Fluid hypersecretion induced by enterotoxin STa in nutritionally deprived rats: jejunal and ileal dynamics in vivo

The effect of luminal enterotoxin Escherichia coliSTa on fluid transport across the jejunum and ileum of fed, starved (72 h) and chronically undernourished (50% control food intake for 21 days) rats was assessed in vivo using a gravimetric technique. Dose-response curves for net fluid secretion (stimulated-basal (30 min)-1) activated by 5,50 and 500 ng ml-1 STa were obtained for jejuna and ilea from fed, starved and chronically undernourished rats. Compared to the fed rats, both dietary deprivations showed enhanced net fluid secretion at 500 ng ml-1, but only the jejunum from chronically undernourished rats showed significantly enhanced secretion at 5 and 50 ng ml-1. Net fluid secretory responses to a standard dose of STa (500 ng ml-1) were monitored in the jejuna and ilea of fed, starved and chronically undernourished rats at 30, 60, 90 and 120 min. The pattern in jejuna and ilea from fed rats was very different; the jejunal secretion over 30 min was transient, but ileal secretion increased continuously to a maximum at 120 min. In both jejunum and ileum from starved rats, the secretory response to STa at 30 min was significantly greater than that in fed rats and subsequently remained near this level. In the jejunum from chronically undernourished rats, the net fluid secreted in response to STa was greatly enhanced at 30 and 60 min, but not at 90 min. The ileal response was significantly greater than that in the fed rats at 30 and 120 min. Luminal procaine (10 mM) selectively increased fluid absorptive tone in the jejunum from fed rats, reduced STa-induced fluid secretion in the ileum from undernourished rats, but had no effect on STa in the jejunum from undernourished rats or in the jejunum or ileum from starved rats. Luminal 8-bromo-cyclic GMP (1 mM) had no effect on basal absorptive tone in the jejunum of fed or chronically undernourished rats, but enhanced the secretory tone of jejunum from starved rats. In the ileum, however, while 8-bromo-cyclic GMP enhanced secretory tone in the fed and starved conditions, it still had no action in the chronically undernourished state. The enhanced fluid secretion observed in the jejunum and ileum of the starved and undernourished rats compared to the fed rats supports previous in vitro findings of an increased electrogenic secretion induced by STa in these dietary deprivations. The fluid hypersecretion could be a cause of the increased severity of diarrhoea often observed in undernourished and starved humans.