Function of juxtamedullary nephrons in normotensive and chronically hypertensive rats

Summary The function of juxtamedullary nephrons was investigated by micropuncture of long loops of Henle at the exposed papilla in normal rats and in the untouched kidney of rats with experimental hypertension (unilateral Goldblattclip). With increasing blood pressure (range from 90–190 mm Hg) a continuous rise in juxtamedullary single nephron glomerular filtration rate was observed. Juxtamedullary single nephron GFR averaged 60×10^–6 ml/min/g K.W. in the control group (mean arterial blood pressure 116 mm Hg) and 114×10^–6 ml/min/g K.W. in the hypertensive group (mean arterial blood pressure (164 mm Hg). There was no change in superficial single nephron GFR (30×10^–6 ml/min/g K.W.) but a slight increase in total kidney GFR from 1.07 to 1.28 ml/min g K.W. In both the normotensive and the hypertensive animals, tubular fluid-to-plasma (TF/P) inulin ratio and intratubular flow rate in the descending limb of the long loops of Henle were not statistically different from those found in the ascending limb. Intratubular flow rate in the hypertensive rats was twice as high as in the controls; the mean TF/P inulin ratios in the two groups did not differ from each other. Appearance time of lissamine green in the long loops of Henle and in the collecting ducts was shortened in the hypertensive animals. It is concluded that there is no autoregulation of glomerular filtration rate in juxtamedullary nephrons. The increased juxtamedullary GFR may contribute to the elevated urinary excretion of the unclipped kidney in hypertensive rats.This paper was presented before the German Physiological Society, Mainz, March 1969 [11].