[Electrolyte secretion in saliva]

Abstract

Because they are easily accessible and because their secretion can be obtained in an almost pure form, the salivary glands are an adequate model for the study of hydroelectrolytic secretion of secreting epithelia which cannot generate an action potential. It is generally accepted that the salivary secretion occurs in two stages: in the acini, where primary saliva is formed similar in ionic constituents to plasmatic water, and in the ducts of the adenomer, where such original saliva is modified by absorption and secretion of electrolytes. Departing from Thaysen's hypothesis, the mechanisms responsible for the preparation of final saliva are reviewed. The authors briefly discuss the evolution of the ideas about salivary secretion emphasizing recent works which modified early theories, particularly the role of the Na-K ATPase and the cotransportation of the Cl- ion. Ideas about what occurs along the ducts are also reviewed, starting with the hypothesis of Brusilow and Cook, which was later on gradually modified. Recent works are compared to those of the authors. Certain topics, such as the impermeability of duct walls to water, existence of a threshold for the transport of Na+, possibility of experimentally obtaining saliva with higher osmotic pressure than plasma are stressed. Finally, the role of loop diuretics which interfere in potassium transport channels is discussed.