Effects of transmural field stimulation in isolated smooth muscle
of the human rectum and internal anal sphincter .
Glavind, E. B., A. Forman, G. Madsen, A. T[stod]ottrup.
Dept. of Obstetrics and Gynecology, University Hospital of Aarhus
and Surgical Research Unit, Dept. of Surgery L, section
Amtssygehuset, University Hospital of Aarhus, Denmark
APStracts 3:0236G, 1996.
Smooth muscle preparations representing the circular muscle layer of
the most distal rectum, and proximal and distal human internal anal
sphincter (IAS) mounted in organ baths for recording of isometric
tension developed spontaneous tension. Transmural electrical field
stimulation (TMS) induced frequency- and impulse duration- dependent
relaxations, sensitive to tetrodotoxin in the stimulation range 0.5 -
40 Hz and 0.04 - 0.6 ms. Poststimulus contractions were most frequent
and prominent in rectal preparations. Maximal relaxations were
comparable in the three locations and achieved at 10 Hz and 0.4 ms.
The frequency inducing half maximal response (F50 ) was lower in
rectal strips compared to IAS. Phentolamine (10-6 M) enhanced
relaxations and diminished off-contractions at 40 Hz in distal IAS.
Nw-nitro-L-arginine (L-NNA) concentration-dependently inhibited both
relaxations and off-contractions (10 Hz, 0.4 ms). pD2 values of L-NNA
were lower in rectal muscle compared to IAS. L-arginine (10-4 M)
inhibited the blocking effect of L-NNA. In half of the preparations
L-NNA reversed the relaxations to duration-contractions (15 - 40 Hz),
which were inhibited by atropine in rectal preparations and
phentolamine in IAS. In conclusion, the excitatory innervation of the
IAS is [alpha]-adrenergic and cholinergic in the rectum. A product of
the L-arginine-NO pathway mediates the TMS-induced inhibition of the
muscle and is also involved in poststimulus contractions.
Received 30 January 1996; accepted in final form 6 November 1996.
APS Manuscript Number G41-6.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996