Increased mastication and submandibular gland development in the rat

The effects of streptozotocin-induced diabetes on norepinephrine and cholinergic enzyme activities in rat parotid and submandibular glands

Autonomic neuropathy is a common complication of diabetes mellitus, and both morphological and physiological data suggest that salivary gland function in diabetic rats is affected by neuropathies involving sympathetic and parasympathetic nerves. Therefore, glandular levels of the adrenergic neurotransmitter, norepinephrine (NE) and two cholinergic enzymes, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), were investigated in 6-month streptozotocin-diabetic rats. Significant, but variable, increases in total parotid NE (ng/gland) were observed in diabetic rats, whereas total submandibular NE was lower in diabetic animals than in controls. However, on a ng/mg tissue basis, NE levels in both the parotid gland, and less dramatically, in the submandibular gland were increased. Somewhat different results were observed for AChE and ChAT. AChE was marginally greater in the parotid glands of diabetic rats, whereas AChE and ChAT levels were significantly lower in diabetic than control submandibular glands. Expressed as enzymatic activity per mg tissue, submandibular gland ChAT, but not AChE, was increased. Short-term (3-day) insulin treatment of diabetic animals had no significant effects on total NE, AChE or ChAT in the parotid gland, but led to a further reduction in submandibular ChAT. With regard to function, changes in AChE appeared to be correlated with previously reported morphological assessments of parotid gland innervation in diabetic animals. Thus, the decreased response of the parotid gland in diabetic rats to parasympathetic stimulation may be related in part to the increase in AChE.

Morphological effects of diabetes on the granular ducts and acini of the rat submandibular gland

Effects of experimental diabetes on rat submandibular glands have been documented, but earlier reports suggested that diabetes caused an extensive cellular degeneration and a replacement of the parenchymal cells by fibrous connective tissue. Such observations, however, are difficult to reconcile with the relatively normal physiological responsiveness of the gland (Anderson and Suleiman, 1989). This study, therefore, reexamined the histological, histochemical and ultrastructural effects of streptozotocin-induced diabetes on rat submandibular glands. The tissues were examined at 3 weeks, and 3 and 6 months after the induction of diabetes, and compared with glands from age-matched controls by both light and electron microscopy. Light microscopically, the proportional volumes of the acini and granular ducts remained constant in control rats at about 48% and 38% respectively. In diabetic animals the volume density of the acini increased progressively to 62%, whereas that of the granular ducts decreased to 20%. The diameter and number of granular ducts were reduced in diabetic animals, but acinar cell profile area was only affected 6 months after the induction of diabetes. Ultrastructurally, there was an accumulation of lipid in the acinar cells and, with increasing duration of diabetes, the number of autophagic structures in both the acini and the granular ducts increased. Although there was evidence of some cellular degeneration it was never excessive. Morphometry showed that the volume density of secretory granules within the acinar cells was unaffected, but there was a significant reduction in the volume density of secretory granules within the granular ducts. Thus, in the rat submandibular gland the greatest effect of streptozotocin-induced diabetes was to cause hypotrophic changes in the cells of the granular ducts. The relative contributions of a direct effect of insulin insufficiency and the hypogonadal effects of diabetes, however, are not known.

Arachidonic acid metabolism in gill homogenate and isolated gill cells from rainbow trout, Oncorhynchus mykiss: the effect of osmolality, electrolytes and prolactin

An assay method based on thin layer chromatography to study the arachidonic acid (AA) metabolism in gill tissues was optimized and the effect of osmotically different incubation mediums on AA metabolism was evaluated. Rainbow trout gill tissues metabolize AA into PGE2 in highest concentration followed by PGD2, PGF2α and 6-keto-PGF1α (the stable metabolite of PGI2) among the prostanoids tested. Approximately 40% of PGE2 is synthesized within the first minute of incubation and is directly dependent on the substrate concentration (AA). As in mammalian tissues, PGE2 synthesis in fish gills is inhibited by the cyclooxygenase inhibitor indomethacin. PGE2 synthesis in gill homogenate and isolated gill cells incubated in trout Ringer was 0.45 and 1.9 ng/mg protein, respectively, and increased to 8.9 and 4.3 ng/mg protein, respectively, when incubated in KPO4 buffer, due to a ten-fold increase in the free AA. The hydroxy acid synthesis of the gill homogenate was higher (13%), and that of the isolated gill cells incubated in KPO4 buffer was lower (44%) compared to gill homogenate and cells incubated in trout Ringer. Gill homogenate incubated in 50 mM phosphate buffer with increasing sodium or potassium concentrations (up to 250 mM) exhibited a concentration-dependent increase in PGE2 synthesis (220% and 72%, respectively). Prolactin stimulated the PGE2 synthesis up to 30% while PGD2, PGF2α and 6-keto-PGF1α synthesis was not affected. This effect of prolactin was maximal when PGE2 synthesis was estimated 30 minutes after prolactin addition and diminished after two hours. These results suggest that rainbow trout gills possess the ability to metabolize AA through the cyclooxygenase and lipoxygenase pathways. PGE2 synthesis may be under the influence of ion balance and prolactin availability, indicating the probable involvement of AA metabolites in the regulation of ion balances across the gill membrane.

Incorporation and metabolism of (n-3) and (n-6) polyunsaturated fatty acids in phospholipid classes in cultured turbot (Scophthalmus maximus) cells

The incorporation and metabolism of various (n-3) and (n-6) polyunsaturated fatty acids (PUFA) supplemented to the culture medium was investigated in a turbot cell line (TF). The distribution, and the occurrence and extent of further metabolism of incorporated PUFA via desaturation/elongation mechanisms in specific phospholipid classes was determined from the different fatty acid compositions. The cells contained Δ6 and Δ4 desaturase activities but were generally deficient in C18-20 elongase activity. Δ5 Desaturase activity was generally masked by this deficiency but was present. The compositional data indicated that there was a high degree of specificity between individual phospholipid classes and particular fatty acids probably driven by the specificities of the acylating enzymes. The highest percentages of the supplemented acids were generally observed in the phosphatidic acid/cardiolipin fraction (PA/CL), suggesting a role for PA in the incorporation of the supplemented acids into the phospholipid pool. PI had a characteristic composition consistent with a putative role as a pool of precursor fatty acid for eicosanoid synthesis. Mechanisms were evident for generating and/or maintaining this composition.

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.

Influence of thyroxine in the regulation of rat parotid salivary protein composition

This study tested the role of thyroxine in the regulation of the protein composition of rat parotid saliva. Thyro-parathyroidectomy was performed on two groups of rats, one of which subsequently received thyroxine replacement; the third group was sham-operated. Parotid saliva was collected on the eighth day after surgery, with pilocarpine and isoproterenol used as a secretory stimulus. The volume of saliva collected in 30 min from the thyro-parathyroidectomized rats was 55% less than that collected from sham-operated rats. In the thyro-parathyroidectomized rats, the protein concentration as measured by absorption at 215 nm was unaltered, but that measured by the Lowry procedure was 43% higher. Spectrophotometric scans of Coomassie Blue-stained gels following sodium dodecylsulfate polyacrylamide gel electrophoresis of the secreted proteins showed an 18% reduction in the proportion of protein attributable to amylase and a 43% reduction in proportion of acidic and basic proline-rich proteins following thyro-parathyroidectomy; deoxyribonuclease and two other major secretory proteins (Fraction I and Fraction V) were increased (38%, 20%, and 46%, respectively). These changes in flow rate, protein concentration by the Lowry assay, and protein composition were prevented by treatment of thyro-parathyroidectomized rats with thyroxine replacement and are in opposition to those changes we reported earlier for hyperthyroid rats. The results indicate that the flow of saliva as well as the synthesis of the various salivary proteins are influenced by thyroxine.

Salivary glands in long-term alloxan-diabetic rats. A quantitative light and electron-microscopic study

Fifty untreated diabetic animals were compared with 58 age-matched non-diabetic controls. Reduced salivary gland weight was evident after one month's diabetes and this was unchanged after 12 months of diabetes. Submandibular/sublingual gland weight was proportional to the reduced body weight in the diabetic rats. Parotid gland weight, however, was proportionally more reduced. Only diabetic rats had lipid inclusions in the acinar cells of their submandibular glands and the morphometrically estimated amount of inclusions was positively correlated to the blood glucose level. Acinar cell size was significantly increased in long-term diabetic rats as compared with short-term diabetic rats and controls. Capillary basement membrane width was significantly increased in long-term diabetic rats compared with age-matched controls and with short-term diabetic rats. Thus, both the degree and duration of diabetes have a major effect on salivary gland morphology in alloxan diabetic rats.

Endocytosis of proteins by salivary gland duct cells

The ability of the intralobular duct cells of the rat parotid gland to take up protein from the lumen was examined by retrograde infusion of exogenous proteins and by immunogold localization of endogenous secretory proteins. Small amounts of native horseradish peroxidase (HRP) were taken up by intercalated and striated duct cells, and were present in small vesicles, multivesicular bodies, and lysosomes. In contrast, HRP modified by periodate oxidation was avidly internalized by the duct cells and was present in large apical vacuoles that acquired lysosomal hydrolase activity. Native and cationized ferritin were taken up in a similar manner when infused at a high concentration (up to 10 mg/mL). At lower concentrations (0.3-1.0 mg/mL), endocytosis of cationized ferritin occurred mainly in small apical tubules and vesicles in striated duct cells. Little native ferritin was taken up at these concentrations. After stimulation of acinar cell secretion by isoproterenol, similar vacuoles were occasionally observed in both intercalated and striated duct cells. Labeling of thin sections with antibodies to amylase and to a 26,000-dalton secretory protein (protein B1), followed by protein A-gold, revealed the presence of these proteins in the vacuoles, indicating endocytosis of acinar secretory proteins by the duct cells. Although uptake of acinar proteins by duct cells occurs at a low rate in normal animals, previous work suggests that extensive endocytosis may occur in certain pathological conditions. This may be a mechanism for removing abnormal or modified proteins from saliva before it reaches the oral cavity.

Regulation of salivary proteins

Previous studies have shown that several factors--such as alloxan-induced diabetes, adrenalectomy, or removal of the thyroid-parathyroid gland complex--can influence the flow rate, protein concentration, and protein composition of rat parotid saliva. The present study was undertaken to explore further the influence of glucocorticoids and thyroxine on rat parotid saliva in hormonally intact animals. As compared with untreated animals, adult male rats treated with 10 micrograms dexamethasone per 100 g body weight for eight days demonstrated a 75% reduction in volume of parotid saliva secreted in response to a uniform stimulus. The protein concentration of the saliva was increased three-fold. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed relative decreases in acidic and basic proline-rich proteins and in a protein identified as Fraction V, while amylase was increased. The electron microscopic appearance of the granules was markedly different from that of the control, in that the granules exhibited an electron-dense periphery and core, with the remainder of the granule having an electronlucent appearance. In contrast, rats treated for eight days with 20 micrograms thyroxine per 100 g body weight exhibited a 50% increase in volume of saliva collected in response to a secretory stimulus. Although the concentration of protein was not different from that of the control, gel electrophoresis showed relative increases in acidic and basic proline-rich proteins and a decrease in Fraction V. Amylase was unchanged. The secretory granules of thyroxine-treated rats were electronlucent and amorphous. The granules appeared to coalesce within the cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoglobulins and innate antimicrobial factors in whole saliva of patients with insulin-dependent diabetes mellitus

We analyzed the flow rate and composition of paraffin-stimulated whole saliva samples from 35 adult diabetic patients and their age- and sex-matched, non-diabetic, clinically healthy controls. All patients had insulin-dependent diabetes (IDDM) with a mean (+/- S.D.) duration of 14.0 +/- 9.1 years. The saliva analysis included the quantitation of total protein, amylase, immunoglobulins (isotypes A, G, and M), and the non-antibody, innate antimicrobial factors (lysozyme, lactoferrin, salivary peroxidase, myeloperoxidase, thiocyanate, and hypothiocyanite). The whole saliva samples from diabetic patients had significantly higher amounts of IgA (p less than 0.001) and IgG (p less than 0.05) than did the controls. No differences between the study groups were observed in flow rate, protein content, amylase activity, or IgM. The levels of innate defense factors were similar in both study groups except for salivary peroxidase, which was higher (p less than 0.02) among diabetics than among controls. Our results indicate that the antimicrobial defense capacity of whole saliva is not impaired in diabetic patients.