AJP - Heart and Circulatory Physiology, Vol 253, Issue 5 1305-H1314, Copyright © 1987 by American Physiological Society
Ascorbic acid: a nonradioactive extracellular space marker in canine heart
G. H. Reil, R. Frombach, R. Kownatzki, W. Quante and P. R. Lichtlen
Abteilung fur Kardiologie und Biophysikalische Gerateabteilung, Medizinische Hochschule Hannover, Federal Republic of Germany.
The distribution pattern of ascorbic acid and L-[14C]ascorbic acid in
myocardial tissue was compared with those of the classical radioactive
extracellular space markers [3H]-inulin, [3H]sucrose, and Na82Br. A new
polarographic technique was developed for analogue registration of ascorbic
acid concentration in coronary venous blood. The kinetic data of the
markers were studied in an open-chest canine heart preparation (n = 17
dogs) during a constant tracer infusion of up to 9 min. Distribution
volumes were calculated based on the mean transit time method of Zierler
(K. L. Zierler, Circ. Res. 10:393-407, 1962). The distribution volume of
ascorbic acid (23.6 ml/100 g wet wt) as well as of L-[14C]ascorbic acid
(24.5 ml/100 g wet wt) in myocardial tissue agreed closely with those of
[3H]inulin (18.6 ml/100 g wet wt) and [3H]sucrose (22.0 ml/100 g wet wt),
as well as 82Br- (27.3 ml/100 g wet wt). The obtained kinetic data
confirmed that ascorbic acid exhibits the physicochemical properties of an
extracellular space marker, though this compound was shown to leak slowly
into myocardial cells. Favorable attributes of this indicator are its low
molecular weight, high diffusibility in interstitial fluid, low binding
affinity to macromolecules, and high transcapillary (1.8 X 10(-5) cm/s) as
well as low transplasmalemmal penetration rate (3.7 X 10(-8) cm/s).
Therefore, this nonradioactive marker can be applied in a safe and simple
fashion, and without untoward side effects in experimental animals as well
as in patients.
