Premium
Is there diurnal variation with the vestibulosympathetic reflex?
Author(s) -
Cook Jonathan S,
ChinSang Stephanie A,
Sauder Charity L,
Ray Chester A
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.616.5
Subject(s) - evening , melatonin , circadian rhythm , blood pressure , heart rate , medicine , endocrinology , reflex , blood flow , physics , astronomy
We previously observed that exogenous melatonin (3 mg) attenuates the vestibulosympathetic reflex (VSR) in humans (Cook and Ray, Clin Auton Res 19:303, 2009). Because melatonin exhibits a circadian rhythm in humans by increasing at night, it was hypothesized that the VSR would be attenuated at night compared to day. Melatonin typically increases 8–10 times over daytime concentrations during the late evening hours. To test this hypothesis, arterial blood pressure, heart rate, calf blood flow and muscle sympathetic nerve activity (MSNA) were measured in 9 healthy subjects (28 ± 1 yr; 5 male, 4 female) at rest and during head‐down rotation (HDR). Each subject was tested around noon and 10–12 hr later that evening (day: 11:34 ± 13 min, night: 22:10 ± 5 min). Subjects were instructed not to sleep between the two testing sessions. During the day, HDR elicited an increase of Δ 3 ± 1 bursts/min (P < 0.05) from baseline with a significant decrease in calf blood flow (Δ 26 ± 7%; P < 0.05). HDR did not elicit changes in heart rate and arterial blood pressure. Contrary to our hypothesis, MSNA and cardiovascular responses to HDR were not significantly altered at night compared to day (Δ 3 ± 1 bursts/min, Δ 25 ± 6%, for MSNA and calf blood flow, respectively). These findings indicate that there is no diurnal variation in the VSR in humans. Moreover, endogenous increases in melatonin do not appear to modulate the VSR. NIH HL077670, NASA Space Fellowship