An improved method for the measurement of renin release from coronal, vibratome-cut kidney slices

Our studies were designed to optimize a system for studying renin release in vitro. Our rat kidney slices (400 micron) were cut coronally on a vibratome, and the medullary tissue was dissected from each slice. Previous investigators obtained kidney slices by slicing sagittally, parallel to the cortical surface, with a hand-held microtome. Slicing on a vibratome and removal of the medulla ensured that the slices were of uniform thickness, weight (18.3 +/- 0.52 mg; n = 24), and renin content. Furthermore, one kidney can provide approximately 30 renal slices whereas the previous methods provided only two slices per kidney. The slices were placed in siliconized vials containing a Krebs-Ringer solution (pH 7.4) at 37 degrees C for 30 min. The Krebs-Ringer solution was decanted and replaced with fresh Krebs-Ringer solution for a 30-minute preincubation period. At the end of the 30-min preincubation period, a 0.2-ml sample was taken for the determination of renin release, and the remaining medium was decanted. Fresh Krebs-Ringer solution and the test substances were subsequently added for the incubation period. Throughout the experiment, the vials were maintained at 37 degrees C, and each vial received a gas mixture of 95% O2-5% CO2 via plastic tubing connected to a needle that was inserted into the snap-cap of each vial but did not bubble the medium. The old (bubbling) method for the bioassay of renin yielded values for renin release that were low and had large interexperimental variation (0.23 +/- 0.04 to 1.9 +/- 0.3 ng angiotensin I (AI)/mg kidney/hr; n = 24).(ABSTRACT TRUNCATED AT 250 WORDS)