Relationship between glomerular filtration rate and renal blood flow at different levels of protein-induced hyperfiltration in man.

1. We studied the relationship between changes in glomerular filtration rate (GFR) determined as inulin clearance (CIn), and changes in renal blood flow (RBF), determined as p-aminohippurate clearance (CPAH), after the ingestion of a large (1.35 +/- SEM 0.04 g/kg, n = 9), moderate (1.08 +/- 0.03 g/kg, n = 10) or mild (0.55 +/- 0.02 g/kg, n = 8) protein load given as a meat meal. Control subjects (n = 10) received a carbohydrate meal. 2. CIn and CPAH increased after a protein meal. Two hours after eating the test meal, GFR levels were (mean +/- SEM) 160.0 +/- 13.8 (P less than 0.05), 141 +/- 7.69 and 127.8 +/- 9.07 ml/min in the groups that received a large, moderate and mild protein load, respectively. Peak CIn values after the meal were 211.6 +/- SEM 14.92 (P less than 0.001), 177.5 +/- 10.88 (P less than 0.01) and 129.0 +/- 8.72 ml/min after a large, moderate and mild protein load, respectively. 3. At peak GFR levels after the meal, filtration fraction (FF) (CIn X 100/CPAH) increased significantly (P less than 0.02) with the large and with the moderate protein load, but not with the mild protein load. 4. There was a significant (P less than 0.001) positive relationship between increments of FF and increments of CIn, but not CPAH, whether the values were expressed as post-meal/pre-meal ratios or as absolute changes.(ABSTRACT TRUNCATED AT 250 WORDS)