Acinar cell proliferation in the parotid and submandibular salivary glands of the neonatal rat

Abstract. Although the rat salivary glands are deficient in acini at birth, acinar cells proliferate rapidly during the early post-natal period. The pattern of acinar cell proliferation was analysed in the parotid and submandibular glands of neonatal rats from day of birth until day 34. Mitotic and [³H]thymidine ([³H]TdR) labelling indices of the two glands show distinctly different patterns. Analysis of cell division in the rat parotid gland demonstrated a peak of mitotic index at 14 days (2.9 ± 0.4%) and labelling index at 16 days (25.2 ± 2.1%). Submandibular gland acinar cell proliferation reaches a zenith between 7–8 days; labelling index (14.2 ± 1.1%) and mitotic index (2.3 ± 0.3%). Cell proliferation decreases rapidly in both glands after reaching a peak in activity. Gland size increases more rapidly in the submandibular gland which correlates with the earlier shift from cell proliferation to differentiation which occurs in this organ. Circadian rhythms of [³H]TdR incorporation were also investigated in this study. A circadian rhythm of [³H]TdR incorporation into DNA occurs at 15 days after birth with a peak at 06.00 hours in both glands and a trough occurring at 15.00 hours in parotid gland and 18.00 hours in the submandibular gland. Determination of specific activity of DNA (ct/min per μg DNA) on days 8, 10, 12, 13, 14, 15, and 16 after birth at 06.00 and 15.00 hours indicated that a circadian rhythm in [³H]TdR incorporation into DNA began on day 14. The developmental switch from suckling to solid food may be an initiating factor in the sychronization of the circadian rhythm in cell proliferation.     

A functional and chemical study of radiation effects on rat parotid and submandibular/sublingual glands.

The aim of this study was to monitor composition and rate of secretion of rat parotid and submandibular/sublingual saliva following local single doses of X-rays ranging from 5 to 20 Gy. Pilocarpine-stimulated samples of parotid and submandibular/sublingual saliva were simultaneously collected with miniaturized Lashley cups before and 1-30 days after irradiation. The lag phase (period between injection of pilocarpine and start of the secretion) and flow rate were recorded and the concentrations of sodium, potassium, calcium, phosphate, and amylase were measured. With increasing dose and time, the salivary flow rate as well as sodium concentration decreased, while potassium concentrations increased throughout the follow-up period. The lag phase and the concentration of amylase reached their maximum at 3 and 10 days after irradiation, respectively. The changes in lag phase and flow rate were most obvious after doses of 15 or 20 Gy and showed a great similarity for parotid and submandibular/sublingual saliva. No dose-response relationship was observed for the changes in concentrations of calcium and phosphate. It is concluded that for radiation doses of 10 Gy and above, irreversible changes (lag phase, flow rate, potassium, sodium) were observed. A saturation of the irradiation effects (lag phase, flow rate) seems to exist at doses larger than 15 Gy. No significant differences were observed between the radiation-induced functional changes in parotid and submandibular/sublingual salivary gland tissue.     

Isoprenaline-induced changes in rat parotid and submandibular glands are age- and dosage-dependent.

Neonatal rats treated with chronic injections of isoprenaline (isoproterenol) for 10 days revealed differential induction of proline-rich proteins and glycoprotein synthesis between the parotid and submandibular glands. Biosynthesis of proline-rich proteins (Mr 17000-35000) and a Mr-220000 glycoprotein were detectable by solubilization in 10%-trichloroacetic acid extracts from parotid glands 14 days after birth. The enzyme lactose synthase (UDP-galactose: 2-acetamido-2-deoxy-D-glucosamine 4 beta-galactosyltransferase) (EC 2.4.1.22) is also induced 4-7-fold in specific activity compared with control neonatal rats, but again only after 14 days post partum, with isoprenaline treatment. This is in accord with the ability of the parotid gland to respond to beta-receptor stimulation and subsequent increases in intracellular cyclic AMP necessary for induction of protein synthesis [Grand, Chong & Ryan (1975) Am. J. Physiol. 228, 608-612]. Induction of the proline-rich proteins and a Mr-190000 glycoprotein in the soluble fraction from the submandibular gland were not detected until 49 days after birth under identical conditions in the same animal. Cyclic AMP in the submandibular gland undergoes increases on beta-receptor stimulation similar to those achieved in the adult animal, 1 day after birth (Grand et al., 1975). This same differential induction between parotid and submandibular gland was obtained with a range of isoprenaline dosages in adult animals. Trichloroacetic acid-soluble proline-rich proteins were isolated from parotid glands at a dosage of 4.0 mg of isoprenaline/kg body wt., but 7.0 mg/kg was required to induce also biosynthesis of these proteins in the submandibular gland. Gland hypertrophy showed the same differential dosage kinetics, based on gland weight, between the two glands; however, hypertrophy could be accomplished at a lower dosage of isoprenaline than that used to induce proline-rich-protein biosynthesis.     

Carbohydrate histochemistry of the opossum submandibular and major sublingual glands.

Submandibular and major sublingual salivary glands of the opossum contain histochemically demonstrable neutral mucosubstances, nonsulfated acid musosubstances and sulfomucins. Sialomucins could not be demonstrated conclusively with the methods used in this study. Special serous cells of the opossum submandibular gland contained low concentrations of acidic mucosubstances but no appreciable concentration of neutral mucosubstances was seen. Sulfomucins were not observed in special serous cells. The mucous tubules of the submandibular gland contained high concentrations of neutral mucosubstances. No appreciable acidic mucosubstance was demonstrated in the submandibular gland mucous tubules. Unlike the mucous tubules of the submandibular gland, the major sublingual gland mucous tubules contained high concentrations of both neutral and acidic mucosubstances. The mucous tubules often contained sulfomucin-positive cells interspersed among cells that contained high concentrations of non-sulfated acidic mucosubstance. Marked staining of sulfated acidic mucosubstance was seen only in the major sublingual gland, in both the mucous tubules and in the seromucous demilunes. The seromucous demilunes contained both sulfated and non-sulfated acidic mucosubstances.     

Cytochemical demonstration of enzymatic activities of the parotid, submandibular, and sublingual glands of Praomys (Mastomys) Natalensis

Histochemical techniques were applied to salivary glands removed from adult multimmate rodents (Praomys) of either sex to detect and localize the following enzymatic activities: acid and alkaline phosphatase, arylsulphatase, ali-esterases, beta-glucuronidase, N-acetyl-betaglucosaminidase, and L-leucyl-aminopeptidase. No reaction was observed for alkaline phosphatase and glucuronidase. The glands reacted differently to the other enzymatic activities. Alkaline phosphatase and glucosaminidase were present only in one glandular type whereas arysulphatase and esterases were present in all types although demonstrating a variable staining intensity in different glands. Sharp differences in some enzymatic activities of the submandibular and parotid glands were related to the sex of the animal.     

The noradrenergic innervation of the excretory ducts of the parotid, mandibular and sublingual glands in the rat

Summary The noradrenergic innervation of the excretory ducts of the parotid, mandibular and sublingual salivary glands in the rat has been examined using fluorescence histochemistry. None of the ducts were found to be innervated directly but, in the mandibular duct, innervated blood vessels are in close proximity to the epithelial cells of the duct and it is suggested that noradrenaline may diffuse from the vascular nerve endings to receptors on the epithelial cells.     

Effect of parotid submandibular and sublingual saliva on wound healing in rats.

1. The effectiveness of wound licking with parotid, submandibular or sublingual saliva on wound healing was evaluated in selectively sialadenectomized rats. 2. The rate of healing of experimentally induced cutaneous wounds was evaluated macroscopically by photography at 0, 2, 4 and 6 days after surgery. 3. Sialadenectomy of all major glands significantly slowed down wound healing compared to sham-operated controls. 4. Parotid licking had no effect compared to controls; submandibular licking and sublingual licking appeared to be very effective. 5. The results suggest that saliva promotes wound healing in experimentally induced cutaneous wounds by communal licking; this is a result of the submandibular and sublingual saliva and not the parotid saliva.     

Histochemical studies of the parotid and submandibular glands of humans

Human parotid and submandibular glands were studied using histological techniques. Proteins rich in arginine, tyrosine, cystine-cysteine and tryptophan were present within secretory granules of seromucous acini and ducts of both glands. Acid phosphatase, ali-esterase, peroxidase and 3-beta-steroid-dehydrogenase were also demonstrated in the two glands.     

Alteration of salt taste sensitivity by the neonatal removal of sublingual glands in the rat

1. Adult rats with the surgical removal of sublingual glands at their 10 days of age did not prefer NaCl solution of any concentration to water, whereas those with sham-operation or the removal of submandibular glands preferred 0.03 or 0.1 M NaCl to water. 2. Magnitudes of inhibition of chorda tympani responses to NaCl by the lingual treatment of 0.1 mM amiloride were greater in neonatally sublingual removed rats than in sham-operated or submandibular removed ones. 3. These results suggest that the removal of sublingual glands in neonatal period of the rat could increase the amount of the amiloride-sensitive Na receptor mechanism on the taste cell membrane in its adulthood.     

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

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

Tyrosylprotein sulfotransferase in rat submandibular salivary glands.

1. The transfer of sulfate ester group from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to poly-(Glu6, Ala3, Tyr1) (EAY; Mr 47 kDa) in rat submandibular salivary gland has been investigated. The highest tyrosylprotein sulfotransferase activity was obtained in the Golgi-enriched fraction in the presence of 2 mM 5'AMP, 20 mM MnCl2 and 50 mM NaF at pH 6.2. 2. The apparent Km values for EAY and PAPS were 1.6 x 10(-6) and 1.9 x 10(-6) M, respectively. 3. Inclusion of NaCl, EDTA, NEM and DTT was inhibitory for the enzyme activity. The enzyme was 28 times less susceptible to 2,6-dichloro-4-nitrophenol inhibition than to phenol sulfotransferase inhibition. 4. This study is the first report characterizing a sulfotransferase activity specific for tyrosylprotein in rat submandibular salivary glands.     

Inositol trisphosphates in carbachol-stimulated rat parotid glands.

Carbachol stimulation of rat parotid gland fragments prelabelled with myo-[3H]-inositol results in a large accumulation after 15 min of [3H]inositol trisphosphate. Only some of this is the D-1,4,5 isomer which would be expected to be derived from the known phosphatidylinositol bisphosphate. The predominant inositol trisphosphate is not susceptible to hydrolysis by human erythrocyte membranes. It yields altritol after periodate treatment followed by reduction and dephosphorylation, and, from partial dephosphorylation experiments, does not have a phosphate in the 2 position; the most likely structure of this inositol trisphosphate is therefore (D/L)-myo-inositol 1,3,4-trisphosphate. The possible origin and significance of this compound are discussed.