EFFECTS ON FLUID AND NA-VIVO( FLUX OF VARYING LUMINAL HYDRAULIC RESISTANCE IN RAT COLON IN)

1. A new method of measuring fluid and ionic movements and the dehydra ting power of the colon in vivo is described. A range of agarose gel c ylinders, with calibrated hydraulic conductivities (L(p)), were insert ed into the lumen of the descending colon of anaesthetized rats. Fluxe s of fluid, Na+ and K+ out of the gels were measured over a period of 60-110 min. 2. Fluid absorption by the colon from 2.5% agarose gels wa s not slower than from solution without gel. Fluid absorption was inhi bited by 66% when the agarose concentration was raised to 10%. In cont rast 2.5% agarose gels caused a 73% (P < 0.001) reduction in water flo w from rat ileum. 3. Increasing gel concentration to 10% or above caus ed the absorbate from the gels to become hypertonic (P < 0.001). 4. Th e measured suction pressure applied by the colonic hypertonic absorbat e to the gels increased from 44 +/- 2.3 cmH(2)O (n=23) with 2.5% agaro se gels to 6713 +/- 960 cmH(2)O (n = 13) with 15% (P < 0.001). 5. Deox ycholate (2 mM) produced a decrease in fluid and Na+ absorption and re duced the suction pressure and power exerted by the colon.