Albumin permeability of the peritubular capillaries in rat renal cortex.

Abstract

SUMMARY1. Two series of experiments were carried out to determine the permeability of the renal cortical peritubular capillaries to albumin under control conditions in the concentrating kidney and after an infusion of hypo-osmotic fluid amounting to 6% body weight.2. In the first series of these experiments the turnover of the interstitial albumin pool of the renal cortex was studied. Specifically, the mean transit time of albumin molecules from arterial plasma to renal lymph was measured in nine rats of each group. Mean values of 39-0 + 2-8 and 30-6 + 2-2 (s.E. of mean) min were found for the control and infused groups, respectively.3. In the second series of experiments the interstitial distribution volume of plasma albumin in renal cortex was determined in twenty-three control and twenty-two infused rats. Mean values of the extravascular distribution volumes were 1-66 + 0-21 and 1-37 + 0-18 (s.E. of mean) /d./100 mg tissue, respectively.4. The unidirectional clearance of albumin from the capillary to the interstitium in the control and infused groups, respectively, was calculated to be 7-1 + 1-0 and 7-5 + 0-9 (s.E. of mean) ml. sec-1 10-4 in 100 g cortical tissue.5. For the reabsorbing surface of the peritubular capillaries in the renal cortex, a lower bound was calculated for A-, the reflexion coefficient of albumin. The reflexion coefficient was found to be higher than 0-998 under both experimental conditions.

Peritubular Capillaries of the Renal Cortex in Experimental Diabetes Mellitus in the Rat

“…The rate of entry of plasma albumin from the peritubular capillaries into the renal cortical interstitium was measured by the method of Bell et al [8] as a unidirectional clearance from the peritubular capillaries into the interstitium. This clearance, @' , indicates the volume of plasma which contains a quantity of albumin entering the interstitium in 1 min.…”

“…Because it is unidirectional, it differs from the widely used permeability x surface area (PS) product [ 111, which is a measure of the net clearance. Measurement of 9' by the method of Bell et al [8] is based on the central volume principle [ 121, and involves two experimental determinations: the volume of distribution of albumin in the renal cortical interstitium, 6 , and the mean transit time of albumin through that distribution volume, f.…”

“…(Specific radioactivity was determined as a ratio of 1311-labelled albumin activity to steady-state 12' 1-labelled albumin activity. The latter tracer was injected about 3 h before the experiment [8].) Both curves were plotted and smoothed.…”

“…The difference between the distribution volumes, V -V,, was subjected to two corrections. First, extravasation of the 1311-labelled albumin was estimated as described by Sell et al [8]. Second, filtered albumin present in the tubular lumina was excluded from the estimate of interstitial albumin pool.…”

“…Correction for 1311 decay was applied when the time of all samples in one experiment exceeded 12 h. The unidirectional clearance of albumin from the peritubular capillaries into the interstitium, 9', was calculated as K/f. Further details of the methods are given by Bell et al [8].…”