AJP - Gastrointestinal and Liver Physiology, Vol 256, Issue 5 919-G924, Copyright © 1989 by American Physiological Society
Noradrenergic influence on epithelial responses of rabbit ileum to secretagogues
K. A. Hubel, K. S. Renquist and G. Varley
Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242.
Norepinephrine is one of three neurotransmitters that may act directly on
enterocytes to enhance absorption; its interaction with secretagogues is of
physiological importance. We have studied the influence of norepinephrine
on the short-circuit current (Isc) responses to acetylcholine (ACh; 10
microM), vasoactive intestinal polypeptide (VIP; 100 pM-10 nM), peptide
histidine isoleucine (PHI; 100 pM-10 nM), histamine (0.1 mM), and to
electrical field stimulation (EFS) of rabbit ileum mounted in flux
chambers. Tetrodotoxin reduced the response to norepinephrine (10 microM)
by 40% and to histamine by 32% but did not affect responses to VIP or PHI.
Norepinephrine decreased the ACh response (EC50, 70 nM) and reduced the
responses to PHI (less than or equal to 87%), to EFS (less than or equal to
75%), and to histamine (less than or equal to 42%). Norepinephrine
decreased the response to VIP (500 pM) but not to higher or lower VIP
concentrations. It enhanced the response to VIP (10 nM) and to theophylline
(5 mM). We conclude that 1) norepinephrine increases absorption by acting
on nerves and enterocytes; 2) the failure of norepinephrine to reduce the
Isc response to VIP when the VIP-induced increment in Isc is comparable to
that caused by EFS is evidence that VIP does not mediate the EFS response;
3) PHI might mediate the EFS response; and 4) VIP, PHI, and histamine
affect enterocytes directly; histamine also affects intrinsic nerves.
