Effects of calcitonin on elemental distribution and ultrastructure of rat submandibular gland acinar cells

The effect of calcitonin on rat submandibular gland acinar cells was investigated by X-ray microanalysis and electron microscopy. Calcitonin caused a transient increase of the cellular calcium and magnesium concentration, but did not affect the intracellular concentration of other electrolytes. The relative volume of intracellular mucus increased from 45% in control glands to 72% at 6 h after administration of calcitonin. Calcitonin caused an inhibition of the cellular response of the acinar cells to beta-adrenergic and cholinergic agonists. The changes in elemental composition and ultrastructure of the gland cells are probably due to inhibition of mucus release from the cells.     

Effects of prior culture or isoproterenol injections on the regeneration of rat submandibular gland autografts

This study compares the acinar cell regnerative response in submandibular gland (SMG) autografts that were cultured before grafting to the rat tongue with the acinar cell regenerative response in direct SMG autografts to the tongue. In addition, the effects of isoproterenol on direct SMG autografts were studied. A portion of the left SMG was excised from each rat and cut into fragments which were autografted either immediately into the middle one-third of the rat's tongue; or were cultured for 1, 4, or 7 days and then autografted to the donor's tongue. After 8 weeks the rats were killed and the tongues were removed and processed for light microscopic study. The histologic preparations showed evidence of cytodifferentiation into acinar cells in four of the previously cultured SMG autografts. Some of the direct SMG autografts did not contain acinar cells, whereas other direct. SMG autografts contained numerous acinar cells and even straited ducts. In the SMG autografts that were cultured for 1 day before autografting and in the direct SMG autografts, that contained ductlike structures that were apparently connected to the epithelial surface of the tongue. Lastly, isoproterenol appeared to accelerate the regenerative responses in some of the direct SMG autografts, and the drug caused acinar cell hypertrophy in two of the direct SMG autografts.     

The effects of 5-bromodeoxyuridine and isoproterenol on the postnatal differentiation of rat submandibular gland

The effects of 5-bromodeoxyuridine (BrdU) on the postnatal differentiation of rat submandibular gland and on the isoproterenol-induced changes of differentiation were studied. The rats were injected with BrdU for three consecutive days, beginning at two days of age. The total dose of BrdU was 0.9 mg/g body weight. BrdU caused a severe retardation of growth up to 15 days of age. A rapid growth of the animals between 15 and 22 days indicated a recovery from the effect of BrdU. The growth of the submandibular gland was retarded similarly with a corresponding decrease in DNA, RNA and protein content. Incorporation of tritiated thymidine into the submandibular gland was not altered in the BrdU-treated animals at one and three days after the last injection of the analog. At days 15 and 22 the rate of thymidine incorporation was greater in the submandibular gland of BrdU-treated rats as compared to littermate controls. Isoproterenol stimulated thymidine incorporation into the submandibular glands of two-week-old rats. This stimulation was not observed in rats which received BrdU at age 7–9 days, prior to the administration of isoproterenol. Electron microscopic observations, including a quantitative analysis of the frequency distribution of the various cell types in the terminal tubules and developing acini, indicated a retardation of acinar cell differentiation in the glands of BrdU-treated rats. In addition, there was an increase in the number and size of the secretory granules in the terminal tubule cells. BrdU treatment, however, caused no obvious pathologic alterations in the submandibular gland. Administration of isoproterenol for five days, beginning at five days of age, caused an apparent acceleration of the differentiation of acinar cells. In the glands of isoproterenol-treated rats the acinar cells were enlarged and were filled with homogenous secretory granules. Pretreatment with BrdU partially inhibited the effects of isoproterenol on differentiation and hypertrophy of the submandibular gland. With the given dose of BrdU, approximately 5% of thymine was replaced by bromouracil in the DNA of the submandibular gland. Such a replacement would be consistent with a direct effect of BrdU on the cytodifferentiation in the submandibular gland. However, because of the severe retardation of growth of the BrdU-treated rats, indirect effects can not be excluded.     

Effects of reserpine treatment on β-adrenergic/adenylate cyclase modulated secretion and resynthesis by the rat submandibular gland

Summary Chronic reserpine (adrenergic blocking) treatment causes a marked accumulation of secretory protein in the rat submandibular gland (SMG) but discharge of this material is delayed in response to isoproterenol stimulation. The purposes of this study were to investigate the effects of chronic reserpine treatment on 1) the number of -adrenergic receptors, 2) the sensitivity of cell-surface-associated adenylate cyclase to various concentrations of isoproterenol, and 3) to correlate these data to morphologic studies of the secretion and resynthesis phases of the isoproterenol-induced secretory cycle in the rat SMG. Animals were injected with reserpine (0.5 g/g b.w.) for 6 days. Plasma membrane fractions were prepared. The adenylate cyclase response to a series of isoproterenol concentrations, and the number of -adrenergic receptors ([³H]-alprenolol binding) were determined. Other animals were given a single dose of isoproterenol (0.8 mg/100 g b.w.) and the SMG was examined by light and electron microscopy at various times (30 min to 24 h) after treatment. Chronic reserpine treatment leads to a 2.5-fold increase in SMG -adrenergic binding sites and a 50-fold increase in adenylate cyclase sensitivity to IPR stimulation when compared to controls. However, secretion and resynthesis of secretory product in response to IPR stimulation was greatly delayed in reserpinized rats.A preliminary report of this data has been previously presented: Cutler, L.S. et al. (1979) J. Dent. Res. 58A:380     

Induction of the synthesis of a specific protein in rat submandibular gland by isoproterenol

Prolonged treatment of rats with the beta-adrenergic agonist, isoproterenol (IPR), produces hypertrophy and hyperplasia of the parotid and submandibular glands. The drug induces the synthesis of several secretory proteins that are absent or occur at very low concentrations in the gland or saliva of the untreated rat. We have measured the relative concentrations of one of these proteins (termed "large mobile" (LM) protein, Menaker et al. (1974) Lab. Invest. 30, 341-349) by using a solid phase enzyme-linked immunoabsorption assay. LM protein was not measurable in gland extracts of 20-day-old fetuses or 2-day-old rats. Its concentration was very low in the glands of 6- and 13-day-old and adult rats. Administration of IPR for 4 to 7 days to adult or 6-day old rats increased the levels of the LM protein by 20 to 25-fold. The LM protein was localized immunocytochemically primarily in the acinar cells in the glands of control and IPR-treated adult rats. In vitro translation studies using a mRNA-dependent reticulocyte lysate system and labeling with [35S]methionine showed: little synthesis of pro-LM from poly(A+) RNA from glands of adult rats and none from 13-day-old animals, and that, in comparison, poly(A+) RNA from glands of adult or 13-day-old IPR-treated rats directed the synthesis of a much greater concentration of pro-LM. The in vitro precursor of the LM protein migrated electrophoretically as a single band in anti-LM immunoprecipitates, and had a molecular weight of 14,000. The LM protein, which appears to be a single, unique polypeptide induced by IPR in the submandibular glands of developing and adult rats, will be useful in studies examining the effects of catecholamine beta-agonists on gene expression in an exocrine cell.     

Effects of irradiation on the submandibular gland of the rat

Summary Single-dose cervical irradiation by cobalt 60 in rats induced lasting functional disturbances of the submandibular gland which were excessive when compaired with the relative integrity of the gland as seen under the light microscope. Enzyme histochemical and ultrastructural studies revealed severe damage shortly after exposure with appearance of karyolytic bodies and autophagosomes accompanied by increased hydrolase activity. Mitochondrial alterations were concomitant with diminished ductal oxidative enzyme activity. Although most of these alterations resolved rapidly as a result of acinar and ductal cell repair and regeneration originating in the intercalated ducts, secretory abnormalities were still observed two months after exposure as evidenced by the accumulation of granules in acinar cells and the heterogeneity of ductal cell granules. These anomalies, comparable to those observed in sialadenoses, probably result from persistent alterations of intralobular nerve endings.The authors wish to thank M.F. Baucher, A. Lesot and M. Tacnet for their technical assistance     

Effects of angiotensin ll on blood flow in rat submandibular gland

The effect of angiotensin II (Ang II) was studied on blood flow in the submandibular gland and tongue in male rats. Blood flow changes were determined with laser Doppler flowmetry and Ang II was infused into the common carotid artery before and after i.v. doses (18 nmol kg^-l) of the angiotensin II antagonist saralasin. Angiotensin II (10–60 pmol min^-l) dose-dependently increased blood pressure and tongue blood flow, whereas glandular blood flow decreased at all of the doses used. After saralasin administration the angiotensin II effects on blood pressure, tongue and glandular blood flow were significantly diminished (glandular blood flow reduction was diminished from 29%-3%, P < 0.005, n = 9). However, the responsiveness of these 3 parameters to local infusions with noradrenaline (0.75–3.0 pmol min^-1) was unaffected by saralasin. The dose of saralasin used in the present study did not affect any of the parameters on it's own. Our results show that vascular receptors sensitive to angiotensin II operate in the submandibular gland but not in the tongue.     

Effects of angiotensin II on blood flow in rat submandibular gland

The effect of angiotensin II (Ang II) was studied on blood flow in the submandibular gland and tongue in male rats. Blood flow changes were determined with laser Doppler flowmetry and Ang II was infused into the common carotid artery before and after i.v. doses (18 nmol kg-1) of the angiotensin II antagonist saralasin. Angiotensin II (10-60 pmol min-1) dose-dependently increased blood pressure and tongue blood flow, whereas glandular blood flow decreased at all of the doses used. After saralasin administration the angiotensin II effects on blood pressure, tongue and glandular blood flow were significantly diminished (glandular blood flow reduction was diminished from 29%-3%, P less than 0.005, n = 9). However, the responsiveness of these 3 parameters to local infusions with noradrenaline (0.75-3.0 pmol min-1) was unaffected by saralasin. The dose of saralasin used in the present study did not affect any of the parameters on it's own. Our results show that vascular receptors sensitive to angiotensin II operate in the submandibular gland but not in the tongue.     

Polarized distribution of key membrane transport proteins in the rat submandibular gland

 Immunofluorescence labelling and confocal microscopy were employed to examine the polarized distribution of several membrane transport proteins believed to be essential for salivary secretion in the rat submandibular gland. The Na⁺/K⁺-ATPase, Na⁺/H⁺ exchanger isoform 1 (NHE1), and the secretory Na⁺/K⁺/2Cl^–cotransporter isoform were all found in the basolateral membranes of acinar and intralobular duct cells. Anion exchanger isoform 2 (AE2) was found only in the basolateral membranes of acinar cells, while AE1 was absent from glandular epithelial cells. Aquaporin 5 was detected in the apical membranes of acinar cells, while the cystic fibrosis transmembrane conductance regulator was found only in apical membranes of intralobular duct cells. NHEs 2 and 3 were found in the apical membranes of both acinar and intralobular duct cells. Our results are generally consistent with the expected distribution of most transporters based on previous physiological and pharmacological experiments. However, the apical localization of NHEs 2 and 3, and the presence of the secretory isoform of the Na⁺/K⁺/2Cl^–cotransporter in intralobular duct cells were not predicted. Received: 10 June 1996 / Received after revision: 9 September 1996 / Accepted: 17 September 1996