title: Effects of bed-rest on urea and creatinine: correlation with changes in fat-free mass.
abstract: BACKGROUND
  Bed-rest experiments are designed for investigation on catabolic effects of hypokinetic conditions and/or for microgravity simulation in on-ground aerospace research. Bed-rest effects include a reduction in fat-free mass and muscle mass. Urea and creatinine are catabolites of endogenous protein and of muscular energetic metabolism which are excreted mainly by the kidney. The study investigated on urea, creatinine, and kidney function during bed-rest.
  
  
  METHODS
  Twenty healthy young men underwent a 7-day adaptation period (day-6 to day-0) and a 35-day bed-rest experiment (day1 to day35) during normocaloric diet. Urine were collected from day-3 to day0 (baseline) and from day1 to day35. Blood samples and anthropometrical data were collected at day0 (baseline) and bed-rest days 7, 14, 21, 28, and 35.
  
  
  RESULTS
  Bed-rest reduced plasma volume, weight, fat-free mass, and muscle mass (P<0.001). During bed-rest there was a transient increase in plasma and urinary urea, a decrease in plasma creatinine, and no change in urinary creatinine. The overall integral of changes from day0 to day35 was on average +101.7 mg/dL for plasma urea (95%CI = +43.4/+159.9), +82.2 g/24 h for urinary urea (95%CI = +55.8/+108.7), -2.5 mg/dL for plasma creatinine (95%CI = -3.1/-1.9). Bed-rest reduced plasma cistatyn C also, which was used as mass-independent marker of glomerular filtration rate (-13.1%, P<0.05). Correlations with final reduction in fat-free mass and muscle mass were significant for the overall integral of changes in urinary urea from day0 to day35 (R = 0.706, P<0.001) and for early changes in urinary urea and plasma urea from day0 to day7 (R = 0.566, P = 0.009 and R = 0.715, P<0.001, respectively).
  
  
  CONCLUSIONS
  Study results shows that urea is a marker of catabolic conditions secondary to hypokinetic conditions.
authors.affiliation: Department of Medicine and Surgery, University of Salerno, Baronissi, Italy.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Bilancio
authors.affiliation: Department of Maternity and Pediatrics, Hospital of Benevento, Benevento, Italy.
authors.forename: Cinzia
authors.initials: C
authors.lastname: Lombardi
authors.affiliation: Institute for Kinesiology Research, University of Primorska, Koper, Slovenia.
authors.forename: Rado
authors.initials: R
authors.lastname: Pisot
authors.affiliation: Department of Medicine, Second University of Naples, Naples, Italy.
authors.forename: Natale G
authors.initials: NG
authors.lastname: De Santo
authors.affiliation: Department of Physics, University of Salerno, Fisciano, Italy.
authors.forename: Pierpaolo
authors.initials: P
authors.lastname: Cavallo
authors.affiliation: Department of Medicine and Surgery, University of Salerno, Baronissi, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Cirillo
mesh_terms: D050154:Adiposity; D000886:Anthropometry; D001510:Bed Rest; D003404:Creatinine / Q000097:blood* / Q000652:urine*; D004032:Diet; D004909:Erythrocyte Indices; D006801:Humans; D008297:Male; D014508:Urea / Q000097:blood / Q000652:urine*; D055815:Young Adult
chemical_list: D014508:Urea; D003404:Creatinine