Circadian variations in pilocarpine and isoprenaline-induced protein secretion by rat parotid gland

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.

Age changes in secretory function of male and female rat parotid glands in response to methoxamine and pilocarpine

Saliva secreted in response to methoxamine and pilocarpine was collected from the cannulated ducts of both parotid glands of male and female rats at weekly age intervals from three to 10 weeks, and at 3.5, 8, and 15 months of age. It was analyzed for the concentrations of protein, potassium, calcium, inorganic phosphate, and for amylase activity. The type of protein were determined electrophoretically, and an amino acid analysis of the total protein was also carried out. The wet weights of the glands increased substantially up to eight weeks of age, then reached almost plateau values, and finally tended to decrease at 15 months of age in both sexes. The salivary volumes secreted in response to methoxamine and pilocarpine were positively correlated with the parotid gland weights in both sexes. The concentrations of protein, potassium, and inorganic phosphate were inversely related to the salivary flow rates only at relatively low rates of flow. The amylase activity was positively correlated with the concentration of protein, independent of the nature of the stimulus, age, and sex. With methoxamine as a stimulus, the amylase activity was positively correlated with the concentration of calcium, independent of age and sex. The types of protein and amino acid concentrations were independent of the nature of the stimulus, age, and sex up to 15 months of age. However, in parotid saliva of several rats at 8 and 15 months of age, unusual proteins were observed electrophoretically, independent of the nature of the stimulus and sex.

Regulation of parotid salivary proteins by glucocorticoids

Previous studies have indicated that adrenal-intact rats treated for one week with pharmacological doses of the synthetic glucocorticoid, dexamethasone, show a significant reduction in the proportion of proline-rich proteins and an increase in the proportion of amylase in rat parotid saliva (Johnson et al., 1987). In order to understand more fully the role of glucocorticoids in the regulation of salivary proteins, we performed bilateral adrenalectomies on groups of rats. Some of the adrenalectomized rats were treated with replacement-level doses of the synthetic glucocorticoid, dexamethasone. The food intake was monitored daily for both groups, and sham-operated pair-fed controls were included so that the effects of alterations of food intake could be separated from those of the experimental procedures. After eight to 12 days, uniformly stimulated parotid saliva was collected from these animals as well as from sham-operated controls fed ad libitum. The volume of saliva collected in 30 min was recorded, and the saliva samples were analyzed for concentration and composition of protein. Although the volume of saliva was not affected, parotid saliva collected from adrenalectomized rats exhibited a two-fold greater proportion of proline-rich proteins and reductions in other major secretory proteins: DNase, Fraction I, and Fraction V. The parotid gland secretory granules of adrenalectomized rats were more electron-lucent than in the ad libitum-fed controls. Treatment of adrenalectomized rats with dexamethasone largely prevented the changes in salivary protein composition as well as the alterations in secretory granule morphology.(ABSTRACT TRUNCATED AT 250 WORDS)

A muscarinic agonist-stimulated chloride efflux pathway is associated with fluid secretion in rat parotid acinar cells

Cl- efflux from rat parotid acinar cells was stimulated by the muscarinic-cholinergic agonist carbachol (K0.5 approximately 1 microM). Carbachol application resulted in a rapid (T1/2 less than 10 sec.) and dramatic (approximately 50%) loss of intracellular Cl- followed by a much slower (T1/2 approximately 2 min) recovery to approximately 70% of original acinar Cl- content. Diphenylamine-2-carboxylate (1 mM), a putative Cl- channel blocker, blunted the initial Cl- loss and enhanced the subsequent recovery of Cl- content, while bumetanide (0.1 mM) blocked Cl- recovery with no effect on Cl- loss. Calculation of the rate of salivary secretion from measurements of sustained stimulated acinar Cl- release in vitro, yielded a value of 14 microliters/gland/min, in excellent agreement with previously published in vivo data. These results demonstrate that Cl- loss via this efflux pathway can account for fluid secretion from the rat parotid gland.

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)

The effects of oxymetazoline on secretion of protein and some electrolytes by rat submandibular and parotid glands

Oxymetazoline is a potent secretagogue for the salivary glands of rats. In the parotid gland, it activates preferentially alpha-adrenoceptors. As for the submandibular glands, it activates alpha-adrenoceptors at relatively low doses but at higher doses it allows secretion of new types of proteins.

Amino acid composition of salivary protein secreted by the parotid glands of rats in response to parasympathomimetic and sympathomimetic drugs

Although the total protein concentration in the saliva varied markedly, depending on the nature of the stimulus, the proportions of the amino-acid residues were independent on the nature of the stimuli, where they were cholinergic, adrenergic or dopaminergic. However, the difference in protein composition of saliva previously shown in chronically isoprenaline-treated rats electrophoretically could be determined by amino-acid analysis.

The effects of alpha-methylnoradrenaline on protein and electrolyte secretion by rat submandibular and parotid glands

alpha-Methylnoradrenaline (alpha-mNA) is a potent secretagogue for the parotid and submandibular glands of rats. With regard to the parotid glands, alpha-mNA activates mainly beta-adrenoceptors. In the submandibular glands, alpha-mNA activates alpha-adrenoceptors at higher doses whereas at relatively lower doses it activates beta-adrenoceptors. alpha-mNA may not stimulate the specific alpha 2-adrenoceptors of the salivary glands of rats.

Differences in basic proline-rich proteins in rat parotid saliva following chronic isoproterenol treatment or maintenance on a liquid diet

The basic proline-rich proteins (BPRP) in the stimulated parotid saliva of rats treated for 8 days with isoproterenol and rats fed a liquid diet for 2 weeks were compared to those in the stimulated parotid saliva of untreated rats fed a stock pelleted-diet (control). In the control, the BPRP were separated into 5 groups designated Peak A (the basic proline-rich glycoprotein), SP-1, SP-2, SP-3 and SP-4. The percentage of BPRP in each group was as follows: Peak A, 6.5 per cent; SP-1, 37 per cent; SP-2, 6.5 per cent; SP-3, 32.4 per cent; SP-4, 17.6 per cent. In the parotid saliva of rats fed the liquid diet, proteins corresponding to Peak A and SP-2 were not present, the proportion of BPRP in SP-4 was increased to almost 90 per cent while the proportions of material in SP-1 and SP-3 were reduced to 3 and 8 per cent, respectively. In the saliva of rats subjected to chronic isoproterenol treatment, a protein corresponding to SP-4 was not present; proteins corresponding to Peak A, SP-1 and SP-3 were present and in amounts similar to their proportion in untreated rats although material in SP-2 increased to 36 per cent.

Effect of increasing the bulk content of the diet on the rat parotid gland and saliva

The present study, along with others, shows that when the requirement of a diet for mastication is increased, enlargement of the parotid gland occurs. This study demonstrated for the first time that the magnitude of the gland enlargement is directly related to the amount of nonnutritive bulk incorporated into the diet, and that the concentration of protein is significantly increased in the parotid saliva of rats fed such a diet. The findings show that, although the concentration of protein is increased in the parotid saliva, the composition of proteins is unchanged, leading to the conclusion that all secretory proteins are increased in parallel. A comparison of the gland enlargement observed in response to the bulk diet with that observed in response to chronic isoproterenol treatment reveals many similarities. However, the fact that the protein composition of the parotid saliva is not altered when rats are fed the bulk diet is in marked contrast to the striking changes observed following chronic isoproterenol treatment. The reason for the dissimilar response is not known. However, an investigation into the differences that exist in the gland response to these two means of inducing gland enlargement may lead to a better understanding of the factors that regulate the size of the rat parotid gland and the complement of proteins in its secretion.

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

The sublingual glands of adult, male rats secreted considerable volumes of saliva in response to several cholinergic agonists, but very little in response to α-adrenergic stimuli and none in response to a β-adrenergic agonist. The types of proteins secreted were quite different from those in submandibular and parotid saliva or serum, and were largely independent of the nature of the stimulus. However, some differences in staining intensity of electrophoretic patterns occurred both between stimuli and with the same stimulus used on different rats.

The effects of epinephrine, norepinephrine, and phenylephrine on the types of proteins secreted by rat salivary glands

The types of proteins secreted by rat submandibular glands in response to secretory stimulation with epinephrine, norepinephrine, or phenylephrine were dose-dependent. At relatively high doses the proteins secreted were characteristic of alpha-adrenergic stimulation, whereas at low doses they were characteristic of beta-adrenergic stimulation.

The secretion of protein and of some electrolytes in response to alpha- and beta- adrenergic agonists by rat parotid and submandibular salivary glands enlarged by chronic treatment with isoproterenol

In comparison with control rats. chronic administration of isoproterenol (IPR) caused enlargement of the parotid and submandibular glands and the synthesis of apparently new proteins, probably by acinar cells. The parotid and submandibular saliva secreted in response to methoxamine or IPR differed markedly in protein and electrolyte content. In addition, with each stimulus, the salivas secreted by control and experimental glands differed in flow rate, protein concentration, and in the concentrations of certain of the electrolytes.