Journal
CLINICAL AUTONOMIC RESEARCH
Volume 17, Issue 3, Pages 186-192Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s10286-007-0417-0
Keywords
dramamine; baroreflex; vestibulosympathethetic reflex; sympathetic activity
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Funding
- NCI NIH HHS [CA00404] Funding Source: Medline
- NCRR NIH HHS [M01 RR10732, C06 RR016499] Funding Source: Medline
- NHLBI NIH HHS [P01 HL077670] Funding Source: Medline
- NIDCD NIH HHS [DC006549] Funding Source: Medline
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The purpose of this study was to examine the effect of dimenhydrinate on resting muscle sympathetic nerve activity (MSNA), the vestibulosympathetic reflex, and the baroreflexes. Sixteen subjects participated in two double-blinded studies that measured mean arterial pressure (MAP), heart rate (HR), and MSNA responses before and after oral administration of dimenhydrinate (100 mg) or a placebo. In study one, 3 min of head-down rotation (HDR) was performed to engage the otolith organs. Dimenhydrinate (n = 10) did not alter resting MSNA, MAP, or HR. HDR increased MSNA before (Delta 5 +/- 1 bursts/min; P < 0.01) and after (Delta 4 +/- 1 bursts/min; P < 0.01) drug administration, but these responses were not different from the placebo (n = 6). In study two, 4 min of lower body negative pressure (LBNP) at -30 mmHg was performed. During the third min of LBNP, HDR was performed. MSNA increased during the first 2 min of LBNP before (Delta 13 +/- 2 bursts/min; P < 0.01) and after (Delta 14 +/- 2 bursts/min; P < 0.01) dimenhydrinate. HDR combined with LBNP increased MSNA further during the third min of LBNP (Delta 18 +/- 2 bursts/min before and Delta 17 +/- 2 bursts/min after dimenhydrinate; P < 0.01). These responses were not significantly different from the placebo. In contrast, HR responses to LBNP during the dimenhydrinate trial were increased when compared to all other trials (Delta 5 +/- 1 beats/min; P < 0.01). These results indicate that dimenhydrinate augments heart rate responses to baroreceptor unloading, but does not alter resting MSNA, the sympathetic baroreflexes, or the vestibulosympathetic reflex.
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