Cigarette smoking increases sympathetic outflow in humans.
BACKGROUND
It is generally accepted that smoking increases blood pressure and inhibits muscle sympathetic nerve activity (SNA). The decrease in muscle SNA with cigarette smoking might be secondary to baroreflex responses to the pressor effect of smoking, thus obscuring a sympathetic excitatory effect of smoking. We tested the hypothesis that smoking increases sympathetic outflow.


RESULTS
We examined the effects of sham smoking, cigarette smoking, and cigarette smoking in combination with nitroprusside on muscle (baroreflex-dependent) SNA in 10 healthy habitual smokers. The 3 sessions were performed in random order, each study on a separate day. In an additional study, we also investigated the effects of sham smoking and cigarette smoking on skin (baroreflex-independent) SNA in 9 subjects. Compared with sham smoking, cigarette smoking alone increased blood pressure and decreased muscle SNA. When the blood pressure increase in response to smoking was blunted by nitroprusside infusion, there was a striking increase in muscle SNA. Muscle SNA increased up to 3-fold the levels seen before smoking (P<0.001), accompanied by an increase in heart rate of up to 37+/-4 bpm. Cigarette smoking also induced a 102+/-22% increase in skin SNA (P=0.03).


CONCLUSIONS
These data provide the first direct evidence that cigarette smoking increases sympathetic outflow.
Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242, USA.
K
K
Narkiewicz
P J
PJ
van de Borne
M
M
Hausberg
R L
RL
Cooley
M D
MD
Winniford
D E
DE
Davison
V K
VK
Somers
D000328:Adult; D000959:Antihypertensive Agents / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002496:Central Venous Pressure / Q000187:drug effects / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D009132:Muscles / Q000294:innervation; D009599:Nitroprusside / Q000494:pharmacology; D012867:Skin / Q000294:innervation; D012907:Smoking; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
D000959:Antihypertensive Agents; D009599:Nitroprusside