A biochemical analysis of parotid and submandibular salivary gland function with age after simultaneous stimulation with pilocarpine and isoproterenol in female NIA Fischer 344 rats.

This analysis of physiological, biochemical and molecular changes related to aging was made in 3-, 12- and 24-month-old rats. The salivary gland weight/body weight ratio and the structural membrane proteins did not change with age for either gland, but a significant age-related decline in DNA synthesis for both glands was detected, unrelated to the hormonal responsiveness at the level of the plasma membrane. There was a marked increase in the concentration of soluble proteins in adolescent parotid gland and, for the two older age groups, in submandibular gland. The saliva flow rate was different when expressed as volume per time, as volume per time and g glandular wet weight, and/or kg body weight. The concentration of secreted proteins was not affected by age in either gland. The total amount of proteins secreted over 30 min revealed no age-related perturbation for the parotid gland, but showed a significant age-related increase in submandibular saliva. Sodium dodecyl sulphate-polyacrylamide gel analysis revealed changes in the protein bands between 39 and 50 kDa in the Coomassie blue-stained gels from 12-month-old animals. Amylase showed an initial increase (12 months), followed by a marked decline in its activity in parotid saliva. The glandular supernatant had low residual cellular amylase activity after stimulation. Therefore, secretory impairment with age after pilocarpine-isoproterenol stimulation was excluded. Analysis of total RNA showed a pronounced decrease of amylase mRNA in the parotid gland between 12 and 24 months of age. No amylase mRNA was expressed in any of the submandibular samples. For epidermal growth factor, total saliva showed a decrease with age. It seemed that the submandibular gland followed the same picture with age as the parotid gland, with a specific decline in the biosynthesis of single secretory proteins.