G. Ojteg et Pj. Wistrand, RENAL HANDLING AND PLASMA ELIMINATION KINETICS OF CARBONIC-ANHYDRASE ISOENZYME-I, ISOENZYME-II AND ISOENZYME-III IN THE RAT, Acta Physiologica Scandinavica, 151(4), 1994, pp. 531-539
Using a radio-immunosorbent technique, the levels of the carbonic anhy
drase (CA) isoenzymes CA I, II and III in plasma (1-3 mu g ml(-1)), ly
mph (0.5-1.6 mu g ml(-1)) and urine (0.03-0.06 mu g ml(-1)), were dete
rmined in the rat. The renal clearances of CA I, II and III were 11+/-
3, 42+/-11 and 35+/-4 nl min(-1) (g kidney wet wt)(-1) (n = 4-5), resp
ectively. After a single i.v. injection of purified native or I-125-la
belled isoenzymes, the elimination of CA I, and CA III from plasma fol
lowed a bi-exponential decline, with half-times of 7 and 9 min for the
rapid phase and 112 min for the slow phase, respectively. Nephrectomy
decreased the rapid phase and the build-up of catabolites. Therefore,
the rapid phase of CA I and III elimination is probably explained by
filtration of unbound isoenzyme at the glomeruli and subsequent degrad
ation by the proximal tubules. The plasma elimination curve for CA II
was different and followed a mono-exponential decline, with a half-tim
e of 210 min both in normal and nephrectomized animals. This indicates
that CA II is not filtered at the glomeruli. However, in acute renal
failure, with leaking tubular cells, CA II was excreted into the urine
. The slow elimination of the major part of the isoenzymes from plasma
is explained by the binding of CA I, II and III to a plasma protein,
immunochemically similar to transferrin, forming a macromolecular comp
lex with a mol wt of 114+/-2 kDa.