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Role of α 2 ‐adrenoceptors in the sympathetic inhibition of motility reflexes of guinea‐pig ileum
Author(s) -
Stebbing M. J.,
Johnson P. J.,
Vremec M. A.,
Bornstein J. C.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.00465.x
Subject(s) - stimulation , medicine , endocrinology , reflex , biology , idazoxan , inhibitory postsynaptic potential , excitatory postsynaptic potential , motility , prazosin , receptor , antagonist , genetics
1 Sympathetic regulation of the motility of guinea‐pig ileum was investigated using mesenteric nerve (MN) stimulation to inhibit motility reflexes, in vitro . 2 Transmural electrical stimulation (5 Hz, 1 s) in intact intestinal segments, or inflation of a balloon against the mucosa in opened segments, evoked contractions of the circular and longitudinal muscles oral to the stimulus. 3 MN stimulation (10 Hz, 5 s) usually abolished contractions of the longitudinal and circular muscles evoked by either electrical or mechanical stimuli. 4 The inhibition was mimicked by UK14,304 (70‐100 n m ) and abolished by idazoxan (100 n m ), revealing an enhancement of circular muscle contractions. There was no evidence for α 2 ‐receptors on the muscle, suggesting sympathetic inhibition was via the myenteric plexus. 5 Possible sites of action of noradrenaline released from sympathetic nerves were investigated using intracellular recordings from the circular muscle in a multichambered organ bath. 6 When in the stimulation chamber, UK14,304 depressed (by 50 %) excitatory junction potentials (EJPs) recorded oral to a distension stimulus, but did not affect inhibitory junction potentials (IJPs) recorded anal to the stimulus. When added to a chamber between the stimulus and recording chambers, UK14,304 depressed EJPs by 40 %, but did not alter IJPs. When in the recording chamber, UK14,304 depressed EJPs by 20 %, but had no effect on IJPs. IJPs were inhibited, however, when UK14,304 was applied to the whole bath. 7 It is concluded that sympathetic activity inhibits intestinal motility mainly via α 2 ‐adrenoceptors on ascending interneurons and intrinsic sensory neurons of the orally directed reflex pathway.