title: Impaired endothelin-1 release in tilt-induced syncope.
abstract: The neurohumoral events associated with neurocardiogenic syncope remain unclear. The simultaneous assessment of changes in endothelium-dependent and independent hormones and in autonomic balance in patients with tilt-induced syncope has been incompletely studied. Forty-six healthy subjects aged between 21 and 83 years (mean +/- SEM 47 +/- 3) underwent a 30-minute head-up tilt test at 60 degrees. Fourteen subjects (10 females and 4 male subjects) exhibited syncope at 16 +/- 2 minutes into the tilt. Hemodynamics were recorded every 5 minutes and blood samples for the measure of catecholamines, endothelin-1 (ET-1), and angiotensin-II (AT-II), were drawn at baseline, and 5, 10, 15, and 30 minutes into the tilt and immediately before syncope. Heart rate variability was analyzed by 5-minute segments during the test. Both catecholamines and ET-1 levels increased consistently in response to head-up tilt in subjects able to tolerate the test. Epinephrine increased to a greater extent before syncope. In contrast, ET-1 failed to increase at any time during the tilt and just before syncope. AT-II increased at 30 minutes into the tilt only in the control group. Finally, power in high-frequency bands decreased less in the group with syncope. Thus, compared with subjects able to tolerate a head-up tilt test, patients with syncope exhibit a greater increase in adrenomedullary activation, no significant increase in ET-1 levels, and a blunting in the decrease of vagal tone before syncope. The lack of increase in ET-1 during tilt may play a role in the inability to support orthostatic stress.
authors.affiliation: Department of Medicine, Montreal Heart Institute, Quebec, Canada.
authors.forename: M
authors.initials: M
authors.lastname: White
authors.forename: P
authors.initials: P
authors.lastname: Cernacek
authors.forename: M
authors.initials: M
authors.lastname: Courtemanche
authors.forename: D
authors.initials: D
authors.lastname: Stewart
authors.forename: M
authors.initials: M
authors.lastname: Talajic
authors.forename: E
authors.initials: E
authors.lastname: Mikes
authors.forename: P
authors.initials: P
authors.lastname: Vantrimpont
authors.forename: L
authors.initials: L
authors.lastname: Bussières
authors.forename: J L
authors.initials: JL
authors.lastname: Rouleau
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000804:Angiotensin II / Q000097:blood; D002395:Catecholamines / Q000097:blood; D019332:Endothelin-1 / Q000097:blood*; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D012815:Signal Processing, Computer-Assisted; D013575:Syncope / Q000097:blood* / Q000209:etiology / Q000503:physiopathology; D018667:Tilt-Table Test
chemical_list: D002395:Catecholamines; D019332:Endothelin-1; D000804:Angiotensin II