Simulated microgravity produces attenuated baroreflex-mediated pressor, chronotropic, and inotropic responses in mice
| Autor: | Jordan Genut, E. M. Brooks-Asplund, Daniel Nyhan, Joshua M. Hare, Kwang H. Lee, Albert S. Jung, Artin A. Shoukas, Robert W. Harrison, Dan E. Berkowitz |
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| Rok vydání: | 2005 |
| Předmět: |
Inotrope
Chronotropic medicine.medical_specialty Cardiotonic Agents Physiology Orthostatic intolerance Blood Pressure Hindlimb Baroreflex Mice In vivo Heart Rate Physiology (medical) Internal medicine medicine Animals Carotid Stenosis Myocytes Cardiac Cardiovascular Deconditioning Weightlessness Simulation business.industry Isoproterenol medicine.disease Myocardial Contraction Mice Inbred C57BL Anesthesia Circulatory system Cardiology Cardiology and Cardiovascular Medicine business |
| Zdroj: | American journal of physiology. Heart and circulatory physiology. 289(2) |
| ISSN: | 0363-6135 |
| Popis: | 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 ∼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 μg/kg). In HLU (denervated) mice, HR and MAP responses were reduced ∼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. |
| Databáze: | OpenAIRE |
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