Renal Hemodynamic Changes in Humans Response to Protein Loading in Normal and Diseased Kidneys JUAN P. BOSCH, M.D.” SUSIE LEW, M.D. SHELDON GLABMAN, M.D. ALLAN LAUER, M.D. New York, New York From the Renal Division and Robert Wood John- son Renal Treatment Center, Department of Medicine, Mount Sinai School of Medicine, New York, New York. This work was presented in part at the American Society of Nephrology Meeting, Washington, D.C., December 1983. Manuscript submitted June 26, 1985, and accepted Novem- ber 21, 1985. *Current address and address for reprint re- quests: Renal Division, George Washington Uni- versity Medical Center, 2 150 Pennsylvania Ave- nue, N.W., Room 505, Washington, DC. 20037. A continuing medical education quiz on this arti- cle (one hour of Category 1 credit) appears on page Al 19 of this issue. This study was undertaken to define the renal hemodynamic changes that mediate the acute response to an oral protein load. Three groups of subjects were studied: (1) disease-free subjects; (2) patients with chronic renal disease of various causes, except for diabetes mellitus, documented by history and/or renal biopsy; and (3) patients with diabetes mellitus, that is, a history of hyperglycemia requiring antihy- perglycemic therapy. All subjects were studied before (baseline) and after (test) ingestion of a protein load. Glomerular filtration rate and effective renal plasma flow were evaluated by inulin and para-amino- hippurate, respectively. In the disease-free subjects, the mean base- line glomeruiar filtration rate and renal plasma flow were 122 f IO ml/minute/l.73 m* and 644 f 64 ml/minute/l.73 m*, whereas test giomeruiar filtration rate and renal plasma flow were 151 f 15 ml/ minute/l .73 m* and 791 f 111 ml/minute/l .73 m*, respectively. In patients with chronic renal disease, the test glomeruiar filtration rate and renal plasma flow were related to the severity of the disease. The more severe the disease, the lower the absolute test values and the smaller the increment from baseline to test values. Patients with diabetes mellitus had a paradoxic response to ingestion of a protein load. Glomerular filtration rate fell while renal plasma flow remained unchanged. lhii response was observed in all diabetic patients regard- less of the type of diabetes or whether clinical evidence of diabetic nephropathy was absent, minimal, or severe. In intact kidneys, the glomerular filtration rate is variable from day to day, and from hour to hour. Disease-free organs have the capacity to increase the rate of filtration in response to a variety of long- and short-term stimuli [l]. Pregnant women, burn patients, and persons on a high protein diet may have a glomerular filtration rate above the range described for a disease-free population [I]. A transient elevation in glomerular filtration rate is observed in humans and laboratory animals following protein ingestion or glycine infusion [1,2]. This augmentation of the resting glomerular filtration rate indicates a renal reserve [ 1,3]. Previous studies from our laboratory revealed an increase in glomeru- lar filtration rate from 123 f 13 to 157 f 13 ml/minute/l.73 m* after normal subjects ingested an acute oral protein load. The rise in glomeru- lar filtration rate observed during a 120-minute period, from 60 to 180 minutes after protein intake, was transient and reproducible in each subject [3]. These findings have been confirmed by others [4,5]. We suggested that an oral protein load can be used to stimulate the glomeru- lar filtration rate above the resting state and thus unmask the filtration capacity and renal reserve. In renal disease, a decrease in filtration November 1986 The American Journal of Medicine Volume 81 809