Micropuncture study of sodium and potassium excretion in the rat parotid saliva

Having demonstrated that the rat parotid gland is able to excrete a hypotonic saliva, we studied the formation of saliva in the different segments of the duct system, through micropuncture and microanalytical techniques. The duct system of the gland is composed of three functionally different segments, acini-intercalated ducts, striated ducts and excretory ducts. a) Acini-intercalated ducts secrete a primary fluid with plasma-like osmolality and sodium and potassium concentration. b) Striated ducts modify the primary fluid by active reabsorption of sodium in excess of water, thus producing hypotonicity. c) Excretory ducts serve as conduits of the saliva to the mouth. A process of reequilibration of the duct fluid to isotonicity occurs in the excretory ducts of the resting gland. Secretion of small amounts of potassium also appears to take place in these ducts.