Proceedings of The Physiological Society
University of Manchester (2006) Proc Physiol Soc 2, PC32
Lack of evidence in vivo for vagally mediated remote effects of Escherichia coli heat stable (STa) enterotoxin on jejunal fluid absorption
Michael L Lucas1, N W Duncan1, N F O'Reilly1, T J McIlvenny1, Y B Nelson1
1. Division of Neuroscience & Biomedical Systems, Institute of Biological & Medical Science, University of Glasgow, Glasgow, United Kingdom.
Heat stable (STa) enterotoxin from E. coli reduces absorption from the jejunum of the anaesthetised rat. STa is claimed (1) remotely to reduce fluid uptake since ileal perfusion with STa apparently reduces jejunal fluid absorption but not after cervical vagotomy. In view of likely cardiovascular effects of vagotomy on uptake and of reflexes caused by ileal perfusion, remote effects of STa were re-examined. Fluid uptake from jejunal loops was measured in anaesthetised (70 mg/kg i.p. Sagatal) unfasted Sprague Dawley rats (2). Twenty five cm loops were perfused with bicarbonate solution (150 mM). The vagus was intact, or sectioned at the neck or below the diaphragm. Completeness of sub-diaphragmatic section was determined by histology. Adequacy of function of isolated vagi were shown by effects of vagal stimulation on respiration and gastric secretion. Results are expressed as the mean and standard error, with the number of animals given. One loop was used per experiment. Significance was calculated after Dunnet’s correction for multiple comparisons; P < 0.01. Normal absorption experiments were intercalated with the vagotomy series, to confirm the activity of the STa. In these experiments, STA reduced fluid absorption in the jejunum from 81.6 ± 12.0 (8) μl/cm/h to 23.4 ± 4.2 (7) μl/cm/h. Control net jejunal fluid absorption of 79.5 ± 14.0 (7) μl/cm/h did not differ from absorption after cervical vagotomy of 75.6 ± 6.0 (6) μl/cm/h or after abdominal vagotomy of 76.1 ± 6.6 (8) μl/cm/h. The creation and perfusion of ileal loops without STa did nothing to net jejunal fluid absorption. E. coli STa added to ileal loops had no remote effect on jejunal fluid absorption as absorption was 94.4 ± 3.4 (7) μl/cm/h with saline and 89.3 ± 8.4 (6) μl/cm/h when STa (80 ng/ml) was included in the ileal loop. There was therefore no evidence for the remote effect of STa that has been claimed. The lack of a remote effect of STa on fluid movement confirms earlier observations (3) and supports the concept of a lack of vagally mediated fluid secretion being a factor in E. coli STa-mediated alterations in net fluid absorption.
Where applicable, experiments conform with Society ethical requirements