Acute extracellular fluid volume changes increase ileocolonic resistancce to saline flow in anesthetized dogs

ABSTRACT

We determined the effect of acute extracellular fluid volume changes on saline flow through 4 gut segments (ileocolonic, ileal, ileocolonic sphincter and proximal colon), perfused at constant pressure in anesthetized dogs. Two different experimental protocols were used: hypervolemia (iv saline infusion, 0.9 per cent NaCl, 20 ml/min, volume up to 5 per cent body weight) and controlled hemorrhage (up to a 50 per cent drop in mean arterial pressure). Mean ileocolonic flow (N = 6) was gradually and significantly decreased during the expansion (17.1 per cent P<0.05) and expanded (44.9 per cent, P<0.05) periods while mean ileal flow (N = 7) was significantly decreased only during the expanded period (38 per cent, P<0.05). Mean colonic flow (N = 7) was decreased during expansion (12 per cent, P<0.05) but returned to control levels during the expanded period. Mean ileocolonic sphincter flow (N = 6) was not significantly modified. Mean ielocolonic flow (n = 10) was also decreased after hemorhage (retracted period) by 17 per cent (P<0.05), but saline flow was not modified in the other separate circuitis (N = 6,5 and 4 for ileal, ileocolonic sphincter and colonic groups, respectively). The expansion effect was blocked by atropine (0.5 mg/kg, iv) both on the ileocolonic (N = 6) and ileal (N = 5) circuits. Acute extracellular fluid volume retraction and expansion increased the lower gastrointestinal resistances to saline flow. These effects, which could physiologically decrease the liquid volume being supplied to the colon, are possible mechanisms activated to acutely balance liquid volume deficit and excess.