Changes in rat parotid salivary proteins associated with liquid diet-induced gland atrophy and isoproterenol-induced gland enlargement.

The composition of secretory proteins in the parotid saliva of untreated rats, fed a stock pelleted diet (CON), was compared to that of rats maintained on a liquefied diet (LIQ), so as to reduce gland secretory activity, and to rats treated chronically with isoproterenol (ISO), so as to enhance activity. Each experimental treatment resulted in marked changes in protein composition. In CON rats, the basic and acidic proline-rich proteins accounted for 25 per cent of all secretory protein. In LIQ rats, the proportion was 13 per cent. Several basic proline-rich proteins were absent and the major acidic proline-rich protein was markedly reduced. Amylase was reduced whereas DNase and a leucine-rich protein (fraction I) were increased. The proportion of cystine-rich protein (fraction V) was not different from CON rats. The changes observed in the saliva of ISO rats were in marked contrast to these findings. Basic and acidic proline-rich proteins were increased and accounted for 90 per cent of all secretory protein, amylase was responsible for the remaining 10 per cent. Thus the composition of secretory proteins in the parotid saliva of rats can be altered by experimental conditions which affect gland secretory activity. The mechanisms by which these changes occur is not known.