Luminal adrenergic agents modulate intestinal transport

Intestinal transport is controlled by luminal solutes, neural pathways, and paracrine or humoral agents. The current study investigated the effect of luminally administered adrenergic agents on the intestinal transport of water and electrolytes. Dogs with 25-cm jejunal Thiry-Vella loops were studied. The loops were luminally perfused with an isotonic solution containing [¹⁴C]PEG, and the fluxes of H₂O, Na⁺, and Cl^- were calculated. Each experiment consisted of three 1-hr periods: basal, luminal agent infusion, and recovery. Luminal adrenergic agents did not alter heart rate. Norepinephrine (α₁ > α₂ and β adrenergic agonist) and phenylephrine (α₁ adrenergic agonist) caused significant absorption of water and sodium. Clonidine (α₂ adrenergic agonist) and isoproterenol (β adrenergic agonist) caused significant secretion of water, sodium, and chloride. Luminally administered adrenergic agents can influence small intestinal water and electrolyte transport. Alpha₁ agonists have a proabsorptive effect, while α₂ and β agonists have a secretory effect. Luminally administered proabsorptive adrenergic agents may prove useful in pathologic secretory states such as diabetic diarrhea, small bowel transplantation, or diarrhea-associated endocrinopathies.