Effects of age on morphology,protein synthesis and secretagogoue-evoked secretory responses in the rat lacrimal gland

This study investigated changes in the morphology and protein synthesis and protein and peroxidase secretion due to peptidergic and aminergic stimulation from rat lacrimal gland acinar cells of 3–5, 9, 12, 20 and 24 month old rats. There was a marked reduction in the presence of Golgi apparatus in the acinar cells of glands from the 24 month old rats coupled to dilatation and degeneration of rough endoplasmic reticulum, when compared to that in the acinar cells of glands from 3–5 and 12 month old rats. Following incorporation of tritiated leucine for 360 min (6 h), the amount of newly synthesised protein in acinar cells of the 12 month old rats was significantly (p < 0.01) higher than that in the acinar cells of 3–5 month old animals. However, at 20 months the amount of newly synthesised protein in these acinar cells was significantly (p < 0.01) reduced to less than that in acinar cells of both the 3–5 and 12 month old animals. Immunohistochemical and immunofluorescence studies identified the presence of substance P (SP), vasoactive intestinal peptide (VIP), histamine and 5-hydroxytryptamine (5-HT) in the lacrimal glands of 3–5 month old rats. Stimulation by either SP, VIP, histamine or 5-HT resulted in significant increases in total protein output and peroxidase release from acinar cells of the 3–5 month old rats. However, all responses to the secretagogues were reduced with ageing from 3–5 to 24 months of age. The results indicate that ageing is associated with alteration in the ability of acinar cells to synthesise and secrete proteins.     

Tight junctional permeability of the resting and carbachol stimulated exocrine rabbit pancreas

The permeability of the pancreatic epithelium to horseradish peroxidase is investigated in the resting and carbachol stimulated rabbit pancreas. Horse radish peroxidase administered to the bathing medium of the isolated rabbit pancreas appears in the secreted fluid of the pancreas in a relatively low concentration. Carbachol stimulates both protein secretion and the passage of horse radish peroxidase into the secretory fluid. Histochemical assessment shows that horseradish peroxidase enters the interstitial spaces of the pancreatic tissue and is present along basal and lateral plasma membranes of acinar and ductular cells. In the absence of carbachol, horseradish peroxidase is seen more frequently in the tight junctions of ductular cells than in those of acinar cells. However, in the carbachol stimulated gland horseradish peroxidase is observed in the junctions between adjacent acinar cells more frequently than in the unstimulated gland. Freeze-fracture of acinar cells shows that the number of tight junctional strands and the tight junction depth are slightly decreased upon carbachol stimulation. The findings suggest that cholinergic stimulation of the exocrine pancreas increases the permeability of the acinar cell junctions to moderately large molecules such as horseradish peroxidase. This may result in an increase of the concentration of the molecule in the secreted fluid.     

Tight junctional permeability of the resting and carbachol stimulated exocrine rabbit pancreas

Summary The permeability of the pancreatic epithelium to horseradish peroxidase is investigated in the resting and carbachol stimulated rabbit pancreas. Horse radish peroxidase administered to the bathing medium of the isolated rabbit pancreas appears in the secreted fluid of the pancreas in a relatively low concentration. Carbachol stimulates both protein secretion and the passage of horse radish peroxidase into the secretory fluid. Histochemical assessment shows that horseradish peroxidase enters the interstitial spaces of the pancreatic tissue and is present along basal and lateral plasma membranes of acinar and ductular cells. In the absence of carbachol, horseradish peroxidase is seen more frequently in the tight junctions of ductular cells than in those of acinar cells. However, in the carbachol stimulated gland horseradish peroxidase is observed in the junctions between adjacent acinar cells more frequently than in the unstimulated gland. Freeze-fracture of acinar cells shows that the number of tight junctional strands and the tight junction depth are slightly decreased upon carbachol stimulation. The findings suggest that cholinergic stimulation of the exocrine pancreas increases the permeability of the acinar cell junctions to moderately large molecules such as horseradish peroxidase. This may result in an increase of the concentration of the molecule in the secreted fluid.     

Cytochemical detection of endogenous peroxidase in the acinar cells of the hamster submandibular gland

The presence of endogenous peroxidase activity in the hamster submandibular gland was investigated cytochemically by light and electron microscopy using diaminobenzidine methods. After fixation of tissue with 2% paraformaldehyde--2.5% glutaraldehyde and incubation in a DAB reaction medium containing 0.01% H₂O₂, the peroxidase reaction product was localized in the nuclear envelope, the cisternae of the endoplasmic reticulum, secretory granules and the Golgi apparatus in both the acinar and granular duct cells of the submandibular gland. This is in contrast to earlier investigators who failed to detect peroxidase activity in acinar cells of the hamster submandibular gland and reported that peroxidase is localized only in the granular duct cells. The discrepancy may be caused by differences in experimental procedures. It is suggested that fixation of tissue with a high concentration of glutaral dehyde and incubation in a DAB reaction medium containing a high concentration of H₂O₂ inhibits the peroxidase activity of acinar cells in the hamster submandibular gland     

Cytochemical detection of endogenous peroxidase in the acinar cells of the hamster submandibular gland

The presence of endogenous peroxidase activity in the hamster submandibular gland was investigated cytochemically by light and electron microscopy using diaminobenzidine methods. After fixation of tissue with 2% paraformaldehyde--2.5% glutaraldehyde and incubation in a DAB reaction medium containing 0.01% H₂O₂, the peroxidase reaction product was localized in the nuclear envelope, the cisternae of the endoplasmic reticulum, secretory granules and the Golgi apparatus in both the acinar and granular duct cells of the submandibular gland. This is in contrast to earlier investigators who failed to detect peroxidase activity in acinar cells of the hamster submandibular gland and reported that peroxidase is localized only in the granular duct cells. The discrepancy may be caused by differences in experimental procedures. It is suggested that fixation of tissue with a high concentration of glutaral dehyde and incubation in a DAB reaction medium containing a high concentration of H₂O₂ inhibits the peroxidase activity of acinar cells in the hamster submandibular gland This revised version was published online in November 2006 with corrections to the Cover Date.     

Fine structural localization of peroxidase activity in the epithelium and the gland of the rat larynx

Summary Endogenous peroxidase activity was demonstrated in ciliated cells and secretory cells of the laryngeal epithelium and gland of rats, using the diaminobenzidine method for cytochemical demonstration of peroxidase activity. The intensity of peroxidase activity was greatly varied from cell to cell, but the fine structural localization of the activity was similar in various cell types. The activity was localized in cisternae of rough-surfaced endoplasmic reticulum including nuclear envelope, some vesicles and saccules of the Golgi complex, large membrane-limited granules, multivesicular bodies and probable lysosomes. In secretory cells, the activity was also found in secretory granules.The significance of peroxidase activity is not unclear, while the activity, at least a part of it, seems to be secreted into the cavity of the larynx. The possibility that peroxidase participates bactericidal mechanism, deserves further investigation.     

Movement of horseradish peroxidase in rabbit submandibular glands after ductal injection

Synopsis Horseradish peroxidase (HRP) has been used as a tracer to study movements of solutions injected retrogradely via the duct of submandibular glands in rabbits. 0.1 ml of solution was injected either manually or by a constant hydrostatic pressure, and the subsequent distribution of HRP in the gland and duct at different times after injection has been examined histochemically at light and electron microscopical levels.Shortly after the injections, strong interstitial staining for peroxidase resulted from passage between acinar cells. Some sites of cellular uptake were observed and staining occurred in some ductal cells even when the duct had been cut at the hilum to minimize pressure effects. It is not known whether this diffuse uptake represents a physiological or pathological phenomenon. Some interstitial activity still remained 24 hr after injection but had disappeared by 48 hr. Inflammatory cells first appeared in the gland about 4 hr after the injection and slowly increased up to about 24 hr after injection.The results indicate that the HRP reaches the interstices of the gland principally by penetration between acinar cells, and that the junctional complexes between striated duct cells appear to be more resistant to disruption by luminal pressures.     

Alteration of tight junctional permeability in the rat parotid gland after isoproterenol stimulation

The permeability of junctional complexes to ultrastructural tracers of different molecular weight and the freeze-fracture appearance of junctional structure were investigated in the resting and stimulated rat parotid gland. Tracers were administered retrogradely via the main excretory duct, and allowed to flow by gravity (16 mmHg) into the gland for 15-60 min. Secretion was induced in some animals by intraperitoneal injection of isoproterenol. In resting glands, the tracers microperoxidase , cytochrome c, myoglobin, tyrosinase (subunits), and hemoglobin were restricted to the luminal space of the acini and ducts. In glands stimulated 1-4 h before tracer administration, reaction product for microperoxidase , cytochrome c, myoglobin, and tyrosinase was found in the intercellular and interstitial spaces, whereas hemoglobin was usually retained in the lumina. In contrast, horseradish peroxidase and lactoperoxidase appeared to penetrate the tight junctions and reaction product was localized in the extracellular spaces in both resting and stimulated glands. Diffuse cytoplasmic staining for horseradish peroxidase and lactoperoxidase was frequently observed in acinar and duct cells. The distribution of horseradish peroxidase was similar in both Sprague-Dawley and Wistar-Furth rats, and at concentrations of 0.1-10 mg/ml in the tracer solution. Freeze- fracture replicas of stimulated acinar cells revealed an increased irregularity of the tight junction meshwork, but no obvious gaps or discontinuities were observed. These findings indicate that (a) tight junctions in the resting rat parotid gland are impermeable to tracers of molecular weight greater than or equal to 1,900; (b) stimulation with isoproterenol results in a transient increase in junctional permeability allowing passage of tracers of molecular weight less than or equal to 34,500; (c) junctional permeability cannot be directly correlated with junctional structure; and (d) the behavior of horseradish peroxidase and lactoperoxidase in the rat parotid gland is inconsistent with their molecular weights. Cell membrane damage due to the enzymatic activity or binding of these two tracers may account for the observed distribution.     

Androgen regulation of secretory component synthesis by lacrimal gland acinar cells in vitro

This study sought to determine whether androgens directly stimulate the production of secretory component (SC) by acinar cells from the rat lacrimal gland. Homogeneous populations of acrinar cells were isolated from lacrimal tissues by serial enzymatic digestion and Ficoll gradient centrifugation and then cultured on reconstituted basement membranes in supplemented, serum-free medium. Acinar cell exposure in vitro to dihydrotestosterone (DHT) resulted in a significant increase in cellular SC output. This hormone action was dose dependent and androgen specific. Testosterone, but not 17 beta-estradiol, progesterone, dexamethasone, or aldosterone, also induced a considerable elevation in acinar cell SC production. The effect of testosterone may not require intracellular enzymatic conversion to DHT. The impact of androgens on SC output was associated with enhanced cellular synthesis and secretion and did not involve variations in acinar cell viability or density. Moreover, the SC response to DHT occurred irrespective of whether lacrimal gland acinar cells were obtained from young adult male or female rats. In contrast, the androgen-related rise in SC production was significantly reduced in acinar cells isolated from tissue of orchiectomized and hypophysectomized rats. In summary, these findings demonstrate that androgens directly increase the synthesis of SC by lacrimal gland acinar cells in vitro. This effect, however, may be significantly altered by prior changes in the endocrine environment of acinar cells in vivo.     

Immunocytochemical localization of a developmentally regulated, isoproterenol-inducible protein (LM protein) in rat submandibular gland

Administration of the beta-adrenergic drug isoproterenol (IPR) produces hyperplastic and hypertrophic enlargements of the submandibular gland of the rat and induces the synthesis of specific proteins in this organ. One of these proteins, the LM (large mobile) protein, was demonstrated immunocytochemically in the submandibular glands of developing untreated and IPR-treated rats. Immunoreactive LM protein was absent in the glands of 20-day-old fetuses and 1- and 2-day-old rats. It was localized in the proacinar and immature acinar cells in the glands of 6- to 21-day-old animals, but it was undetectable at 28 days of age. In the glands of adult rats, secretory granules of the granular convoluted tubule cells showed immunostaining for the LM protein which was also present in trace amounts in the acinar cells. Daily administration of IPR for 5 days to newborn or 8- or 15-day-old rats caused an apparent acceleration of proacinar/acinar cell differentiation, and consequently it increased the frequency of cells immunostained for the LM protein as well as the amount of immunoreactive material in these cells. Thus, the expression of LM protein in the submandibular gland is developmentally regulated, and it is restricted to the stage of differentiation of proacinar cells from terminal tubule cells. IPR is capable of inducing this protein in fully differentiated acinar cells in 3-week-old or older animals.     

The fine structural localization of peroxidase activity in digestive organs of rats and mice

Summary An endogenous peroxidase activity is demonstrated in acinar cells of the salivary gland and epithelial cells of the colonic crypt of normal rats and mice using electron microscopic histochemistry. The main site of the enzymatic activity is cisternae of the rough endoplasmic reticulum including those of the nuclear envelope, while the intensity of the activity is greatly variable among cell types. Some vesicular and cisternal elements of the Golgi apparatus and secretory granules exhibit the reaction, but it is not consistent in all cells with the peroxidase-positive endoplasmic reticulum. It is very interesting that the peroxidase activity is positive in the rough endoplasmic reticulum-Golgi complex-secretory granule system (EGG system) of the cells located at the beginning and the end of the digestive tract. This suggests a peroxidase-dependent anti-infectious mechanism.Some large and small membrane-limited non-secretory granules and mitochondria also reacted.     

Immunoelectron microscopical demonstration of endogenous avidin in secretory granules of the hen oviduct mucosa: a preliminary study

Summary The localization of avidin in the oviduct of the laying hen was investigated using ultrastructural immunoperoxidase techniques. Endogenous avidin was localized in secretory granules of both tubular gland cells and non-ciliated single epithelial cells in the magnum mucosa. These immunospecific granules were electron-dense and heterogeneous with a patchy core and dense peripheral region, especially in acinar cells. The size varied from small to large in the gland cells (500–2200 nm in diameter) and remained small in the epithelial cells (180–720 nm). Columnar epithelial cells containing avidin granules strongly resembled the protodifferentiated tubular gland cells appearing in the magnum mucosa of chicks artificially pretreated with ovarian hormones. On the other hand, no avidin was observed in either epithelial goblet cells or ciliated cells in adult hens, although both cell types were shown to produce avidin in young chicks when synchronized by the administration of progesterone. The present results parallel those obtained with biotinylated enzyme affinity methods in our previous cytochemical study.Therefore, avidin is one of the proteins produced and stored in the secretory granules of the tubular gland cells and protodifferentiated acinar cells present in the epithelial layer of the laying hen oviduct. It is not present in goblet cells. Although the initiation of a synthesis may be triggered by progesterone, it is still not clear whether different hormone dependent proteins are localized in the same granules in both the adult hen and the immature chick.     

Monoclonal antibodies against rat saliva and salivary gland antigens

Hybridomas were produced by the fusion of NS1 myeloma cells with spleen cells of a BALB/c mouse immunized with rat submandibular saliva. Growth of hybridomas was evident in 60/96 wells, and colonies secreting antibodies against saliva components were identified in 20 wells by using a solid phase enzyme-linked immunoassay. Cloning of cells from 12 wells yielded originally 43 hybridoma cell lines secreting anti-saliva antibodies. After recloning, one hybridoma (4Cl3) was selected for further studies. The hybridoma (4Cl3) cells were grown as ascites tumors, and the antibodies were purified from the ascitic fluid by diethylaminoethyl Affi-gel Blue chromatography. The purified antibody (MA4), immunoglobulin G1, immunoprecipitated a 39K dalton protein from submandibular saliva, and also reacted with a protein of the same electrophoretic mobility on immunoblots. From extracts of submandibular gland slices, incubated with [3H]leucine, the antibody again immunoprecipitated a 39K protein, indicating that this protein is synthesized in the gland. MA4 was used for immunocytochemical stainings of submandibular glands of rats of different ages. In general, immunostaining was seen only in acinar cells. Thus, there was no staining in the glands of 1-day-old rats that lack differentiated acinar cells. In the glands of 1- to 4-week-old rats the number of immunoreactive cells and the extent of immunostaining paralleled the differentiation of the acinar cells. In the glands of adult rats a uniform staining of the secretory granules of the acinar cells was observed. The immunoreactive 39K protein seemed to be restricted to the acinar cells in the submandibular gland; there was no immunostaining in the parotid, sublingual, or lingual salivary glands, or in the pancreas, colon, and duodenum. Stimulation of saliva secretion by isoproterenol resulted in a virtual depletion of the antigen from the acinar cells. These results indicate the feasibility of producing mouse hybridomas that secrete antibodies against rat saliva components. The monoclonal antibody at hand will be useful in analyzing the differentiation of the acinar cells, and the factors that influence this differentiation process.     

Occurrence and Nuclear Localization of cAMP Response Element- Binding Protein in the Post-natal Development of the Rat Submandibular Gland

Cyclic AMP response element-binding protein (CREB) is a 43-kDa polypeptide that binds a cAMP response element located at the 5 promoter region of cAMP regulatory genes. The spatial and temporal distribution of CREB in the post-natal development of the rat submandibular gland was investigated using immunohistochemistry with a specific antibody. At birth, cells of the terminal tubules and ducts in the submandibular gland showed a nuclear CREB immunoreactivity of moderate intensity. At 1–2 weeks after birth, an intense CREB immunoreactivity was localized primarily to acinar cells. When the r352;-adrenergic agonist isoproterenol was administered to 2-week-old rats, a twofold transient increase in the number of immunoreactive acinar cells was induced. Beginning 3 weeks after birth, CREB immunoreactivity shifted from acini to the duct system and showed a clear localization in the cells of the intercalated ducts and distal portions of striated ducts, where the granular convoluted tubule develops after 4 weeks. Immunopositive materials were localized exclusively in the nuclei of both acinar and ductal immunoreactive cells. After the development of the granular convoluted tubules, CREB immunoreactivity was absent in the tubule cells and was gradually reduced in intensity over the entire gland. In order to examine a hypothesis that CREB is involved in the initial differentiation of the granular convoluted tubular cells, testosterone was administered to hypophysectomized adult rats. Whereas the tubular cells of hypophysectomized rats showed a complete regression, and no CREB immunoreactivity was found in any acinar or duct cells, administration of testosterone for a few days induced an intense CREB immunoreactivity in the nuclei of duct cells, followed by their differentiation into the granular convoluted tubular cells. These results suggested that CREB is involved not only in the growth and differentiation of acinar ce lls that are regulated by r352;-adrenergic nerves but also in those of the duct system, and especially in the androgen-regulated differentiation of the granular convoluted tubular cells, during the post-natal development of the rat submandibular gland.     

Histochemical Phenotypes of Von Ebner's Gland of Ferret and their Functional Implications

Von Ebner's gland of ferret was examined by means of light microscopy, protein, mucosubstance and enzyme histochemistry, and neurohistology. Acinar cells were replete with granules containing neutral mucosubstances and disulphides, and showed strong diffuse acid phosphatase activity and weak granular staining for peroxidase. Staining for cytochrome oxidase, succinate dehydrogenase, and NADH and NAD(P)H dehydrogenases was also seen. Basolateral plasmalemma of acinar cells showed weak, ouabain-sensitive Na⁺,K⁺-ATPase activity. Ductal cells were of a simple appearance, contained thiols and showed variable staining for acid phosphatase, dehydrogenases and cytochrome oxidase. Variable amounts of β-glucuronidase reaction product were localized in the glandular parenchyma, being marked in atrophic areas. Prominent stellate myoepithelial cells embracing acini and also basal ductal cells were demonstrated by alkaline phosphatase. Thiamine pyrophosphatase reaction product was concentrated in blood vessels around parenchyma, with little Golgi-like staining in acinar cells. Acetylcholinesterase activity was associated with an extensive network of nerve fibres embracing parenchyma, whereas catecholamine fluorescence was not seen. The results suggest that the acini of von Ebner's gland of ferret synthesise neutral secretory glycoproteins and peroxidase. Water mobilization is inconspicuous. Lysosomal activities feature in the parenchyma, possibly a consequence of processing secretory products in acini, absorption in ducts and/or adaptation atrophy. The gland receives a rich cholinergic-type innervation, and has extensive myoepithelial and microvascularbreak networks.     

Localization and expression of BCAT during pregnancy and lactation in the rat mammary gland

During lactation, branched-chain aminotransferase (BCAT) gene expression increases in the mammary gland. To determine the cell type and whether this induction is present only during lactation, female rats were randomly assigned to one of three experimental groups: pregnancy, lactation, or postweaning. Mammary gland BCAT activity during the first days of pregnancy was similar to that of virgin rats, increasing significantly from day 16 to the last day of pregnancy. Maximal BCAT activity occurred on day 12 of lactation. During postweaning, BCAT activity decreased rapidly to values close to those observed in virgin rats. Analyses by Western and Northern blot revealed that changes in enzyme activity were accompanied by parallel changes in the amount of enzyme and its mRNA. Immunohistochemical studies of the mammary gland showed a progressive increase in mitochondrial BCAT (mBCAT)-specific staining of the epithelial acinar cells during lactation, reaching high levels by day 12. Immunoreactivity decreased rapidly after weaning. There was a significant correlation between total BCAT activity and milk production. These results indicate that the pattern of mBCAT gene expression follows lactogenesis stages I and II and is restricted to the milk-producing epithelial acinar cells. Furthermore, BCAT activity is associated with milk production in the mammary gland during lactation.     

Histochemical phenotypes of von Ebner's gland of ferret and their functional implications

Von Ebner's gland of ferret was examined by means of light microscopy, protein, mucosubstance and enzyme histochemistry, and neurohistology. Acinar cells were replete with granules containing neutral mucosubstances and disulphides, and showed strong diffuse acid phosphatase activity and weak granular staining for peroxidase. Staining for cytochrome oxidase, succinate dehydrogenase, and NADH and NAD(P)H dehydrogenases was also seen. Basolateral plasmalemma of acinar cells showed weak, ouabain-sensitive Na⁺,K⁺-ATPase activity. Ductal cells were of a simple appearance, contained thiols and showed variable staining for acid phosphatase, dehydrogenases and cytochrome oxidase. Variable amounts of -glucuronidase reaction product were localized in the glandular parenchyma, being marked in atrophic areas. Prominent stellate myoepithelial cells embracing acini and also basal ductal cells were demonstrated by alkaline phosphatase. Thiamine pyrophosphatase reaction product was concentrated in blood vessels around parenchyma, with little Golgi-like staining in acinar cells. Acetylcholinesterase activity was associated with an extensive network of nerve fibres embracing parenchyma, whereas catecholamine fluorescence was not seen. The results suggest that the acini of von Ebner's gland of ferret synthesise neutral secretory glycoproteins and peroxidase. Water mobilization is inconspicuous. Lysosomal activities feature in the parenchyma, possibly a consequence of processing secretory products in acini, absorption in ducts and/or adaptation atrophy. The gland receives a rich cholinergic-type innervation, and has extensive myoepithelial and microvascularbreak networks.     

Immunohistochemical and ultrastructural investigation of acinar cells in submandibular and sublingual glands of rats fed a liquid diet

In atrophic parotid glands induced by liquid diet, acinar cell apoptosis is increased while proliferative activity is reduced. This study aimed to clarify how liquid diet affects submandibular and sublingual glands, including acinar cell apoptosis and proliferation. Seven-week-old male Wistar rats were fed either a liquid (experimental group) or pellet diet (control group) from 3 to 21 days, respectively. Submandibular and sublingual glands were weighed and examined histologically, ultrastructurally, and immunohistochemically using antibodies to cleaved caspase-3 (Casp-3) and 5-bromo-2′-deoxyuridine (BrdU). Weights of submandibular and sublingual gland from the experimental group were not significantly different from controls at any time point. Histological and ultrastructural characteristics of experimental acinar cells in both glands were normal. Acinar cells in control and experimental submandibular glands were positively stained with periodic acid Schiff (PAS) and weakly stained by alcian blue (AB). In control and experimental sublingual glands, mucous acinar cells were PAS-positive and strongly AB-positive. Although Casp-3- and BrdU-positive acinar cells were identified in both glands in the experimental group, their labeling indices were not significantly different from controls. In conclusion, liquid diet in rats does not induce atrophic alterations to acinar cells, including apoptosis and proliferative activity in submandibular and sublingual glands.     

Rate of protein synthesis in rat salivary gland cells after pilocarpine or feeding

The effect of pilocarpine and food uptake on the rate of incorporation of [3H]-leucine in vivo was measured by means of quantitative radioautography in three exocrine cells of the rat: the acinar and the granular duct cells of the submandibular and the acinar cells of the parotid gland. The three cell types react differently. The submandibular acinar cells showed a decrease in incorporation rate after pilocarpine administration but not after feeding. The incorporation rate of the granular duct cells of the submandibular gland remains constant after both stimulations. The acinar cells of the parotid gland show an increase in incorporation rate of [3H]-leucine in response to both. The contrast between the submandibular and the parotid gland could also be demonstrated radiobiochemically, the results reflecting the incorporation rates of the acinar cells of both glands, giving no information on the contribution of other cell types. The decrease in incorporation rate of the submandibular gland acinar cells is accompained by a shift of polyribosomes towards monomers.