In the absence of an ability to absorb fluid by cellular uptake mechanisms, fluid movement in vivo from the perfused rat intestine is absorptive when the diastolic blood pressure is normal or very low but is secretory when blood pressure falls below normal. This pattern of fluid movement is consistent with changes in capillary pressure within the villus. Whether flow moves into or out of the intestine is determined by changes in the Starling forces across intestinal capillaries. These observations indicate that secretion caused by some bacterial enterotoxins may act solely on the vasculature of the small intestine. This contradicts a major current theory of secretion that requires the source of the fluid to be from the epithelial cell. The significance of this work is that the intestinal arterioles rather than the epithelial cells may determine secretion. If substantiated, this may allow the development of the effective anti-secretory drugs that have not been forthcoming with development strategies based on the enterocyte model of deranged intestinal secretion
