Urea and osmotic excretion in rats exposed to chronic centrifugation.
BACKGROUND
A reduction in vasopressin was attributed to the initial diuresis reported in rats exposed to chronic centrifugation. However, it was suggested that urea may also contribute an osmotic component to this observed diuresis.


OBJECTIVE
Increased urea excretion will contribute to osmotic excretion during chronic centrifugation, which may be partly responsible for the initial diuresis previously observed.


METHODS
Eight Sprague-Dawley rats were centrifuged (12 d at -2Gx) and eight were used as a control group. Daily urine samples were collected and an aliquot measured for excreted solutes and aldosterone.


RESULTS
Urine volume was elevated over the first 7 d of centrifugation with a peak on day 4. Urea and osmotic excretion were elevated over the first 5 d. Excreted Na+ was elevated on days 1 and 2, which coincided with an increase in excreted aldosterone over the first 3 d of centrifugation. Urea excretion accounted for up to 54% of the increase in osmotic excretion during the initial portion of centrifugation suggesting that urea was, in part, responsible for the observed increase in urine output despite a reduction in water consumption. Following the first day of centrifugation, aldosterone appears to regulate Na+ as suggested by the reduction in Na+ excretion between days 2 and 3 when aldosterone excretion was elevated.


CONCLUSIONS
It would appear that centrifugation induced an acute increase in protein catabolism as indicated by the increase in urea excretion which resulted in an increase in obligatory water loss. This increased diuresis may have acute consequences on the hydration state of centrifuged rats.
Ortiz
R M
RM
Life Science Division, NASA Ames Research Center Moffett Field, CA, USA. rortiz@mail.arc.nasa.gov
Wang
T J
TJ
Wade
C E
CE
D000450:Aldosterone / Q000097:blood / Q000652:urine; D000818:Animals; D001806:Blood Urea Nitrogen; D015992:Body Mass Index; D002498:Centrifugation / Q000009:adverse effects*; D002908:Chronic Disease; D004195:Disease Models, Animal; D004231:Diuresis / Q000502:physiology*; D008297:Male; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000097:blood / Q000652:urine; D013997:Time Factors; D014508:Urea / Q000652:urine*; D014556:Urine / Q000737:chemistry* / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology*
D000450:Aldosterone; D014508:Urea; D012964:Sodium