Intestinal Ioidide Secretion and its Dependence Upon Mucosal I Permeability

Iodide secretion across different regions of rat small inlestine ha.s been investigated in vitro using the standard Wilson- Wisema technique. Net I secretion was observed along the entire small intestine, being significantly higher in the central region. Anaerobic conditions, ouabain {2 mM) and Na• free Ringer solution prevented net I· secretion, whilts, both theophyilline (1 mM) and carbachol {0,1 mM) enhanced the observed basal intestinal I· secretion. Furthermore, Caº'-deprived bathing solutions significantly reduced intestinal 1- secretion. Epithelial 1- uptake from both mucosa) and serosa) sides was measured by using a Ussing-type chamber technique. The initial rate of I·-uptake across the mucosal mem­brane was significantly higher in the central region than in the proximal part of rat small intestine. No significant differences were observed in the rate of I·-uptake from the serosa) side. These studies suggest that mucosa! 1- permeability might determine the direction of net 1- intestinal transport and that cytosolic Caº+ may be a physiological regulator of intestinal 1- transport