Effects of Bed-Rest on Urea and Creatinine: Correlation with Changes in Fat-Free Mass

Abstract

BackgroundBed-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.MethodsTwenty 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.ResultsBed-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).ConclusionsStudy results shows that urea is a marker of catabolic conditions secondary to hypokinetic conditions.

Whole-body net protein balance plateaus in response to increasing protein intakes during post-exercise recovery in adults and adolescents

“…Urinary urea and creatinine excretion was determined by enzymatic assay according to manufacturer’s instructions (BioAssay Systems, QuantiChrom DIUR-100, DICT-500, Hayward, CA). Amino acid deamination and oxidization is reflected by an increase in urinary urea production [ 15 ] and urinary creatinine excretion is related to FFM [ 31 ]. Thus, the ratio of urea/creatinine was used herein as an estimate of total amino acid oxidation.…”

Hemolysis during and after 21 days of head-down-tilt bed rest

“…Head-down-tilt (HDT) bed rest has been used to mimic some adaptive and recovery effects of microgravity (Hargens et al 2013). HDT bed rest induces a shift in body fluids which decreases intravascular plasma volume and concentrates erythrocytes (Hargens et al 2013;Bilancio et al 2014;Otto et al 2017). The adaptive response to this hemoconcentration involves the loss of erythrocytes that can reach clinical anemia levels (Trudel et al 2009).…”

Effect of Dietary Crude Protein on Productive Efficiency, Nutrient Digestibility, Blood Metabolites and Gastrointestinal Immune Markers in Light Lambs

“…Blood urea is considered to be an indicator of ingested (dietary) or mobilized (body) protein, while circulating creatinine highlights the creatine degradation which is involved in muscle energy metabolism [31]. During the growing and finishing phases, the circulating urea concentrations were greater in the CP20/19 group compared to the CP18/17 group.…”