AJP - Heart and Circulatory Physiology, Vol 258, Issue 3 778-H786, Copyright © 1990 by American Physiological Society
Sensory nerves mediate neurogenic escape in rat gut
G. Remak, O. D. Hottenstein and E. D. Jacobson
Department of Medicine, University of Colorado School of Medicine, Denver 80262.
We investigated the involvement of primary sensory nerves in intestinal
autoregulatory escape induced by postganglionic nerve stimulation (NS) in
anesthetized rats. Anterior mesenteric artery (AMA) blood flow velocity
(BF) was measured with a pulsed Doppler flowmeter. Periarterial NS elicited
an abrupt fall in BF, which was followed by a recovery in BF toward the
basal value, despite sustained NS. This recovery from NS constituted the
neurogenic escape phenomenon. Vasoconstrictor responses to NS were
abolished by periarterial application of tetrodotoxin. Acute, surgical
interruption of proximal periarterial nerves had no effect on BF responses
to distal NS, suggesting a peripheral rather than a central nervous
mechanism for the escape phenomenon. Escape from NS-induced
vasoconstriction was significantly inhibited by prior administration of the
selective sensory neurotoxin capsaicin as either subcutaneous injection in
neonatal life, acute application to periarterial nerves, or acute injection
into the jejunal lumen. In rats pretreated 24 h with reserpine, NS provoked
a vasodilator response that was inhibited by intrajejunal capsaicin.
Increases in arterial blood pressure (BP) and heart rate observed during NS
were blocked by periarterial (but not intrajejunal) application of
capsaicin. Transmural electrical field stimulation elicited significantly
greater nerve-induced contractions in AMA rings from control rats. Our
findings support the hypothesis that postganglionic NS activates both
vasoconstrictor sympathetic nerve branches and vasodilator afferent
C-fibers. The latter nerves release vasodilator peptides in the periphery
during continuous low frequency NS that appear to be essential for
autoregulatory escaped in our model.
