Effects of induced hypothermia on renal sympathetic nerve activity and baroreceptor reflex in urethane-anesthetized rabbits.
OBJECTIVE
To evaluate the role of the autonomic nervous system in hemodynamic changes during induced hypothermia.


METHODS
Prospective, randomized animal study.


METHODS
An animal research laboratory in a medical university.


METHODS
A total of 29 anesthetized rabbits.


METHODS
Animals were anesthetized by intraperitoneal urethane. After tracheostomy and administration of gallamine, respiration was maintained by mechanical ventilatory support. The animals were divided into five groups (one control and the four experimental groups); animals were treated with an intact neuraxis and normothermia (control group), animals with an intact neuraxis (intact group), cervical vagotomized animals (vagotomy group), the carotid sinus and aortic nerves denervated animals (SAD group), and animals with SAD plus vagotomy (SADV group). The left renal sympathetic nerves were exposed by a retroperitoneal approach.


RESULTS
We examined the effects of surface cooling on HR, mean arterial pressure, central venous pressure, and renal sympathetic nerve activity (RSNA) in the animals. Changes of baroreflex sensitivity and plasma catecholamines were also measured simultaneously. Surface cooling caused progressive and profound decreases in HR in all experimental groups. In all groups, RSNAs increased at the early phase, which were followed by return to the precooling level.


CONCLUSIONS
Hemodynamics and RSNA during induced hypothermia are regulated by mechanisms other than the baroreceptor reflex system, possibly the dermal cold receptors. Suppression of the baroreflex occurred on HR but not on RSNA during hypothermia, which may indicate direct effects of hypothermia on the heart. RSNA responses may be activated earlier than systemic catecholamine responses during induced hypothermia.
Xu
H
H
Department of Anesthesiology, Kagawa Medical University, Japan.
Aibiki
M
M
Seki
K
K
Ogura
S
S
Yokono
S
S
Ogli
K
K
D000320:Adrenergic Fibers / Q000502:physiology*; D018686:Anesthetics, Intravenous; D000818:Animals; D017704:Baroreflex / Q000502:physiology*; D001784:Blood Gas Analysis; D001831:Body Temperature / Q000502:physiology; D002395:Catecholamines / Q000097:blood; D002496:Central Venous Pressure / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007036:Hypothermia, Induced / Q000009:adverse effects* / Q000379:methods; D007668:Kidney / Q000294:innervation*; D011817:Rabbits; D011897:Random Allocation; D013562:Sympathectomy; D014520:Urethane; D014628:Vagotomy
D018686:Anesthetics, Intravenous; D002395:Catecholamines; D014520:Urethane