Secretory responses of the rat submandibular and parotid glands to sequential stimulation with pilocarpine and isoproterenol

Salivary secretion assay for drug efficacy for cystic fibrosis in mice

Computerized assays on cultured cells ex vivo have been used to screen thousands of compounds for their effectiveness in correcting the basic physiological defect in cystic fibrosis (CF). While a number of these compounds appear promising, their effectiveness will almost certainly need to be demonstrated in animals before therapeutic tests in humans will be possible. We show herein that the function of salivary secretion in the mouse model for CF could be used as a simple, easy and rapid in vivo assay for drug effects. We demonstrate that salivary secretory capacity stimulated with a beta-adrenergic agonist closely reflects the genotype of origin. Specifically, the mean maximal secretory rate of saliva in normal wild type (+/+) mice was about 1.5 times higher than that of the mean rate in heterozygote (+/-) mice and more than 50 times greater than in CF (-/-) mice. Total saliva secreted per stimulated period obeyed a similar phenotype-genotype segregation. The data indicate that salivary secretory rates in CF mice could be used to assay potential drugs for their effectiveness in correcting the secretory defect in cystic fibrosis.

Early radiation effects on muscarinic receptor-induced secretory responsiveness of the parotid gland in the freely moving rat

Although the salivary glands have a low rate of cell turnover, they are relatively radiosensitive. To study the possible mechanism behind this inherent radiosensitivity, a rat model was developed in which saliva can be collected after local irradiation of the parotid gland without the use of anesthetics or stressful handling. Saliva secretion was induced by the partial muscarinic receptor agonist pilocarpine (0.03-3 mg/kg) with or without pretreatment with the beta-adrenoceptor antagonist propranolol (2.5 mg/kg), or the full muscarinic receptor agonist methacholine (0.16-16 mg/min), and measured during 5 min per drug dose before and 1, 3, 6 and 10 days after irradiation. The maximal secretory response induced by pilocarpine plus propranolol was increased compared to that with pilocarpine alone but did not reach the level of methacholine-induced secretion, which was about five times higher. One day after irradiation a decrease in maximal pilocarpine-induced secretion was observed (-22%) using the same dose of pilocarpine that induces 50% of the maximal response (ED(50)), in both the absence and presence of propranolol, indicating that the receptor-drug interaction was not affected by the radiation at this time. The secretory response to methacholine 1 day after irradiation, however, was normal. At day 3 after irradiation, the maximal methacholine-induced secretion was also affected, whereas pilocarpine (+/-propranolol)-induced maximal secretion decreased further. At day 6 after irradiation, maximal secretory responses had declined to approximately 50% regardless of the agonist used, whereas ED(50) values were still unaffected. No net acinar cell loss was observed within the first 10 days after irradiation, and this therefore could not account for the loss in function. The results indicate that radiation does not affect cell number or receptor-drug interaction, but rather signal transduction, which eventually leads to the impaired response. We hypothesize that the early radiation effect, within 3 days, may be membrane damage affecting the receptor-G-protein signaltransfer. Later critical damage, however, is probably of a different nature and may be located in the second-messenger signal transduction pathway downstream from the G protein, not necessarily involving cellular membranes.

Morphological and functional characteristics of acinar atrophy and recovery in the duct-ligated parotid gland of the rat

Although acinar atrophy occurs frequently in salivary diseases, the relationship between structural changes and functional decrements is not well-established, and the potential for recovery of histological and functional integrity has not been wholly quantified. We aimed, therefore, to develop further our understanding of pathological acinar atrophy. Stensen's duct was ligated for periods up to six weeks and, in separate experiments, was de-ligated after two weeks and allowed to recover for up to two weeks. Qualitative and quantitative histological analyses were carried out. Additionally, the ability of enzymatically dispersed cells from ligated and de-ligated glands to respond to neurohormonal stimuli was also measured. The results confirmed that totally obstructed glands undergo a rapid, progressive severe atrophy amounting to absolute losses of over 85% of acinar tissue by two weeks. Acinar shrinkage and cell losses through apoptosis accounted for the glandular atrophy. Remaining intralobular epithelia consisted of extremely atrophic acini and numerous duct-like structures with intermediate forms. Dispersed cells from atrophic glands exhibited agonist-induced release of chloride similar to normal. Together, these structural-functional results confirm the persistent viability of acinar-like cells in the obstructed gland and suggest that the duct-like structures are derived from surviving atrophic acini. De-ligated glands exhibited a near-normal recovery of structure by two weeks. Their enzymatically dispersed cells responded normally to agonist stimulation. The results support the view that pathological atrophy is largely similar to physiological atrophy, providing a mechanism for acinar cell survival under adverse conditions, with the possibility of eventual recovery.

Pilocarpine alters caries development in partially-desalivated rats

This study examined the effect of pilocarpine on caries and saliva composition in rats with compromised salivary gland function. Eight litters of specific-pathogen-free female Sprague-Dawley rats were divided into five groups for surgery. Partial desalivation was performed in either of three ways: (1) Both parotid ducts were ligated; (2) both submandibular/sublingual (SM/SL) glands were excised, or (3) one parotid duct was ligated, and submandibular/sublingual glands were removed unilaterally. Completely desalivated animals and unoperated animals served as positive and negative controls, respectively. One week following surgery, groups were subdivided so that half of each group had osmotic pumps implanted which delivered pilocarpine HCl (24 mg/kg/day). All animals were infected with Streptococcus sobrinus 6715 and fed cariogenic diet ad libitum for 28 days. Caries scores, microbiological data, and saliva flow rate and composition were determined for all animals. Animals which had both SM/SL glands removed and received pilocarpine developed significantly lower sulcal caries (p < or = 0.05) compared with the animals that had both SM/SL removed but did not receive pilocarpine. The concentration of protein in parotid saliva in these pilocarpine-treated animals was unaffected, and no differences were observed in the electrophoretic profiles on SDS-PAGE. Pilocarpine appears to exert its greatest caries-protective effect when the parotid glands remain intact.

A biochemical analysis of parotid and submandibular salivary gland function with age after simultaneous stimulation with pilocarpine and isoproterenol in female NIA Fischer 344 rats

This analysis of physiological, biochemical and molecular changes related to aging was made in 3-, 12- and 24-month-old rats. The salivary gland weight/body weight ratio and the structural membrane proteins did not change with age for either gland, but a significant age-related decline in DNA synthesis for both glands was detected, unrelated to the hormonal responsiveness at the level of the plasma membrane. There was a marked increase in the concentration of soluble proteins in adolescent parotid gland and, for the two older age groups, in submandibular gland. The saliva flow rate was different when expressed as volume per time, as volume per time and g glandular wet weight, and/or kg body weight. The concentration of secreted proteins was not affected by age in either gland. The total amount of proteins secreted over 30 min revealed no age-related perturbation for the parotid gland, but showed a significant age-related increase in submandibular saliva. Sodium dodecyl sulphate-polyacrylamide gel analysis revealed changes in the protein bands between 39 and 50 kDa in the Coomassie blue-stained gels from 12-month-old animals. Amylase showed an initial increase (12 months), followed by a marked decline in its activity in parotid saliva. The glandular supernatant had low residual cellular amylase activity after stimulation. Therefore, secretory impairment with age after pilocarpine-isoproterenol stimulation was excluded. Analysis of total RNA showed a pronounced decrease of amylase mRNA in the parotid gland between 12 and 24 months of age. No amylase mRNA was expressed in any of the submandibular samples. For epidermal growth factor, total saliva showed a decrease with age. It seemed that the submandibular gland followed the same picture with age as the parotid gland, with a specific decline in the biosynthesis of single secretory proteins.

Effect of parotid submandibular and sublingual saliva on wound healing in rats

1. The effectiveness of wound licking with parotid, submandibular or sublingual saliva on wound healing was evaluated in selectively sialadenectomized rats. 2. The rate of healing of experimentally induced cutaneous wounds was evaluated macroscopically by photography at 0, 2, 4 and 6 days after surgery. 3. Sialadenectomy of all major glands significantly slowed down wound healing compared to sham-operated controls. 4. Parotid licking had no effect compared to controls; submandibular licking and sublingual licking appeared to be very effective. 5. The results suggest that saliva promotes wound healing in experimentally induced cutaneous wounds by communal licking; this is a result of the submandibular and sublingual saliva and not the parotid saliva.

The effects of a liquid diet on initial and sustained, stimulated parotid salivary secretion and on parotid structure in the rat

Adult male rats were maintained on a nutritionally adequate liquid diet, or laboratory chow and water (controls), for 7 days. They were then anaesthetized and parotid flow was recorded after isoprenaline or pilocarpine stimulation, each collected over two, timed sampling periods--an initial 5 min and a subsequent 15 min. The isoprenaline-induced flow rates in liquid diet rats were reduced to 45 and 30% of those in control rats for the first and subsequent samples respectively (p less than 0.02). After pilocarpine stimulation there were no significant differences in the first samples, but in the subsequent samples the flow rate in liquid diet rats was reduced to 54% of that in controls (p less than 0.001). The parotid gland weights were reduced by 35% in liquid diet rats compared to controls (p less than 0.05). On computerized planimetric analysis, parotids (from rats that had not been given secretagogues) had significantly smaller mean acinar areas, mean acinar profile perimeters and mean acinar transection diameters after liquid feeding (p less than 0.001). The findings support the notion that there is a functional reserve capacity available in atrophied glands to support the relatively fast flow that occurs on initial stimulation but which becomes exhausted during sustained stimulation. This exhaustion occurs more severely and more rapidly in the low-volume, protein-rich saliva elicited by sympathomimetic stimulation than in the high-volume, low-protein saliva formed in response to parasympathomimetic stimulation.

Introduction of cyclic AMP phosphodiesterase into rat submandibular acini prevents isoproterenol-stimulated cyclic AMP rise without affecting mucin secretion

Cyclic AMP phosphodiesterase has been incorporated into isolated rat submandibular acini by hypotonic swelling. This resulted in complete inhibition of the cyclic AMP rise stimulated by isoproterenol (10 microM), but had no effect on the stimulation of mucin secretion. Acini swollen in the absence of cyclic AMP phosphodiesterase showed similar cyclic AMP and mucin secretion responses to those of unswollen acini. The dissociation between cyclic AMP rise and mucin secretion was not due to stimulation of different beta-receptor subtypes since both responses to isoproterenol were inhibited by the beta 1 antagonist atenolol, but not by the beta 2 antagonist, butoxamine. The results are the first to directly demonstrate that a maximally effective concentration of isoproterenol can increase mucin secretion in the absence of a detectable increase in cyclic AMP.

Isoproterenol-induced desensitization of mucin release in isolated rat submandibular acini

Release of [14C]glucosamine-labelled mucins was studied in vitro using well-characterised preparations of rat submandibular acini. Mucin release was stimulated by forskolin, an activator of the catalytic subunit of adenylate cyclase, and 3-isobutyl-1-methylxanthine (IBMX), a cyclic nucleotide phosphodiesterase inhibitor. Both stimulated in a dose-dependent manner to the same maximum as that seen with isoproterenol. Neither forskolin nor IBMX added in the presence of isoproterenol increased secretion above the maximum in response to isoproterenol alone, suggesting a similar mechanism of action, mediated by cyclic AMP. Prior exposure of acini to isoproterenol (10 microM) for 45 min, followed by washout resulted in (a) persistent increase in basal secretion which was abolished by propranolol and (b) reduced stimulation of mucin secretion in response to either a second isoproterenol challenge, noradrenaline or forskolin. Thus, exposure of rat submandibular acini in vitro desensitizes the cells to subsequent stimulation. Although this mimics the decreased beta-adrenergic secretory responses seen in submandibular cells from cystic fibrosis patients, results suggest that the isoproterenol-induced desensitization is at the level of beta-receptor and adenylate cyclase, rather than distal to cyclic AMP.

Differential effects of prostaglandins and isoproterenol on cAMP content and Na, K pump activity in rat submandibular acini

The beta-adrenergic agonist isoproterenol and prostaglandins E1 and E2 (but not F2 alpha) increased the cAMP content of rat submandibular acini in vitro, but only isoproterenol enhanced ouabain-sensitive 86Rb (K) uptake. These findings suggest that cAMP is not involved in the activation of the Na, K pump in salivary cells.

The effects of various secretagogues on the mucin content of pure submandibular salivas

The concentrations of a specific mucin and total protein were compared in pure submandibular saliva samples elicited by pilocarpine (PILO), epinephrine (EPI), and isoproterenol (IPR) in mice. At the dosages employed, IPR-stimulated samples contained, on the average, the highest concentrations of protein and mucin. EPI samples contained intermediate levels, and PILO the lowest concentrations. The average mucin-to-protein ratio in the PILO saliva samples was intermediate between the IPR and EPI samples. Non-stimulated saliva samples showed a broader range of mucin to total protein than did the stimulated saliva sets. Within the PILO saliva samples, there was a very strong positive correlation between the mucin content of saliva and the mucin content in the pre-secretory gland prior to stimulation. The mucin content of EPI and IPR samples also showed strong positive relationships with the content of mucin in the gland. The mucin and protein in EPI saliva samples were significantly correlated in at least one of the collections, whereas in the IPR samples, there was a much weaker relationship. With the exception of the third sequential collection of EPI saliva, all nine of the other EPI, IPR, and PILO collection sets showed only a weakly negative or no correlation between flow rate and saliva mucin or protein content. This is in sharp contrast with the strongly negative correlation which was noted between saliva protein or mucin contents and flow rate when all of the data were combined. These observations suggest that the nature of the stimulant is a very important determinant of overall flow rates, saliva protein, and mucin concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic regulation of formation of inositol phosphates in rat submandibular acini

Formation of inositol phosphates in response to adrenergic secretagogues was studied in rat submandibular acini labelled with myo-[2-3H]inositol. Noradrenaline rapidly (within 5 s) increased radioactivity incorporated into inositol 1,4,5-trisphosphate and inositol tetrakisphosphate, with less rapid (within 1 min) increases in inositol 1,3,4-trisphosphate being observed. Inositol polyphosphate formation was less sensitive to noradrenaline than was stimulation of mucin secretion and was mediated by stimulation of alpha- but not beta-adrenergic receptors. The beta-adrenergic agonist isoproterenol, which is a potent stimulator of mucin secretion [McPherson & Dormer (1984) Biochem. J. 224, 473-481] did not increase formation of inositol mono-, bis- or polyphosphates during a 15 min incubation. The results suggest that inositol phosphates do not mediate beta-adrenergic stimulation of mucin secretion in rat submandibular acini. In addition, rat submandibular acinar cells contain a Ca2+ pool which can be mobilized by isoproterenol [McPherson & Dormer (1984) Biochem. J. 224, 473-481], without involvement of inositol polyphosphates as second messengers.

Fimbria-specific antibodies in serum and saliva of mice immunized with Actinomyces viscosus T14V fimbriae

Fimbria-specific antibody responses were compared in mice immunized with purified fimbrial adhesins in the region of the submandibular gland (i.e., local site) or at a remote site in the back. One hundred micrograms of fimbriae isolated from Actinomyces viscosus T14V was used as the vaccine. Four subcutaneous injections of the vaccine in the local site induced greater amounts of fimbria-specific immunoglobulin G (IgG) in serum and saliva than three injections. However, there was no difference in the response of fimbria-specific IgA in serum and saliva. Fimbria-specific IgG in serum and saliva were first detected 21 days after the primary immunization at both the local or remote sites. Fimbria-specific IgA in serum was first detected 28 days after the primary immunization at both the local or remote sites. However, fimbria-specific IgA in saliva occurred only in mice immunized with the fimbrial vaccine at the local site and was first detected 14 days after the primary immunization. Both serum and saliva from mice immunized 4 times with the fimbrial vaccine in the local site inhibited in vitro adsorption of strain T14V cells to hydroxyapatite beads pretreated with normal mouse saliva, whereas adsorption of strain T14V cells suspended in serum and saliva from sham-immunized animals was not inhibited. Collectively, these data suggest that mice immunized locally in the submandibular gland region with a vaccine composed of purified fimbrial adhesins provide a potential model for evaluating the efficacy of fimbria-specific antibodies in saliva to inhibit strain T14V colonization of tooth surfaces.

Effects of cyclic nucleotide derivatives on acetylcholine-induced secretion from isolated, perfused rat submandibular salivary glands

The effects of dibutyryl cAMP, 8-bromo-cGMP, 3-isobutyl-1-methyl xanthine (MIX) and isoproterenol were examined. When administered simultaneously with acetylcholine (10(-6) M) in concentrations of 10(-5) M, both isoproterenol and cAMP reduced fluid secretion (16 and 31 per cent, respectively) and enhanced the decay in rate of flow with time, while cGMP and MIX increased salivary volumes (25 and 19 per cent, respectively). Isoproterenol-decreased Na and Cl and increased K and residual anion concentrations. These effects, except for increased K, were also observed with MIX, cAMP and cGMP did not significantly affect cation concentrations but reduced Cl and increased residual anion, although to a lesser extent than isoproterenol or MIX. The cyclic nucleotides did not affect the flow of saliva when added to the perfusate for 40 min after 40 min of acetylcholine stimulation. Prior exposure to cGMP increased the volume of saliva secreted after re-exposure to acetylcholine alone and both cGMP and cAMP increased the Na and reduced the K concentration of the stimulated secretion. These results suggest that cyclic nucleotides are involved in salivary fluid and electrolyte secretion and can modulate the effects of cholinergic stimuli. cGMP may be involved mainly in fluid secretion and, as salivary fluid originates almost exclusively in salivary acini, it may exert its action in acinar cells and activate specific components of the mechanism of primary secretion. cAMP may be primarily involved in transductal electrolyte transport, and may also inhibit certain parts of the fluid secretory mechanism, or reduce the effectiveness of cholinergic stimuli in activating them.(ABSTRACT TRUNCATED AT 250 WORDS)

Mucin release and calcium fluxes in isolated rat submandibular acini

A method is described for preparing isolated rat submandibular acini by collagenase digestion followed by mechanical dispersion. As assessed by Trypan Blue exclusion, phase contrast microscopy, ATP content and release of mucins and lactate dehydrogenase, the acini are morphologically and functionally intact. Secretory function of isolated acini was similar to that of intact tissue in terms of time-course, dose dependence and degree of stimulation of mucin release by adrenergic secretagogues. Mucin release was increased to the same extent (approx. 3-4-fold) by either isoproterenol or noradrenaline at a maximally effective concentration (10 microM). Stimulation of mucin release by isoproterenol (10 microM), noradrenaline (10 microM) or adrenaline (10 microM) was inhibited by propranolol (30 microM) but not by phentolamine (30 microM). Isoproterenol (10 microM) increased both 45Ca2+ uptake and efflux from the acini, which was shown to represent a net release of calcium. However, there was a delay (approx. 10 min) in onset of stimulation of 45Ca2+ mobilization which was not apparent in isoproterenol stimulation of mucin release. Our results indicate that increases in intracellular calcium mobilization in response to a beta-adrenergic secretagogue do not trigger mucin secretion from rat submandibular acini.

Submandibular gland secretory function in young adult and aged rats

An evaluation of submandibular gland secretory function was performed in young adult and aged male and female rats. No significant alterations in submandibular salivary flow rate or the concentrations of total protein, Na+,K+ and neutral sugar in the secreted saliva, were observed between different aged animals. Significant sex differences in salivary flow rate and total protein content were found.