Effects of parasympathomimetic and sympathomimetic drugs on the secretion and composition of rat sublingual saliva

Physiological cAMP-elevating secretagogues differentially regulate fluid and protein secretions in mouse submandibular and sublingual glands

The mechanisms underlying the functional differences in sympathetic and parasympathetic regulation of the major salivary glands have received little attention. The acute effects of parasympathetic muscarinic (carbachol)-dependent and combined parasympathetic-dependent plus cAMP-dependent pathways on fluid secretion rates, ion composition, and protein content were assessed using a newly developed ex vivo preparation that allows the simultaneous perfusion of the mouse submandibular (SMGs) and sublingual glands (SLGs). Our results confirm that the muscarinic-dependent pathway accounts for the bulk of salivation in SMGs and SLGs, whereas costimulation with a cAMP-increasing agent (forskolin, isoproterenol, or vasoactive intestinal peptide) did not increase the flow rate. Costimulation with carbachol plus the β-adrenergic agonist isoproterenol decreased the concentration of NaCl and produced a substantial increase in the protein and Ca²⁺ content of SMG but not SLG saliva, consistent with a sparse sympathetic innervation of the SLGs. On the other hand, forskolin, which bypasses receptors to increase intracellular cAMP by directly activating the enzyme adenylate cyclase, enhanced the secretion of protein and Ca²⁺ by both the SMGs and SLGs. In contrast, isoproterenol and vasoactive intestinal peptide specifically stimulated protein secretion in SMG and SLG salivas, respectively. In summary, cAMP-dependent signaling does not play a major role in the stimulation of fluid secretion in SMGs and SLGs, whereas each cAMP-increasing agonist behaves differently in a gland-specific manner suggesting differential expression of G protein-coupled receptors in the epithelial cells of SMGs and SLGs.

Opposite effects of antidepressants on unstimulated and stimulated salivary flow

In this study, effects on both stimulated and non-stimulated salivary flow as well as salivary components of different antidepressant drugs were compared. Rats received imipramine (IMI; 10mg/ml), fluoxetine (FLU; 20 mg/ml) or moclobemide (MOC; 30 mg/ml) by gavage. The drugs were administered 24, 5 and 1 h before saliva collection (sub-acute treatment) or as a once a day treatment for 14 days (chronic treatment). Animals were sedated with thiopental and saliva was collected using pre-weighed cotton balls inserted in the mouth for 1 min before and after pilocarpine stimulus. Pilocarpine-stimulated saliva was also collected for biochemical assays of total proteins, amylase, phosphate and calcium, performed through automated colorimetric methods. Non-stimulated salivary flow was decreased by sub-acute IMI 10 mg/kg treatment. Pilocarpine-stimulated salivary flow was significantly increased by acute treatments with IMI, FLU and MOC in comparison to the control group. The same opposite pattern of effects on non-stimulated and pilocarpine-stimulated salivation was seen after chronic treatment with the antidepressants. Increased levels of calcium following sub-acute treatment with IMI and after prolonged treatment with FLU and MOC were detected. In the assayed samples, phosphate was found to be increased following chronic treatment with FLU or MOC. These results may explain the discrepant effects of the antidepressants on salivation described in pre-clinical and clinical studies.

Alteration by ouabain of rat submandibular glands function

1. Effects of various doses of intraperitoneal ouabain (1,2 and 5 mg/kg) on rat submandibular saliva were investigated in this study. 2. Potassium and calcium and their product (K+ x Ca2+) were found to be elevated in all groups. 3. Changes in salivary flow were not the major cause of the alterations in electrolytes. 4. Protein concentrations were elevated in the doses of 1 and 2 mg/kg of the drug and somewhat reduced in the dose of 5 mg/kg of ouabain but still above the base line. 5. The results show that there is an ouabain-induced close parallelism between magnesium and total protein secretion from rat submandibular glands.

Muscarinic cholinergic receptor subtypes in rat sublingual glands

Mucin glycoprotein secretion by rat sublingual glands is regulated primarily by muscarinic cholinergic receptors. Studies were conducted to identify muscarinic receptor subtypes in whole glands as well as in isolated acinar structures. In radioligand binding studies, we used subtype-selective antagonists in competition studies to initially determine receptor subtype heterogeneity. In membranes from whole glands, both pirenzepine and methoctramine displayed two affinity sites (M1 and M3) of nearly equal proportions. In contrast, acinar membranes contained a 1:2 and 2:1 ratio of M1 to M3 sites for pirenzepine and methoctramine, respectively. In all cases, p-fluoro-hexahydro-siladifenidol and 4-diphenylacetoxy-N-methylpiperidine each bound to a single class of binding sites. Northern analysis using oligonucleotide probes specific for the 5' ends of the translated regions of m1 through m5 receptors detected only m1 and m3 subtypes in poly(A)+ RNA from whole glands. We also used antisera specific for each receptor subtype to immunoprecipitate solubilized receptors from membrane preparations. Only m1 (51.7 and 64.9%) and m3 (48.3 and 34.7%) subtypes were found consistently in membranes from whole sublingual glands and isolated acini, respectively. Studies with other exocrine glands generally described the predominance of m3 receptors, and m1 receptors, if present, were presumably associated with contaminating neural structures. Our results therefore demonstrate that mucous acini from rat sublingual glands contain abundant amounts of both m1 and m3 receptors.

Rat sublingual gland as a model to study glandular mucous cell secretion

To study the regulation of mucous cell secretion, we have developed an in vitro cell model consisting of enzymatically dispersed mucous acinar structures (cell aggregates) from rat sublingual glands. Histological and ultrastructural evidence demonstrates that the cell aggregates are highly enriched in mucous cells, retain the morphological and ultrastructural features observed in intact glands, and undergo transition to an extensive secretory state when stimulated by 10 microM carbachol. The secretory responsiveness of the cell aggregates was verified in pharmacological studies. Carbachol stimulated secretion in a dose-dependent manner with high affinity (concentration causing half-maximal response = 0.3 microM) and was completely inhibited by atropine. Secretion was also stimulated by vasoactive intestinal peptide and substance P but not by alpha- or beta-adrenergic agonists. Biochemical characterization of secretion during nonstimulated and carbachol-stimulated conditions (after preincubation in [3H]glucosamine) demonstrated that, in response to carbachol, cell aggregates synthesized and secreted mucins which were similar to mucin glycoproteins isolated from whole glands. Collectively, our results establish that the rat sublingual cell aggregate model is a viable and pharmacologically responsive cell system to study the regulation of mucous cell secretion.

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.

An adaptation of the Lashley cup for use in rat saliva collection

A miniaturized Lashley cup for collecting rat parotid and submandibular/sublingual saliva is described. The small dimensions of the cup enabled its proper positioning on the orifices of both salivary ducts. The method avoids surgical intervention, causes no tissue damage, allows simultaneous collection of both types of saliva and its appropriate for long-term studies of salivary composition and secretion in the rat.

Alteration of membrane phospholipids in hypertrophied rat salivary glands induced by chronic administration of isoproterenol

Hypertrophy of parotid and submandibular glands, and elevated phospholipid content per gland in both were induced. However, phospholipid content per tissue weight increased only in the parotid gland. Sublingual gland phospholipids were unaffected with regard to the gland weight and phospholipid content; phospholipid class compositions were altered in each of the three glands, typically an increase of phosphatidylcholine and decreases of sphingomyelin and phosphatidic acid. Concerning fatty-acyl groups in phospholipid, prominent increase of octadecadienoic acid was observed in total and individual phospholipids of both parotid and submandibular glands. However, eicosatetraenoic acid decreased in the total phospholipids of these two glands. In the sublingual gland, phospholipids, fatty-acyl compositions were not changed by isoproterenol. The results suggest that isoproterenol-induced changes of membrane phospholipids are regulated by at least two different effects, one for fatty-acyl groups and another for base moieties of phospholipids.

Amylase activity, protein and urea in saliva of the red kangaroo (Macropus rufus)

Parotid and mandibular salivas, produced at flow rates of 0.055 +/- 0.0038 to 4.45 +/- 0.101 and 0.052 +/- 0.0059 to 4.30 +/- 0.072 ml min-1 respectively by intracarotid infusion of acetylcholine or methacholine, were analysed. During acetylcholine stimulation, the protein concentration ranged from 86.4 +/- 10.17 to 235.0 +/- 23.5 mg l-1 in parotid and from 102.9 +/- 11.54 to 379.6 +/- 38.01 mg l-1 in mandibular saliva. The minimum protein concentrations in parotid and mandibular salivas occurred at 0.5 and 1.0 ml min-1 respectively with the concentration rising progressively at lower and higher flow rates. Both glands maintained constant levels of protein during 90 min of sustained stimulation at constant flow rates of 0.5 and 2.0 ml min-1. The optimum pH for salivary amylase activity lay between 7.4 and 7.9 (mean 7.5-7.6). The amylase activity of parotid saliva ranged between 32.2 +/- 3.81 and 94.5 +/- 24.05 mukat l-1 and the activity/protein ratio was similar at all flow rates (mean, 0.39 +/- 0.049 mukat amylase/mg protein). Amylase levels in arterial plasma were constant within experiments but varied from 8.0 +/- 0.07 to 26.4 +/- 0.24 mukat l-1 between experiments, and were always less than corresponding parotid values. Mandibular amylase activities were low, highly variable or often absent. Methacholine-evoked parotid saliva had lower protein concentrations but similar amylase/protein ratios to acetylcholine-stimulated saliva. Urea concentrations in arterial plasma were constant within experiments but varied from 6.71 +/- 0.092 to 14.2 +/- 0.14 mmol l-1 between experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of membrane phospholipid and its fatty acid compositions in developing rat salivary glands

1. Membrane phospholipid and its fatty acid compositions have been analyzed in 3- and 9-week-old rat salivary glands. 2. When compared between the three major glands (parotid, submandibular, sublingual) in adult rats, phospholipid compositions were similar, but for their fatty acid, characteristic properties from each phospholipid were shown. 3. Alterations in their compositions were also observed during development of the salivary glands.

Gap junctions in rat sublingual gland

Gap junctions were observed in rat sublingual gland to link serous cells to serous cells, mucous cells to mucous cells, and myoepithelial cells to myoepithelial cells. In addition to connecting homologous cells, gap junctions were present between conterminous serous and mucous cells. Since the rat sublingual gland is innervated solely by parasympathetic nerves, the presence of gap junctions between disparate secretory cell types raises the possibility that serous and mucous cells in this organ secrete simultaneously in response to parasympathetic stimulation.

The effects of an incisal bite plane on rat sublingual glands

Application of an incisal bite plane for as little as three d caused a significant increase in the size of the sublingual glands of rats, with some evidence of hyperplasia and hypertrophy of the acinar cells. The enlargement had few effects on salivary secretion, and the gland changes were reversible.