Salt-loading and simulated microgravity on baroreflex responsiveness in rats.
Cardiovascular adaptations observed during exposure to microgravity results in impairment of baroreflex activity partially as a result of fluid and electrolyte shifts. The head-down tilt rat model mimics some of the physiological observations that have been made in astronauts. We examined the effects of salt-loading on baroreflex activity after 7 day simulated microgravity (30 degrees tail-suspension) and the subsequent 6 hr post-suspension in Sprague-Dawley (SD) rats, using low salt (0.3% NaCl) and high salt (8% NaCl) diets. In suspended animals on a low salt diet, the baroreflex response curve was shifted to the left, while the heart rate (HR) range and MAP50 values were reduced compared to their parallel tethered, non-suspended controls. For non-suspended animals, salt-loading shifted the curve to the right with a reduced HR range. In salt-loaded, suspended animals, the curve and its parameters resemble those of non-suspended animals on a low salt diet. In summary, these data have demonstrated that a short-term (seven days) simulated weightlessness may elicit cardiovascular deconditioning in rats after release from the simulation manifested as an altered responsiveness in baroreceptor-heart rate reflex and a lowered blood pressure while the rats are tethered and horizontal. Our results also suggest the counteracting effect of salt loading on cardiovascular deconditioning.
Department of Pharmacology/Toxicology, Morehouse School of Medicine, Atlanta, GA, USA. bayorh@msm.edu
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Bayorh
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Socci
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Wang
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Emmett
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Thierry-Palmer
D000818:Animals; D017704:Baroreflex / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D018493:Cardiovascular Deconditioning / Q000187:drug effects* / Q000502:physiology; D004039:Diet, Sodium-Restricted; D004305:Dose-Response Relationship, Drug; D018475:Head-Down Tilt; D019417:Hindlimb Suspension; D008297:Male; D023421:Models, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley; D012982:Sodium, Dietary / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D018544:Weightlessness Countermeasures; D018474:Weightlessness Simulation
D012982:Sodium, Dietary