The effect of norepinephrine on intestinal transport and perfusion pressure in the isolated perfused rabbit ileum

Norepinephrine (NE) is an autonomic neurotransmitter and a potent vasoactive agent, with putative effects on intestinal absorption and secretion. To characterize the effects of NE on intestinal water and ion transport, independent of changes in intestinal blood flow, we studied the effects of three doses of NE (0.1, 0.4, and 2.0 μg/min) on the isolated, vascularly perfused rabbit ileum at a constant vascular perfusion rate. Twenty-centimeter segments of New Zealand white rabbit distal ileum (n = 21) were vascularly perfused at a fixed rate of 1.5 ml/min using a modified Krebs buffer solution (37°C) containing washed human red blood cells with a hematocrit of 15-20%. The intestinal lumen was perfused at 2 ml/min with a warm buffered isotonic electrolyte solution containing 10 μCi[¹⁴C]PEG as a nonabsorbable volume marker. Net fluxes of H₂O, Na⁺, and Cl^- were calculated during 20-min basal, NE infusion, and recovery periods. Perfusion pressure was monitored continuously. NE caused statistically significant graded increases in vascular resistance, as reflected by perfusion pressure, with increasing doses. NE stimulated absorption of H₂O, Na⁺, and Cl^- with a less distinct response to increasing dose. These data suggest that the separate effects of NE on absorption and hemodynamics may be mediated through different pathways or different receptors in the intestine.