S.C. Brazelton, C.L. Chapman, S.M. Holt, K. Wiedenfeld Needham, C.T. O’Connell, H.N. Medved, W.A.B. Howells, E.L. Reed, J.R. Halliwill, FACSM, C.T. Minson, FACSM

University of Oregon, Eugene, OR

Oral protein loading increases glomerular filtration rate (GFR) via nephron recruitment and/or glomerular hyperfiltration. This response reflects renal functional reserve where filtration capacity is increased to maintain GFR at basal levels or increase GFR when stressed. Passive heating induced mild hypohydration (3% reduction in body mass) attenuates oral protein induced increases in creatinine clearance (CCr). It is not known whether mild hypohydration, independent of heat stress, also attenuates increases in CCr during oral protein loading. PURPOSE: To test the hypothesis that increases in CCr following oral protein loading are attenuated during prolonged mild hypohydration compared to euhydration. METHODS: In a block-randomized crossover design, twenty healthy adults [(9 females (F) and 11 males (M); age: 21 (3) years] completed 24 hours of fluid deprivation (HYPO) and 24 hours of normal fluid consumption (EUHY). The protocols were separated by ³72 hours. After the 24-hour protocols, participants underwent oral protein loading by ingesting a whey protein shake (1.0 g protein and 10 ml water per kg body mass) within 10 minutes. Body fluid loss was estimated via the percent change in body mass (∆BM) over the 24-hour protocol. Blood and urine samples were collected at baseline and 150-min post-protein consumption (POST) to calculate CCr. Data are presented as mean with 95% confidence intervals. RESULTS: ∆BM was reduced in HYPO vs. EUHY [-2.6% (-3.0, -2.2) vs. 0.1% (-0.3, 0.4), P<0.0001]. Baseline CCr was elevated in HYPO vs. EUHY [261 ml/min (218, 303) vs. 143 ml/min (118, 168), P<0.0001]. There were no differences in CCr between conditions at POST [HYPO: 246 ml/min (212, 280); EUHY: 231 ml/min (196, 265), P=0.2691]. At POST, CCr was elevated from baseline in EUHY (P<0.0001) but not HYPO (P=0.2941). CONCLUSION: These findings suggest that CCr is not altered with oral protein loading during prolonged mild hypohydration. Whether our findings suggest that a ceiling effect was reached in the HYPO condition (i.e., maximum CCr was already achieved at baseline) or are influenced by increased tubular creatinine secretion during hypohydration requires further investigation.

Supported by NIH R01HL144128 and F32HL164021.

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