AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 4 1102-R1110, Copyright © 1994 by American Physiological Society
Does the spinal cord generate functionally significant sympathetic activity in the awake rat?
K. A. Trostel and J. W. Osborn
Department of Veterinary Biology, University of Minnesota, St. Paul 55108.
Previous studies reach conflicting conclusions regarding the presence of
physiologically significant sympathetic nerve activity (SNA) in conscious
rats with transection of the cervical spinal cord (CST). The objective of
the current study was to determine whether either spinally generated SNA or
nonspecific effects of antagonists are responsible for the natriuresis and
decreased heart rate that accompany adrenergic blockade in CST rats. To
test the first possibility, adrenergic antagonists (phentolamine and
propranolol) were administered to three groups of CST rats: 1) renal
denervated, 2) adrenalectomized or sham-adrenalectomized, and 3) rats who
received the ganglionic blocker hexamethonium. Neither renal denervation,
adrenalectomy, nor ganglionic blockade prevented either the three- to
fivefold increase in sodium excretion or the 25-50 beats/min decrease in
heart rate previously reported. We then administered combinations of
different adrenergic antagonists to CST rats to test for nonspecific
effects of the drugs. Whereas idazoxan+propranolol reproduced the
natriuresis seen with phentolamine+propranolol,
prazosin+yohimbine+propranolol did not. We conclude that there is no
evidence for functionally significant spinally generated SNA in conscious
CST rats and that the natriuresis observed with phentolamine administration
is due to imidazoline binding.
