A histological study of the effects of different alpha-adrenergic and cholinergic agonists on the rat submandibular gland

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.

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.

Histological and ultrastructural studies of the effects of tachykinins on protein secretion from the lingual epithelium and the lingual gland of the Tokyo daruma pond frog (Rana porosa porosa)

Four tachykinins were each administered at 20 micrograms/kg body wt. All the tachykinins had a positive effect on granular secretion from the lingual epithelium, and the loss of cytoplasm from cells of the lingual epithelium was greatest with physalaemin and eledoisin, moderate with neurokinin A, and smallest with substance P. These reactions were very different from those in mammals, in which tachykinins induce only watery secretions. Only physalaemin had a positive effect on protein secretion from the lingual gland. Transmission electron microscopy revealed that electron-dense granules in cells of the lingual epithelium were discharged during stimulation with physalaemin and eledoisin by typical exocytosis. Discharge of these granules was indistinct after the administration of substance P and of neurokinin A. Exocytosis of electron-dense granules from cells of the lingual gland was clearly detectable by electron microscopy after the administration of physalaemin, reflecting observations made by light microscopy. However, mucous granules in the lingual gland were secreted by an exocrine process only after administration of physalaemin.

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.

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.

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.

Aspects of salivary gland radiosensitivity: effects of sialagogues and irradiation

Rat submandibular glands were exposed to fractionated irradiation of 50 Gy, as given comparably in clinical practice. The induced changes were compared by giving only irradiation or radiation in conjunction with stimulating the salivary glands with cyclocytidine prior to treatment. Cyclocytidine is an alpha-adrenergic agonist that effectively depletes the serous cells of their granules and their heavy metal content. Findings in the present study show that the administration of the drug prior to each irradiation reduces the radiation-induced destruction in the epithelial cells in the submandibular gland.

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

A dual innervation in salivary glands has been discussed. It is unclear how alpha-adrenergic and cholinergic agents stimulate the secretory cells. Different effects on serous and mucous cells are reported after stimulating with carbachol, clonidine, noradrenaline, cyclocytidine and pilocarpine, respectively. In the rat, carbachol and clonidine predominantly affect the mucous cells, however, with different morphological effects. Cyclocytidine exclusively degranulates the serous cells. Noradrenaline stimulates both serous and mucous cells and gives rise to vast cytoplasmic changes. Pilocarpine only shows effect on the mucous cells with formation of intracytoplasmic vacuoles. The effects reported are discussed with regard to experiments on salivary gland radiosensitivity.

An ultrastructural study of salivary gland radiosensitivity after alpha-adrenergic stimulation

The submandibular glands in 32 rats were exposed to either fractionated irradiation comparable to 50 Gy or a single fraction of 50 Gy. Prior to irradiation half the rats were given cyclocytidine, an alpha-adrenergic agonist which depletes serous cell granules. The results suggest that irradiation causes a significant, irreversible destruction of serous cells. Visible morphological changes were: intracytoplasmic vacuoles, destroyed mitochondria with disrupted cristae and derangement of the endoplasmic reticulum. Animals treated with cyclocytidine had diminished radiation injury. This drug may act as radioprotector, depleting secretory heavy metal granules, reducing radiation damage in the submandibular salivary glands.

Salivary gland morphology after alpha-adrenergic and cholinergic stimulation. An ultrastructural study

The submandibular glands in 100 rats were subjected to different sialagogues: carbachol, clonidine, noradrenalin, and cyclocytidine. The morphological effects of these drugs were compared ultrastructurally. Clonidine, which is an alpha-2-agonist affected mostly the mucous cells, with formation of cytoplasmic vacuoles between the mucous droplets. Noradrenalin and cyclocytidine, both alpha-1-agonists, showed depletion of secretory granules in the serous cells. Noradrenalin also induced cytoplasmic disorganization with enlarged mitochondria, irregular endoplasmic reticulum, and shrinking of the secretory lumen. Carbachol, a cholinergic agonist, was found to produce widespread vacuolization in the cytoplasm of both serous and mucous cells. Small vesicles appeared and mitochondria were destroyed. To induce experimentally a complete depletion of granular serous cells, without other changes in ultrastructural morphology, cyclocytidine was found to be the most efficient drug.