Diurnal variation in secretory components of the rat parotid gland

Effects of glucose and sucrose variants of the caries-promoting Diet 2000 on the feeding patterns and parotid glands of prematurely weaned rats

OBJECTIVE

The hypothesis of this study was that feeding glucose instead of sucrose in the cariogenic Diet 2000 to rats weaned at age 18 days would result in greater light/dark differences in feeding activity and secretion and storage of parotid salivary enzymes.

DESIGN OF STUDY

Diet 2000 and a stock commercial diet (controls) were prepared in pelleted and powdered forms, as the increased mastication required by pellets has been shown to support circadian rhythms in rats. Food jars were weighed at lights on and just prior to lights off daily. Rats were euthanized at 25 days and their parotid glands removed, weighed, and analyzed for specific activities of the salivary enzymes α-amylase and deoxyribonuclease I.

RESULTS

Light/dark differences in feeding activity were strong in the rats fed the pelleted stock diet and both powdered and pelleted glucose 2000 diets, moderate with the pelleted sucrose 2000 diet, and not significant with the powdered sucrose 2000 and stock diets. Light/dark differences in the parotid salivary enzymes were strong with the powdered glucose 2000 diet and the pelleted forms of the glucose and sucrose 2000 and stock diets, and not significant with the powdered stock and sucrose 2000 diets.

CONCLUSION

Caries reportedly is higher in sucrose than glucose fed to rats in the standard powdered form of Diet 2000, mainly due to the colonizing advantage Streptococcus mutans gains with sucrose. These results suggest that additional factors are more feeding during lights on and less stimulation of parotid salivary secretion with the sucrose powder.

Impaired autophagic flux mediates acinar cell vacuole formation and trypsinogen activation in rodent models of acute pancreatitis

The pathogenic mechanisms underlying acute pancreatitis are not clear. Two key pathologic acinar cell responses of this disease are vacuole accumulation and trypsinogen activation. We show here that both result from defective autophagy, by comparing the autophagic responses in rodent models of acute pancreatitis to physiologic autophagy triggered by fasting. Pancreatitis-induced vacuoles in acinar cells were greater in number and much larger than those induced with fasting. Degradation of long-lived proteins, a measure of autophagic efficiency, was markedly inhibited in in vitro pancreatitis, while it was stimulated by acinar cell starvation. Further, processing of the lysosomal proteases cathepsin L (CatL) and CatB into their fully active, mature forms was reduced in pancreatitis, as were their activities in the lysosome-enriched subcellular fraction. These findings indicate that autophagy is retarded in pancreatitis due to deficient lysosomal degradation caused by impaired cathepsin processing. Trypsinogen activation occurred in pancreatitis but not with fasting and was prevented by inhibiting autophagy. A marker of trypsinogen activation partially localized to autophagic vacuoles, and pharmacologic inhibition of CatL increased the amount of active trypsin in acinar cells. The results suggest that retarded autophagy is associated with an imbalance between CatL, which degrades trypsinogen and trypsin, and CatB, which converts trypsinogen into trypsin, resulting in intra-acinar accumulation of active trypsin in pancreatitis. Thus, deficient lysosomal degradation may be a dominant mechanism for increased intra-acinar trypsin in pancreatitis.

Changes in the distribution and fine structure of the intralobular blood vessels of the submandibular gland in the postnatally developing mouse

Previous studies have shown that the blood vessels supplying the endocrine organs and the mucosa of the intestinal canals change in terms of not only their distribution but also their structure with the development and growth of each organ. We examined changes in the distribution and structure of intralobular blood vessels, including capillaries, throughout the postnatal development of the submandibular gland, an exocrine organ. The mouse submandibular gland from days 0 (birth) to 49 was investigated chronologically and ultrastructurally. The capillaries changed from continuous to fenestrated on day 10, coincident with an increase in the number of acini to more than the number of terminal tubules. The number of sections of intralobular blood vessels per unit area gradually decreased with increasing acinar size and was lowest on day 21 when pups were weaned; the same number was maintained from then on. In contrast with the reduction in the number of intralobular blood vessels, the number of capillary pores appeared to increase gradually. Acinar size increased further till day 28. Capillary pore number also increased further, till day 35, apparently in relation to the increasing acinar size. These findings suggest that the changes in distribution and structure of the intralobular blood vessels in the submandibular gland of the postnatally developing mouse are closely related to the development of the parenchymal cells in preparation for weaning and sexual maturity.

Influence of streptozotocin-induced diabetes on hexokinase activity of rat salivary glands

The influence of diabetes on the enzyme hexokinase (HK) was examined in the salivary glands of rats. Diabetes was induced by an intraperitoneal injection of streptozotocin (60 mg/Kg body weight) in overnight fasted rats (180-200 g). The animals were killed 48 hours and 30 days after the induction of diabetes and the submandibular and parotid salivary glands extracted for use. Hyperglycemia was evaluated by determining the blood sugar. The area occupied by each intralobular component, acini, ducts, total parenchyma and stroma was measured, and no differences were observed compared with control. In the soluble fraction of the submandibular gland, no difference in the specific activity of HK was observed, between the diabetic and control animals, however, the activity per gland and per g of tissue showed lower values than control. The specific activity of the bound form was reduced in the diabetic gland. The results obtained for the parotid gland were different from the submandibular. The specific activity of both the soluble and bound forms were increased in the diabetic animals. The DEAE-cellulose column chromatography of the soluble and bound forms of the enzyme from both glands showed a first peak appearing during the washing of the column and two other peaks were eluted by the gradient. Thus, three isoenzymes in the submandibular and parotid salivary glands for the control and diabetic rats have been found.

Expression of DNase I in rat parotid gland and small intestine is regulated by starvation and refeeding

DNase I in rats is mainly expressed in the parotid gland and the small intestine and functions as a digestive enzyme. Male Wistar rats were deprived of food for 48 h, refed with nonpurified diet for 2 h and killed at 0, 0.33, 0.67, 1, 2, 6 or 12 h. The activity and mRNA of DNase I in the parotid gland and the small intestine were determined. We found that in rats that were not fed for 48 h there was accumulation of DNase I in the parotid gland but not in the small intestine. In the parotid gland, refeeding decreased DNase I activity (P < 0.05), perhaps due to an increase in secretion. The increase in DNase I mRNA probably resulted from the need for protein synthesis. However, in the small intestine, both the enzyme activity and the amount of mRNA were up-regulated by refeeding (P < 0.05). Exposing rats to food in a sealed transparent flask also caused a 2.5-fold increase in DNase I mRNA within 30 min in the parotid gland. These data suggested that the expression of rat parotid DNase I is up-regulated by feeding and that mastication is not essential for the regulation.

The effect of dietary consistency and water content on the parotid glands of submandibular and sublingual duct-ligated rats

The aim here was to estimate the significance of oral sensation and mastication on functional changes in the parotid glands of partially desalivated rats. Submandibular and sublingual duct-ligated and sham-operated control rats were fed three diets of similar chemical composition but different physical presentations. Two were solid, either pellets or powder, and one was liquid. Water and food intakes were similar for both the duct-ligated rats and sham-operated control rats when they ate the pelleted or powdered-diet, though more food was wasted by the duct-ligated rats in the powdered-diet group than in the pelleted-diet group. No food was wasted in the rats fed the liquid-diet. Parotid gland weight and amylase activity were greatest with the submandibular and sublingual duct-ligated rats fed the powdered-diet and smallest with the duct-ligated and sham-operated control rats fed the liquid-diet. The amount of food wasted correlated positively with the parotid gland weight and parotid amylase activity of the rats. These findings support the view that it is the contact of dry food with the oral mucosa rather than the jaw movements involved in mastication that increases parotid gland weight and amylase activity in partial desalivated rats.

Resting (basal) secretion of proteins is provided by the minor regulated and constitutive-like pathways and not granule exocytosis in parotid acinar cells

Resting secretion of salivary proteins by the parotid gland is sustained in situ between periods of eating by parasympathetic stimulation and has been assumed to involve low level granule exocytosis. By using parotid lobules from ad libitum fed rats stimulated with low doses of carbachol as an in vitro analog of resting secretion, we deduce from the composition of discharged proteins that secretion does not involve granule exocytosis. Rather, it derives from two other acinar export routes, the constitutive-like (stimulus-independent) pathway and the minor regulated pathway, which responds to low doses of cholinergic or beta-adrenergic agonists (Castle, J. D., and Castle, A. M. (1996) J. Cell Sci. 109, 2591-2599). The protein composition collected in vitro mimics that collected from cannulated ducts of glands given low level stimulation in situ. Analysis of secretory trafficking along the two pathways of resting secretion has indicated that the constitutive-like pathway may pass through endosomes after diverging from the minor regulated pathway at a brefeldin A-sensitive branch point. The branch point is deduced to be distal to a common vesicular budding event by which both pathways originate from immature granules. Detectable perturbation of neither pathway in lobules was observed by wortmannin addition, and neither serves as a significant export route for lysosomal procathepsin B. These findings show that parotid acinar cells use low capacity, high sensitivity secretory pathways for resting secretion and reserve granule exocytosis, a high capacity, low sensitivity pathway, for massive salivary protein export during meals. An analogous strategy may be employed in other secretory cell types.

Effect of 24 hours light on circadian rhythms of secretory enzymes and morphology of rat von Ebner's glands

Von Ebner's glands of the rat are minor salivary serous glands in the posterior portion of the tongue. They secrete two digestive enzymes, lingual lipase and amylase. In this investigation, circadian rhythm in feeding was established under a normal 12 h light/12 h dark cycle, with the rats eating primarily during the dark period. At lights on, the size of the acinar cells and the area of the inclusive secretory granules, and the amount of digestive enzyme activity (lingual lipase and amylase) remaining in the gland was significantly less than in the mid-afternoon, after very little daylight food consumption. However, after 7 days of continuous light the circadian rhythm was altered: the food consumption during the normal night-time hours (5 p.m. to 8 a.m.) went from 88% of total 24 h food consumption to 45%, and during normal daylight hours (8 a.m. to 5 p.m.) from 12% to 55%. These changes were correlated with histometric findings of a near reversal of the areas of acinar cells and secretory granules of a.m. and p.m. samples under continuous light. Lingual lipase activity in the glands went from 35% under 12 h light to 61% under continuous light in the a.m. and from 65% to 39% in the p.m. Amylase activity also showed nearly a reversal in activity remaining in the gland, from 36% at 12 h light to 58% at 24 h light in the a.m. and 64% to 41% for the p.m. samples. These results indicate that the von Ebner's glands of the rat have a circadian rhythm of secretion and storage of secretory proteins that is subject to light entrainment similar to that seen in other exocrine glands such as the parotid and pancreas.

Proliferative activity by cell type in the developing rat parotid gland

BACKGROUND

In contrast to the considerable amount of research that has been done on the proliferative activity of the several types of parenchymal cells in the developing submandibular glands of rodents, systematic studies of cellular proliferation in the developing parotid gland have been confined to the acinar cells. The purpose of the present study was to attempt to fill this knowledge gap.

METHODS

Tritiated thymidine was parenterally administered to Sprague-Dawley rats at ages representative of the pre- and postnatal development of the parotid gland, and glands were harvested for autoradiography 90 min after injection. Mitotic activity among all cell types was verified by electron microscopy.

RESULTS

At all ages, the % labeled cells was much greater among the acini than any other cell type, including well-differentiated cells at 25 and 40 days. However, there were only small alterations in the proportions of cells comprised by the major cell types.

CONCLUSIONS

Current theories on the histogenesis of salivary glands and their neoplasms are based on the renewing population model, in which both normal differentiated cells and neoplastic cells arise from undifferentiated stem cells in the ducts. However, these results suggest that most of the migration and redifferentiation in the developing rat parotid gland must be in the opposite direction, i.e., the acinar cells redifferentiate into ductal cells. They also indicate that until there are precise data on the rates of cell death among the several cell types, it remains more appropriate for salivary glands to be categorized as an expanding, rather than renewing, population.

Chronology of peroxidase activity in the developing rat parotid gland

The course of development of salivary peroxidase, an enzyme that has an important role in oral defense mechanisms, has been well documented in rat submandibular glands. However, the only report on salivary peroxidase activity in the other major salivary glands of the rat has been a cytochemical study of the adult parotid gland. In the present investigation, the accumulation of salivary peroxidase activity in developing parotid glands of rats was followed both biochemically and cytochemically. Specific activity (units per mg protein) attributable to salivary peroxidase began at 1 day after birth, then rose rapidly but unevenly, with peaks at 21 and 70 days, and no difference between the sexes at any age. Activity per gland increased progressively to 42 days in both sexes and was significantly higher in males at 70 days. The cytochemical observations on peroxidase activity localized to the rough endoplasmic reticulum and secretory granules of the developing acini were well correlated with the biochemical findings. Peroxidase-negative cells occurred in immature acini at 1 and 7 days, but only in the intercalated ducts thereafter. This observation suggests that the acini are a source of some of the ductal cells, at least during early postnatal development. The developmental pattern of specific activity differed from those of other rat parotid secretory enzymes, indicating that control of their synthesis during development is noncoordinate. The patterns of specific activity of the parotid and submandibular glands were complementary, suggesting that their combined secretions may supply biologically significant peroxidase activity to the oral cavities of rats throughout postnatal development.

Alpha-amylase circadian rhythm of young rat parotid gland: an endogenous rhythm with maternal coordination

The circadian rhythm of alpha-amylase, E.C. 3.2.1.1. alpha-1,4-glucan-4-glucanohydrolase) in the parotid glands of 25-day-old rats were studied under different experimental designs (fasting, reversed photoperiod, constant lighting conditions and treatment with reserpine and alpha-methyl-p-tyrosine). The rhythm of fasted rats did not change. There were modifications in the rhythm of rats submitted to a reversed photoperiod or treated with reserpine or alpha-methyl-p-tyrosine. The rhythm was present, with changes in the acrophase, in parotids of rats kept during their gestation and postnatal life in constant light or dark. Results suggest that the circadian rhythm of alpha-amylase in parotid gland of young rats is endogenous, synchronized by the photoperiod, and with maternal coordination.

Effects of 5-fluorouracil on protein synthesis and secretion of the rat parotid gland

100 mg/kg of FU were injected intraperitoneally once daily for three days. Animals were anaesthetized with 50 mg/kg of sodium pentobarbital before cannulation of the parotid duct. The total volume, amylase and protein content of the saliva were determined after stimulation with either 5 mg/kg pilocarpine or 5 mg/kg isoproterenol in FU-treated, pair-fed, and control animals. Saliva from FU-treated animals was significantly lower (p less than 0.05) in volume, amylase and protein content than that of both control groups. SDS, anionic and cationic gel electrophoresis of parotid saliva revealed no qualitative changes in the types of proteins secreted. FU reduced the total glandular amylase per unit DNA in both unstimulated and isoproterenol-stimulated parotids (p less than 0.05). Decreased protein synthesis may be the mechanism underlying the depleted secretory protein stores because the contents of isolated secretory granules from experimental glands contained less radiolabelled protein than those of either control group, and whole-gland homogenates had marked reductions in the activities of three lysosomal enzymes and in total RNA content. The secretory granules of experimental animals contained less labelled protein than those of controls, but experimental animals secreted a greater proportion of their total glandular radiolabelled secretory protein into saliva relative to amylase, suggesting that newly synthesized secretory proteins were preferentially secreted.

Chronic treatment with beta adrenergic agonists and antagonists alters the composition of proteins in rat parotid saliva

This investigation was undertaken to determine the role of beta-adrenergic receptors in the regulation of the protein composition of rat parotid saliva. Chronic treatment of rats with dobutamine, a beta 1-adrenergic agonist, resulted in changes in parotid saliva volume, protein concentration, and composition which were essentially the same as those changes which occurred following chronic treatment with isoproterenol, a non-specific beta-adrenergic agonist. Chronic treatment with the beta 2-adrenergic agonist, terbutaline, had no effect on parotid saliva volume, protein concentration, or composition. Chronic treatment of rats with a beta 1-adrenergic antagonist, metoprolol, had different effects on saliva dependent on the manner by which the drug was delivered. Twice-daily injections of metoprolol led to a decrease in flow rate, but protein concentration and composition were unaltered. When metoprolol was delivered by surgically implanted osmotic minipumps, neither the flow of parotid saliva nor its concentration of protein was altered; however, there was a reduction in the proportion of proline-rich proteins in saliva. Comparable changes in parotid saliva protein composition occurred when the minipumps delivered propranolol, a non-specific beta-adrenergic antagonist. Chronic treatment of rats with an alpha 2-adrenergic agonist (clonidine) or antagonist (yohimbine) was without effect on parotid saliva flow rate, protein concentration, or composition. These findings suggest that the synthesis of proline-rich proteins is regulated, in part, by beta-adrenergic receptor stimulation, and primarily by the beta 1-receptor subtype.

Ultrastructural immunocytochemical localization of secretory proteins in autophagic vacuoles of parotid acinar cells of starved rats

Previous studies have shown that reduction of mastication has marked effects on the structure and biochemistry of the rat parotid gland. Acute starvation results in the formation in the acinar cells of large autophagic vacuoles which contain lysosomal hydrolases and within which secretory granules appear to undergo degradation. In this study we used electron microscopic immunocytochemistry and antibodies to two secretory proteins, alpha-amylase and B1-immunoreactive protein, to determine whether secretory proteins are present in autophagic vacuoles of parotid acinar cells of starved rats. Small vacuoles were observed after 24-h starvation; they increased in size and number up to 72-h starvation. Both secretory proteins were present in the secretory granules and in the dense content of the autophagic vacuoles, as shown by immunogold labelling. The lighter matrix of the vacuoles was unlabelled. These findings confirm that secretory granules may fuse with lysosomal structures, where their content of secretory proteins is presumably degraded. Thus, the rat parotid appears to be similar to other secretory cells in which cellular levels of stored secretory proteins may be regulated by the process of crinophagy.

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.

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)

Ontogeny of alpha-amylase circadian rhythms in rat parotid gland

The content of alpha-amylase (alpha-1,4-glucan-4-glucanohydrolase, EC 3.2.1.1.) and total soluble proteins of parotid glands (from rats exposed to a photoperiod of 14 hr light: 10 hr dark), have been determined every 2 or 3 hr over 24 hr periods in 15, 25 and 90-day-old rats. In 35-, 45- and 72-day-old rats, determinations were performed only at 0100 and 1400 hr. The alpha-amylase and total soluble protein contents from 90-day-old rats show a circadian variation, with a maximum value at 2200 hr and a minimum at 1400 hr. Parotids from 15- and 25-day-old rats also show a circadian rhythm. The minimum value is recorded at 0100 hr and the maximum at 1400 hr. At day 35 and after, there is an inversion of the amylase rhythm. In immature rats, it appears that alpha-amylase and soluble protein are under the influence of another synchronizer, whose timing is independent of that imposed by mastication of solid food.

Morphological and biochemical changes in mucous cells of the murine sublingual salivary gland during the carbamylcholine-induced secretory cycle

Changes in these cells have been evaluated over 6 h following cholinergic stimulation. Carbamylcholine administration resulted in the release of almost 50 per cent of secretory material within 15 min, which caused a reduction of 33 per cent in cell size. After 2 h the cells were depleted of secretory material. However, in the second hour the release of secretory material was accompanied by an enlargement of the nucleus, Golgi complexes and rough endoplasmic reticulum (RER), which suggests an elevation of biosynthetic activity. The enlargement of the RER was not the result of an increase in RNA, i.e. in the number of ribosomes, but of dilatation of its cisternal spaces. Before release took place, there was a continuous coalescence of secretory granules. After this extensive fusion, which is probably the result of an altered physiological state of the granule membrane and subsequent water uptake caused by cholinergic stimulation, the viscous mucins could be squeezed out, water transport is likely to assist in this ejection. Refilling of the mucous cells was almost complete within 6 h after stimulation.

Circadian changes of the rat pancreas acinar cell. A quantitative morphological investigation

The dynamics of the physiologic secretory cycle of the rat pancreatic acinar cells along a 24-h span with an alternating 12 : 12 light to dark cycle have been quantitated by morphometric methods. Significant circadian changes could be detected in cell volume and the volumes and surface areas of secretory granules and several organelles involved in the secretory process. During the dark period, which is the activity and feeding period, there is a decrease in the size of cells and individual zymogen granules as well as in the amount of secretory material. This is paralleled by a drop in the number of ribosomes and Golgi vesicles (after a transient increase) and a loss of cytoplasmic membranes. Most of the cell's zymogen content is refilled during the first hours of the light period, when cellular autophagy reaches maximal values.

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.

A morphometric study of 24-hour variations in subcellular structures of the rat pancreatic acinar cell

Subcellular structures of pancreatic acinar cells were examined at six evenly spaced time points in the 24-h period (light cycle: 06.00 h--18.00 h) in four Wistar male rats at each time point. At each sampling point, the area and circumference of acinar cell bodies and the area, number and circumference of their cytoplasmic organelles were measured using a semiautomatic computer system for morphometry and a point-counting method. The area, number and circumference-area ratio of the cytoplasmic organelles were subjected to strong circadian variations, and the cellular area and circumference exhibited weak circadian variations. Variation pattern of the cytoplasmic organelles suggested an intracellular route for secretory proteins during a 24-h span. From the results it was possible to divide the 24-h period into three stages. 1. The resting or protein synthetic stage (00.00 h to 08.00 h): the area of the rough surfaced endoplasmic reticulum (rER) was strongly increased, and that of zymogen granules was clearly decreased. 2. The granule accumulation stage (08.00 h to 16.00 h): the area of the rER was markedly decreased; that of zymogen granules was increased. 3. The secretion stage (16.00 h to 00.00): as a result of the release of zymogen granules from the acinar cell, the area of zymogen granules decreased, and that of the rER increased. The relationship between the area of the rER and zymogen granules varied in a reciprocal manner. Other cytoplasmic organelles, namely the Golgi complex, condensing vacuoles, mitochondria and lysosomes also varied prominently during the 24-h span, corresponding to variations in the rER and zymogen granules.

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 zinc deficiency on rat parotid gland

Hitherto, the effect of zinc deficiency on the rat parotid gland was not known. Male rats were fed either a low zinc diet (0.4-0.8 ppm Zn) or a zinc adequate diet (approximately 40 ppm Zn) for 35-42 days. The experimental animals exhibited retarded body growth, anorexia, loss of hair and decreases in plasma and hair zinc levels. In comparison to the ad libitum controls, the parotid glands of the pair-fed group showed a decrease in cell number, but an increase in cell mass, protein and amylase content. In the parotid glands of the experimental group, cell number was comparable to the pair-fed group, but there was a decrease in cell mass and protein content as compared to the pair-fed group. These findings suggest that zinc deficiency and its associated reduced food intake impair growth of the parotid gland and, further, that zinc deficiency per se appears to lead to a diminution in gland protein synthesis. It is proposed that a compromise in parotid gland function could be a contributory factor underlying the increased susceptibility to dental cares known to occur in zinc deficiency.

Effect of a ground versus a pelleted bulk diet on the rat parotid gland

Rats were fed a stock pelleted diet (control diet) or the same stock diet to which 30 per cent non-nutritive cellulose had been added (bulk diet). The control diet and the bulk diet were fed to rats in two consistencies, pelleted or ground. Compared to the parotid glands of rats fed the pelleted control diet, those of rats fed either of the ground diets were not different, but parotid gland wet weight, DNA and RNA content and total gland amylase and protein were significantly greater in rats fed the pelleted bulk diet for 2 wk. The cell indices of RNA/DNA and amylase/DNA were significantly greater in rats fed the pelleted bulk diet, but were not significantly changed in rats fed the ground bulk diet. Thus there is a significant increase in cell number and cell content of amylase when rats are fed a bulk diet that is pelleted and no such increases are found when the bulk diet is ground. The findings support the contention that the physical consistency of the diet and its requirement for mastication are major factors contributing to the regulation of parotid-gland size and secretory-enzyme content.

Alteration of neonatal rat parotid gland acinar cell proliferation by guandethidine-induced sympathectomy

Newborn rats were injected with guanethidine-sulfate (20 micrograms/g body weight) every 48 hr from 12 hr after birth until day 14 (eight injections per animal). The guanethidine treatment resulted in an 86% absolute reduction in cell number in the superior cervical ganglia of 15 day old rats. The cells which remained after guanethidine treatment showed destruction of mitochondria and an extensive decrease in endoplasmic reticulum. Chemical sympathectomy with guanethidine induced a 3.1 hr lengthening of the acinar cell generation cycle time (17.4 hr to 20.5 hr), resulting from a longer G1 period (6.9 hr in the control group as compared to 10.5 hr in the guanethidine-treated group), as well as a cecrease in the mean percentage of [3H]thymidine-labeled acinar cells (22.3 +/- 0.5% to 19.3 +/- 0.5%) and mean acinar cell mitotic index (2.6 +/- 0.2% to 2.1 +/- 0.1%). A circadian rhythm was found to exist in parotid gland acinar cell mitotic activity of 15 day old rats and the amplitude of the rhythm was reduced from 26.5% to 14.9% in guanethidine-treated rats. This study indicates that the diminution of sympathetic influence on the developing parotid gland results in a slight, but significant alteration in acnar cell proliferation.

The protein composition of rat parotid saliva and secretory granules

Rat parotid saliva was collected by surgical cannulation of the ducts and stimulation with pilocarpine; The secreted salivary proteins were resolved on columns of DEAE-Sephadex into five major Fractions, I-V, which were characterized by polyacrylamide disc gel electrophoresis, amino acid analyses and enzymatic assay. Rat parotid secretory granules were isolated by density gradient centrifugation and lysed in hypotonic buffers. Granule content proteins were resolved and examined by the same techniques as for secreted proteins. In both experiments, Fraction I contained RNAase and a major unidentified protein, M1, Fraction II contained the isoenzymes of amylase; DNAase was present in Fraction III and, to a lesser degree, in Fraction IV. The proportions of the enzyme-containing peaks were the same in saliva and granule contents. Fractions IV and V contain proteins of unknown function; Fraction IV contains exceptionally high levels of glutamic acid, glycine and proline in its protein moieties and approx. 6-8% neutral sugars.