title: Rats exhibit aldosterone-dependent sodium appetite during 24 h hindlimb unloading.
abstract: Hindlimb unloading (HU) is an animal model of microgravity and bed rest. In these studies, we examined the role of ingestive behaviours in regulating body fluid balance during 24 h HU. In the first experiment, all rats were given distilled water to drink while two groups were also given access to a sodium chloride solution (0.9% or 1.8%). Water and saline intakes were measured before, during and after 24 h of HU. Rats reduced water intake during 24 h HU in all conditions. During HU, rats increased their intakes of both saline solutions (0.9% NaCl (n= 11): control 7.8 +/- 3 ml; HU 18.2 +/- 4 ml; recovery 8.9 +/- 2.5 ml; 1.8% NaCl (n= 7): control 1.0 +/- 0.4 ml; HU 3.8 +/- 0.3 ml; recovery 1.2 +/- 0.5 ml). Although water intake decreased there was no reduction in total fluid intake when saline was available. Plasma volumes were reduced during HU compared to rats in a normal posture when only water was available to drink (control (n= 11) versus HU (n= 11): 4.0 +/- 0.2 versus 3.4 +/- 0.2 ml (100 g body weight)(-1)). When 0.9% saline was available in addition to water, plasma volumes after 24 h HU were not different from rats in a normal posture (control (n= 11) versus HU (n= 12): 4.3 +/- 0.4 versus 4.3 +/- 0.1 ml (100 g body weight)(-1)). Plasma aldosterone but not plasma renin activity was significantly elevated after 24 h HU. Central infusions of spironolactone blocked the increased intake of 1.8% saline that was associated with 24 h HU. Thus, HU results in an aldosterone-dependent sodium appetite and the ingestion of sodium may help maintain plasma volume.
authors.affiliation: Department of Physiology, University of Missouri, Clumbia, MO, USA.
authors.forename: Margaret J
authors.initials: MJ
authors.lastname: Sullivan
authors.forename: Eileen M
authors.initials: EM
authors.lastname: Hasser
authors.forename: Julia A
authors.initials: JA
authors.lastname: Moffitt
authors.forename: Stacy B
authors.initials: SB
authors.lastname: Bruno
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Cunningham
mesh_terms: D000450:Aldosterone / Q000097:blood*; D000818:Animals; D001066:Appetite; D001522:Behavior, Animal; D004326:Drinking; D005070:Evans Blue / Q000032:analysis; D019417:Hindlimb Suspension / Q000502:physiology*; D008297:Male; D000451:Mineralocorticoid Receptor Antagonists / Q000008:administration & dosage; D010953:Plasma Volume / Q000187:drug effects; D011189:Potassium Chloride / Q000008:administration & dosage*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012083:Renin / Q000097:blood; D012965:Sodium Chloride / Q000008:administration & dosage*; D012982:Sodium, Dietary / Q000494:pharmacology; D013148:Spironolactone / Q000008:administration & dosage; D013997:Time Factors
chemical_list: D000451:Mineralocorticoid Receptor Antagonists; D012982:Sodium, Dietary; D013148:Spironolactone; D012965:Sodium Chloride; D005070:Evans Blue; D000450:Aldosterone; D011189:Potassium Chloride; D012083:Renin