AJP - Renal Physiology, Vol 250, Issue 4 590-F595, Copyright © 1986 by American Physiological Society
Electrolyte handling by the superficial nephron of the rabbit
N. L. Wong, S. J. Whiting, C. L. Mizgala and G. A. Quamme
A micropuncture study of the rabbit was performed to evaluate the function
of the superficial nephron. The mean glomerular filtration rate of the left
micropunctured kidney was 4.0 +/- 0.8 ml/min. The concentration profile of
electrolytes within the proximal tubule was similar to that of species
previously investigated except for potassium. The mean tubular fluid
(TF)-ultrafilterable (UF) concentration ratios were as follows: sodium,
1.01 +/- 0.03; chloride, 1.14 +/- 0.04; calcium, 1.12 +/- 0.04; magnesium,
1.47 +/- 0.08; and phosphate, 0.94 +/- 0.09, with a mean TF-plasma (P)
inulin concentration ratio of 1.78 +/- 0.14 (n = 32). The TF/UF potassium
value significantly increased in association with TF/P inulin to a mean
value of 1.26 +/- 0.06. Accordingly, 29% of the filtered potassium was
reabsorbed in the superficial proximal tubule compared with 43% of the
filtered sodium. The loop of Henle reabsorbed 55-60% of the filtered
sodium, chloride, and calcium, whereas considerably less magnesium (33%)
was reabsorbed. Segments beyond the distal tubule collection site
reabsorbed little of the delivered magnesium, which supports the notion
that the loop of Henle is the principal segment accounting for adjustments
in magnesium balance. These studies indicate that the superficial nephron
of the rabbit performs similar to other species reported, except potassium
reabsorption is significantly less in the proximal convoluted tubule.
