MO940: Effects of Erythrocytes and Albumin in The Perfusate of an In Situ Perfusion Model of Isolated Rat Kidney
Authors: Kobayashi Kozue , Watazawa Seiji , Furihata Toshiki , Tsuchiya Benio , Kokubo Kenichi , Kubota Masaru 
Published: May 2022

Abstract

BACKGROUND AND AIMS
The conventional perfusion model of the isolated rat kidney circulates perfusate to the isolated kidney removed from the body. On the other hand, an in situ perfusion model, within the body, of an isolated kidney is expected to allow research on drug metabolism and physiological functioning of the kidney under physiological conditions and also allow local organ therapy, such as selective perfusion of the organ with therapeutic agents such as anticancer agents. The aims of the present study were to establish an in situ perfusion model of an isolated rat kidney and to clarify the composition of the perfusate necessary to obtain physiological perfusion of the isolated kidney model.

METHOD
Male Sprague Dawley rats (300–350 g) were used for the experiments. Cannulations of the renal vein, renal artery and ureter were performed, in that order, for the left kidney, and the perfusion experiment was performed for 2 h. The flow rate of the perfusate during the organ perfusion was adjusted (0.3–2.0 mL/min) to maintain the renal artery pressure at 100–120 mm Hg. The circulation conditions were adjusted to maintain the renal artery pressure in the aforementioned range and urine production until the end of the perfusion experiment. The perfusate was oxidized with a 95% oxygen and 5% carbon dioxide gas mixture during the experiment and had the following composition: Na+, 140 mEq/L; K+, 5 mEq/L; Ca2+, 1.9 mEq/L; Mg2+, 2.5 mEq/L; Cl−, 126 Eq/L; and HCO3−, 25 mEq/L. The effects of erythrocytes (Ht: 25%) in the perfusate on the renal arterial pressure, urine production rate and oxygen-carrying capacity were examined, as also those of albumin (4 g/dL) in the erythrocyte-containing perfusate on the blood flow resistance of the kidney and urine production rate during the circulation experiment.

RESULTS
When a perfusate not containing erythrocytes was used, urine production from the isolated kidney decreased with time, and the renal artery pressure failed to be maintained within the target range. In contrast, when a perfusate containing erythrocytes was used, urine was constantly produced, and the renal artery pressure was maintained within the target range throughout the 2-hour experimental period. When a perfusate containing erythrocytes and albumin was used, the urine production rate of the kidney was close to the physiological urine production rate in rats and significantly lower than that observed when the perfusate did not contain albumin.
Urine production was maintained from the isolated rat kidney until the end of the perfusion experiment when the perfusate contained erythrocytes, suggesting that a perfusate with adequate viscosity and sufficient oxygen-carrying capacity is important to maintain the renal artery pressure and renal functions. The addition of albumin to the perfusate containing erythrocytes resulted in appropriate physiological urine production, probably due to the higher colloid osmotic pressure of the perfusate.

CONCLUSION
We established an in situ perfusion model of an isolated rat kidney that exhibited almost physiological functioning when the perfusate used contained erythrocytes to supply sufficient oxygen and albumin to maintain the colloid osmotic pressure.