The Role of gastrointestinal peptides in regulating gallbladder transport function

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The transport of fluid and electrolytes across mammalian and amphibian gallbladder has been studied extensively as the gallbladder mucosa concentrates hepatic bile 8-10 fold yet bile remains isotonic to plasma. There is a net absorption of NaCl and NaHCO3 , whereas organic components like bile salts are retained against high concentration gradients. Active transport of Na+ and er is essential to the normal concentrating function of the gallbladder. The concentrated bile in this organ provides biological detergents for fat absorption in the duodenum and changes the physicochemical properties predisposing to nucleation of cholesterol from bile and hence gallstone formation. NaCl is believed to be absorbed by electroneutral coupled cotransport; Na+ is extruded across the basolateral membrane by the sodium pump (Na+-??-ATPase). An alternative double-exchange mechanism has been postulated (Na+ /H+ and c1· /HCO3 ·). Water movement is passive, following the osmotic gradients established by active electrolyte absorption. The normal regulation of Na+ and fluid absorption is poorly understood. Two candidate gut peptides were examined: secretin, which stimulates ductular bile flow in dogs, and VIP, which is thought to mediate secretion in cholecystitis. Both peptides act through cAMP. The Ussing chamber technique was used to assess transport in the gallbladder of the guinea pig. Using 22Na+ , sodium transport and short-circuit current (lsc) were measured and results plotted as a function of log doses of each peptide. The unstirred water layer, an important barrier to transport, was also quantitated.
Bibliography: p. 82-90.
Koziol, K. A. (1989). The Role of gastrointestinal peptides in regulating gallbladder transport function (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/19875