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In order to analyse the mechanism of inhibition of water diuresis in adrenal insufficiency renal surface tubulus of male albino rats (group I: controls, group II: 8 days or more after bilateral adrenalectomy) have been perfused using the free flow microperfusion technique.

The passage time of I131-Hippuran and I131-Inulin was measured with Anger camera-scintigraphy after rapid arterial injection of these substances and compared with the results obtained with the Lissamingreen method. Corresponding to the passage time of Lissamingreen through the loops of Henle, there was a decrease in the kidney size in the scintiphotogram. in further agreement with the intravital microscopy, the passage time of the radioactivity was prolonged during hypotension and high intra-pelvic pressure. Similar results were obtained with collimator measurements of I125-Inulin and I125-Hippuran on the renal surface and with simultaneous measurements of the passage time of Lissamingreen.

In the present study it is demonstrated that reabsorptive functions of the proximal tubule during partial renal artery clamping display significant differences when compared to spontaneous GFR variations. During moderate clamping fractional fluid reabsorption was 69.8% and fell during severe clamping to 55.2%. Proximal tubular passage time increased progressively with the degree of clamping. This indicates that radius does not change as a function of GFR, a finding supported by microphotography of the renal surface. During moderate arterial clamping proximal reabsorptive rate was correlated to the tubular cross-sectional area, but in the face of severe clamping this relationship was abolished. We conclude, therefore, that mechanisms other than tubular geometry participate in regulating proximal tubular reabsorption, when GFR is altered by arterial constriction.