22. FLUID TRANSPORT IN THE GALLBLADDER

Abstract

This chapter discusses the fluid transport in the gallbladder. Several local mediators affect the rate of gallbladder NaCl and water transport both in vivo and in vitro . Some of these mediators may regulate gallbladder water and electrolyte transfer under physiological conditions by modifying NaCl influx, active Na + extrusion, and/or modifying junctional permeability. Cyclic AMP has been proposed as a second messenger for the effects of several such mediators, and has been found to inhibit NaCl coupled influx, the rate limiting step for transepithelial Na + transport. Prostaglandins E 1 and F 2 have the ability to totally inhibit fluid absorption in the gallbladder and reverse it to net secretion. Fluid secretion in inflamed gallbladders was reversed to net absorption in response to nitric oxide synthase blocker N W -nitro-L-arginine. A number of studies suggest that gallbladder fluid transport across the gallbladder mucosa is subject to physiological regulation. The influence of fasting and feeding on the concentrating function of the gall bladder in primates has also been investigated. During the day fasting animals had a net hourly absorption rate corresponding to one third of the fasting gallbladder volume. Feeding reverses the direction of transport from net absorption to net secretion into the gallbladder lumen.