I NVESTIGATION of the process of salivary secretion in the human being has been complicated by an apparent large variability in the rate of secretion not only as applied to large numbers of individuals but even for a single individual during a relatively short period of collection under seemingly constant conditions."' 2 Recent workers have attempted to control this variability by collecting for study the so-called "resting saliva," that is, saliva secreted by a fasting subject under standardized conditions of rest.2-5 Collection of saliva under such conditions of reduced external stimulation has succeeded only partially in reducing this variability in the rate of salivary flow.The crucial question, on which the cause and possibility of control of variability in secretion rate would seem to hinge, is whether salivary secretion in the human being occurs spontaneously or only in response to nervous or humoral stimulation. If secretion occurs spontaneously, then measurement of the rate of secretion under conditions of rigid control of external stimulation may give a true rate of flow of resting saliva. Individual variations and variability within a group would then have to be accepted as a real characteristic of the secretion process.However, if secretion does not occur spontaneously, then there is no true resting saliva, and the secretion collected under so-called resting conditions results, nonetheless, from stimulation. Variability in secretion rate would then reflect variations in intensity of stimulation, either internal or external, and would be extremely difficult to control. The basic question of whether salivary secretion in the human being occurs spontaneously or only in response to nervous or humoral stimulation has not up to the present time received a full or satisfactory answer based on experimental data. The early observations of Mitscherlich6 and of Zebrowskij made on isolated human subjects with fistular openings of a parotid duct, indicate that no measurable secretion by the parotid gland occurs in the absence of stimulation. The experiments of Lashley,8 which involved collection of the secretion of the parotid glands from normal subjects by the use of parotid cups, reveal that, under all ordinary conditions of rest while in the
Inulin, sodium, potassium and chloride levels were determined on serum and submaxillary, parotid and pancreatic glands of inulin-administered nephrectomized rats. Methods of tissue preparation and analysis were examined in some detail. From data obtained, volumes of inulin and electrolyte distribution were calculated. Volumes of distribution in submaxillary, parotid and pancreatic glands, in that order, were, for inulin, 198 ml/kg, 257 ml/kg and 209 ml/kg; for sodium, 232 ml/kg, 318 ml/kg and 275 ml/kg; and, for chloride, 365 ml/kg, 460 ml/kg and 388 ml/kg. Comparison of these values led to the conclusion that intracellular sodium in these glands is possible and that intracellular chloride is likely. Intracellular potassium seems present in concentration similar to that in mammalian muscle. From electrolyte data and levels of amylase in parotid gland and its secretion, it is speculated that parotid secretion could be formed from a small fraction (approx. 10%) derived from unmodified intracellular fluid to which is then added solution having electrolyte composition of extracellular fluid. The closely isotonic secretion of rat parotid gland can thus be predicted without assuming appreciable reabsorption of electrolytes or water.
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