EFFECT OF ALPHA-METHYLNOREPINEPHRINE, AN ALPHA(2)-ADRENERGIC AGONIST,ON JEJUNAL-ABSORPTION IN NEURALLY INTACT CONSCIOUS DOG

Although alpha2-adrenergic agonists stimulate absorption in the mammal ian small and large intestine in vitro, the possibility of central neu ral effects have confounded interpretation of in vivo studies. Our aim was to assess the effects of intravenous administration of alpha-meth ylnorepinephrine (MNE), an alpha2-adrenergic agonist that does not cro ss the blood-brain barrier, on net jejunal absorption of water and ele ctrolytes 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 so lution containing [C-14]polyethylene glycol was infused at 5 ml/min. N et jejunal fluxes of water and electrolytes were determined before, du ring, and after a 1.5-hr infusion of MNE (900 nmol/kg/hr). MNE increas ed net jejunal water absorption (from 12.9 +/- 1.8 to 22.5 +/- 1.5 mul /cm/min, P < 0.05). Peripheral alpha2-adrenergic receptors mediate a n et proabsorptive response in the neurally intact canine jejunum in viv o independent of direct central neural effects.