Journal
JOURNAL OF PHYSIOLOGY-LONDON
Volume 557, Issue 2, Pages 661-670Publisher
WILEY
DOI: 10.1113/jphysiol.2004.062265
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Funding
- NHLBI NIH HHS [R01 HL062579, K02 HL03620, R01 HL55306, R01 HL055306] Funding Source: Medline
- NIDDK NIH HHS [R01 DK057822, R01 DK57822] Funding Source: Medline
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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.
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