Relationship between perfusion pressure and renin release in the isolated rat kidney

Isolated rat kidneys were perfused with either a modified Krebs-Henseleit solution containing a gelatine preparation (Haemaccel, 35 g/1) or with a suspension of washed bovine red blood cells (RBC). Wh en perfusion pressure (PP) was varied repeatedly in the range between 30 and 210 mm Hg autoregulation of renal plama flow (RPF) was almost complete in RBC perfused kidneys. Changes of PP by steps of 20 mm Hg at intervals of 5 min resulted in an incomplete autoregulation of RPF and glomerular filtration rate (GFR). Renin release (RR) was inversely related to PP in the range between 50 and 150 mm Hg, while perfusion at a pressure below or above that range had no further effect on RR. The most marked increase in RR was obtained, when PP was reduced from 90 to 70 mm Hg. After reduction of PP, an increase in RR was measurable within 1 min, and a maximum was reached after 5 min. In kidneys perfused with a cell-free medium at a PP of 45 mm Hg for up to 30 min, RR remained elevated for the entire period of pressure reduction. Injection of microspheres into the renal artery resulted in a prompt decrease of RPF, GFR and urinary sodium excretion, but the values returned towards control levels within 15 min; RR increased only transiently after a short initial fall.