PAH clearance after renal ischemia and reperfusion is a function of impaired expression of basolateral Oat1 and Oat3

Abstract

Determination of renal plasma flow (RPF) by para-aminohippurate (PAH) clearance leads to gross underestimation of this respective parameter due to impaired renal extraction of PAH after renal ischemia and reperfusion injury. However, no mechanistic explanation for this phenomenon is available. Based on our own previous studies we hypothesized that this may be due to impairment of expression of the basolateral rate limiting organic anion transporters Oat1 and Oat3. Thus, we investigated this phenomenon in a rat model of renal ischemia and reperfusion by determining PAH clearance, PAH extraction, PAH net secretion, and the expression of rOat1 and rOat3. PAH extraction was seriously impaired after ischemia and reperfusion which led to a threefold underestimation of RPF when PAH extraction ratio was not considered. PAH extraction directly correlated with the expression of basolateral Oat1 and Oat3. Tubular PAH secretion directly correlated with PAH extraction. Consequently, our data offer an explanation for impaired renal PAH extraction by reduced expression of the rate limiting basolateral organic anion transporters Oat1 and Oat3. Moreover, we show that determination of PAH net secretion is suitable to correct PAH clearance for impaired extraction after ischemia and reperfusion in order to get valid results for RPF.

Keywords: clearance; experimental; ischemic acute kidney injury; perfusion.

Figure 1.

Cartoon illustrating para‐aminohippurate (PAH) net secretion and PAH excretion ratio. The equations for calculation of the respective parameters are given in the methods section.

Figure 2.

(A) para‐aminohippurate (PAH) clearance in rats 24 h after renal ischemia. PAH clearance was determined as given in the methods section. Rats were either sham operated or subjected to renal ischemia. *indicates statistical significant difference from sham operated animals. n = 8 for the respective experimental groups. (B) Real renal plasma flow (RPF) in rats 24 h after renal ischemia. Real RPF was calculated as corrected PAH clearance (corrPAH clearance) as given in the methods section. Rats were either sham operated or subjected to renal ischemia. *indicates statistical significant difference from sham operated animals. n = 8 for the respective experimental groups. (C) Comparison of PAH clearance and Real RPF in rats 24 h after renal ischemia. PAH clearance and Real RPF was calculated as corrected PAH clearance (corrPAH clearance) as given in the methods section. The respective mean in sham treated animals was set as 100% and the respective parameters in the animals subjected to ischemia and reperfusion were calculated in% in order to allow statistical comparison. Rats were either sham operated or subjected to renal ischemia. *indicates statistical significant difference from sham operated animals. n = 8 for the respective experimental groups.

Figure 3.

(A) Correlation of para‐aminohippurate (PAH) extraction ratio to relative expression of Oat1. Parameters were determined and calculated as given in the methods section and were grouped for every single animal (n = 16). Data were obtained from rats that were either sham operated or subjected to renal ischemia. The inlay is showing relative expression of Oat1 determined by qPCR *indicates statistical significant difference from sham operated animals. n = 8 for the respective experimental groups. (B) Correlation of PAH extraction ratio to relative expression of Oat3. Parameters were determined and calculated as given in the methods section and were grouped for every single animal (n = 16). Data were obtained from rats that were either sham operated or subjected to renal ischemia. The inlay is showing relative expression of Oat1 determined by qPCR *indicates statistical significant difference from sham operated animals. n = 8 for the respective experimental groups.

Figure 4.

(A) para‐aminohippurate (PAH) extraction ratio in rats 24 h after renal ischemia. PAH extraction ratio was determined as given in the methods section. Rats were either sham operated or subjected to renal ischemia. *indicates statistical significant difference from sham operated animals. n = 10 for the respective experimental groups. (B) PAH net secretion in rats 24 h after renal ischemia. PAH net secretion was determined as given in the methods section. Rats were either sham operated or subjected to renal ischemia. *indicates statistical significant difference from sham operated animals. n = 10 for the respective experimental groups. (C) Correlation of PAH net secretion to PAH extraction ratio. Parameters were determined and calculated as given in the methods section and were grouped for every single animal (n = 16). Data were obtained from rats that were either sham operated or subjected to renal ischemia.