title: Influences of chemical sympathectomy and simulated weightlessness on male and female rats.
abstract: Maximum oxygen consumption (VO2max) has been shown to be reduced after periods of simulated weightlessness. To assess the role of the sympathetic nervous system in these reductions, Sprague-Dawley rats were either chemically sympathectomized (SYMX) or injected with saline (SHAM) and assigned to head-down suspension (HDS), horizontal restraint with the hindlimbs weight bearing (HWB), or cage-control (CC) conditions. VO2max, run time (RT), and mechanical efficiency (ME) were measured before suspension and on days 7 and 14. Male and female SHAM HDS groups exhibited reduced measures of VO2max (12-13%) after 7 and 14 days, and this decrease was attenuated in the SYMX and HWB rats. HDS resulted in a significant reduction in RT (9-15%) in both the male and female rats, and ME was significantly reduced after HDS in male and female SYMX and male SHAM rats (23-33%) but not in the female SHAM rats. Lesser reductions in ME were observed in the HWB rats. HDS and HWB were associated with lower body, fat-free, and fat masses, which were similar in male and female rats as well as for the SHAM and SYMX conditions. In a related HDS experiment with normal rats, plasma norepinephrine and epinephrine were increased by 53 and 42% after 7 days, but only epinephrine returned to baseline after 14 days. It was concluded that chemical sympathectomy and/or a weight-bearing stimulus will attenuate the loss in VO2max associated with simulated weightlessness in rats despite similar changes in body mass and composition. The mechanism(s) remains unclear at this time.
authors.affiliation: Department of Exercise and Sport Sciences, School of Health Related Professions, University of Arizona, Tucson 85721.
authors.forename: C R
authors.initials: CR
authors.lastname: Woodman
authors.forename: C S
authors.initials: CS
authors.lastname: Stump
authors.forename: J A
authors.initials: JA
authors.lastname: Stump
authors.forename: L A
authors.initials: LA
authors.lastname: Sebastian
authors.forename: Z
authors.initials: Z
authors.lastname: Rahman
authors.forename: C M
authors.initials: CM
authors.lastname: Tipton
mesh_terms: D000311:Adrenal Glands / Q000502:physiology; D000818:Animals; D001823:Body Composition / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D002395:Catecholamines / Q000097:blood; D004326:Drinking / Q000502:physiology; D004435:Eating / Q000502:physiology; D005260:Female; D006145:Guanethidine / Q000494:pharmacology; D006321:Heart / Q000502:physiology; D008297:Male; D009132:Muscles / Q000502:physiology; D009929:Organ Size / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012149:Restraint, Physical; D012737:Sex Factors; D013563:Sympathectomy, Chemical; D013564:Sympathetic Nervous System / Q000502:physiology*; D014893:Weightlessness / Q000009:adverse effects*
chemical_list: D002395:Catecholamines; D006145:Guanethidine