Measurement of Renal Blood Flow in the Rat

Abstract

A radioactive microsphere technique has been developed for the measurement of renal blood flow and intrarenal blood flow distribution in the dog (1, 2). Various techniques have been proposed (3-5) for the measurement of renal blood flow (RBF) in the rat in addition to the conventional PAH clearance method. This study presents a simple method for the assessment of RBF in rats using radioactive microspheres.

Method. Eight male Sprague-Dawley rats weighing 200-240 g were fed with Purina Lab Chow and given tap water ad lib. All animals were lightly anesthetized with ether and cannulated with polyethylene tube No. 10 (i.d. 0.011 in., o.d. 0.024 in.) through the femoral artery for blood collection and through the carotid artery into the left ventricle for injection of microspheres. After awakening from anesthesia, animals were placed in restraining cages and allowed to recover for 45-60 min prior to injection. Radioactive microspheres, 15 μm ± 5 μm diameter, (3m Co., St. Paul, MN) were utilized to measure renal blood flow (RBF) and its intracortical distribution. Two different nuclides were used, ⁸⁵Sr and ¹⁴¹Ce, for two separate measurements taken 1 hr apart. For each measurement, approximately 0.1 ml of 2 mg/ml concentration of microspheres in 10% dextran was injected through the carotid artery catheter within 5-7 sec. Just prior to injection, the spheres were sonicated for 5-10 min and then vigorously agitated with a vortex mixer for at least 3 min. Immediately upon injection of the spheres into the left ventricle, the femoral catheter was opened and blood was allowed to flow freely into a preweighed tube for exactly 1 min. Approximately 0.2 ml of blood was collected from the femoral artery in each minute. The adequacy of 1-min collection periods, vis à vis complete removal of microspheres from the circulation, was tested in a separate group of five animals.