Increased urinary protein excretion after intravenous injection of furosemide in man

The furosemide-induced increase in protein excretion, and its relations to 1) the size of protein molecules as reflected by three enzymes, and 2) glomerular filtration rate (GFR), plasma renin activity (PRA) and prostaglandin (PG) E2 and F2 alpha excretions were studied in 14 outpatients with normal renal function and 13 healthy males. Furosemide (120 mg) was given intravenously, and thereafter the protein excretion and the above parameters were monitored for 1--2 hours. In both groups, furosemide caused a transient increase in protein excretion. The excretion of the largest molecule, beta-glucuronidase, rose to 6.3-fold, while those of N-acetyl-beta-D-glucosaminidase and of the smallest molecule, alpha-amylase, increased by 91 and 37%, respectively. GFR increased, too, but markedly less than the protein excretion. PGE2 and PGF2 alpha excretions increased more than GFR and changed simultaneously with the excretion of proteins. Furosemide also caused a marked increase in PRA. This lasted, however, much longer than the rise in PG and protein excretion or GFR. The results suggest that the furosemide-induced increase in protein excretion is 1) related to the molecular size of proteins, 2) partly due to the rise in GFR, 3) simultaneous with the change in PG excretion. Our findings also agree with the view that furosemide causes changes in glomerular permeability.