Effect of alpha- and beta-adrenergic agonists on fluid and calcium secretion by rat salivary glands

Assessment of the toxic effects of levetiracetam on biochemical, functional, and redox parameters of salivary glands in male Wistar rats

Levetiracetam (LEV) is an anticonvulsant for epilepsy. The toxic effects of this medication in tissues have been associated with redox state imbalance, which can lead to salivary gland dysfunction. Therefore, the current work investigated the effects of LEV on the biochemical, functional, and redox parameters of the parotid and submandibular glands in rats. For this, male Wistar rats (Rattus norvegicus albinus) were randomly divided into 3 groups (n = 10/group): Control (0.9% saline solution), LEV100 (100 mg/kg), and LEV300 (300 mg/kg). After 21 consecutive days of intragastric gavage treatments, pilocarpine stimulated saliva secretion was collected for salivary biochemical analysis. The extracted salivary glands were utilized for histomorphometry and redox state analyses. Our results showed that LEV300 increased plasma hepatotoxicity markers and reduced salivary amylase activity and the acinar surface area of the parotid gland. Total oxidant capacity and oxidative damage to lipids and proteins were higher in the parotid gland, while total antioxidant capacity and uric acid levels were reduced in the submandibular gland of the LEV100 group compared to Control. On the other hand, total oxidant capacity, oxidative damage to lipids and proteins, total antioxidant capacity, and uric acid levels were lower in both salivary glands of the LEV300 group compared to Control. Superoxide dismutase and glutathione peroxidase activities were lower in the salivary glands of treated animals compared to Control. In conclusion our data suggest that treatment with LEV represents a potentially toxic agent, that contributes to drug-induced salivary gland dysfunction.

Effects of isoproterenol on aquaporin 5 levels in the parotid gland of mice in vivo

In the membrane fraction of mouse parotid gland (PG), the protein level of aquaporin 5 (AQP5), a member of the water channel family, was increased by injection (ip) of isoproterenol (IPR), a β-adrenergic agonist, at 1 h, and stayed at high levels until 6 h; this change occurred simultaneously as amylase secretion. The AQP5 level then decreased and returned toward the original level at 12-48 h. After IPR injection, the AQP5 mRNA gradually increased and reached a maximum at 24 h. The facts suggest a rapid appearance of AQP5 at plasma membrane by IPR and subsequent degradation/metabolism by activation of proteolytic systems. Pretreatment of animals with two calpain inhibitors, N-Ac-Leu-Leu-methininal (ALLM) and calpeptin, as well as a protein synthesis inhibitor, cycloheximide (CHX), significantly suppressed the IPR-induced AQP5 degradation in the PG membrane fraction; such suppression was not observed by two proteasome inhibitors, MG132 and lactacystin, or the lysosome denaturant chloroquine, although most of these inhibitors increased AQP5 protein levels in unstimulated mice. The AQP5 protein was also degraded by μ-calpain in vitro. Furthermore, we demonstrated that μ-calpain was colocalized with AQP5 in the acinar cells by immunohistochemistry, and its activity in the PG was increased at 6 h after IPR injection. These results suggest that the calpain system was responsible for IPR-induced AQP5 degradation in the parotid gland and that such a system was coupled to the secretory-restoration cycle of amylase in the PG.

Effects on salivary flow rate and composition of withdrawal of and re-exposure to the beta 1-selective antagonist metoprolol in a hypertensive patient population

Secretion rates and composition of unstimulated and chewing-stimulated whole saliva and 3% citric acid stimulated parotid and submandibular-sublingual secretions were studied in 12 hypertensive patients during withdrawal of and re-exposure to antihypertensive pharmacotherapy. All the patients' blood pressures were well controlled by monotherapy with metoprolol, a beta 1-selective adrenoceptor antagonist. Blood pressure measurements and saliva sampling were performed at about 9:30 a.m., 2 h after intake of breakfast, on days 0 (medicated baseline), 7, 14, 28 (nonmedicated experimental values and nonmedicated baseline) and 35 (medicated experimental values). A significant increase in unstimulated whole saliva secretion rate was observed when metoprolol was withdrawn and a corresponding decrease when the drug was reintroduced. A positive correlation was found between diastolic blood pressure levels and chewing-stimulated whole saliva secretion rates. In unstimulated whole saliva and 3% citric acid stimulated submandibular-sublingual secretion, the output of total protein, amylase, potassium, calcium and phosphate was significantly increased during the withdrawal period and decreased when metoprolol was reintroduced. For chewing-stimulated whole saliva, the corresponding changes were restricted to output of total protein and amylase, while for citric acid stimulated parotid secretion, no changes in salivary composition were observed. Finally, in all secretions one or both of the ratios hexosamine/total protein and sialic acid/total protein were affected, indicating a possible effect of beta-adrenoceptor antagonists on salivary protein synthesis.

Effects of the beta-adrenoceptor antagonists atenolol and propranolol on human parotid and submandibular-sublingual salivary secretion

The aim of the study was to evaluate the effects of a beta 1-selective (atenolol 50 mg q.d.) and a non-selective (propranolol 80 mg b.i.d.) beta-adrenoceptor antagonists on human stimulated parotid and submandibular-sublingual (SM-SL) gland secretion. A randomized double-blind, placebo-controlled cross-over ("Latin square") design was used in 19 healthy male volunteers. Stimulated parotid and SM-SL saliva were sampled immediately before and 7 days after the start of each treatment period. Stimulation of salivary secretion was achieved by use of a 3% citric acid solution. Plasma concentrations of propranolol and atenolol were determined from blood samples. The salivary secretion of both glands was assessed for flow rate, amylase, lysozyme, and salivary peroxidase activity and for concentrations of total protein, hexosamine, sialic acid, Ca2+, Cl-, K+, Mg2+, Na+, and PO4(3-). In both parotid and SM-SL secretions, the total protein and phosphate concentrations and amylase activity were significantly decreased during the two active treatment periods. In SM-SL gland secretion, there were significant changes in potassium and calcium concentrations during active treatment as compared with baseline, with potassium showing a decreased and calcium an increased concentration. During atenolol treatment, salivary peroxidase activity decreased significantly in SM-SL secretion. In parotid secretion, the hexosamine/total protein ratio decreased and the sialic acid/hexosamine ratio increased during atenolol treatment, which may indicate an effect on protein synthesis. No significant effects on salivary secretion rates were disclosed.

Effects of clonidine on the calcium content and morphology of rat salivary glands

These effects were examined with and without pretreatment of animals with reserpine and the adrenergic antagonists prazosin (alpha 1), yohimbine (alpha 2) and propranolol (beta). The effects of clonidine on glandular concentrations of norepinephrine and dopamine also were examined. These effects were compared with those of xylazine, a presynaptic alpha 2-adrenergic agonist. A single, high dose of clonidine followed by an overnight fast caused marked increases in calcium content and acinar secretory granules in the submandibular and sublingual glands, similar to those caused by reserpine. However, the calcium content of the parotid gland was not altered by clonidine, although there seemed to be a modest increase in acinar secretory granules. The clonidine-induced increase in submandibular calcium content could not be attributed to any adrenergic receptor activity since it was not blocked by either alpha- or beta-adrenergic antagonists. Unlike reserpine, clonidine did not affect catecholamine concentrations in the parotid and submandibular glands. Pretreatment with reserpine did not significantly alter the clonidine-induced increase in submandibular calcium content. It is likely that the greater accumulation of acinar secretory granules is related to the increased calcium stores of the glands in clonidine- and/or reserpine-treated rats. The large differences in calcium content among the three glands might be attributable, in part, to differences in the calcium-binding capacity of their secretory granules. Possible mechanisms for the clonidine effects on salivary-gland calcium include disturbances in membrane-associated pools or gating mechanisms for calcium, which need further study.

Effects of the beta-adrenoceptor antagonists atenolol and propranolol on human whole saliva flow rate and composition

The effects of beta-adrenoceptor antagonists on salivary secretion have been extensively studied in animals but not in man. The aim here was to compare salivary flow rate and composition in man during 1 week of treatment with a non-selective (propranolol 80 mg b.i.d.) and a beta 1-selective (atenolol 50 mg o.d.) antagonist with that of placebo. The randomized, double-blind, cross-over ("Latin square") design was used and 42 healthy male volunteers were recruited to the study. The treatment periods were separated by a wash-out period of 2 weeks. Whole saliva was sampled on day 0 (before) and on day 7 during each treatment. The plasma concentration of propranolol and atenolol was determined from blood samples obtained on day 7. Resting saliva was assessed for flow rate, amylase activity and concentration of total protein, hexosamine and sialic acid. Stimulated saliva was assessed for flow rate, pH, buffer pH, amylase activity and concentration of total protein, Ca2+, Mg2+, Na+, K+, Cl- and PO4(2-). In resting as well as stimulated whole saliva both the total protein concentration and the amylase activity were significantly decreased during the active treatment periods (p less than 0.05-p less than 0.001). At lunchtime during atenolol treatment the hexosamine/total protein and the sialic acid/total protein ratios were significantly increased (p less than 0.05-p less than 0.01), suggesting a possible effect on protein synthesis. In addition, the concentrations of Ca2+, PO4(2-), Cl- and Mg2+ were significantly altered during the active treatment periods (p less than 0.05-p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Effects of chronic clonidine administration on parasympathetic-evoked rat saliva

Effects of chronic administration of clonidine on parasympathetic-evoked saliva from both parotid and submandibular glands were investigated. Clonidine at 1 mg/kg/day for 5 or 7 days caused a significant reduction in the salivary secretion (flow rate and total volume) evoked by parasympathetic nerve stimulation of parotid but not submandibular glands. Ion concentrations (Na, K and Ca) of parasympathetically nerve-evoked parotid saliva were not altered. However, the total protein concentration as well as output, amylase activity, and output of such saliva were markedly increased. Possible mechanisms for clonidine-induced increase in nerve-elicited salivary protein concentration include release of neuropeptides, and changes in adrenergic receptor binding which need further study.

Physostigmine-induced salivary secretion in the rat

The purpose of this study was to see if physostigmine, a reversible cholinesterase inhibitor, affects the secretion and composition of saliva of the major salivary glands of the rat. Low doses of physostigmine did not elicit secretion. At higher doses there was significant flow from the parotid and submandibular glands within 5 min; however, no sublingual secretion was observed. The submandibular flow rate was highest for the first 5 min, then declined rapidly. The parotid flow rate initially was one-fifth of the maximum submandibular rate and then gradually decreased. The concentrations of Ca, Na and K of physostigmine-induced parotid saliva, and the Na of submandibular saliva, were similar to those with carbachol stimulation. The Ca and K concentrations of submandibular saliva were significantly higher than with carbachol or parasympathetic stimulation, and resembled those of alpha-adrenergic stimulation. The protein concentrations of physostigmine-evoked saliva from both glands were similar. The amylase activity of physostigmine-evoked parotid saliva was much higher than that of carbachol or parasympathetic stimulation. Physostigmine-evoked secretion was completely blocked by atropine, a cholinergic antagonist, and by reserpine, partially blocked by phentolamine, an alpha-adrenergic antagonist and not affected by surgical sympathectomy. Morphologically, physostigmine resulted in a moderate decrease in the number of acinar, but not ductal, secretory granules of both the parotid and submandibular glands, while the sublingual gland was unaffected. Numerous patches of parotid acini also developed vacuoles or vesicles. These results suggest that physostigmine-induced salivary secretion is mediated primarily by direct effects on cholinergic and alpha-adrenergic receptors.

The influence of varying the electrical frequency of sympathetic nerve stimulation on fluid and calcium secretion of the rat parotid salivary gland

The effects of varying this frequency were studied in the absence and presence of the specific adrenergic antagonists. There were no appreciable differences in fluid and calcium secretion at different frequencies of stimulation when the nerve was stimulated alone or in the presence of the selective antagonists. Thus, it is difficult to differentiate between the effects of alpha- and beta-adrenergic receptor stimulation by varying the frequency of nerve stimulation. The findings also confirmed that both types of receptors are activated together when the sympathetic nerve is stimulated. beta-Adrenergic receptors play a major role in secretion of both fluid and Ca; alpha-adrenergic receptors seem to have a minor role in their regulation.

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.

Effect of clonidine on secretion of fluid and ions by the parotid and submandibular glands of the rat

Secretion in response to this alpha 2-adrenergic agonist was evaluated in the presence and absence of several adrenergic antagonists, reserpine and sympathectomy (Sx). In both glands, the response was qualitatively but not quantitatively similar to that induced by the alpha 1-adrenergic agonist, phenylephrine, in the presence of propranolol. With clonidine, the volume of submandibular saliva was much higher but the Ca concentration was 3-4 times lower than that of the parotid; both salivas had low Na but high K concentrations. Clonidine-induced secretion was almost completely blocked by the alpha 1-adrenergic antagonist, prazosin and a mixed alpha-adrenergic antagonist, phentolamine, and markedly reduced by the alpha 2-adrenergic antagonist, yohimbine, but unaffected by the beta-adrenergic antagonist, propranolol. Reserpine reduced the parotid, but enhanced the submandibular secretory response to clonidine. Results in Sx glands were similar. Thus, in the rat glands clonidine may activate alpha 1-rather than alpha 2-adrenoceptors, which appear to play a part similar to alpha 1-adrenoceptors only after reserpine or Sx.

Calcium levels in rat submandibular gland and saliva after sympathetic nerve stimulation in the presence of alpha, beta 1 and beta 2-adrenergic antagonists

Calcium concentration was reduced by 51 per cent compared with unstimulated contralateral glands after 60-min of electrical stimulation to the sympathetic nerve. When the alpha-adrenergic antagonists, phentolamine or phenoxybenzamine, were given 20 min before stimulation, the decrease in glandular calcium concentration (45-47 per cent) was similar to that after nerve stimulation alone; with the selective beta 2-adrenergic antagonist added to the phentolamine, the percentage decrease was similar to that found after phentolamine and sympathetic nerve stimulation only. When atenolol, a beta 1-adrenergic antagonist, was given with phentolamine, there was no secretion after subsequent nerve stimulation, nor was calcium concentration different from that of unstimulated glands. When propranolol (3 mg/kg, body wt), or atenolol + butoxamine (3 mg/kg, body wt), was given prior to stimulation there was a decrease of 21-22 per cent in gland-calcium concentration. Calcium concentration of nerve-stimulated saliva was nearly 6 m-equiv./l, and twice as high with phentolamine prior to stimulation; for butoxamine together with phentolamine the change was similar to that with phentolamine alone. When beta-adrenergic antagonists were given prior to nerve stimulation, concentration of the saliva was either unchanged (propranolol) from that with nerve stimulation alone or somewhat decreased (atenolol + butoxamine). Thus sympathetic stimulation results in activation of alpha and beta 1-adrenoceptors; calcium secretion is principally regulated by the beta-adrenoceptors, and beta 1-receptors have the principal role.

Modification of dobutamine- and terbutaline-induced calcium and fluid secretion from rat salivary glands by atenolol and butoxamine

Saliva was elicited from rat salivary glands by terbutaline at i.p. doses of 1, 5, 10 and 25 mg/kg b.wt. but not by doses of 0.1 or 0.5 mg/kg b.wt. Dobutamine elicited no secretion at 1 or 2 mg/kg but did at 5, 10 and 25 mg/kg b.wt. At 5 mg/kg terbutaline evoked nearly maximal volumes but with dobutamine, volumes were small at this dosage. At dosages of 10 and 25 mg/kg volumes with the two agonists were similar for parotid, but with submandibular, the volumes evoked by dobutamine were nearly two times as high as those elicited by terbutaline. Mean [Ca] of parotid saliva was also similar at all dosages of dobutamine (approximately 12 mEq/liter) and generally similar at all dosages of terbutaline (11-15 mEq/liter). Mean [Ca] of dobutamine-elicited submandibular saliva was approximately 6, 7 and 8 mEq/liter at 5, 10 and 25 mg/kg b.wt, respectively. With parotid, [Ca] was approximately 10 mEq/liter at 1, 5 and 10 mg/kg b.wt. but increased to 16-18 mEq/liter at 25 mg/kg. The time course of calcium secretion is described for both agonists at each dosage. [Ca] of both glands was decreased 60 min after i.p. injection of 10 or 25 mg/kg doses of dobutamine or terbutaline but was not changed by 5 mg/kg doses. Administration of 10 mg/kg of atenolol, the selective beta 1 antagonist, 20 min prior to injection of a 10 mg/kg dose of either terbutaline (beta 2 agonist) or dobutamine (beta 1 agonist) blocked secretion from both glands, and prevented the usual agonist-induced reduction in glandular concentration of calcium. Butoxamine, on the other hand, did not modify effects of terbutaline on fluid secretion or depletion of glandular calcium; it did partially inhibit dobutamine-induced fluid and calcium secretion but not depletion of glandular calcium. The present data suggest that beta adrenoceptors of salivary glands are predominantly of the beta 1 subtype and that it is these that regulate calcium and fluid secretion. On the basis of the data with the antagonists, it is concluded that terbutaline activates beta 1 rather than beta 2 receptors since the beta 1 antagonist but not the beta 2 antagonist blocked secretory responses to terbutaline.