Can Continuous Intraperitoneal Infusion of 125I-Iothalamate and 131I-Hippuran Be Used for Measurement of GFR in Conscious Rats?

We previously described a method to measure GFR in conscious spontaneously voiding rats. This method circumvents the need for anesthesia and for bladder instrumentation. It's main principle is the correction of renal 125I-iothalamate clearance for incomplete urine collection by the ratio of plasma and renal clearance of co-infused 131I Hippuran. A disadvantage of this technique is the requirement of an intra-arterial catheter for infusion of the renal function tracers. We therefore tested whether intraperitoneal infusion of 125I-Iothalamate and 131I-Hippuran can be used for such a GFR measurement in conscious spontaneously voiding rats.We found that during intraperitoneal administration, stable plasma levels of 131I-Hippuran could be obtained. However, urinary recovery of 131I-Hippuran was incomplete (66 ± 32%), leading to a significant overestimation of GFR by 140 ± 113% in comparison with the GFR measured by the intra-arterial technique. Thus intraperitoneal infusion of renal function tracers cannot rep...