Stoichiometry of neurally-induced vip release, no formation and
relaxation in rabbit and rat gastric muscle.
Jin, J. G., K. S. Murthy, J. R. Grider, and G. M. Makhlouf.
Departments of Medicine and Physiology, Medical College of
Virginia, Richmond, Virginia 23298-0711
APStracts 3:0056G, 1996.
VIP release, NO formation and relaxation induced by nerve stimulation
were examined in rabbit and rat gastric muscle. VIP stimulated NO
formation in muscle strips, while NO stimulated VIP release. Nerve
stimulation (0.025-16 Hz or 2-940 pulses) elicited frequency
-dependent stimulation of VIP release, NO formation, and relaxation,
all significant at 2-3 pulses. L-NNA abolished NO formation,
abolished VIP release and relaxation at low frequencies, and partly
inhibited them at higher frequencies. Oxy-hemoglobin (oxy-Hb)
inhibited VIP release and relaxation by 80% at low frequencies and
20-30% at higher frequencies. VIP10-28 abolished NO formation and
relaxation at lower frequencies and partly inhibited them at higher
frequencies; in contrast, VIP10-28 augmented VIP release in both
species. The pattern of inhibition was similar in both species.
Inhibition of maximal NO formation by VIP10-28 (82% in rabbit; 48% in
rat) implied that a major component of NO is formed in muscle cells
by the action of VIP. Thus, (a) inhibition of relaxation by L-NNA
reflects suppression of NO and VIP release from nerve terminals and
NO formation in muscle cells; (b) inhibition by VIP10-28 partly
reflects suppression of NO formation in muscle cells; and (c)
inhibition by oxy-Hb reflects neutralization of extracellular NO and
suppression of VIP release. The study demonstrates the dual origin of
NO from nerves and muscle and its interplay with VIP in regulating
relaxation.
Received 27 November 1995; accepted in final form 29 February
1996.
APS Manuscript Number G504-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 March 96