Effect of alpha-methylnorepinephrine, an alpha 2-adrenergic agonist, on jejunal absorption in neurally intact conscious dog.

Although alpha 2-adrenergic agonists stimulate absorption in the mammalian small and large intestine in vitro, the possibility of central neural effects have confounded interpretation of in vivo studies. Our aim was to assess the effects of intravenous administration of alpha-methylnorepinephrine (MNE), an alpha 2-adrenergic agonist that does not cross the blood-brain barrier, on net jejunal absorption of water and electrolytes in the neurally intact, conscious dog. Absorption from a 30-cm proximal jejunal segment was studied using a triple-lumen perfusion technique in seven dogs. A warmed, isosmolar, balanced electrolyte solution containing [14C]polyethylene glycol was infused at 5 ml/min. Net jejunal fluxes of water and electrolytes were determined before, during, and after a 1.5-hr infusion of MNE (900 nmol/kg/hr). MNE increased net jejunal water absorption (from 12.9 +/- 1.8 to 22.5 +/- 1.5 microliters/cm/min, P < 0.05). Peripheral alpha 2-adrenergic receptors mediate a net proabsorptive response in the neurally intact canine jejunum in vivo independent of direct central neural effects.