Faculty Bibliography

A study of saliva-mediated aggregation and adhesion has been carried out in a group of caries-resistant (CR) and caries-susceptible (CS) individuals. The submandibular saliva of the CS group had a much greater potency, as determined by dilution, in promoting adherence to hydroxyapatite beads than did the saliva of CR group. In contrast, the CR group demonstrated a twofold enhancement of saliva-mediated aggregation compared with the CS group. These observations support the hypothesis that saliva-mediated aggregation and adherence are important factors in caries resistance.

Comparison of saliva-mediated aggregation of Streptococcus sanguis, Streptococcus mitis, and Streptococcus mutans and adhesion of these organisms to saliva-coated hydroxyapatite showed that there was no relationship between these two activities. Adsorption of salivary aggregating activity to bacteria appears to have little effect on the ability of the residual saliva to support adherence; conversely, adsorption of salivary adherence factors to hydroxyapatite does not affect aggregation. Although heating saliva significantly reduces bacterial aggregation, it has little or no effect on adherence. A comparison of aggregation and adhesion with serial dilutions of saliva demonstrated that adhesion could still be detected at 100 to 500-fold-lower concentrations of salivary protein that bacterial aggregation. These findings support the concept that aggregation and adherence involve two distinct mechanisms of microbial clearance in the oral cavity.

Using a quantitative assay to measure saliva-mediated bacterial aggregating activity, we have surveyed 20 streptococcal strains with saliva samples obtained from a large population study. Individual saliva samples demonstrated characteristic levels of aggregating activity for Streptococcus sanguis M5. In general, high activity for this strain was associated with high activity for other strains of S. sanguis. Streptococcus mitis, and Streptococcus salivarius. The population distribution of aggregating activity for Streptococcus mutans, however, was different.

Two new assays for saliva-mediated aggregation of oral bacteria have been developed, based on the use of [3H]thymidine-labeled cells. One assay separates free cells from aggregated cells by centrifugation through sucrose, whereas the other utilizes membrane filters (8 micrometers, Nuclepore) to effect the separation. Comparison of these assays with the turbidity method reveals that they are faster (X20 to 40) and require 10 times less saliva and bacteria. The aggregation of Streptococcus sanguis M5, as determined with these assays, is complete in 5 min and is dose dependent on added cells and saliva. The reaction exhibits a temperature optimum of 42 degrees C with no reaction at 0 degrees C. If the pH is reduced to below 5, saliva-dependent aggregation is inhibited. The salivary factor(s) are heat labile, losing 100% of their activity after 100 degrees C, 10 min or 70 degrees C, 30 min.

In vivo injection of isoproterenol(IPR) (4 mg/kg) in normal rats caused fat cell adenylate cyclase to become desensitized to stimulation by IPR in vitro. In contrast, adenylate cyclase from tissues of burn-injured rats (20% body surface, full-thickness scald) remained fully responsive to stimulation by IPR for several days after injury even though catecholamine excretion was elevated more than twofold. Furthermore, fat cell adenylate cyclase from burn-injured animals was not desensitized after acute in vivo IPR injections, whereas adenylate cyclase from the shams did become desensitized after acute IPR injections. To determine whether the apparent resistance to desensitization in burn-injured rats might be an adaptation to the chronic elevation of catecholamines that follows burn injury, two other rat models in which catecholamines are chronically elevated were studied: one was produced by a twice daily schedule or IPR (1 mg/kg) injections for 3 weeks; the other by 3 weeks' cold exposure (0--4 degrees C). As had been observed in burn injury, adenylate cyclase remained fully responsive to IPR in both models, and adenylate cyclase from the cold-acclimated rats was resistant to desensitization by acute injections of IPR. It therefore seems likely that chronic elevations of catecholamines evoke regulatory mechanisms in target cells to circumvent the desensitizationwhich would otherwise occur consequent to acute exposures to catecholamines. In burn injury this may result in an inadvertent adaptation which contributes to hypermetabolism.

A new transplantable murine salivary gland carcinoma (myoepithelioma) was further characterized by comparing total protein patterns with normal submaxillary qland proteins. Analysis by isoelectric focussing or by labelling studies with radioactive leucine showed considerable differences between tumour and normal proteins. In contrast, analysis of staining patterns after electrophoresis in sodium dodecyl sulphate containing gels revealed a striking similarity between normal proteins, tumour proteins and proteins obtained from metastatic growths. It thus appears that tumour proteins closely resemble the normal proteins from the tissue of origin with respect to molecular size as determined by electrophoretic mobility, while significant differences occur in charge and labelling kinetics

A single injection of isoproterenol (IPR) stimulates cell proliferation in rodent salivary glands after a lag period of about 24 hrs. Among the many events occurring prior to stimulated DNA synthesis, there is an early increase in cAMP levels and elevated transport of amino acids into the parotid gland. Amino acid transport is also elevated in liver and pancreas, tissues not induced to proliferate by IPR. IPR-stimulated alpha-aminoisobutyric acid (AIB) transport in parotid, pancreas and liver is augmented by prior injection of theophylline and is mimicked by dibutyryl cAMP. In all three tissues, changes in cAMP levels and subsequent increases in AIB transport appear to be closely related events. Since only the parotid gland is stimulated to grow after IPR injection, amino acid transport and growth would not appear to be directly related.