post-IR in male Wistar rats exposed to 15 Gy of head and neck irradiation following stimulation for granule secretion (degranulation).

METHODS AND MATERIALS

At 4 days, it was demonstrated that IR reduced P flow rate, P gland weight, total body weight, and submandibular/sublingual gland weight by 89, 33, 30, and 32% (p < 0.01), respectively, while SM flow rate was not altered significantly. At 2 months, these parameters were reduced by 59, 37, 31, and 37%, respectively, and the SM flow rate was reduced by 39% (p < 0.01).

RESULTS

Pilocarpine, a muscarinsic agonist which, albeit its efficacy as a salivary watery secretion stimulator, causes only limited degranulation, did not protect significantly any of the reduced parameters at either term. In contrast, cyclocytidine, an adrenergic agonist that is a very potent salivary degranulating agent, protected the P against the weight loss at 4 days and 2 months, and against the flow rate reduction at 2 months. The P weight and flow rate were protected to the extent that their values were not significantly different than those of the nonirradiated controls. Cyclocytidine also partially protected against the body weight reduction at 2 months. Our results emphasize the importance of secretion granules as mediatory agents in IR-induced P damage, and more so at the extended term. The demonstrated protective role of adrenergic agonists against IR damage to the P may be of importance in the clinical setting.

Histological and ultrastructural study of the effects of cholinergic and adrenergic agonists on salivary secretion from the lingual epithelium and the lingual gland of the Tokyo Daruma pond frog

Comparative observations of the effects of cholinergic and adrenergic agonists (such as pilocarpine, phenylephrine and isoproterenol) on the secretion of salivary fluid and of secretory granules from the lingual epithelium and the lingual gland in the Tokyo Daruma pond frog, Rana porosa porosa, were made by light and transmission electron microscopy. The effect of pilocarpine on the loss of cytoplasm in both the lingual epithelium and the lingual gland was the strongest, and that of isoproterenol was the weakest. Transmission electron microscopy revealed that electron-dense granules, located in cells in both the lingual epithelium and the lingual gland, were discharged by exocytosis after stimulation by phenylephrine and isoproterenol. Immediately before secretion of these granules, they became somewhat larger and round or distorted in shape. However, after administration of pilocarpine, no obvious discharge of electron-dense granules was apparent and, instead, granules in some cells began deteriorating within the cells and those in other cells developed electron-dense and electron-lucent areas. A dot-like pattern was recognized in the electron-dense areas of these granules. These phenomena were assumed to be secondary effects accompanying the secretion of salivary fluid from cells of the lingual epithelium and the lingual gland. By contrast, mucous granules in the lingual gland were secreted by a holocrine process.

Asynchronous reformation of individual kallikrein-related secretory proteinases in rat submandibular glands following degranulation by cyclocytidine

Time scales for the reformation of the secretory granules in granular tubules and their constituent proteinases were assessed after inducing a massive degranulation by intraperitoneal injection of cyclocytidine in conscious animals. The minimum working dose of cyclocytidine to produce the maximum degranulation and depletion of proteinase activity, at 3 h after injection, was 75 mg/kg. Histologically, although most granular tubule cells then appeared to be extensively degranulated, isolated individual cells showing little or no degranulation always persisted. Acinar cells also showed some depletion of secretory material. At 15 h after injecting cyclocytidine the formation of new granules had begun in the granular tubule cells, but it was not extensive or uniform in adjacent cells; however, the acinar cells already appeared to be regranulated. The pattern of granule reformation in granular tubule cells progressed gradually, so that 7-10 days after cyclocytidine-induced degranulation the cells were mostly packed with granules and showed similar appearances to those of normal resting control glands. Individual proteinases in extracts of the glands were assayed specifically using fluorogenic oligopeptide amidase substrates, with and without appropriate inhibitors. This revealed a 95% reduction in total proteinase activity 3 h after cyclocytidine (75 mg/kg). In the same extracts, acinar peroxidase was reduced by 28%. Peroxidase levels recovered to control values within 15 h after cyclocytidine but recovery of proteinases progressed more gradually and did not occur uniformly for the different constituent proteinases. Tissue kallikrein (rK1) showed the most rapid recovery and had reached levels approaching normal within 3 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural changes in salivary glands after different adrenergic and cholinergic stimulations. A long-term morphological study in the rat

We have compared four different sialogogues and their degranulating effect on serous and mucous cells, and their long-term effects. From this and earlier experiments, even within the groups of alpha- and beta-adrenergic agents used, the effects varied on the serous and mucous cells. Previous studies have shown that cyclocytidine effectively degranulates serous cells without signs of cellular damage, while carbachol predominantly affects mucous acinar cells but gives early rise to permanent gland damage. Noradrenaline affects both serous and mucous cells, predominantly affecting serous cells with initial mitochondrial damage. Clonidine partially depletes both serous and mucous cells of their granules, producing permanent cellular damage. One month after a single injection of cyclocytidine the early findings described had disappeared. Carbachol showed permanent damage to salivary gland parenchyma, and both noradrenaline and clonidine demonstrated a long-term effect on acinar mucinous cells.

The effects of clonidine and three 2-imidazoline derivatives on the secretion of protein and some electrolytes by rat submandibular and parotid glands

1. Three imidazoline analogues of clonidine were potent secretagogues for the parotid and submandibular glands at relatively high doses. 2. Salivation in response to clonidine was completely abolished by prazosin, phentolamine, phenoxybenzamine and dihydroergotamine. 3. The gamma-type of proteins was secreted in response to three of the analogues, whereas with p-aminoclonidine the alpha-type of proteins was secreted by the submandibular gland. 4. Albumin was specifically secreted by the submandibular gland in response to clonidine but not to isoproterenol or phenylephrine.

Comparison of cyclocytidine and sympathetic nerve induced changes in norepinephrine and adrenoceptors in salivary glands

Norepinephrine (NE) concentration of parotid and submandibular glands of young rats was reduced 51% and 39%, respectively at 1 h, and 60% and 47% at 2 h after i.p. administration of a single dose (500 mg/kg body weight) of the anti-tumor agent, cyclocytidine (CC). For adult rats, the reductions were 44% and 46%, respectively, at 1 h and 54% and 49% at 2 h. This decrease from controls was generally similar to the decrease induced following 1 and 2 h of electrical stimulation (square wave pulses of 4 V, 5 ms duration, and frequency of 16 Hz) of the sympathetic innervation to these glands (young rats, 59% and 58% at 1 h; 66% and 63% at 2 h; for adult rats, 51% and 55% at 1 h and 69% and 53% at 2 h for parotid and submandibular, respectively). The changes in density of beta-adrenoceptors induced by direct nerve stimulation also corresponded to the changes induced by CC (CC induced a decrease in parotid of 12%, compared with a decrease of 11% with electrical stimulation; a 15% and 18% reduction in number of beta-adrenoceptors of submandibular gland was found at 1 h after CC and electrical stimulation, respectively). Compelling evidence for the mechanism of CC action was thus established, showing that CC mimics effects of sympathetic nerve stimulation (inducing reduction in NE concentration and transient change in beta-adrenoceptor density) by causing release of NE from sympathetic nerve endings.

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

The 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.

The effect of pilocarpine and atropine administration on radiation-induced injury of rat submandibular glands

In the management of head and neck tumors by radiotherapy, the patients are prone to suffer from radiation-induced damage of the salivary glands. This experiment was carried out to examine the effect of pilocarpine and atropine on the rat submandibular gland and to establish whether it is possible to protect the salivary glands from irradiation by altering the amount of secretory granules in the serous cells prior to irradiation. The submandibular glands of rats were irradiated after pretreatment with or without drugs. Single irradiation of 18 Gy caused significant damage to the submandibular glands without pretreatment, showing the most severe changes 1 week after irradiation and slowly recovering thereafter. Pilocarpine pretreatment was protective against irradiation, displaying much less damage after irradiation of the same dosage, and with complete recovery after 4 weeks. On the other hand, atropine-pretreated animals revealed more extensive damage than the other two groups, possibly due to the retention of secretory granules.