This study tested the role of thyroxine in the regulation of the protein composition of rat parotid saliva. Thyro-parathyroidectomy was performed on two groups of rats, one of which subsequently received thyroxine replacement; the third group was sham-operated. Parotid saliva was collected on the eighth day after surgery, with pilocarpine and isoproterenol used as a secretory stimulus. The volume of saliva collected in 30 min from the thyro-parathyroidectomized rats was 55% less than that collected from sham-operated rats. In the thyro-parathyroidectomized rats, the protein concentration as measured by absorption at 215 nm was unaltered, but that measured by the Lowry procedure was 43% higher. Spectrophotometric scans of Coomassie Blue-stained gels following sodium dodecylsulfate polyacrylamide gel electrophoresis of the secreted proteins showed an18% reduction in the proportion of protein attributable to amylase and a 43% reduction in proportion of acidic and basic proline-rich proteins following thyro-parathyroidectomy ; deoxyribonuclease and two other major secretory proteins (Fraction I and Fraction V) were increased (38%, 20%, and 46%, respectively). These changes in flow rate, protein concentration by the Lowry assay, and protein composition were prevented by treatment of thyro-parathyroidectomized rats with thyroxine replacement and are in opposition to those changes we reported earlier for hyperthyroid rats. The results indicate that the flow of saliva as well as the synthesis of the various salivary proteins are influenced by thyroxine.
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