Chronically Reserpinized Rat as a Model for Cystic Fibrosis: Na+ Transport Inhibitory Effect in Submaxillary Saliva

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Abstract
Summary: The retrograde perfusion assay in the rat parotid gland was used to investigate the effects of salivary secretions from control and reserpine-treated rats on Na+ reabsorption. Results demonstrated that submaxillary saliva from the treated animals caused a 69% inhibition of Na+ reabsorption, accompanied by a 28% reduction in the volume of saliva secreted, and a 22% reduction in flow rate. By contrast, submaxillary saliva from control rats caused a 6% inhibition of Na+ reabsorption, a 6% reduction in volume, and a 5% reduction in flow rate. Parotid saliva from reserpinetreated rats also inhibited Na+ reabsorption to the extent of 39% and caused a 38% reduction in volume and a 33% reduction in flow. Parotid saliva from control rats only inhibited Na+ reabsorption to the extent of 2.7% and caused a 4-6% reduction in salivary volumes and flow rates. The inhibition of Na+ reabsorption and the reduction in salivary volume and flow rates caused by submaxillary saliva of reserpine-treated rats were either abolished or significantly reduced when the saliva was previously heated to 100°C, frozen, and then thawed or kept in glass tubes at 4°C for 24 hr. These results indicate that saliva from reserpine-treated rats has comparable effects in this assay system to those of saliva from cystic fibrosis (CF) patients and further support its use as an animal model for this disease. Speculation: A similar Na+ transport inhibitory effect to that produced by CF saliva in the parotid retroperfusion assay has been found in submaxillary saliva, and to a lesser extent in parotid saliva, of reserpine-treated rats. This suggests that the same inhibitory component or components are present in both types of secretion.