Regulation of parotid salivary proteins by glucocorticoids

Previous studies have indicated that adrenal-intact rats treated for one week with pharmacological doses of the synthetic glucocorticoid, dexamethasone, show a significant reduction in the proportion of proline-rich proteins and an increase in the proportion of amylase in rat parotid saliva (Johnson et al., 1987). In order to understand more fully the role of glucocorticoids in the regulation of salivary proteins, we performed bilateral adrenalectomies on groups of rats. Some of the adrenalectomized rats were treated with replacement-level doses of the synthetic glucocorticoid, dexamethasone. The food intake was monitored daily for both groups, and sham-operated pair-fed controls were included so that the effects of alterations of food intake could be separated from those of the experimental procedures. After eight to 12 days, uniformly stimulated parotid saliva was collected from these animals as well as from sham-operated controls fed ad libitum. The volume of saliva collected in 30 min was recorded, and the saliva samples were analyzed for concentration and composition of protein. Although the volume of saliva was not affected, parotid saliva collected from adrenalectomized rats exhibited a two-fold greater proportion of proline-rich proteins and reductions in other major secretory proteins: DNase, Fraction I, and Fraction V. The parotid gland secretory granules of adrenalectomized rats were more electron-lucent than in the ad libitum-fed controls. Treatment of adrenalectomized rats with dexamethasone largely prevented the changes in salivary protein composition as well as the alterations in secretory granule morphology.(ABSTRACT TRUNCATED AT 250 WORDS)