[51Cr]EDTA for measuring total and single nephron glomerular filtration rate in the rat

Clearance and micropuncture experiments were performed in halothane anaesthetized rats. The aim was a comparison of paired estimates of glomerular filtration rate (GFR) from the renal clearance of [51Cr]EDTA (C[51Cr]EDTA) with simultaneous estimates of polyfructosan ((Inutest) CIn), 3H,-and 14C-labelled inulin clearance (C[3H]In and C[14C]In, respectively) and proximal tubular fluid/plasma concentration ratios (TF/P) of [51Cr]EDTA and TF/P ratios of 14C-labelled inulin measured in the same samples. C[51Cr]EDTA correlated well with, but underestimated CIn by approximately 10%. The correlation coefficient (r) was 0.92. C[51Cr]EDTA also correlated with, and underestimated C[14C]In by 6%, r = 0.88, whereas it overestimated C[3H]In by 5%, still with a close correlation (r = 0.92). Paired data on proximal (TF/P) ratios of [51Cr]EDTA and [14C]inulin were collected from early, mid and late proximal convolutions. The data were scattered around the line of identity, r = 0.91. It is concluded that [51Cr]EDTA is a valid alternative for estimates of total renal and single nephron GFR in rats and has the advantage of being less expensive than [14C]inulin.