[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) C_In), ³H,- and ¹⁴C-labelled inulin clearance (C_3H]In and C_14C]In, respectively) and proximal tubular fluid/plasma concentration ratios (TF/P) of ¹⁵Cr]EDTA and TF/P ratios of ¹⁴C-labelled inulin measured in the same samples. C_51Cr]EDTA correlated well with, but underestimated C_In by ? 10%. The correlation coefficient (r) was 0.92. C_51.Cr]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 ¹⁵Cr]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 ¹⁵Cr]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.