Submandibular salivary glands and saliva : an experimental study in male mice on cellular growth

Cells turn over at an enormous rate in man and animals. Man loses 250 g of cells into the intestinal lumen every 24 hours (Leblond and Walker, 1956). The regulatory mechanisms of cellular proliferation have been extensively studied (for reviews see: D011ling and Riecken, 1974; Williamson, 1978a,b). Although many factors are postulated to be of influence, the exact regulatory mechanism is as yet not fully known (Lipkin, 1973; Gospodarowicz and Moran, 1976). Studies of intestinal adaptation are increasingly relevant to modern surgical practice. First of all because recently developed techniques, including hyperalimentation, ensure the survival of many patients with massive enterocolic resections, who would formerly have died from shortage of functioning small bowel. Secondly because of the increasing numbers of enteric bypass procedures performed for morbid obesity or hyperlipidemia. In the third place because different patterns of cell proliferation may be linked with increasing susceptibilities for cancer (Cayama et al., 1978). Factors that seem to play an important role in the regulation of cellular growth are of humoral, neural and luminal origin. There is considerable evidence that luminal factors play a dominant role in this regulation (Li et al., 1979). Of these luminal factors food, pancreaticobiliary secretions and gastric secretions have been studied most, and all of these factors seem to have an influence on intestinal adaptation (Weser et al., 1977; l~illiamson, 1978a,b). Compensatory gut proliferation still occurs without gastric juice (Hughes et al., 1976; Tilson and Axtmayer, 1976; Dembrinski and Johnson, 1979) or pancreaticobiliary secretions (Shelitto et al., 1978). On the other hand, small bowel deprived of intraluminal food, no longer maintains its normal resorptive function and morphology, and causes decreased cell proliferation (Gleeson et al., 1972). This can be completely reversed by restoring intestinal continuity. Therefore, other intraluminal factors seem to be important as well, and could be produced more proximal in the gastrointestinal tract than duodenum or stomach. The hypothesis that a factor that regulates cell proliferation is secreted in saliva, is consistent with these observations.