Functional significance of histologic alterations induced by Escherichia coli pig-specific, mouse-negative, heat-stable enterotoxin (ST_b)

Abstract

In contrast to cholera enterotoxin and other Escherichia coli enterotoxins, a pig-specific, heat-stable E. coli enterotoxin (ST_b) causes morphologic lesions (loss of villous epithelial cells and partial villous atrophy). These lesions reflect a loss of absorptive cells and thus suggest that ST_b causes impaired absorption as well as inducing net secretion. The present studies assess functional significance of morphologic changes induced by ST_b. Net fluid movement, mucosal surface area, sucrase activity and the electrical response induced by alanine were measured in swine jejunal loops exposed to E. coli culture filtrates with and without ST_b. Net fluid secretion (-11.1±1.1 ml) occurred in some ST_b loops (secretors) and net absorption (2.7±0.3 ml) in others (nonsecretors), but net absorption occurred in all control loops (4.9±0.2 ml). The mucosal surface area of St_b loops was about 20% less than that of controls (P<0.01). Sucrase activity was also lower (about 15%) in ST_b loops than in control loops (P<0.01). The electrical response induced by alanine in mucosa from nonsecreting ST_b loops did not differ from that induced in mucosa from control loops. However, the response to alanine in mucosa from secreting ST_b loops was reduced about 70% from that in mucosa from nonsecreting ST_b loops or from control loops (P<0.05). It is concluded that reduced sucrase activity is a functional correlate to villous atrophy induced by ST_b, that ST_b impairs alanine absorption in some loops (secretors), and that the impaired alanine absorption is independent of the decreased surface area caused by St_b. Because the impaired alanine absorption occurred independent of the decreases in surface area, it is suggested that the secretory response to ST_b is associated with an impairment of active absorption of alanine.