hide
Free keywords:
Human Salivary Glands; Salivary Cation Excretion; Sodium Reabsorption; Potassium Secretion / Speicheldrüsen des Menschen; Kationenausscheidung; Natriumresorption; Kaliumsekretion
Abstract:
Human saliva was collected separately from the three major salivary glands by catheterization of the main ducts and the effect of secretion rate on salivary Na and K concentrations was studied.
In the resting state, with flow rates of 0.1 to 0.4 ml/min, Na concentration of submandibular and parotid saliva was 2 meq/l and K concentration ∼20 meq/l. Similar data were obtained from the resting sublingual gland.
Following stimulation with pilocarpine salivary Na concentrations rose in all glands in a typical nonlinear fashion, whereas K concentrations declined and reached constant values, which were significantly greater than those of plasma. This result confirms earlier observations in the submandibular and parotid gland of human beings and of various animals and demonstrates unequivocally that the sublingual saliva in man unlike that in cat and dog is poor in Na.
By means of microanalytical methods it was possible to investigate changes in cation concentrations when the salivary flow rates were less than the normal resting values; experiments were also done when salivary flow was stopped completely.
In the submandibular gland Na concentration remained at 1.4 meq/l, whereas K concentrations rose to values of 74 meq/l. K concentrations, however, did not reach a plateau value even after a contact time of 15 min. These results, together with measurements of transepithelial P.D. (reported in the following paper), indicate that Na resorption and probably also K secretion, are governed by active transport mechanisms in the duct epithelium. Thus the main duct epithelium exhibits the properties which are generally taken to be essential for the upper part of the glandular duct system, which forms final saliva from primary secretion.
Similar data were obtained in the upper portion of the parotid duct. In the lower portion of this duct, however, cation concentrations followed a different pattern in showing a tendency to equilibrate with plasma. Such results would be expected if there were no mechanisms for active transport in the lower portion of the main parotid duct.
In order to describe the salivary Na concentration as a function of flow rate a mathematical model was developed. It is based on the assumption that primary secretion is plasmalike and that the hypotonicity of final saliva results from active resorption of sodium in the duct system in accordance with Thaysen's hypothesis. Furthermore the rate of sodium resorption is assumed to be constant and the duct wall is considered impermeable to water. Under conditions of high salivary flow rates there was a good agreement between predicted values and experimental data. This model permits the calculation of the amount of sodium that is actively reabsorbed in the salivary duct system.
