Parotid protein secretion from the rabbit during feeding

Rabbits were trained to accept a standardized feeding regime. Under anaesthesia both parotid ducts were cannulated in a retrograde direction and saliva was subsequently collected in feeding sessions involving pellets and carrots before and after the administration of propranolol. Salivary total protein and amylase concentrations were assayed and protein analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Propranolol produced a reduction in protein secretion but not fluid secretion, indicating that protein secretion is partly under beta-adrenergic control. A transient increase in protein secretion was seen 8 h after the administration of propranolol and suggested the existence of different neural mechanisms involved in protein secretion compared to synthesis. Protein output (with high fluid secretion) during feeding on pellets was higher than on carrots (with high protein concentration) and suggested a significant role of the parasympathetic nervous system. The pattern of protein secretion as seen by SDS-PAGE was similar in individual rabbits and remained largely unchanged with the different foods and in the presence of propranolol.