title: Influence of acute alcohol ingestion on sympathetic neural responses to orthostatic stress in humans.
abstract: Acute alcohol consumption is reported to decrease mean arterial pressure (MAP) during orthostatic challenge, a response that may contribute to alcohol-mediated syncope. Muscle sympathetic nerve activity (MSNA) increases during orthostatic stress to help maintain MAP, yet the effects of alcohol on MSNA responses during orthostatic stress have not been determined. We hypothesized that alcohol ingestion would blunt arterial blood pressure and MSNA responses to lower body negative pressure (LBNP). MAP, MSNA, and heart rate (HR) were recorded during progressive LBNP (-5, -10, -15, -20, -30, and -40 mmHg; 3 min/stage) in 30 subjects (age 24 ± 1 yr). After an initial progressive LBNP (pretreatment), subjects consumed either alcohol (0.8 g ethanol/kg body mass; n = 15) or placebo (n = 15), and progressive LBNP was repeated (posttreatment). Alcohol increased resting HR (59 ± 2 to 65 ± 2 beats/min, P < 0.05), MSNA (13 ± 3 to 19 ± 4 bursts/min, P < 0.05), and MSNA burst latency (1,313 ± 16 to 1,350 ± 17 ms, P < 0.05) compared with placebo (group × treatment interactions, P < 0.05). During progressive LBNP, a pronounced decrease in MAP was observed after alcohol but not placebo (group × time × treatment, P < 0.05). In contrast, MSNA and HR increased during all LBNP protocols, but there were no differences between trials or groups. However, alcohol altered MSNA burst latency response to progressive LBNP. In conclusion, the lack of MSNA adjustment to a larger drop in arterial blood pressure during progressive LBNP, coupled with altered sympathetic burst latency responses, suggests that alcohol blunts MSNA responses to orthostatic stress.
authors.affiliation: Dept. of Exercise Science, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, USA. jcarter@mtu.edu
authors.forename: Jason R
authors.initials: JR
authors.lastname: Carter
authors.forename: Sarah F
authors.initials: SF
authors.lastname: Stream
authors.forename: John J
authors.initials: JJ
authors.lastname: Durocher
authors.forename: Robert A
authors.initials: RA
authors.lastname: Larson
mesh_terms: D001794:Blood Pressure / Q000187:drug effects; D002492:Central Nervous System Depressants / Q000097:blood / Q000494:pharmacology*; D000431:Ethanol / Q000097:blood / Q000494:pharmacology*; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D007024:Hypotension, Orthostatic / Q000503:physiopathology*; D008150:Lower Body Negative Pressure; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation; D012039:Regional Blood Flow / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects*; D014655:Vascular Resistance / Q000187:drug effects; D055815:Young Adult
chemical_list: D002492:Central Nervous System Depressants; D000431:Ethanol