Hindlimb muscle glucose uptake and metabolism in rats exposed to simulated microgravity.
AuthorStump, Craig Stephan.
Committee ChairTipton, Charles M.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractOver the last 30 years data from manned spaceflight missions have indicated that microgravity affects a number of physiological systems including the skeletal muscles. The purpose of the experiments in this dissertation was to examine the influence of 14 days of simulated microgravity on insulin and exercise stimulated glucose utilization in rat hindlimb muscles. To accomplish this aim, male Sprague-Dawley rats (250-325 g) were suspended in a head down position (SUS) so that one or both hindlimbs were non-weight bearing. The results from hindlimb perfusion experiments indicated that glucose uptake rates for the entire hindquarter at both submaximally and maximally stimulating insulin concentrations were significantly higher (p ≤ 0.05) in the SUS rats (77% and 15%, respectively) than the cage control rats (CC), suggesting increases in insulin sensitivity and responsiveness. Insulin sensitivity for ¹⁴C glucose incorporation into glycogen was also increased for the soleus (SOL), plantaris (PL), and extensor digitorum longus (EDL) muscles in the SUS rats. When the suspended (SUS-E) and control (CC-E) rats were exposed to acute treadmill exercise at 80-90% of VO₂ max, hindlimb glucose uptake and its incorporation into glycogen in the absence of insulin were higher in the PL, EDL, and white gastrocnemius (GW) muscles from the SUS-E rats. However, hindlimb muscle responses to insulin appeared to be impaired after exercise for the SUS-E rats when compared to the CC-E rats, especially in the SOL muscle. To examine the influence of non-weight bearing per se on muscles during simulated microgravity, rats were suspended with the left hindlimb non-weight bearing (NWB) and the right hindlimb bearing 20% of pre-suspension body mass (WB). The results indicated that ³H 2-deoxyglucose uptake was significantly higher for the SOL, PL, EDL and GW muscles (21-80%), at a maximally stimulating insulin concentration, in both SUS-NWB and SUS-WB hindlimbs despite the prevention of SOL and PL muscle mass losses in the SUS-WB hindlimbs. Collectively, the results from this dissertation indicate that the suspension of the rat with hindlimbs non-weight bearing leads to enhanced muscle responses to insulin for glucose uptake and metabolism, and suggest that systemic influences may be involved. In addition, exercise induced glucose and glycogen utilization increase to a greater extent in the hindlimb muscles of suspended rats when compared to their controls; but, there was evidence that muscle responses to insulin were attenuated with exercise in the suspended animals.
Degree ProgramAnimal Physiology