CHAPTER VIII 

 THE INORGANIC COMPONENTS OF SALIVA 



SECRETION OF WATER 



While the secretion of water is considered in Chapter III in con- 

 nection with the innervation of the salivary glands, it merits more 

 detailed discussion here because it is the most abundant consti- 

 tuent of saliva. When parasympathetic nerve stimulation is com- 

 menced, the saliva flow appears with short latency — usually not 

 more than a second — the secretion rate rapidly reaches a maximum 

 and usually declines slightly to a plateau level and then falls off 

 rather slowly during continued stimulation. (Fig. 8.1 ; Beznak and 

 Farkas, 1937; Maltesos and Weigmann, 1939). The polyphasic 

 curves obtained by Holtzlohner (193 1) appear to be due to the 

 use of unphysiologically high rates of nerve stimulation. In those 

 few salivary glands with an active sympathetic secretomotor inner- 

 vation, the secretion produced by sympathetic stimulation has 

 usually a longer latent period and the rate of flow is less well 

 maintained and rather high stimulation frequencies may be needed 

 to produce any secretion at all. In the case of parasympathetic 

 stimulation, the rate of secretion is nearly linearly related to rate 

 of stimulation in both submaxillary and parotid glands (Fig. 8.2) 

 up to a maximum rate which is reached at 10 c/s in the cat or dog 

 submaxillary and at 20-25 c/s in the dog parotid gland. This 

 maximum rate of secretion seems to be a specific property of the 

 gland. In the presence of eserine or other anticholinesterase drugs 

 the maximum rate is reached at considerably lower rate of stimu- 

 lation but the maximum secretion rate is not itself increased 

 (Beznak and Farkas, 1937; Burgen, Keele and Slome, 1949). The 

 maximum rates of water secretion are, for the dog parotid, 0-35- 

 0-70 ml./g. min; the dog submaxillary 0-8-1-3 ml./g. min; the cat 

 sublingual 0-05 ml./g. min (Burgen, unpublished; Lundberg, 

 1957). The only procedure known to increase the maximum rate 

 of secretion is an increase in plasma potassium (Langley, Gun- 

 thorpe and Beall, 1958; Burgen, unpublished). In dogs from birth 

 onwards, the maximum rate of salivary secretion per unit weight 



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