Parotid Salivary Flow and Composition During Infusion of Acetylcholine and Atropine into the Carotid Artery of Conscious Sodium‐Replete Sheep

Abstract

The rate of salivary flow and the concentrations of the major electrolytes in parotid saliva and arterial plasma of conscious sodium-replete sheep were measured during resting salivary secretion and when salivary flow was either increased by intracarotid infusion of acetylcholine at 10-30 nmol. min-' for 20 min or reduced by intracarotid infusion of atropine at 14 nmol. min-' for 50 min. During both treatments salivary phosphate concentration was always negatively correlated with salivary flow and salivary bicarbonate concentration was always positively correlated with flow. The chloride concentration of the saliva during the acetylcholine infusion experiments was positively correlated with salivary flow whereas when atropine was infused the chloride concentration was negatively correlated with flow. Acetylcholine infusion caused the potassium concentration of the saliva to increase significantly resulting in a marked increase in the total rate of loss of potassium in the saliva. The salivary potassium concentration fell significantly at the onset of atropine infusion and then rose progressively so that the potassium concentration was elevated by the end of the infusion. In both treatments the concentrations of sodium and hydrion were negatively correlated with salivary flow rate. The maximum sodium concentration which occurred in the low-flow saliva of the atropine infusion was substantially higher than the concentration that would be achieved by equilibrium with the aqueous phase of arterial plasma. It was concluded that the negative correlation between salivary flow and sodium concentration occurred because the reabsorption of sodium from the saliva by the excurrent duct system was minimal in sodium-replete sheep which would have low levels of mineralocorticoids in the circulation. The inconsistency between this study and previous reports presumably reflects differences in the criteria used to define the sodium status of the animals.During parasympathetic or parasympathomimetic stimulation of most salivary glands the sodium concentration of the saliva usually increases as the rate of flow increases so that over most of the flow range the concentration of sodium is positively correlated with the rate of salivary flow [Gregersen and Ingalls, 1931;Thaysen, Thorn and Schwartz, 1954;Brusilow and Cooke, 1959;Yoshimura, Iwasaki, Nishikawa and Matsumoto, 1959;Mangos and Braun, 1966; Petersen and Poulsen, 1967]. Most observations made on saliva from sheep salivary glands have agreed with this generalization. Coats and Wright [1957] found that after an initial transient fall the sodium concentration of parotid saliva increased as the salivary flow rate rose during electrical stimulation of the parotid nerve of anaesthetized sheep. A similar relation between sodium concentration and salivary flow has also been found in the submaxillary saliva of anaesthetized sheep during stimulation of the submaxillary nerve [Kay, 1960]. A positive correlation between parotid salivary flow and sodium concentration has been reported in...

Salivary Electrolyte Concentrations and Electrical Potential Difference Across the Parotid Salivary Duct of Anaesthetized Sodium-Replete Sheep

“…These changes in salivary electrolyte composition in these anaesthetized sheep are wholly consistent with previous observations on conscious sodium-replete sheep in which rate of salivary flow was altered by ipsilateral intracarotid infusion of acetylcholine (Beal 1979). …”

“…The sodium concentration of parotid saliva from sheep has also been reported to increase with increasing flow rate (Coats and Wright 1957). However, in more recent studies the sodium concentration of parotid saliva was found to be negatively correlated with salivary flow rate in conscious sodium-replete sheep and goats when flow rate was altered by a variety of procedures (Olsson 1976;Beal 1977Beal , 1979. One of the major differences between these studies on sheep saliva is that the sheep were anaesthetized in the earlier studies when the positive correlation was found whereas the animals were conscious during the later studies when a negative correlation was observed.…”

“…(2) Concentration of salivary sodium in sheep was negatively correlated with parotid salivary flow during flow-rate changes caused by acute hyperkalaemia which has been shown to lower activity in the parotid nerve (Beal 1977). (3) Concentration of salivary sodium in sheep was negatively correlated with parotid salivary flow during flow-rate changes caused by ipsilateral intracarotid infusion of atropine (Beal 1979). (4) Concurrent increases in salivary sodium concentration and decreases in parotid salivary flow occurred during low-rate infusion of NaCl into the third ventricle of goats.…”

“…Previous reports have indicated that the relation between salivary flow and chloride concentration tends to be rather unpredictable (Coats and Wright 1957;Kay 1960;Beal 1979). During stimulation of salivary flow rate by acetylcholine infusion, the concentration of chloride fell in five experiments and rose in three.…”

“…The concentrations of sodium, potassium, chloride and total inorganic phosphate and total CO2 content in parotid saliva and in carotid arterial plasma were estimated as described by Beal (1979).…”