title: A compartmental analysis of  24 Na kinetics in rat cerebrum, sciatic nerve and cerebrospinal fluid.
abstract: 1. The kinetics of (24)Na exchange in rat cerebrospinal fluid, brain and sciatic nerve were studied during steady-state plasma isotope conditions. The entrance of (24)Na into brain and sciatic nerve was found to fit a three compartmental model. Using newly derived equations for compartmental analysis, the first compartment (24)Na space of brain was found to be about 22% and the second compartment space about 6%; the corresponding sciatic nerve spaces were 26 and 11%, respectively. In the discussion, arguments are presented that suggest that the first compartment is the extracellular space (ECS) and the second compartment is the intracellular space. The t((1/2)) for compartmental equilibration between plasma and brain ECS was 2 hr and from ECS to intracellular space 14 hr; in nerve the respective t((1/2))'s were (2/3) hr and 10 hr.2. A third compartment of 18% was found in sciatic nerve which was interpreted to be anatomically confined to the epi- and perineurium; in brain the corresponding space was 2% and was felt to be anatomically and kinetically an inactive closed compartment in parallel with the blood.3. There were two t((1/2))'s for plasma-c.s.f. (24)Na equilibration of less than 10 min and 2 hr.4. Profiles of brain, from cortex to ventricle, at 6 min, demonstrated a gradient of decreasing (24)Na radioactivity from ventricle to cortex.
mesh_terms: D000818:Animals; D001826:Body Fluids / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D002540:Cerebral Cortex / Q000378:metabolism; D002552:Cerebral Ventricles / Q000378:metabolism; D003238:Connective Tissue / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D010953:Plasma Volume; D051381:Rats; D012584:Sciatic Nerve / Q000378:metabolism*; D012964:Sodium / Q000097:blood / Q000134:cerebrospinal fluid* / Q000378:metabolism*; D012975:Sodium Isotopes
chemical_list: D012975:Sodium Isotopes; D012964:Sodium