Simulated microgravity produces attenuated baroreflex-mediated pressor, chronotropic, and inotropic responses in mice.
Journal Article
Whether myocardial contractile impairment contributes to orthostatic intolerance (OI) is controversial. Accordingly, we used transient bilateral carotid occlusion (TBCO) to compare the in vivo pressor, chronotropic, and inotropic responses (parts 1 and 2) to open-loop selective carotid baroreceptor unloading in anesthetized mice. In part 3, in vitro myocyte responses to isoproterenol in mice exposed to hindlimb unweighting (HLU) for approximately 2 wk were determined. Heart rate (HR) and mean arterial pressure (MAP) responses to TBCO were measured. In control mice, TBCO increased HR (15 +/- 2 beats/min, P < 0.05) and MAP (17 +/- 2 mmHg, P < 0.05). These responses were markedly potentiated in denervated control (DC) mice, in which the aortic depressor nerve and sympathetic trunk were sectioned before measurement. Baroreflex responses to TBCO were eliminated by blockade with hexamethonium bromide (10 microg/kg). In HLU (denervated) mice, HR and MAP responses were reduced approximately 70% compared with DC mice. In part 2, myocardial contractile responses to TBCO were measured with a left ventricular micromanometer-conductance catheter. TBCO in DC mice increased the slope of the end-systolic pressure-volume relation (end-systolic elastance) by 86 +/- 13%. This inotropic response was attenuated (14 +/- 10%, P < 0.005) after HLU. In part 3, contractile responses to isoproterenol were impaired in myocytes isolated from HLU mice. In conclusion, selective carotid baroreceptor unloading stimulates HR, blood pressure, and myocardial contractility, and HLU attenuates each response. These findings have important implications for the management of OI in astronauts, the elderly, and individuals subjected to prolonged bed rest.
Full Text
Duke Authors
Cited Authors
- Jung, AS; Harrison, R; Lee, KH; Genut, J; Nyhan, D; Brooks-Asplund, EM; Shoukas, AA; Hare, JM; Berkowitz, DE
Published Date
- August 2005
Published In
Volume / Issue
- 289 / 2
Start / End Page
- H600 - H607
PubMed ID
- 15778286
Pubmed Central ID
- 15778286
International Standard Serial Number (ISSN)
- 0363-6135
Digital Object Identifier (DOI)
- 10.1152/ajpheart.01091.2004
Language
- eng
Conference Location
- United States