Nonuniformity in the von Bezold-Jarisch reflex.
The von Bezold-Jarisch reflex (BJR) is a vagally mediated chemoreflex from the heart and lungs, causing hypopnea, bradycardia, and inhibition of sympathetic vasomotor tone. However, cardiac sympathetic nerve activity (CSNA) has not been systematically compared with vasomotor activity during the BJR. In 11 urethane-anesthetized (1-1.5 g/kg iv), artificially ventilated rats, we measured CSNA simultaneously with lumbar sympathetic activity (LSNA) while the BJR was evoked by right atrial bolus injections of phenylbiguanide (0.5, 1.0, 1.5, and 2 microg). Nerve and heartbeat responses were analyzed by calculating normalized cumulative sums. LSNA and heartbeats were always reduced by the BJR. An excitatory "rebound" component often followed the inhibition of LSNA but never outweighed it. For CSNA, however, excitation usually (in 7 of 11 rats) outweighed any initial inhibition, such that the net response to phenylbiguanide was excitatory. The differences in net response between LSNA, CSNA, and heartbeats were all significant (P < 0.01). A second experimental series on seven rats showed that methyl atropine (1 mg/kg iv) abolished the bradycardia of the BJR, whereas subsequent bilateral vagotomy substantially reduced LSNA and CSNA responses, both excitatory and inhibitory. These findings show that, during the BJR, 1) CSNA is often excited, 2) there may be coactivation of sympathetic and parasympathetic drives to the heart, 3) divergent responses may be evoked simultaneously in cardiac vagal, cardiac sympathetic, and vasomotor nervous pathways, and 4) those divergent responses are mediated primarily by the vagi.
Salo
Lauren M
LM
Howard Florey Institute, University of Melbourne, Victoria, 3010, Australia.
Woods
Robyn L
RL
Anderson
Colin R
CR
McAllen
Robin M
RM
D000818:Animals; D001286:Atropine Derivatives / Q000494:pharmacology; D001645:Biguanides / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002628:Chemoreceptor Cells / Q000502:physiology*; D006321:Heart / Q000294:innervation / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D008160:Lumbosacral Plexus / Q000502:physiology; D008297:Male; D010276:Parasympatholytics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000502:physiology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000502:physiology*; D014628:Vagotomy; D014630:Vagus Nerve / Q000502:physiology*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
D001286:Atropine Derivatives; D001645:Biguanides; D010276:Parasympatholytics; D017366:Serotonin Receptor Agonists; C006649:methylatropine; C008846:phenyl biguanide