Effect of isoproterenol analogs on the polypeptide composition of mouse parotid glands: relationship to enhanced growth

Morphological alterations in salivary glands of mice (Mus musculus) submitted to tannin enriched diets: comparison with sialotrophic effects of sympathetic agonists stimulation

In order to study the effects of tannins at histomorphological level, mice were either fed with three structurally different types of tannins (tannic acid, chestnut, and quebracho) or treated with isoproterenol, during 10 days. Acini of parotid and submandibular glands increased significantly, being the increase higher for parotid compared to submandibular glands, and higher in the quebracho compared with the other tannin groups. Sublingual acinar size also increased after tannin consumption, by opposition to isoproterenol-treated animals. The results present evidences that the effects produced by tannins are dependent on their structure.

Induction of salivary polypeptides associated with parotid hypertrophy by gallotannins administered topically into the mouse mouth

Isoproterenol-induced salivary polypeptides (IISP), a group of proline-rich proteins synthesized by mouse parotids, have been considered as markers for isoproterenol-induced parotid hypertrophy. Rodents fed diets containing high-tannin cereals (sorghum), also develop parotid hypertrophy. To test whether tannins are directly involved in provoking sialotrophic growth, we studied the effect of intraperitoneal and topical oral administrations of tannic acid (TA) on the induction of IISP polypeptides in endogamic mice (A/Snell). TA was characterized by HPLC chromatography and spectral analysis and shown to be composed solely of gallotannins, a complex family of glucose and gallic acid esters. IISP polypeptides were monitored in saliva by SDS-polyacrylamide gel electrophoresis during 36 h after ending TA stimulation. Single daily intraperitoneal administrations of TA for 3 consecutive days (0.033 mg/g bw/day), at variance of parallel administrations of isoproterenol (0.042 mg/g bw/day) failed to induce IISP polypeptides. However, repeated topical applications of TA into the mouse mouths (1.21 mg/g bw divided into three equal doses given at 4-h intervals within a single day) resulted in unequivocal induction of IISP polypeptides. That response was clearly intensified by increasing the stimulation frequency to eight equivalent doses given at 1.5-h intervals within a single day (corresponding to 3.23 mg/g bw) and even further by repeating this protocol for 3 days. Under these productive schemes of stimulations by TA, electrophoretic fractionation of parotid homogenates showed new polypeptide bands migrating in parallel to salivary IISP. These results suggest that topically administered gallotannins are effective inducers of trophic growth in mouse parotids.

Codominant expression of genes coding for different sets of inducible salivary polypeptides associated with parotid hypertrophy in two inbred mouse strains

Experimental mouse parotid hypertrophy has been associated with the expression of a number of isoproterenol-induced salivary proline-rich polypeptides (IISPs). Mouse salivary proline-rich proteins (PRPs) have been mapped both to chromosomes 6 and 8. Recently, mice of two inbred strains (A/Snell and A. Swiss) have been found to differ drastically in the IISPs. In this study, mice of both strains were used for cross-breeding experiments addressed to define the pattern of inheritance of the IISP phenotype and to establish whether the IISPs are coded on a single or on several chromosomes. The IISP phenotype of individual mice was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of whole saliva collected after three daily stimulations by isoproterenol. Parental A/Snell and A. Swiss mice were homogeneous for distinctive strain-associated IISP-patterns. First filial generation (F1) mice obtained from the cross of A/Snell with A. Swiss mice expressed with no exception both the A/Snell and A. Swiss IISPs (coexpression). In the second filial generation (F2) both parental IISP phenotypes reappeared together with a majority of mice expressing the F1-hybrid phenotype (1:2:1 ratio). Backcrosses of F1 x A/Snell and F1 x A. Swiss produced offsprings displaying the F1 and the corresponding parental phenotypes with a 1:1 ratio. No recombinants were observed among F2 mice or among mice resulting from backcrosses. Thus, genes coding for the IISPs that are expressed differentially in both mouse strains are located on the same chromosome, probably at the same locus (alleles) or at quite closely linked loci (nonalleles).

Differential expression of isoproterenol-induced salivary polypeptides in two mouse strains that are congenic for the H-2 histocompatibility gene complex

Two inbred mouse strains, A/Snell and A.Swiss, which were produced as congenic with regard to the H-2 histocompatibility gene complex, are homozygous for two different groups of isoproterenol-induced salivary polypeptides (IISP). These polypeptides, which have been considered as markers of the hypertrophic growth of the parotid acinar cells, are members of the complex family of salivary proline-rich proteins (PRP) on the basis of both their massive accumulation in the parotid acinar cells in response to chronic isoproterenol, secretory character, high solubility in trichloroacetic acid and metachromatic staining by Coomassie blue. IISP expressed in both mouse strains were identified by unidimensional SDS-polyacrylamide electrophoresis and Coomassie blue staining both in parotid gland homogenates and in whole salivas obtained from mice repeatedly stimulated at 24-h intervals with isoproterenol. Parotid glands from 40 mice (20 A/Snell and 20 A.Swiss) and salivas from 270 mice (200 A/Snell and 70 A.Swiss) were analyzed. One of the congenic strains (A/Snell) expressed five IISP (Mr 65, 61, 51.5, 38, and 37 kDa) and the other strain (A.Swiss) expressed six IISP (Mr 59, 57, 54.5, 46, 36, and 34 kDa). No inter-individual intra-strain variations were observed, thus defining strain-associated patterns of IISP (PRP).

Cell-enlargement-related polypeptides are induced via beta(1)-adrenoceptors in mouse parotids

Induction of cell and gland enlargement (growth-in-size) and induction of a group of secretory polypeptides (polypeptides C-G) seem to occur in close relationship in mouse parotid glands stimulated chronically by the nonselective beta-adrenergic agonist isoproterenol. To determine whether beta(1), beta(2), or both subtypes of beta-adrenergic receptors are involved in those responses, dose-dependency studies were carried out during a 7-day period of daily stimulations to assess the relative abilities of the selective beta-adrenergic agonists dobutamine (beta(1)) and salbutamol (beta(2)) to induce polypeptides C-G and growth-in-size. The relative abilities of the selective beta-adrenoceptor antagonists atenolol (beta(1)) and I.C.I. 118.551 (beta(2)) to interfere with the induction of both responses by chronic treatment with the various beta-adrenergic agonists were also studied. Parotid growth-in-size was assessed by evaluating wet weight, whole protein content, and light microscopy histology. The presence of polypeptides C-G was evaluated after SDS-polyacrylamide gel electrophoresis and Coomassie blue staining. Under these experimental conditions, dobutamine was found to be at least one order of magnitude more potent than salbutamol at inducing growth-in-size. Dobutamine was also found to be clearly stronger than salbutamol as an inducer of polypeptides C-G. On the other hand, atenolol was more effective than I.C.I. 118.551 at preventing the induction of polypeptides C-G and growth-in-size by isoproterenol, dobutamine, or salbutamol. Taken together, these results suggest that in mouse parotid glands, polypeptides C-G and growth-in-size are induced preferentially via adrenergic receptors of the beta(1)-subtype.

Plasma membrane desialylation and DNA synthesis are induced via adrenergic receptors of the beta 1-subtype in mouse parotid glands

Induction of DNA synthesis and plasma membrane desialylation in the early prereplicative period in isoproterenol-stimulated mouse parotid glands seem to occur in a close relationship. beta 1, beta 2 or both subtypes of adrenergic receptors could be involved in those responses. To discriminate between those alternatives, dose-dependency studies were addressed to assess the abilities of the selective beta-adrenergic agonists dobutamine (beta 1) and salbutamol (beta 2) to induce plasma membrane desialylation and DNA synthesis. Likewise, the abilities of the selective beta-adrenoceptor antagonists atenolol (beta 1) and ICI 118,551 (beta 2) to interfere with the induction of both responses were also studied. Dobutamine was found to be at least 10-fold more potent than salbutamol in inducing DNA synthesis whereas ICI 118,551 was much weaker than atenolol, as inhibitor of the agonist-induced DNA synthesis. On the other hand, dobutamine was also more potent than salbutamol in provoking plasma membrane desialylation. However, whenever an increase in the rate of DNA synthesis was induced by either agonist, a constant 50% reduction in the levels of sialic acid in the plasma membranes was observed. In the same direction, atenolol, at variance to ICI 118,551, was able to produce a full suppression of the plasma membrane desialylation induced by either selective agonist. Taken together, these results suggest that in mouse parotid glands, both DNA synthesis and plasma membrane desialylation during the early prereplicative period are induced preferentially via adrenergic receptors of the beta 1-subtype.

Current status of histogenetic and morphogenetic concepts of salivary gland tumorigenesis

Because of their complexity and relative infrequency, salivary gland tumors commonly result in diagnostic problems. Histogenetic and morphogenetic concepts of tumorigenesis in these glands are reviewed and their relevance to routine diagnosis and classification of salivary gland tumors evaluated. Evidence is presented from animal and human studies that under steady-state and pathophysiological conditions, all cell types present in the normal gland, including acinar cells, are capable of rapidly entering the cell cycle and are, therefore, possible targets for neoplastic transformation.