Hypercapnia selectively attenuates the somato-sympathetic reflex.
The effects of hyperoxic hypercapnia (5, 10 or 15% CO2 in O2) on splanchnic sympathetic nerve activity (sSNA) and sympathetic reflexes such as the somato-sympathetic reflex or baroreflex were studied in urethane anaesthetised, paralysed, artificially ventilated and vagotomized Sprague-Dawley rats. Hypercapnia caused a small increase in mean arterial blood pressure (MAP) in the 10% CO2 group and a fall in heart rate (HR) in all three groups. sSNA increased in all three groups. Phrenic frequency and amplitude increased during hypercapnia, with frequency adapting back towards baseline during the CO2 exposure. The somato-sympathetic reflex was attenuated in the 5% CO2 group and abolished in the 10 and 15% CO2 groups, whereas there was little effect on the sSNA baroreflex. Hypercapnia significantly affects phrenic nerve activity (PNA), sSNA and selectively inhibits the somato-sympathetic reflex with little effect on the sSNA baroreflex.
Makeham
John M
JM
Department of Physiology, Hypertension and Stroke Research Laboratory, University of Sydney, NSW, Australia.
Goodchild
A K
AK
Costin
N S
NS
Pilowsky
Paul M
PM
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D017704:Baroreflex / Q000502:physiology*; D001784:Blood Gas Analysis / Q000379:methods; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000379:methods; D004594:Electrophysiology / Q000379:methods; D006339:Heart Rate / Q000187:drug effects; D006935:Hypercapnia / Q000503:physiopathology*; D008297:Male; D010791:Phrenic Nerve / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D012018:Reflex / Q000187:drug effects*; D013153:Splanchnic Nerves / Q000187:drug effects* / Q000502:physiology; D013997:Time Factors; D014628:Vagotomy / Q000379:methods
D002245:Carbon Dioxide