ACUTE EXTRACELLULAR FLUID VOLUME CHANGES INCREASE ILEOCOLONIC RESISTANCE TO SALINE FLOW IN ANESTHETIZED DOGS

We determined the effect of acute extracellular fluid volume changes o n saline flow through 4 gut segments (ileocolonic, ileal, ileocolonic sphincter and proximal colon), perfused at constant pressure in anesth etized dogs. Two different experimental protocols were used: hypervole mia (iv saline infusion, 0.9% NaCl, 20 ml/min, volume up to 5% body we ight) and controlled hemorrhage (up to a 50% drop in mean arterial pre ssure). Mean ileocolonic flow (N = 6) was gradually and significantly decreased during the expansion (17.1%, P<0.05) and expanded (44.9%, P< 0.05) periods while mean ileal flow (N = 7) was significantly decrease d only during the expanded period (38%, P<0.05). Mean colonic flow (N = 7) was decreased during expansion (12%, P<0.05) but returned to cont rol levels during the expanded period. Mean ileocolonic sphincter flow (N = 6) was not significantly modified. Mean ileocolonic flow (N = 10 ) was also decreased after hemorrhage (retracted period) by 17% (P<0.0 5), but saline flow was not modified in the other separate circuits (N = 6, 5 and 4 for ileal, ileocolonic sphincter and colonic groups, res pectively). The expansion effect was blocked by atropine (0.5 mg/kg, i v) both on the ileocolonic (N = 6) and ileal (N = 5) circuits. Acute e xtracellular fluid volume retraction and expansion increased the lower gastrointestinal resistances to saline flow. These effects, which cou ld physiologically decrease the liquid volume being supplied to the co lon, are possible mechanisms activated to acutely balance liquid volum e deficit and excess.