Luminal adrenergic agonists modulate ileal transport by a local mechanism.
Intestinal transport is controlled by neural pathways, hormones, and luminal agents. Luminal adrenergic agents influence water and ion transport in the jejunum. This study tested two hypotheses: (i) luminal adrenergic agents influence ileal water, ion and glucose transport, and (ii) luminal adrenergic agents exert their effects locally and selectively. Absorption studies (n = 46) were performed on dogs with two adjacent 25-cm ileal Thiry-Vella fistulas (TVF). Perfusion with [14C]polyethylene glycol was used to calculate absorption of water, ions, and glucose from the distal TVF. Experiments were composed of three 1-hr periods: basal, luminal adrenergic agonist infusion, and recovery. In group 1 the adrenergic agonists were administered to the distal TVF: norepinephrine (alpha 1 > alpha 2 and beta), phenylephrine (alpha 1), clonidine (alpha 2), and isoproterenol (beta). In group 2 the adrenergic agonists were administered to the proximal TVF, with absorption measured in the distal TVF. In group 1 norepinephrine and phenylephrine caused a significant increase in water absorption (P < 0.05). Clonidine and isoproterenol caused decreased absorption of water and ions, with clonidine causing significantly decreased absorption (P < 0.05) of water, ions, and glucose. In group 2 there were no changes in distal TVF absorption. Luminal adrenergic agents did not alter the heart rate in either group. Luminal adrenergic agonists modulate ileal transport via a local mechanism. A proabsorptive response is observed with alpha 1 agonists, while alpha 2 and beta agonists cause a prosecretory effect. Inhibition of glucose absorption appears to be selectively mediated via the alpha 2-adrenergic receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
Barry
M K
MK
Department of Surgery, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287-4606.
Aloisi
J D
JD
Yeo
C J
CJ
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002395:Catecholamines / Q000097:blood; D003000:Clonidine / Q000494:pharmacology; D004285:Dogs; D005260:Female; D007082:Ileum / Q000378:metabolism*; D007408:Intestinal Absorption / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D013566:Sympathomimetics / Q000494:pharmacology*
D002395:Catecholamines; D013566:Sympathomimetics; D007545:Isoproterenol; D003000:Clonidine; D009638:Norepinephrine