AJP - Gastrointestinal and Liver Physiology, Vol 248, Issue 3 313-G319, Copyright © 1985 by American Physiological Society
Studies of carnitine metabolism in relation to intestinal absorption
H. Gudjonsson, B. U. Li, A. L. Shug and W. A. Olsen
We studied the postabsorptive fate of L-[3H]carnitine after intraluminal
injection into the proximal intestine of anesthetized rats. Carnitine
absorption was characterized by slow appearance in the circulation with
blood levels still rising 2 h after administration. Absorption via the
portal vein was followed by hepatic extraction and appearance in bile with
reabsorption of a fraction, thus establishing an enterohepatic circulation.
About half of the [3H]carnitine in blood obtained 4 h after administration
was free, with the rest largely acetylcarnitine. In contrast the increase
in blood carnitine content after intraluminal administration of unlabeled
carnitine was almost exclusively limited to the esterified fraction. We
hypothesize that release of esterified endogenous or stored carnitine from
some other site accounted for the increase in esterified carnitine. The
liver may be that site: although about 50% of hepatic [3H]carnitine was in
ester form after administration of labeled carnitine, the increase after
unlabeled carnitine was primarily in the free fraction, suggesting that a
large amount of esterified carnitine had been released. Thus the liver
appears to be an important storage and excretory site for exogenous as well
as endogenous carnitine, which may be released with an appropriate signal
from the intestine.
