Assessing small intestinal function in health and disease in vivo and in vitro.

Diet, dysfunction and disease induce primary and secondary changes in intestinal structure and function. The major techniques used to assess such changes in human and animal intestinal absorption and secretion in situ, in vivo and in vitro are reviewed concisely but critically and the problems of normalisation of the data explored. Exploitation of the various electrical potential differences generated by and across the intestinal epithelium allows the kinetic characterisation of the electrogenic glucose absorption mechanism, the measurement of functional lactase activity, the assessment of the thickness of the unstirred layer, the estimation of intestinal tonic (diffusive permeability and the recording of electrogenic secretion coupled with motility changes in the jejunum, in situ, of conscious man in health and disease. The use of animal intestine has allowed direct and indirect evidence of multiple hexose carriers to be obtained and a new technique allowing corrected kinetic parameters of Km and Jm to be estimated in vivo. Application of the technique to experimental conditions will allow a better assessment of the adaptive capabilities of the enterocytes absorptive functions.